Text

Submits Equipment Selected for NRC Test Program.Equipment Qualification Test Plan & Specific Technical Details Should Be Discussed W/Equipment Qualification Branch Personnel During Test Program
	ML20127A108
Person / Time
Issue date:	11/19/1981
From:	Rosztoczy Z; Office of Nuclear Reactor Regulation
To:	Reinmuth G, Danielle Sullivan; NRC OFFICE OF INSPECTION & ENFORCEMENT (IE), NRC OFFICE OF NUCLEAR REGULATORY RESEARCH (RES)
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ML20127A112	List: ML20127A108; ML20129D638; NUREG-3418, Partial Response to FOIA Request for Five Categories of Documents Re NUREG/CR-3597,NUREG/CR-3418 & Board Notification 84-032.Forwards App a Documents.Documents Also Available in PDR;
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	v • d • e

S o UNITED STATES -

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NUCLEAR REGULATORY COMMISSION

.. E CASHINGTON. D. C. 20555

. . . NOV 191931 l

MEMORANDUM FOR: G.W. Reinmuth, Chief .

Vendor and Special Projects. Branch Division of Resident and Regional Reactor Inspection, IE D.F. Sullivan, Acting Chief l Electrical Engineering Branch Division of Engineering Technology, RES FROM: Z.R. Rosztoczy, Chief I Equipment Qualification Branch Division of Engineering j

SUBJECT:

EQUIPMENT SELECTION FOR THE NRC TEST PROGRAM The NRC equipment qualification test program is conducted by IE/RES. The I objective of this program is to develop confidence in the current equipment I test methods / procedures and better understanding of equipment behavior. The !

EQB of NRR provides technical input to this test program. The EQB was requested !

by IE/RES to provide a list of equipment of their concern for this test program.

The EQB and IE personnel have mutually agreed upon these equipment selection ':

lists which are based on current NTOL audit experiences and the on-going in- I dustry equipment qualification test programs. Two separate equipment lists are provided based on our priority and concerns. These are as follows:

Equipment List #1 (1) ASCO - Solenoid Valves (NP Series with long term operability and spray)

(2) Joy / Reliance - Fan Motor's (3) GE - Penetratiori (4) PYCO, Thermal Electric, RFD and Rosemount - RTD .

(5) brcoid, Barksdale and Solon - Pressure Switches

. (6) Coaxial Cable , .

CONTACT: Kulin D. Desai NRR/DE/EQB Ext. 49-28205 t s

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G.W. Reinmuth NOV 191981 D.F. Sullivan .

Equipment List #2 (1) Level Switches / Sensors -

(2) Limit Switches l (3) Rotork Actuator (4) Bailey Transmitter

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It is requested that the equipment qualification test plan and specific technical details should be discussed with the EQ3 personnel during this test program. -

z t+. ti \L-l Z.R. Rosztoczy, Chi D Equipment Qualification Iranch Division of Engineering ,

cc: R. Vollmer .

J. Sniezek W. Johnston E. Jordan A.Bennett W. Farmer U. Potapovs -

EQ Section Personnel e , ,

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QUICK LOOK REPORT RTD Screening Test E. E. Minor Sandia National Laboratories Albuquerque, NM 87185 Operated by Sandia Corporation for the U.S. Department of Energy Prepared for Office of Nuclear Regulatory Research Division of Engineering Technology U.S. Nuclear Regulatory Commission 25 April 1983 FIN A1355 N

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c-Acknowledgements sincere appreciation is extended to Tim Gilmore, John Lewin, Mike Luker, and Gerry Seitz for their assistance and suggestions during the preparation for and performance of this test. The help of Frank Those throughout the period of the test and the preparation of the report is gratefully acknowledged. .

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g 6, e ,L Quick Look Report RTD Screening Test Furpose This test was conducted to screen resistance temperature detectors (RTDs) from three different suppliers (1) to determine the advisability of proceeding with the test program outlined in " Test Plan for Equipment Qualification Research Test of Resistance Temperature Devices," Rev.1, November 1982; (2) to evaluate basic designs; and (3) to expose several manufacturers' products. The ten RTDs were exposed to a LOCA harsh environment (temperature / pressure and chemical spray) beginning at low temperature / pressure and increasing in increments to a high temperature / pressure.

Evaluation Criteria To evaluate the results of the test, the following s

criteria were established:

1. Evidence of a moisture leak was considered indicative of a potential problem.

2. Temperature indications which differed from the thermocouple readings far enough that the divergence could not be reasonably explained by thermal lag in the system were considered reason to suspect a problem.

j. 3. Temperature indications which differed by more than j' five or six degrees from those obtained by other RTDs were considered reason to suspect a problem when both

,! RTDs were in a " steady-state" environment.

4. For dual-element RTDs, a divergence of more than 3'C

' between the temperatures indicated by the two elements was considered reason to suspect a problem with at least one of the elements.

Generally, when a short occurred, the divergence of the shorted

element was of sufficient magnitude and occurred on repeated i

readings so that it gave a clear indication of problems.

I squipment Selection and Description The Equipment Qualification Branch, Office of Nuclear Reactor Regulation, United States Nuclear Regulatory Commission, chose RTDs as generic equipment candidates for l

tests which would be used to generate data to evaluate 4

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i. e qualification test methods for accident conditions.* The choice was based on the wide use of this type of equipment throughout the nuclear power industry. Because of the wide use of these or similar models of RTDs, Sandia recommended one model of Supplier A and two models of Supplier B RTDs for test. The NRC approved this selection and requested that Supplier C RTDs also be tested. Supplier C RTDs were added because of their extensive use in older plants. Supplier A was in the process of planning and conducting qualification tests on their componentar their test is nearing completion.

Supplier B components of the same design as those used in the tests described herein have been purchased and qualified by another corporation. Supplier C has not qualified their RTDs for nuclear use to the current standards and does not plan to do so; their RTDs, however, have been widely used in older plants.

Supplier A RTDs contain two 100-ohm platinum elements with three leads coming from each element. The elements are connected to a terminal board located in a cast-iron body. The outgoing leads are assembled in this body, then a cast-iron cap is screwed onto the body to seal the assembly. We wired the RTDs with four wires to make them compatible with our data collection instruments. The port through which the leads pass must be sealed. Supplier A leaves this responsibility to the utility installing the RTDs.

Both Supplier B and C RTDs are four-wire, single-element RTDs with 200-ohm elements. Neither supplier uses the cast-body and cap design, but instead the leads feed from the element through a sealed connection into a cable which is covered with a stainless steel braided flexible hose. The

" outboard" end of the flexible hose is terminated in a fitting

l from which the leads protrude. This end must then be protected ll by a junction box or by some other means, ii Table 1 l

RTDs Tested During Screening Test Serial No.,

1 RTD No. Description 1 Supplier A 9409 j-2 Supplier A 9410 3 Supplier A 9412 4 Supplier A 9415 5 Supplier B, Model 1 102 6 Supplier B, Model 1 103 7 Supplier B, Model 2 101 8 Supplier B, Model 2 102 9 Supplier C 8138 10 Supplier C 8147

Unclassified USNRC memo, Rosztoczy to Reinmuth, dated 11/19/81, subject: " Equipment Selection for the NRC Test Program."

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l e m H Sequence'of Tests Tests were conducted in accordance with " Screening Test plan for Equipment Qualification Research Test of Resistance Temperature. Devices," Rev. 2, February 1983. Tests were performed in the following sequence:

- Pretest Visual Inspect, ion and Functional Check

- LOCA Harsh Environment

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- Visual Inspection and. Functional Check Visual Inspection and Functional Check 8

Visual inspection consisted of an inspection for obvious damage of external, parts only. All pipe joints were securely tightened. After wiring was completed, the cap threads of the Supplier A RTDs were lubricated with. nuclear grade anti-seize compound (Never-Seez). They were then installed onto the RTD bodies and tightened to a torque of 50 to 60 foot-pounds.

(This torque value was obtained from Supplier A by telephone on l' l! August 19, 1982, and reconfirmed by telephone on January 25, l 1983.) Pipe joints were not checked for torque values. The i tightness of pipe joints is generally defined in terms of the number of threads engaqad. These data were not determined.

Instead, Supplier B assemblien were checked (as assemblies) to a minimum torque of 40 foot-pounds and o maximum of 60 foot-pounds. This verified that all pipe threads were tightened to a torque of at least 40 foot-pounds. During i

visual inspection, the only damage obsurved was the marks left

. on the stainleos steel pipe nipples from tightening the l aasnmbly into the test fixture. Tnis damage had no effect on the test results. It should -be noted that Supplier A RTDs used in this test were modified by replacing the three-inch nipple-union-nipple assembly with a three-inch black iron -

nipple. The threads of this-nipple ware wrapped with teflon tape for assembly. Otherwise, RTDs yore tested as they came

, from'the suppliers. , ,

Functional checks consisted of compcring each RTD's reading with readings obtained from roference thermocouples in j the same environment. The thermocouples had been calibrated againot NHS secondary vtandardt. In addition, prior to closing i the tcat chamber and,after connecting the RTDs to the data recording.cystem, each RTD in turn was first immersed in an ice g

water bath then heated with an air gun to determine (1) that it

, responded to the approximately correct temperature and (2) that

it was connected to the proper channel of the data recording I system.

I Preparation for_ Harsh Environment Tests

!' Supplier A RTDs were received without cables. Prior to tightening the caps to the required torque, the caps were

! removed and the necessary leads were ins *.alled. In addition, a

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grounded-junction thermocouple was welded into the head of each of the four supplier A RTDs to record the temperature as close to the sealing gasket as possible. Flexible steel hose was installed around the leads from each Supplier A RTD, extending from the RTD body to the cover plate through which the leads exited from the exposure, chamber. Each end of the flexible hose was covered with Raychem heat-shrinkable tubing to ensure a well-sealed interface.

Supplier B RTDs included their own armored cables. These were securely connected to fittings at the cover plates.

Supplier C RTDs also included their own armored cables.

However, to protect the open and of the cables, a length of beta-ucriptite-filled epoxy was molded around the cables at the point where the cables exited from the exposure chamber. A short length of 1/2-inch stainless steel tubing was placed over the cables and molded into the outboard end of the beta-ucriptite-filled epoxy. This was secured in a Swage-Lok fitting as it exited the chamber to protect the cables at that interface and to prevent steam from leaking.

LOCA Harsh Environment Exposure The RTDs were exposed to the temperature / pressure environment depicted in the profile shown in Figure 1. Figure 1A shows the planned profile and Figure 1B shows the actual profile as read by pressure transducers attached to the chamber. Saturated steam was used to maintain the profile.

The primary control was pressurer the temperature attained at each level was the temperature associated with saturated steam at the desired pressure at the altitude of the test facility (5440 feet above sea level) . Figure 2 depicts instrumentation inside the chamber, showing the placement of thermocouples used to measure the test-chamber temperatures. Measurements on Figure 2 are taken downward from the top flange of the container head.

As soon as possible after the first 15-psig pressure plateau was reached, chemical spray was introduced into the chamber. Spray was continued throughout the period of exposure in the test chamber. The spray was introduced primarily to provide a conductive medium so that leaks would be more easily recognized by aberrant readings caused by electrical short circuits in the system. The exposure was terminated at the end of 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months .

Chemical spray composition was as follows (per IEEE-323-74):

- 0.28 molar H3B03 (3000 ppm boron)

- 0.64 molar Na28023

- NaOH to make a pH between 10.0 and 11.0 at 77*F (25'C) 4

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Test Results Exposure was begun at 0830, March 16. Within the first minute, a large steam leak was apparent around the cable of RTD No. 1 where the cable came out of the chamber. Post-mortem after the test revealed that the leak was around the screw cap sealing gasket at the RTD head. By 0831, its readings had begun to diverge from the chamber temperature. By 0832 RTD No. l 1 was clearly producing erroneous temperature indications. By 0846 (16 minutes into the test) the test was temporarily shut .

l down, the cables were cut on RTD No.1 and the steam leak sealed.

During the same time period, RTD No. 2 and RTD No. 3 also gave erroneous readings, suggesting that water had leaked into the RTDs. (Af ter the conclusion of the exposure, RTD No. 2 was found to be leaking at the head gasket and also to have a small hole through the body casting. RTD No. 3 was found to have a small leak in the head gasket and a small leak in the flexible metal hose used to protect the cable.) By the end of the test, RTD No. 3 was also leaking at the Seal-Tite connector at the chamber head because the heat-shrinkable tubing had shrunk too far and had uncovered the connector. The problems with flexible hose and heat-shrinkable tubing are not attributable

, to Supplier A, as these elements were Sandia-furnished. (The flexible hose was supplied as nuclear-grade material, and the heat-shrinkable tubing had been used in the same way in previous Sandia tests.) ,

At 0930, March 16, the test was restarted. During the course of the test, Supplier B and Supplier C RTDs functioned properly. At some time during the test, every RTD from Supplier A gave erroneous (low) readings. At other times they l

recovered and provided reasonably accurate temperature indications. Post-test inspection revealed that moisture had entered all four Supplier A units.

Table 2 provides a running account of significant events i throughout the harsh environment exposure. After RTD No. 1 was cut out of the test and the chamber resealed, the three remaining Supplier A RTDs functioned adequately during portions of the test.

Post-Test Investigations i

The results described below follow the sequence in which the inspections were performed. The inital configuration was with all RTDs still mounted in the chamber head, but with the lower part of the chamber removed.

Post-exposure temperature readings were taken with the RTD immersed first in an ice bath then in hot water at approxi-mately 50*C. Supplier B and Supplier C RTDs functioned satisfactorily. RTD No. 2 and RTD No. 4 functioned properly f

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". during this test. RTD No. 1 and RTD No. 3 gave readings far below the temperature being measured.

Insulation resistance measurements at 10 volts were taken of all units while they were still mounted in the test chamber head. All readings were above 1x1010 ohms for Supplier B and Supplier C RTDs. RTD No. 1 leads had been cut and this test could not be applied. RTD No. 2 had one channel which tested from 1.5x107 to 2.4x107 ohms; the other channel tested below the range of the IR tester (0.5x106 chms) but tested from 15 kilohms to 17 kilohms with a Simpson Model 250L Multimeter. RTD No. 3 (both channels) tested below the range of the IR tester; readings with the Simpson meter were in the 1 kilohm to 2 kilohm range. RTD No. 4 readings were all around 1 megohm. -

During assembly of the test specimens, the caps of all four Supplier A RTDs had been tightened to a minimum torque of 50 foot-pounds with a breakover torque wrench. A post-test check of the torque on each cap was made in the tightening direction first, then breaking torque was measured. In the tightening direction, RTD No. 2 read 50 foot-pounds; breakaway torque was approximately 35 foot-pounds. (Note that breakaway torque values are generally less reliable.) RTDs No. 1, 3, and 4 showed no movement in the tightening direction with 60 foot-pounds applied. Breakaway torque for these units were read as approximately 100 foot-pounds, approximately 55 foot-pounds, and approximately 30 foot-pounds, respectively.

After removal from the test fixture, insulation resistance (IR) measurements at 10 volts were again taken. All readings were above lx1010 ohms for Supplier B and Supplier C RTDs.

On RTD No. 1, all leads were shorted. Readings taken with a multimeter were less than 100 ohms for all leads of both elements. RTD No. 2 (-) channel IR readings were all less than 0.5x106 (the lower limit of the instrument) . With a Simpson Multimeter Model 250L the (+) channel resistance readings were in the 15 kilohm to 17 kilohm range. RTD No. 3 leads all read less than 0.5x106 ohms with the IR tester. With a Simpson Multimeter the resistance readings were 1 kilohm to 2 kilohms. l RTD No. 4 IR readings were in the lx107 ohm range. These i l

tests were made first through the cables, then through the elements with cables removed but element leads still connected l to the terminal boards. !

After the above tests were completed, the element leads were disconnected from the terminal boards and IR readings were taken from the element leads to ground. RTD No. 1 readings were still below the lower limit of the IR tester. A Fluke Model 8040A Multimeter was used to measure the two elements.

The (+) element read approximately 500 kilohms and the (-)

element read approximately 150 kilohms. (When the elements were removed from their thermowell, it was found to be full of l

_10 water.) RTD No. 2 readings were in the 1-2x107 ohm range with the IR tester, RTD No. 3 readings were in the 1-2x106 ohm range, and RTD No. 4 readings were in the 2-3x107 ohm range.

During inspection of the castings, RTD No. 2 was found to have a small hole through the body. Examination revealed that one of the tapped holes used for mounting the terminal board .

into the casting had a small break-through. Discoloration ,

inside the casting indicated that water had leaked through this external hole into the tapped hole and then into the RTD body. ,

RTD No. 3 appeared to have a leak around the ground screw, in the cast body, as indicated by discoloration around the screw.

These two RTDs (No. 2 and No. 3) were inspected with dye penetrant, but no definitive results could be obtained to show a leak through either casting. They were then x-rayed with the machine set to 240KV. RTD No. 2 did not show a through hole on the x-ray negative because, in the region through which the exposure had to be made, too much metal was present for the small hole to show on the x-ray negative. However, after the non-destructive test methods failed to show the hole, a small pin was pushed into the hole from the outside of the body and the tip of the pin could be seen in the threaded hole inside the body, providing conclusive evidence that the tapped hole had broken through the casting. RTD No. 3, when x-rayed in the !

proper orientation, showed a small hole from outside going into a region of high porosity in the casting. The high-porosity region was adjacent to the threaded ground-screw hole. It is 4 reasonable to assume that this provided the leakage path for water, resulting in the discoloration around the ground screw and the moisture inside the RTD.

RTD No.1, No. 2, and No. 4 had leaked at the gasket. ,

, Before head-cap removal, a low-pressure air source (less than 4 psig) was held to the end of the flexible hose as it exited the chamber and Leak-Tec solution was applied to each RTD and cable system to determine the leak area. The areas found to be leaking by this test were those areas where discoloration occurred in the RTDs as described previously. As described above, RTD No. 1 had leaked very severely immediately upon

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admission of steam into the chamber. Leakage into RTD No. 4 i was much less severe.

At the end of this report, pictures and data are displayed. Figures 3 through 14 depict the test setup and the conditions found after exposure. Figure 15 through 27 show graphically the data collected during exposure. Refer to the captions on these figures for the RTDs and the time periods being depicted.

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List of Diagnostic Equipment Calibration Expiration Date Cal. Certificate No.

Accurex Auto-Data 10 4/20/83 3-210-1/12793 Heise Pressure Gauge 2/28/84 26953 Heise Digital Pressure Transducer 3/31/84 S7-5982 Hewlett-Packard 4329A

{ (IR Tester) 10/14/83 02898/9496

Simpson 250L Multimeter --- ---

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Fluke 8040A Multimeter --- ---

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! *The multimeters had not been calibrated. Readings taken by thee instruments are considered approximations. These instruments were

! used when insulation resistance readings were below the lower limit of the 10-volt scale of the HP 4329A (approximately 0.5x106 ohms).

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..* I Table 2 Sequence of Significant Events 0830 Test begun 0831 Chamber pressure: 10.7 psig. RTD No.1 appeared slightly different than other Supplier A RTDs. Channel 1 read slightly low (17.9'C) and channel 2 read slightly high (21.5'C). Other Supplier A RTDs read from 18.3*C to 18.6*C. Steam was leaking from the chamber around the

,. cable of No. 1.

,0832 Chamber pressure: 14.6 psig. RTD No. 1, channel 1 read 16.8'Cr. channel 2 read 101.9'C. Other Supplier A RTDs read from 23.9'C to 29.0*C. Thermocouple in No. I head:

.95.0*C.

j 0833 RTD No. 1, channel 1, read -53.2*C; channel 2 read 3 112.8'C. At this time, No. 3 appeared abnormal; No. 3, channel 1, read 42.5'C; channel 2 read 15.2*C.

! 0834 RTD No. 1, channel 1, read 26.4*C; channel 2 read i 103.7'C. No. 3, channel 1, read 49.7'C; channel 2 read 35.3'C. RTD No. 2 began to show abnormal readings at this time with channel 1 reading 61.4'C, channel 2 reading 22.6*C.

h 0835 No. 1, No. 2, and No. 3 continued to give abnormal j readings. No. 4 continued normally. This situation i continued to exist until the test was shut down to seal the steam leak around No.'l.

0843 Steam lines were closed and pressure was removed from the l-

' vessel.

0846 No. 1 leads were cut and the exit port was sealed.

0930 , Test was restarted. No. 1 was no longer being

! monitored. No. 2, channel 1, read 70.2*C; channel 2 read i 72.9'C. No. 3, channel 1, read 84.8'C; channel 2 read l 77.9'C. Both channels of No. 4 read 91.4*C, which 1

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{ the chamber of 96.l'C in the steam inlet area to 86.2*C !

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0931 Chamber temperature had risen to approximately 109'C and I

f. the pressure transducer indicated 14.8 psig. No. 4, channel 1, read 98.8'C; channel 2 read 98.7'C. No. 2 read 61.2*C and 61.6*C on channels 1 and 2, respectively. No. 3 read 71.6*C and 68.4'C on channels 1 and 2.

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m i 0932 Chamber temperature stabilized at about 108.5'C with a pressure of 14.8 psig. No. 4 read 107.S*C on both

, channels. No. 2 read 85.3*C and 88.3*C; No. 3 read 85.5'c and 80.8'C.

! Chamber temperature: 109'C; pressure: 15.4 psig. No.

0933

4, channel 1, read 109.4*C; channel 2 read 109.2*C. No.

2 read 99.7*C and 103.l'C; No. 3 read 96.8'c and 93.9'C.

0934 No. 4, channel 1, 109.8'C, channel 2, 109.6*C. No 2:

I 105.3*C, 106.9'C. No. 3: 104.4*C, 102.5*C. Chamber temperature as monitored by thermocouples: approximately 109'C.

, 0935 No. 4, channel 1, 109.2*C; channel 2, 109.5'C. No. 2:

106.8'C, 107.5'C. No. 3: 106.7'C, 104.6*C.

0936 No. 4, channel 2, 106.l'C; channel 2, 109.4*C. Channel 1 had dropped 3*C in one minute, with chamber temperature remaining stable. This was the first apparent anomaly for No. 4.

0937 No. 2 now read 107.7'C and 108.0*C (very close to chamber thermocouples). No. 3, channel 1, read 107.8'C; channel 2 still read low (105.7 'C) . No. 4, channel 1, read 105.3'C (low); channel 2 read 109.1*C.

0938 .s. 2: 108.3*C, 108.3*C; No. 3: 108.2*C, 106.0'C; No.

4: 106.9'C, 109.5'C.

0939 No. 2: 108.3*C, 108.2*C; No. 3: 108'.1' C , 105.9'C; No.

4: 108.8'C, 109.4*C.

-All Supplier A units remained relatively stable until 1000 at the above levels.

1000 This was the time designated to raise the pressure to 25 psig. However, because of difficulty with a clogged steam trap, this step was postponed until 1020. Chamber temperature was about 107.4'C. At 1000, No. 2, channel 1, read 106.8'C; channel 2 read 107.2*C. No. 3, channel 1, read 107.2*C; channel 2 read 106.3*C. No. 4, channel 1, read 102.7'C; channel 2 read 104.3*C. Note that No. 4 now gave evidence of enough difference from the chamber temperature to suggest a steam leak.

1020 Pressure was increased to 25 psig. Temperature was rising accordingly. At 1020, chamber temperature was approximately lll*C. No. 2, channel 1, read 107.l*C; channel 2 read 107.9'C. No. 3, channel 1, 107.9'C; channel 2, 106.4'C. No. 4 channel 1, 104.4*C; channel 2, 104.8'C. When the chamber stabilized at about 121*C, all RTDs appeared to be reading at or near the correct temperature.

.~ ' ,. l

_14 l

1045 Pressure was increased to 35 psig with a corresponding l rise in temperature. All RTDs appeared to be functioning properly (i.e., reading correct temperatures).

1115 Pressure was increased to 45 psig. All RTDs were functioning normally.-

1140 Pressure was increased to 55 psig. All RTDs were functioning properly.

1205 Pressure was increased to 65 psig. All RTDs ok.

1230 Pressure was increased to 75 psig. All RTDs ok.

l All RTDs ok.

1255 Pressure was increased to 85 psig.

1320 Pressure was increased to 95 psig. All RTDs ok.

1345 Pressure was increased to 105 psig. All RTDs ok.

'1410 Pressure was incressed to 115 psig. All RTDs ok.

1435 Pressure was reduced to 65 psig. All RTDs ok.

1500 Pressure was reduced to 15 psig. All RTDs ok.

1700 No. 2, channel 1, read 102.3'Cr channel 2 read 118.2*C.

Thermocouples read about 118.5'C. Evidently this unit

had begun to leak again. About this time a small steam i leak was observed around the no. 2 cable where it left j the chamber. This steam leak continued for the remainder t of the test.

Channel 1 of No. 2 continued to read low for the remainder of the test. Channel 2 remained at or near the ;

correct temperature.

2200 No. 3, channel 2, read 116.7'C (about 2*C low) . Channel i 1 of No. 2 was still low at 105.9"C.

2230 No. 3, channel 2, read 114.4'C. This condition persisted throughout the test. -

1 I 0100 Both channels of No. 3 were low with channel 1 reading 115.0*C and channel 2 reading 114.4*C. The chamber temperature was approximately 118.5'C. This RTD continued to read low throughout the remainder of the test.

0930 Pressure was reduced to zero (i.e., steam was shut off) and chemical spray was turned off. Channel 2 of No. 2 was still indicating properly and both channels of No. 4 l

!L were still indicating properly. Channel 1 of No. 2 and i both channels of No. 3 were giving false readings.

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J

SCREENING TEST PLAN FOR

,, EQUIPMENT QUALIFICATION RESEARCH TEST OF RESISTANCE TEMPERATURE DEVICES Earl E. Minor February 1983 Rev. 2 Sandia National Laboratories Albuquerque, New Mexico 87185 Operated by Sandia Corporation for the U. S. Department of Energy Prepared for Office of Nuclear Regulatory Research Division of Engineering Technology U. S. Nuclear Regulatory Commission FIN A1355

. yph -

2' z . . , , c 4 . o -r um # ' - V gY'

7 SCREENING TEST PLAN FOR

, EQUIPMENT QUALIFICATION RESEARCH TEST OF RESISTANCE TEMPERATURE DEVICES

l. INTRODUCTION 1.1 Objectives The purpose of this test is to expose ten RTDs from three different suppliers to LOCA harsh environment (temperature / pressure and chemical spray). The results will be used to determine the advisability of proceeding with the test program outlined in " Test Plan for Equipment Qualification Research Test of Resistance Temperature Devices," Rev. 1, November 1982, or proceeding with that test program with modifications.

1.2 Applicable Documents

- Test Plan for Equipment Qualification Research Test of Resistance Temperature Devices, Rev.1, November 1982.

1.3 Equipment Descriptions 1.3.1 Supplier A This RTD is of the three-wire duplex type. Thus, .

it contains two 100-ohm platinum elements each of which is of the three-wire configuration. Overall length of the RTD is approximately 13 inches.

Approximately 8 inches is inserted into a I

j thermowell which is mounted into a mounting

bracket (for our purposes) . The element is covered by a stainless steel sheath. The RTDS are purchased without cables. Six-conductor, 22 AWG, twisted copper wire with fiberglass insulation was purchased from the supplier to use with these RTDs. The thermowell (designed to be inserted into a medium. such as core coolant water) is of 316 stainless steel and is approximately 8-3/4 inches long. It contains 1-inch NPT external threads for mounting and a 0.260-inch bore to contain the RTD element.

4

.~. , ,-- . . . . I. '. . . . . . . .

, i ,- ,

l 1.3.2 Supplier B, Model 1 This RTD is a fast-response RTD designed for

. direct immersion-into the fluid being measured.

Overall length of the RTD is approximately 7-1/2 inches, of which about 3 inches protrudes above ,

the mounting surface. In addition, a four-foot l 3

.. cable extends from the end of the RTD. The i I elementfis a single, four-wire, 200-ohm platinum i

~

. element. Protection of the element is provided by a sheath.of 316 stainless steel. The cable is i

composed of four AWG 22 stranded, nickel-plated i' copper wires covered with mica tape glass braid,

. silicone varnish impregnated. Over the cable is a

' stainless steel bellows hose with overbraid which

- is installed to provide protection in a nuclear

,l. power plant environment.

<p

' l.3.3 Supplier B, Model 2 This RTD is approximately 21 inches long plus a four-foot cable. It extends about 6-1/4 inches from the top of the mounting surface into the medium being monitored, mounted in a thermowell.

The thermowell material is 316 stainless steel.

The element is like the previously-described Model 1 element; that ,is, it is a single, four-wire, i

200-ohm platinum element around a 446 stainless steel mandrel and is protected by a 446 stainless steel outer shell. The element is encapsulated in aluminum oxide. The cable is identical to that used in Model 1 and, like that cable, is protected by a stainless steel bellows hose with stainless

steel overbraid. -

1.3.4 Supplier C I This RTD has been designed for use in processes or systems where fast response is required. It i

contains a single 200-ohm platinum sensing l element. The element is protected by a stainless steel sheath and is designed to be immersed directly into the medium without a thermowell.

The RTD is approximately 9-1/2 inches long with about 4-1/2 inches below the mounting surface.

The cable is approximately 20 feet long, containing four leads plus a ground wire. The leads are nickel-coated, copper-stranded wire with Kapton insulation. Covering the cable is a shield

' of braided, nickel-clad copper covered with a jacket of polimide/ fluorinated ethylene tape. The outer jacket is braided 304 stainless steel.

i 1

L

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j 1.4 Test Sequence 1

- Pretest Visual Inspection and Functional Check i

- LOCA Harsh Environment '

- Visual Inspection and Functional Check 3 VISUAL INSPECTION AND FUNCTIONAL CHECK 2.1- Visual inspection shall consist of an inspection for

. obvious damage of external parts only. All joints shall !

I be inspected to ensure that they have been securely j tightened.

i i 2.2 A functional check shall consist of comparing each RTD's .

+ reading with a reading obtained from a reference

~

thermocouple in the same environment. The reference thermocouple will have been calibrated by Sandia's Secondary Standards Laboratory.- The intent is only to show that the RTD is still functional as indicated by a temperature reading of approximately the correct value.

1

'3. LOCA HARSH ENVIRONMENT TEST 3.1 Exposure to Harsh Environment Four RTDs from Supplier A, four from Supplier B (two of each model), and two from Supplier C will be exposed in the HIACA* LOCA Chamber to the temperature / pressure environment shown in Figure 1. Saturated steam will be used to maintain the temperature / pressure profile.

Chemical spray will be introduced into the test chamber as soon as possible after the first 65 psig plateau is attained and will continue for 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months or until the end of test, whichever comes first. The solution will be sprayed at an approximate rate of 0.15 gal / min per square foot of chamber surface projected perpendicular to the

direction of spray. Composition of the spray will be as follows:

0.28 Molar H 3B03 (3000 ppm boron) 0.064 Molar Na2S0 23 NaOH to make a pH between 10.0 and 11.0 at 77'F (25'C) l- i

's f l l! *High Intensity Adjustable Cobalt Array

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3.2 Interface Protection In general, cables and interconnections will be protected in a manner typical of nuclear power industry practice.

RTDs from Supplier A will have the cables covered with waterproof flexible conduit. The connections at the RTDs

- and at the exit ports from the test chamber will be covered with heat-shrinkable tubing. Every reasonable effort will be made to ensure that no failures will occur The RTDs from Suppliers B and C will be at interfaces.

protected only by the sheaths manufactured into the cables.

3.3 Torque Requirements The heads of RTDs from Supplier A will be torqued to 50 + 5 foot-pounds. The nipples and unions will be securely tightened. Suppliers B and C will be inspected j

to ensure the assembly is securely tightened.

I y 4. POST-TEST INSPECTION 4.1 Functional Tests A functional check will be performed as specified in 1

}

l paragraph 2.2.

I .

4.2 visual Inspection A visual inspection will be performed as specified in paragraph 2.1. All important effects will be recorded.

I Photographs will be taken of any noticeable physical damage.

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TEST PLAN FOR EQUIPMENT QUALIFICATION RESEARCH TEST OF RESISTANCE TEMPERATURE DEVICES Earl E. Minor November 1982 Rev. 1 Sandia National Laboratories Albuquerque, New Mexico 87185 Operated by Sandia Corporation for the U. S. Department of Energy Prepared for

. Office of Nuclear Regulatory Research Division of Engineering Technology U. S. Nuclear Regulatory Commission FIN A1355 A A >

w 11 sec a ' # T h TT'

~

Table of Contents Page

1. Introduction 1.1 objectives 1.2 Applicable Standards and Documents 1.3 Equipment Description 1.4 Rationale for Component Selection 1.5 List of Sensitive Materials 1.6 Aging and Test Sequence

2. Visual Inspection and Functional Check

3. Accelerated Aging 3.1 Description of Aging Variations 3.2 Thermal Aging 3.3 Radiation Aging 3.4 Vibration Aging

4. Design Basis Events 4.1 Seismic 4.2 LOCA Exposure

5. Post-Test Inspection 5.1 Functional check 5.2 Visual Inspection

6. Report f

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i 1

, l, ' ' *:

4 . ,.

Test Plan for Bquipment Qualification Research Test of .

Resistance Temperature Devices

1. Introduction

', 1.1 objectives The purpose of this test program is to assess the I methodology for qualification of safety-related equipment used in nuclear power stations. This will be accomplished by aging the Resistive Temperature Devices (RTDs)The in a plan is l'

variety of ways and evaluating their responses.

expected to show which aging technique produces the most severe aging. Three artificially aged units (one of each model) will be placed outside the test chamber and monitored 2

to obtain data for comparison Also with three their counterparts unaged units will exposed to DBE environments.

be exposed to DBE environments (LOCA radiation, seismic,If, and steam and chemical spray) to obtain comparative data.

at the end of the test, no detectable difference exists, it can be concluded that the harsh environment imposed masks the difference in aging and any aging difference is therefore negligible. .

1.2 Applicable Standards and Documents i

IEEE Std 323-1974, "IEEE Standard for Qualifying Class 1E Equipment for Nuclear Power Generating Stations."

IEEE Std 344-1975, "IEEE Recommended Practices for j

Seismic Qualification of Class 1E Equipment for Nuclear I

Power Generating Stations."

i

IEEE Std 381-1977, "IEEE Standard Criteria for Type

! Tests of Class 1E Modules Used in Nuclear Power Generating Stations."

j.

IEEE Std 382-1980, "IEEE Standard for Qualification of

. Safety-Related Valve Actuators." (Used for vibration aging.)

{

U.S. Nuclear Regulatory Commission, Regulatory Guide 1.89, November A974, " Qualification of Class 1E Equipment for Nuclear Power Plants."

'

U.S. Nuclear Regulatory Commission, Regulatory Guide 1.100, Revision 1, August 1977, " Seismic Qualification of Electric Equipment for Nuclear Power Plants."

4 1

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_ __ .__,-_ .-.___.._ _ _ _ . _ E!

l i

l

= U.S. Nuclear Regulatory Commission, NUREG-0588, Revision )

1, " Interim Staff Position on Environmental l Qualification of Safety-Related Equipment."

4

+ ANSI / ASTM E644-78, " Standard Methods for Testing Industrial Resistance Thermometers."

1.3 Equipment Descriptions 1.3.1 Supplier A 1

This RTD is of the three-wire duplex type. Thus, it contains two 100-ohm platinum elements each of which is of the three-wire configuration. Overall length of the RTD is approximately 13 inches. Approximately 8 inches is inserted into a thermowell which is mounted into a mounting bracket (for our purposes).

The element is covered by a stainless steel sheath.

! The RTDs are purchased without cables.

Six-conductor, 22 AWG, twisted copper wire with fiberglass insulation was purchased from the supplier to use with these RTDs. The thermowell (designed to be inserted into a medium such as core coolant water) is of 316 stainless steel and is approximately 8 3/4

' t inches long. It contains 1-inch NPT external threads for mounting and a 0.260-inch bore to contain the RTD element.

1.3.2 Supplier B, Model 1 This RTD is a fast-response RTD designed for direct immersion into the fluid being measured. Overall ,

length of the RTD is approximately 7 1/2 inches, of which about 3 inches protrudes above the mounting surface. In addition, a four-foot cable extends from the end of the RTD. The element is a single, four-wire, 200-ohm platinum element. Protection of the element is provided by a sheath of 316 stainless i steel. The cable is composed of four AWG 22 stranded, nickel-plated copper wires covered with l

l

mica tape glass braid, silicone varnish impregnated.

Over the cable is a stainless steel bellows hose with overbraid which is installed to provide protection in a nuclear power plant environment.

I 1.3.3 Supplier B, Model 2 This RTD is approximately 21 inches long plus a four-foot cable. It extends about 6 1/4 inches from the top of the mounting surface into the medium being

' monitored, mounted in a thermowell. The thermowell I

I _ _

^

material is 316 stainless steel. The element is like that is, it the previously-described Model 1 element; is a single, four-wire, 200-ohm platinum element around a 446 stainless steel mandrel and is protected by a 446 stainless steel outer shell. The element is encapsulated in aluminum oxide. The cable is identical to that used on Model 1 and, like that cable, is protected by a stainless steel bellows hose with stainless steel overbraid.

1.3.4 Supplier C This RTD has been designed for use in processes It contains or systems where fast response is required.

a single 200-ohm platinum sensing element. The element is protected by a stainless steel sheath and is designed to be immersed directly into the medium without a thermowell. The RTD is approximately 9 1/2 inches long with about 4 1/2 inches below the mounting surface. The cable is approximately 20 The feet long, containing four leads plus a ground wire.

.: leads are nickel-coated, copper-stranded wire with Kapton insulation. Covering the cable is a shield of I braided, nickel-clad copper covered with a jacket of polyiside/ fluorinated ethylene tape. The outer jacket is braided 304 stainless steel.

1.4 Rationale for Component Selection RTDs were selected by the Equipment Qualification Branch, Office of Nuclear Reactor Regulation, Nuclear Regulatory l Commission, as a candidate for testing because of theA large Supplier and

numbers anstalled in nuclear power plants.

Supplier B RTDs were selected for test because they haveand are currently b 323-1974 been marketed.

qualified to IEEE StdThe models were selected based on an engineerin evaluation by Sandia of designs such'that typical urits will be tested. These models were recommended to theInNRC by the case Sandia and procured based on NRC concurrence. For of supplier A RTDs, this resolved into one model.

Supplier B components, two models have been chosen to typify two basic designs. RTDs from other suppliers which are (1) they are in operating plants were not selected because Thermoelectric; or

being phased out of the plants - e.g.,

(2) they exist in small quantities; or (3) a source of supply no longer exists - e.g., Sostman (the company is no longer in business).

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.- e 1.5 List-of sensitive Materials Activation Supplier A Energy Sour _ce Thermotorg CN 9000 0.98 eV EPRI NP-1588 and Supplier A

( Armstrong Gasket) Eng.

Nitrile base synthetic fiber 1.20 eV seal "

silicone rubber insulation 1.16 eV Activation Supplier B Energy Source Epoxy, Emerson & Cuming 0.98 eV EPRI NP-1588 2762 FT (Catalyst 17) "

Aeroseal Silicone Sealants 1.16 eV "

GE resins (SR 17 and SR 98 1. 2 eV Varnishes)

Activation Supplier C Energy Source Ethylene propylene 1.28 EPRI NP-1588 "

Polyiside/ fluorinated 1.57 ethylene "

Rapton 1.29 Other components unknown 1.6 Aging and Test Sequence In general, aging and test sequences will contain the following elements:

Protest Visual Inspection and Functional Check

Aging Sequence (Check function between each step in the sequence)

Visual Inspection and Functional Check

Vibration Exposure

Visual Inspection and Functional.. Check

Seismic Exposure a Visual Inspection and Functional Check

LOCA Radiation

Visual Inspection and Functional Check

LOCA Harsh Environment

Visual Inspection and Functional Check

- w-.- -

NOTES. During thermal aging, radiation aging, and LOCA radiation, all units will be monitored at least once each day (except weekends) to determine functionability by performing a functional check as described in Paragraph 2.2 of this document. During harsh environment exposure, each unit will be monitored periodically and recorded throughout the exposure. During the temperature / pressure peaks at the start of the test, the temperature read by each unit will be recorded at approximately 20-minute intervals. During the steady phase of the test, the interval will be extended to approximately four hours.

See Figure'l for a graphic representation of the test sequence.

2. Visual Inspection and Functional Check 2.1 Visual inspection shall consist of an inspection for obvious

' ' damage of external parts only. Magnification shall not be used unless it is necessary for investigation after damage

> is observed.

2.2 A functional check shall consist of comparing each RTD's reading with a reading obtained from a reference

' thermocouple in the same environment. The reference

'. thermocouple will have been calibrated by Sandia's Secondary

' Standards Laboratory. The intent is only to show that the RTD is still functional as indicated by a temperature l

reading of approximately the corr'ect value.

I 2.3 These checks shall be performed in the sequence indicated in Paragraph 1.6 of this document.

l

3. Accelerated Aging For methodology studies the RTDs will be divided into five groups which will be aged using five different techniques.

The aging technique for each group is discussed below. See Figure 1 for a graphic representation of the aging and test sequences.

NOTE: Prior to aging, 50 pound-feet of torque will be applied to all threaded caps and to the mounting of li

, all RTDs into thermowells and brackets.

! i. 3.1 Description of Aging Variations i,

3.1.1 Group 1 - Thermal followed by Radiation (High Dose l'I Rate)

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Group 1 will be thermally aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) at 134*C (273*F) then exposed to gamma radiation at a rate of approximately 0.7 Mrad / hour (air equivalent) for a total aging dose of 50-Mrad (+

10%) . Time of exposure will be approximately 3 days. This technique is commonly used by the nuclear industry except that usually the industry appliesFor a total integrated dose of 200 Mrad at one time.

Sandia's tests, vibration aging.will follow the 50-Mrad aging.

Group 1 will consist of two Supplier A, one Supplier B Model 1 and one Supplier B Model 2, and two Supplier C RTDs. .

1 3.1.2 Group 2 - Radiation (High Dose Rate) followed by Thermal A

Group 2 will be exposed to gamma radiation at a rate of approximately 0.7 Mrad / hour for an aging dose of 50 Mrad (+ 104). Time Then of exposure will be approximaEely 3 days. this group will be thermally aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) at 134*C (273*F), followed by vibration aging.

Group 2 will co'nsist of two Supplier A, one Supplier B Model 1, and one Supplier B Model 2 for aging. :

i 3.1.3 Group 3 - Radiation (Low Dose Rate) followed by .

<- Thermal I Group 3 will be radiation aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) at a dose rate of approximately 70 krad/ hour l J i for a total aging dose of 50 Mrad (+ 104). This l j group will then be thermally aged for 30 days (720 l I

hours) at 134*C (273*F), followed by vibration aging. l I

f Group 3 will consist of two Supplier A, one Supplier l B Model 1, and one Supplier B Model 2, and (for aging j

only, without exposure to the additional 150 Mrad of LOCA radiation) one additional Supplier A and one 4

i additional Supplier B Model 1. The additional two RTDs will not be subjected to DBE environments but

!1 1

will be monitored outside the test chamber as controls of the experiment.

3.1.4 Group 4 - Thermal followed by Radiation (Low Dose Rate)

Group 4 will be thermally aged for 30 days (720

! hours) at 134*C (273*F), then exposed to gamma l

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radiation at a rate of approximately 70 krad/ hour for a total aging dose of 50 Mrad (+-10%). Radiation Time of exposure will be 30 days (720 ho~urs).

aging will be followed by vibration aging. , ,

Group 4 will consist of two Supplier A, one Supplier B Model.1, and one Supplier B Model 2, and (for aging i

only, without exposure to the additional 150 Mrad of LOCA radiation) one additional Supplier B Model 2 which will not be subjected to DBE environments but will be monitored outside the test chamber.

11 3.1.5 Group 5 - Simultaneous Thermal and Radiation (Low

' Dose Rate)

Group 5 will be aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) ina The dose combined-radiation and thermal environment.

rate will be 70 krad/ hour and the temperature will be 134'C (273*F) . This aging exposure will be followed by vibration aging.

Group 5 will consist of two supplier A, one supplier B Model 1, and one Supplier B Model 2.

4; 3.1.6 Summary Twelve supplier A (one model), 14 Supplier B (two models), and two Supplier C RTDs will be tested.

' Table 1 summarizes the five groups.

l 3.2 Thermal Aging The commonly-used theory for accelerated thermal aging is based on a temperature-dependent reaction which follows the Arrhenius equations t exp (-Eg/kT) = constant (1)

I I

I where t = time exp = exponent to base e

' = activation energy '

EA I k = a constant related to Boltzmann's constant T = absolute temperature j I i

Equation (1) may be reduced to the following forms I

(2) 9-=y- (in t, - In t,) +

h-i k

5-~-- - .

'*-""'D-"t---Me-,,,, ,

where the subscripts "a" and "s" indicate " accelerated" and

" service", respectively.

'l A service temperature of 60'C (140'F) was chosen to - '

represent service ambient temperature inside containment.

supplier A and Supplier B RTDs were qualified using 60'C and 50*C, respectively, as service temperatures. Actual service conditions for RTDs will vary widely depending on the function monitored by the RTD being considered. The most severe environment commonly monitored is the temperature of the primary coolant water, which is estimated to reach 343*C (650*F) at the

! pressurizer. The parts surrounded by primary coolant water and thus exposed to these temperatures are the thermowells and the ends of the RTDs which are inserted The into materials the thermowells most sensitive (including the platinum elements) .

to aging (see para 1.5) are not inside the stream of coolant i water in the pipe but are in the ambient air surrounding the l pipe. The actual service temperature of these materials is not

! known. Forty years was chosen as the life of the components, i corresponding to a 40-year desired life for the power station, The most sensitive materials in the RTDs have an activation t

energy (EA ) of 0.98 eV, so our accelerated thermal aging was i

l based on a service temperature of 60*C, an expected life of 40 years, and an activation energy of 0.98 ev.

An accelerated aging temperature was computed using the i

following parameters:

f

! ts = 40 years = 3.5 x 10 5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months = service time

= accelerated time

ta = 30 days = 720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months

= 333*K = service temperature

' Ts = 60*C = activation energy i

Eg = 0.98 eV i

i k = 8.617 x 10-5 eV/K

= +

(in t, - In t,)

1

=

8.617 x 10-5 (in 720 - in 3.5 x 105) ,333

= 2.459 x 10-3 therefore, Ta = 407K = 134*C (273*F)

I i Thus, RTDs are to be thermally aged at a temperature of 134*C (273*F) for 720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months (30 days).

l

)

i Table 1 t Summary of Five Aging Groups Thermal Simultaneous Vibration Remarks Thermal Radiation See Para.

Group 1 30 days 50 Mrad 9 3.4 2 Sup. A 9 134 C .7 Mrad /

2 Sup. B hour 2 Sup. C 50 Mrad 0 30 days See Para.

Group 2 3.4 2 Sup. A .7 Mrad / 6 134 C 2 Sup. B hour See Para. For aginij, add 1 Group 3 30 days 30 days Sup. A and 1 Sup. B

.07 Mrad / 9 134 C 3.4 2 Sup. A tiodel 1 2 Sup. B hour (50 Mrad)

See Para. For aging, add 1 Group 4 30 days 30 days

.07 Mrad / 3.4 Sup. B Model 2 2 Sup. A 9 134 C 2 Sup. B hour (50 Mrad)

Group 5 30 days 0 See Para.

2 Sup. A

.07 Mrad / 3.4 '

2 Sup. B hour and 134*C s

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3.3 Radiation Aging Aged RTDs will be subjected to a total integrated dose of 50 ,

Mrad (air) . As outlined in Paragraph 2.1 and illustrated in Figure 1, a variety of sequences and dose rates have been' Materials chosen for aging methodology comparisons.

research on materials similar to those used in the RTDs has demonstrated that radiation aging preceding thermal aging is generally more severe than thermal aging preceding radiation andthatradiationagingatalowdogerateismoresevere than radiation at a high dose rate. ( 2) The principal ,

factor increasing degradation at a low dose rate is that i;

' more oxygen is allowed to diffuse into the material. (3,4)

Groups 1 and 2 will be exposed at a high dose rate. Groups 3, 4, and 5 will be exposed at a relatively low dose rate.

Group 5, in addition to low-dose-rate exposure, will be simultaneously radiation and thermally aged to determine if

' a synergism exists. (See Table 1.)

For the purpose of this test, "high dose rate" and " low dose l rate" are defined as follows:

High dose rate - approximately 0.7 Mrad / hour Low dose rate - approximately 0.07 Mrad / hour

j These dose rates will be more closely defined immediately -

i prior to exposure.

3.4 vibration Aging l '

I '

3.4.1 The RTDs will be exposed to vibration aging to simulate to some degree the vibration experienced In use, by i components mounted in coolant water pipes.

these exposures are caused by starting and stopping of pumps, opening and closing of valves, flow of water, and vibration transmitted from heavy machinery to coolant water pipes through the building structure. The vibration is primarily low-frequency and small-amplitude. As a compromise, the vibration

. exposure outlined in IEEE Std. 382-1980 will be used for vibration aging of the RTDs. The specimens will lf be vibrated in all axes as defined in Figure 2.

3.4.2 The RTDs will be mounted on Sandia-designed fixtures in a vertical orientation similar to in-plant installation.

3.4.3 Sinusoidal motion will be applied by exposing the actuator to 0.75 g or such reduced acceleration at l low frequencies as will not exceed 0.25 inch double i

amplitude with the frequency sweeping from 5 to 200 l

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to 5 Eg at'a rate of 2 octaves / min. Ninet'y minutes of vibration shall be applied along each of the x, y, and s axes. (See Figure 2.)

'3.4.4 Input motion to the actuator will be monitored and controlled by accelerometers located on the test fixture adjacent to the mounting surface of the RTD.

4. Design Basis Events t

! 4.1 Seismic

'l ! 4.1.1 Mounting

, r A total of 25 RTDs will be subjected to seismic testing, composed of 11 Supplier A, 12 Supplier B (six of each model) , and two Supplier C. Three of j these units, one Supplier A and one of each model of

.j Supplier B, will be unaged. The units will be i

f mounted on Sandia-designed mounting brackets which can hold two units each. These brackets will also be For seismic used for mounting during LOCA exposure.

testing, the brackets will be mounted to a rigid fixture which may be either bolted or welded to the vibration table. The mounting orientation will be jj with the longitudinal axis of the RTDs in the vertical direction. The 23 RTDs will be tested simultaneously in the following sequence:

i Functional check (para. 2.2)

' Five operating' basis earthquake (OBE) tests, front-to-back and vertical (FB/V) orientation Five OBE tests, side-to-side and vertical (SS/V) '

orientation Functional check (para. 2.2)

One safe shutdown earthquake (SSE) . test, SS/V one SSE test, FB/V Functional check and visual inspection (para. 2.2 and 2.1)

The sequence described above is intended to represent most nuclear power stations but is not intended to envelope the most severe case possible. It is based upon a biaxial machine; however, if triaxial equipment is available to the test laboratory performing the seismic test, the sequence will be adapted to accommodate the triaxial equipment.

4.1.2 Excitation 4.1.2.1 Simultaneous Biaxial Excitation Each horizontal axis shall be excited separately, ll but each one shall be excited simultaneously with i

Il

'3 .-_..___.___-___._-- __

J .

l the vertical axis, e.g. longitudinal simultaneous with vertical and then lateral simultaneous with !

vertical. Triaxial excitation, if available, may be utilized in place of biaxial excitation ~.

i 4.1.2.2 Random Multifrequency Tests ,

The test items shall be subjected to 30-second l duration biaxial multifrequency random motion which shall be amplitude controlled in 1/6-octave '

bandwidths spaced 1/6 octave apart over the i t

frequency range of 1-40 Es. Two (2) simultaneous, but independent, random signals shall be used as the excitation to produce phase-incoherent horizontal and vertical motions. The amplitude of each 1/6 octave bandwidth shall be independently adjusted in each axis until the Test Response Spectra (TRS) envelope the Required Response spectra (RRS). (See Figures 3 and 4.)

The RRS shown in Figures 3 and 4 may be revised at the discretion of SNLA within the limitations of

j. the test equipment.

4.1.3 Instrumentation 4.1.3 1 Excitation Control ,

Accelerometers shall be used as means of control.

The test facility shall be responsible for placement in the proper locations with Sandia concurrence.

l 4.1.3.2 Specimen Response Pieso-electric or resistive accelerometers shall be mounted on each test item to monitor response l- of the seismic excitation. The number and placement of these accelerometers shall be l determined by the test facility and approved by

. SNLA. Each accelerometer's response will be recorded.

TRS plots of each accelerometer for each test in each orientation will be included in the test report.

4.2 LOCA Exposure

. 4.2.1 LOCA Radiation The units shall be exposed to gamma radiation at a dose rate of approximately 0.7 Mrad (air equivalent)

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=1 ,

E "hl per hour for approximately nine days for a total = -

integrated dose of 150 Mrad to simulate LOCA Including aging, the total integrated 7 radiation.

dose will then be 209 Mrad (+ 10%). A cobalt-60 " __

j source will be used as the sTmulator. ]

4.2.2 Exposure to Harsh Environment ]

a As previously stated, 12 Supplier A, 14 Supplier B, =

and two Supplier C RTDs will be used in the test. 3 Eleven Supplier A units will be exposed to harsh sa r!

environments, ten of which have been aged as described in Paragraph 3 and one of which has not "

[

l been artificially aged. Twelve Supplier B units will

! be exposed, six Model 1 and six Model 2. Ten of the Supplier B units (five of each model) will have been [

aged as described in Paragraph 2.1 and two units (one =

of each model) will not have been aged. Two Supplier C RTDs will be exposed. The three unaged units will ;

l be exposed to obtain comparative data with their l

artificially aged counterparts. In addition, one y aged Supplier A and two aged Supplier B units (one of :

each model) will be monitored outside of the environmental chamber as controls for the experiment. I Chemical spray will be introduced into the test chamber when the first peak in the temperature / 4 pressure profile his been attained. Spray will be 1 turned off before ramp-down and will be reinitiated =

when the second peak is attained. A.t the end of 24 -

l hours (from start of test) chemical spray will be 5

i. removed. The solution will be sprayed at an l

approximate rate of 0.15 gal / sin per square foot of _:

l chamber surface projected perpendicular to the _;

direction of spray. Composition of the chemical 4 spray will be as follows: 7 0.28 molar H 3B03 (3,000 ppm boron) 5 2

0.064 molar Na2S023 ? _

NaOH to make a pH between 10.0 and 11.0 at 77'F (25'C).

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The exposure profile shall be as shown in Figure 5. _

This profile represents Sandia's current capability.

t ~4.2.3 Interface Protection In general, cables and interconnections will be protected in a manner typical of nuclear power 5

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industry practice. RTDs from Supplier A and Supplier B will have the cables covered with waterproof flexible conduit. The connections at the RTDs and at the exit ports from the test chamber will be covered with heat-shrinkable tubing. Every reasonable effort will be made to ensure that no failures will occur at interfaces. The two Supplier C RTDs will be handled as a special case. One of these RTDs will be protected in the manner described above. The other will be protected only by the sheaths manufactured into the cable. Both situations presently exist in

! utilities and our intent is to determine the vulnerability of these units under both conditions.

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5. Post-Test Inspection

5.1 Functional Tests i A functional check will be performed as specified in i

Paragraph 2.2.

5.2 Visual Inspection A visual inspection will be performed as specified in i Paragraph 2.1. All important effects shall be recorded.

Photographs shall be taken of any noticeable physical damage.

6. Report The reports shall describe the test, procedures, and l results. The reports shall also include whatever rationale I and justification may be required to establish conclusions.

. Each equipment supplier shall receive a copy of the report pertaining to his product and will be allowed to comment.

Any comment will be included in the body of the report or as an addendum to the report.

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References

1. L. D. Bustard, " Ethylene Propylene Cable Degradation *During LOCA Research Tests: Tensile Properties at the Completion of Accelerated Aging," NUREG/CR-2553, SAND 82-0346, Sandia National Laboratories, Albuquerque, NM, May 1982.

2. J. Seguchi, et al., " Radiation Induced Oxidative Degradation of Polymers IV. Dose Rate Effects on Chemical and Mechanical Properties," Takasaki Radiation Chemistry Research

! Establishment, JAERI, Takasaki, Gunma-ken, 370-12, Japan, 1980.

3. S. Machi, " Radiation Degradation of Polymeric Materials Used in Nuclear Reactor," Japan Atomic Energy Research Institute, Takasaki Radiation Chemistry Research Establishment, Takasaki, Gunma, 370-12, Japan, 1980.

4. K. J. Gillen, et al. , . " Loss of Coolant Accident (LOCA)

Simulation Tests on Polymers: The Importance of Including f oxygen," NUREG/CR-2763, SAND 82-1071, Sandia National Laboratories, Albuquerque, NM, July 1982.

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_ 4-4' TEST PLAN FOR EQUIPMENT QUALIFICATION RESEARCH TEST OF RESISTANCE TEMPERATURE DEVICES i

Earl E. Minor September 1982 l

Rev. 0 Sandia National Laboratories Albuquerque, New Mexico 87185 Operated by Sandia Corporation

.. for the )

U. S. Department of Energy Prepared for Office of Nuclear Regulatory Research Division of Engineering Technology U. S. Nuclear Regulatory Commission -

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t. ** s Table of Contents Page

1. Introduction '

1.1 Objectives Applicable Standards and Documents l.2 1.3 Equipment Description 1.4* Rationale for Component Selection 1.5 List of Sensitive Materials 1.6 Aging and Test Sequence,

2. visual Inspection and Functional Check

'3. Accelerated Aging 3.1 Description of Aging Variations 3.2 Thermal Aging 3.3 Radiation Aging 3.4 vibration Aging

4. . Design Basis Events 4.1 Seismic 4.2 LOCA Exposure

5. Post-Test Inspection 5.1 Functional Check 5.2 Visual Inspection ,

6. Report ,

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Test Plan for Equipment Qualification Research Test of Resistance Temperature Devices l 1. Introduction 1.1 Obiectives The purpose of this test program is to assess the methodology for qualification of safety-related equipment used in nuclear power stations. This will be accomplished by aging the Resistive Temperature Devices (RTDs) in a variety of ways and evaluating their responses. The plan

.is expected to show which aging technique produces the most severe aging. Three artificially aged units (one of each model) will be placed outside the test chamber and monitored to obtain data for comparison with their counterparts exposed to DBE environments. Also three unaged units will be exposed to DBE environments (LOCA radiation, seismic, and steam and chemical spray) to obtain comparative data. If, at the end of the test, no detectable difference exists, it can be concluded that the harsh environment imposed masks the difference in aging and any aging difference is therefore negligible.

1.2 Applicable Standards and Documents

IEEE Std 323-1974, "IEEE Standard for Qualifying Class lE Equipment for Nuclear Power Generating Stations."

IEEE Std 344-1975, "IEEE Recommended Practices for Seismic Qualification of Class lE Equipment for Nuclear Power Generating Stations."

- IEEE Std 381-1977, "IEEE Standard Criteria for Type Tests of Class lE Modules Used in Nuclear Power Generating Stations."

. IEEE Std 382-1980, "IEEE Standard for Qualification of Safety-Related Valve Actuators." (Used for vibration aging.)

- U.S. Nuclear Regulatory Commission, Regulatory Guide 1.89, November 1974, " Qualification of Class lE Equipment for Nuclear Power Plants."

- U.S. Nuclear Regulatory Commission, Regulatory Guide 1.100, Revision 1, August 1977, " Seismic Qualification of Electric Equipment for Nuclear Power Plants."

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. U.S. Nuclear Regulatory Commincion, NUREG-0588, Revision 1, " Interim Staff Position on Environmental Qualification of Safety-Related Equipment."

- ANSI / ASTM E644-78, " Standard Methods for Testing Industrial Resistance Thermometers."

1.3 Equipment Descriptions 1.3.1 Pyco RTDi-P/N- 122-4030-04-2.7-8.5-GS This RTD is of the three-wire duplex type. Thus, it

- contains two 100-ohm platinum elements each of which is of the three-wire configuration. Overall length of the RTD is approximately 13 inches.

Approximately 8 inches is inserted into a thermowell (P/N ll6-0056-7-SA182F316) which is mounted into a' i mounting bracket (for our purposes). The resistance of the element changes 0.01385 ohm per degree Celsius. The element is covered by a stainless :

steel sheath. The thermowell (designed to be inserted into a medium such as core coolant water) is of 316 stainless steel and is approximately 8 3/4 inches long. It contains 1-inch NPT external

. threads for mounting and a 0.260-inch bore to contain the RTD element.

1.3.2 RdF'RTD,'P/N 21292-48 This RTD is a fast-response RTD designed for direct !

immersion into the fluid being measured. Overall length of the RTD is approximately 7 1/2 inches, of ,

which about 3 inches protrudes above the mounting surface. In addition *, a four-foot cable extends from the end of the RTD. The element is a single, four-wire, 200-ohm platinum element. Protection of the element is provided by a sheath of 316 stainless steel. The cable is composed of four AWG 22 stranded, nickel-plated copper wires covered with mica tape glass braid, silicone varnish impregnated. Over the cable is a stainless steel bellows hose with overbraid which is installed to provide protection in a nuclear power plant environment.

1.3.3 RdF RTD, P/N 21293-48 This RTD is approximately 21 inches long plus a four-foot cable. It extends about 6 1/4 inches from the top of the mounting surface into the medium

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being monitored, mounted in a thermowell, P/N 52918. The thermowell material is 316 stainless steel. The element is like the P/N 21292-48 element; that is, it is a single, four-wire, 200-ohm platinum element around a 446 stainless steel mandrel and is protected by a 446 stainless steel outer shell. The element is encapsulated in aluminum oxide. The cable is identical to that used on P/N 21292-48 and, like that cable, is protected by a stainless steel bellows hose with stainless

steel overbraid.

. NOTE: If efforts to obtain Rosemount RTDs succeed, the appropriate equipment and test description will be incorporated into the test plan.

1.4 Rationale for Component Selection RTDs were selected by the Equipment Qualification Branch, Office of Nuclear Reactor Regulation, Nuclear Regulatory Commission, as a candidate for testing _because of the large numbers installed in nuclear power plants. Pyco and RdF i- RTDs were selected for test because they have been qualified to IEEE Std 323-1974 and are currently being marketed. The models were selected based on an engineering evaluation by Sandia of designs such that typical units will be tested. These models were recommended to the NRC '

by Sandia and procured based on NRC concurrence. In the case of Pyco RTDs, this resolved into one model. For RdF components, two models have been chosen to typify two basic designs. RTDs from other suppliers.which are in operating plants were not selected because (1) they are being phased out of the plants - e.g., ThermoElectrict or (2) they exist in small quantitiest or (3) a source of supply no longer exists - e.g., Sostman (the company is no longer in business).

1.5 List of Sensitive Materials Activation Pyco Energy Source Thermotorg CN 9000 0.98 eV EPRI NP-1588 i- (Armstrong Gasket) and Pyco Eng.

Nitrile base synthetic fiber 1.20 eV seal "

Silicone rubber insulation 1.16 eV r

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4 Activation RdF Energy- Source Epoxy, Emerson & Cuming 0.98 eV EPRI NP-1588 2762 FT (Catalyst 17) "

Aeroseal Silicone Sealants 1.16 eV "

GE resins (SR 17 and SR 98 1. 2 eV Varnishes) 1.6 Aging and Test Sequence In general, aging and test sequences will contain the following elements:

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Pretest Visual Inspection and Functional Check

Aging Sequence (Check function between each step in the i sequence)

Visual Inspection and Functional Check

Vibration Exposure

Visual Inspection and Functional Check

Seismic Exposure

Visual Inspection and Functional Check

LOCA Radiation a Visual Inspection and Functional Check

LOCA Harsh Environment

Visual Inspection and Functional Check

~

NOTE: During thermal aging, radiation aging, and LOCA radiation, all units will be monitored at least once each day (except weekends) to determine functionability by performing a functional check.

During harsh environment exposure, each unit will be monitored periodically and recorded throughout the exposure. During the temperature / pressure peaks at the start of the test, the temperature read by each unit will be recorded at approximately 20-minute

. intervals. During the steady phase of the test, the interval will be extended to approximately four 4 hours. '

See Figure 1 for a graphic representation of the test l sequence.

2. Visual Inspection and Functional Check ;

NOTE: All RTDs will'have been calibrated by Sandia's Secondary Standards Laboratory before entering the test sequence.

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2.1 visual inspection shall consist of a visual inspection for obvious damage of external parts only. Magnification shall not be used unless it is necessary for investigation after damage is observed.

2.2 A functional check shall consist of comparing each RTD's reading with a reading obtained from a reference thermocouple in the same environment. The reference thermocouple will have been calibrated by Sandia's Secondary Standards Laboratory. The intent is only to show that the RTD is still functional as indicated by a temperature reading of approximately the correct value.

2.3 These checks shall be performed in the sequence indicated in Paragraph 1.6 of this document.

3. Accelerated Aging For methodology studies the RTDs will be divided into five groups which will be aged using five different techniques.

The aging technique for each group is discussed below. See Figure 1 for a graphic representation of the aging and test sequences.

3.1 Description of Aging Variations 3.1.1 Group 1 - Thermal followed by Radiation (High Dose Rate)

Group 1 will be thermally aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) at 134*C (273*F) then exposed to gamma radiation at a rate of approximately 0.7 Mrad / hour (air equivalent) for a total aging dose of 50 Mrad

(+ 10%). Time of exposure will be approximately 3 days. This technique is commonly used by the nuclear industry except that usually the industry applies a total integrated dose of 200 Mrad at one time. For Sandia's tests, vibration aging will follow the 50-Mrad aging.

Group 1 will consist of two Pyco, One RdF Model 21292-48, and one RdF Model 21293-48.

3.1.2 Group 2 - Radiation (High Dose Rate) followed by Thermal Group 2 will be exposed to gamma radiation at a rate of approximately 0.7 Mrad / hour for an aging dose of 50 Mrad (+ 10%). Time of exposure will be approximately 3 days. Then this group will be thermally aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) at 134*C (273*F), followed by vibration aging.

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.s Group 2 will consist of two Pyco, one RdF Model 21292-48, and one RdF Model 21293-48 for aging.

3.1.3 Group 3 - Radiation (Low Dose Rate) followed by Thermal Group 3 will be radiation aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) at a dose rate of approximately 70 krad/ hour for a total aging dose of 50 Mrad (+ 10%). This group will then be thermally aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) at 134*C (273*F), followed by vibration aging.

Group 3 will consist of two Pyco, one RdF Model 21292-48, and one RdF Model 21293-48, and (for aging only, without exposure to the additional 150 Mrad of LOCA radiation) one additional Pyco and one additional RdF Model 21292-48. The additional two RTDs will not be subjected to DBE environments but will be monitored outside the test chamber as controls of the experiment.

3.1.4 Group Thermal followed by Radiation (Low Dose Rate) .

Group 4 will be thermally aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) at 134*C (273*F), then exposed to gamma radiation at a rate of approximately 70 krad/ hour for a total aging dose of 50 Mrad (+ 10%). Time of exposure will be 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) . Radiation aging will be followed by vibration aging.

Group 4 will consist of two Pyco, one RdF Model 21292-48, and one RdF Model 21293-48, and (for aging only, without exposure to the additional 150 Mrad of LOCA radiation) one additional RdF Model 21292-48 which will not be subjected to DBE environments but will be monitored outside the test chamber.

3.1.5 Group 5 - Simultaneous Thermal and Radiation (Low Dose Rate)

Group 5 will be aged for 30 days (720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months ) in a combined radiation and thermal environment. The l dose rate will be 70 krad/ hour and the temperature will be 134*C (273*F). This aging exposure will be followed by vibration aging.

Group 5 will consist of two Pyco, one RdF Model 21292-48, and one RdF Model 21293-48.

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3.1.6 Summary 1

Twelve Pyco (one model) and 14 RdF (two models) RTDs will be tested. Table 1 summarizes the five groups.

3.2 Thermal Aging Accepted theory for accelerated thermal' aging is based on a

, temperature-dependent reaction which follows the Arrhenius equation:

t exp (-EA /kT) = constant (1) where t = time exp = exponent to base e Eg = activation energy 4

. k - = a constant related to Boltzmann's constant T = absolute temperature Equation (1) may be reduced to the following form:

't y =

E II" D a - 1" U s ) + -

(2) l where the subscripts "a" and "s" indicate " accelerated" and

" service", respectively.

A service temperature of 60*C (140*F) was chosen to represent a conservative service ambient temperature inside con-tainment. Actual service conditions for RTDs will vary widely depending on the function monitored by the RTD being considered.

9Mun most severe environment commonly monitored is the temperature of the primary coolant water, which is estimated to reach 343*C (650'F) at the pressurizer. The parts surrounded by primary coolant water and thus exposed to these temperatures are the thermowells and the ends of the RTDs which are inserted into the thermowells (including the platinum elements). The materials most sensitive to aging (see para 1.5) are not inside the stream of coolant water in the pipe but are in the ambient air surrounding the pipe. The actual service temperature of these materials is not known so a conservative estimate of ambient temperature, 60*C (140*F), was used in our calculations.

Forty years was chosen as the life of the components, corresponding to a 40-year desired life for the power station.

The most sensitive materials in the RTDs have an activation O -

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' Summary of Five Aging Groups i

Thermal Radiation Thermal Simultaneous Vibration Remarks l

Group'l 30 days 50 Mrad 6 See Para.

] 2 Pyco e 134 c .7 Mrad / 3.4

2 RdF hour Group 2 50 Mrad e 30 days See Para.

2 Pyco .7 Mrad / 6 134 ~C' 3.A 2 RdF hour i

Group 3 30 days ;30 days See Para. For aging, add 1

. 2 Pyco .07 Mrad / e 134~C 3.4 Pyco-and ] RdF i 2 RdF hour Mod. 21292-AR i (50 Mrad) i

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3.A RdF Mod. 21293-48 2 RdF hour -

(50 Mrad)

Group 5 30 days O See Para.

2 Pyco .07 Mrad / 3.4 l 2 RdF hour and i 134~C 1

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energy (EA ) of.0.98 ev, so our accelerated thermal aging was based on a service temperature of 60*C, an expected life of 40 years, and an activation energy of 0.98 eV.

An accelerated aging temperature was computed using the following parameters:

ts = 40 years = 3.5 x 105 hours0.00122 days 0.0292 hours 1.736111e-4 weeks 3.99525e-5 months = service time ta = 30 days = 720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months = accelerated time Ts = 60*C = 333*K = service temperature

= activation energy EA = = 8.617 0.98 eVx 10-5 ey/g k .

.= (in t, - in t,) +

-5 5

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= (in 720 - In 3.5 x 10 ) +

33

= 2.459 x 10-3 therefore, Ta = 407K = 134*C (273*F)

Thus, RTDs are to be thermally aged at a temperature of 134*C (273*F) for 720 hours0.00833 days 0.2 hours 0.00119 weeks 2.7396e-4 months (30 days) . .,

3.3 Radiation Aging 1

Aged RTDs will be subjected to a total integrated dose of 50 Mrad (air). As outlined in Paragraph 2.1 and illustrated in Figure 1, a variety of sequences and dose rates have been chosen for aging methodology comparisons.

Materials research on materials similar to those used in the RTDs has demonstrated that radiation aging preceding thermal aging is generally more severe than thermal aging preceding radiation and that radiation aging at a low dose rate ip more severe than' radiation at a high dose rate. (1,2) The principal factor increasing degradation l at a low dose rate is that more oxygen is allowed to i diffuse into the material. (3,4) Groups 1 and 2 will be i exposed at a high dose rate. Groups 3, 4, and 5 will be l l

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exposed at a relatively low dose rate. Group 5, in addition to low-dose-rate exposure, will be simultaneously radiation and thermally aged to determine if a synergism exists. (See Table 1.)

For the purpose of this test, "high dose rate" and " low dose rate" are defined as follows:

High dose rate - approximately 0.7 Mrad / hour Low dose rate - approximately 0.07 Mrad / hour These dose rates will be more closely defined immediately

prior to exposure.

3.4 Vibration Aging 3.4.1 The RTDs will be exposed to vibration aging to simulate to some degree the vibration experienced by components mounted in coolant water pipes. In use, these exposures are caused by starting and stopping of pumps, opening and closing of valves, flow of water, and vibration transmitted from heavy machinery to coolant water pipes through the building structure. The vibration is primarily low-frequency and small-amplitude. As a compromise, the vibration exposure outlined in IEEE Std.

382-1980 will be used for vibration aging of the

'RTDs. The specimens will be vibrated only in the x and y axes defined in Figure 2. Vibration along the z-axis is deemed insignificant and will not be applied.

3.4.2 The RTDs shall be mounted on Sandia-designed fixtures in a vertical orientation similar to in-plant installation.

3.4.3 Sinusoidal motion will be applied by exposing the actuator to 0.75 g or such reduced acceleration at low frequencies as will not exceed 0.25 inch double amplitude with the frequency sweeping from 5 to 200 to 5 Hz at a rate of 2 octaves / min. Ninety minutes of vibration shall be applied along each of the x and y axes. (See Figure 2.)

3.4.4 Input motion to the actuator will be monitored and controlled by accelerometers located on the test fixture adjacent to the mounting surface of the RTD.

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4. Design Basis Events 4.1 Seismic l

4.1.1 Mounting ,

i A total of 23 RTDs will be subjected to seismic testing, composed of 11 Pyco and 12 RdF (six of each

, model). Three of these units, one Pyco and one of ;

' each model of RdF, will be unaged. The units will be mounted on Sandia-designed mounting brackets i which can hold two units each. These brackets will also be used for mounting during LOCA exposure. For i seismic testing, the brackets will be mounted to a l rigid fixture which may be either bolted or welded to the vibration table. The mounting orientation i will be with tbs longitudinal axis of the RTDs in the vertical direction. The 23 RTDs will be tested simultaneously in the following sequence:

, Functional check Five operating basis earthquake (OBE) tests, front-to-back and vertical (FB/V) orientation Five OBE tests, side-to-side and vertical (SS/V)

! orientation Functional check One safe shutdown earthquake (SSE) test, SS/V j One SSE test, FB/V Functional check and visual inspection ;

The sequence described above is intended to

represent most nuclear power stations but is not

., intended to envelope the most severe case possible.

It is based upon a biaxial machiner however, if I triaxial equipment is available to the test laboratory performing the seismic test, the sequence

'will be adapted to accommodate the triaxial equipment. ;

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4.1.2 Excitation ,

l I 4.1.2.1 Simultaneous Biaxial Excitation Each horizontal axis shall be excitea separately, but each one shall be excited simultaneously with the vertical axis, e.g. longitudinal simultaneous with vertical and then lateral simultaneous with )

vertical. Triaxial excitation, if available, may l be utilized in place of biaxial excitation. l I

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'The test items shall be subjected to 30-second duration biaxial multifrequency random motion i

.which shall be amplitude controlled in 1/6-octave l bandwidths spaced 1/6 octave apart over the '

frequency. range of 1-40 Hz. Two (2) simultaneous, but independent, random signals l shall be:used as the excitation to produce phase-incoherent horizontal and vertical '

motions. The amplitude of each 1/6 octave bandwidth shall be independently adjusted in each ;

axis until the Test Response Spectra (TRS) envelope the Required Response Spectra (RRS). ;

(See Figures 3 and 4.)

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The RRS shown in Figures 3 and 4 may be revised at the discretion of SNLA within the limitations of the test equipment.

4.1.3 Instrumentation

l 4.1.3.1 Excitation Control Accelerometers shall be used as means of control. The test facility shall be responsible for placement in the proper locations with Sandia concurrence. -

4 4.1.3.2 Specimen Response Piezo-electric or resistive accelerometers shall be mounted on each test item to monitor response of the seismic excitation. The number and placement of these accelerometers shall be determined by the test facility and approved by SNLA. Each accelerometer's response will be recorded.

TRS plots of each accelerometer for each test in each orientation will be included in the test

> report.

4.2 LOCA Exposure 4.2.1 LOCA Radiation i

The units shall be exposed to gamma radiation at a dose rate of approximately 0.7 Mrad (air equivalent) per hour for approximately nine days for a total integrated dose of 150 Mrad to simulate LOCA

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. radiation. Including aging, the total integrated L dose will then be 200 Mrad (+ 10%). A cobalt-60 4

source will be used as the sTmulator.

4.2.2 Exposure to Marsh Environment As previously stated, 12 Pyco and 14 RdF RTDs will be used in.the test. Eleven Pyco units will be exposed _to harsh environments, ten of which have been aged as described in Paragraph 3 and one of which has not been artificially aged. Twelve RdF units will be exposed, six Model 21292 and six Model 21293. Ten of the RdF units (five of each model) will have been aged as described in Paragraph 2.4 and two units (one of each.model) will not have been aged. The'three unaged units will be exposed.to obtain comparative data with their artificially aged counterparts. In-addition, one aged Pyco and two aged RdF units (one of each model) will be monitored outside of the environmental chamber as controls for the experiment.

Chemical spray'will be introduced into the test chamber when the first peak in the temperature / pressure profile has been attained.

Spray will be turned off after ramp-down and will be

' reinitiated when the second peak is attained. At .

the end of 24 hours2.777778e-4 days 0.00667 hours 3.968254e-5 weeks 9.132e-6 months (from start of test) chemical spray will be removed. The solution will be sprayed at an approximate rate of 0.15 gal / min per square foot of chamber surface projected perpendicular to the direction of spray. Composition of the chemical spray will be as follows: .

0.28 molar-H 3BO3 (3,000 ppm boron) 0.064 molar Na2S0 23 NaOH to make a pH between 10.0 and 11.0 at 77'F (25'C).

The exposure profile shall be as shown in Figure 5.

This profile represents Sandia's current capability.

4.2.3 Interface Protection

. In general, cables and interconnections will be protected in a manner typical of nuclear power industry practice. For both Pyco and RdF units, 2

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.o . s-waterproof flexible conduit will be installed over the cables and sealed to the head of the RTDs. Care will be taken to ensure that connections necessary to feed cables out of the test chamber are fully protected.

5. Post-Test Inspection 5.1 Functional Tests A functional check will be performed as specified in Paragraph 2.2.

5.2 visual Inspection A visual inspection will be performed as specified in Paragraph 2.1. All important effects shall be recorded.

Photographs shall be taken of any noticeable physical damage.

6. Report The reports shall describe the test, procedures, and results. The reports shall also include whatever rationale and justification may be required to establish conclusions.

Each equipment supplier shall receive a copy of the report pertaining to his product and will be allowed to comment. ,

Any comment will be included in the body of the report or as an addendum to the report.

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References l i

< l i 1. L. D. Bustard, " Ethylene Propylene Cable Degradation During l LOCA Research Tests: Tensile Properties at the Completion J

of Accelerated Aging," NUREG/CR-2553, SAND 82-0346, Sandia National Laboratories, Albuquerque, NM, May 1982.

2. J. Seguchi, et al., " Radiation Induced Oxidative Degradation of Polymers IV. Dose Rate Effects on Chemical and Mechanical Properties," Takasaki Radiation Chemistry

'Research Establishment, JAERI, Takasaki, Gunma-ken, 370-12, Japan, 1980.

3. S. Machi, " Radiation Degradation of Polymeric Materials Used in Nuclear Reactor," Japan Atomic Energy Research Institute, Takasaki Radiation Chemistry Research Establishment, Takasaki, Gunma, 370-12, Japan, 1980.

4. K. J. Gillen, et al., " Loss of Coolant Accident (LOCA)

Simulation Tests on Polymers: The Importance of Including oxygen," NUREG/CR-2763, SAND 82-1071, Sandia National Laboratories, Albuquerque, NM, July 1982.

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, NURES/CR-3691 l SAND 84-0422

! nv Printed September 1984 An Assessment of Terminal Blocks in the Nuclear Power Industry Charles M. Craft Prepared by ,,

Sarda National Laboratores Atuguerque, New Mexco 87185 and Lrvermore, Cahfomia 94550 fer the Uruted States Department of Energy '(, il urder Contract DE-AC04-76DP00789 i ,d '.

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NOTICE This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United <

States Government nor any agency thereof, or any of their em- )

expressed or implied, or assumes ployees, makes any legalliability any warranty,ility for any third party's use, or the or responsib results of such use, et any information, apparatus product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights.

Available from 'I GPO Sales Program Division of Technical Information and Document Control i U.S. Nuclear Regulatory Commission I Washington, D.C. 20555 i and National Technical Information Service Springfield, Virginia 22161 l

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f NUREG/CR-3691 SAND 84-0422 RV AN ASSESSMENT OF TERMINAL BLOCKS IN THE NUCLEAR POWER INDUSTRY September 1984 Charles M. Craft Sandia National Laboratories Albuquerque, NM 87185 operated by Sandia Corporation for the U. S. Department of Energy Prepared for Instrumentation and Control Branch Division of Facility Operations Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Washington, DC 20555 Under Interagency Agreement DOE-40-550-75 NRC Fin No. A-1327 s .

Abstract The primary application of terminal blocks in the nuclear power industry is instrumentation and control (I&C) circuits. The performance of these circuits can be degraded by low level leakage currents and low )

. insulation resistance (IR) between conductors or to ground. Analyses of these circuits show that terminal blocks, when exposed to steam environments, experience leakage currents and low surface IR levels sufficient to affect some I&C applications. Since the mechanism ' reducing j surface IR (conductive surface moisture films) is primarily controlled by external environmental factors, the deseadation of terminal block performance is mostly independent of terminal block design. Testing shows that potential methods of reducing surface leakage currents will-not reduce them sufficiently to prevent terminal blocks from affecting I&C circuits. Therefore, terminal blocks can cause erroneous indications or actions of the I&C circuits in which they are a component. Most of the present qualification tests of temminal blocks do not address the issue of low level leakage currents, and hence do not demonstrate that

terminal blocks will operate properly in I&C circuits. ,

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N Table of contents a-Page '

w.]

Executive Summary.................................................... 1 m

1.0 Introduction.................................................... 4 523 1.1 Background................................................. 4 1.2 Objectives................................................. 4 1.3 Terminal Blocks in the Nuclear Power Industry.............. 4 23:

1.3.1 Why Terminal Blocks?................................ 4 25 1.3.2 Terminal Blocks Usage............................... 5 Hi 1.3.3 Terminal Block Applications......................... 10 ,_-

m 2.0 Terminal Block Life Cyc1e....................................... 12 m" 2.1 Terminal Block Design ..................................... 12 L-2.1.1 Terminal Block Materials............................ 12 a 2.1.2 Quality Assurance in Terminal Block Design.......... 17 2.2 Terminal Block Manufacture................................. 17 2-2.2.1 Manufacturing Process............................... 17 2.2.2 Quality Assurance in Manufacture.................... 17 2.3 Terminal Block Selection, Procurement, and Installation............................................... 18 2.3.1 Role of Architect / Engineering (A/E) Firms........... 18 i?

2.3.2 Construction and Installation Practices............. 18 as_ .

2.4 Inspections and Maintenance................................ 19 --

2.4.1 Utility Inspections and Maintenance................. 19 15 2.4.2 NRC Inspection Activities........................... 19 _]

2.5 Summary.................................................... 20 5;

3.0 Testing of Terminal B1ocks...................................... 21 EE E

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3.1 Standard Industry Tests.................................... 21 3.2 Nuclear Qualification Tests................................ 21 ,

3.2.1 Franklin Research Center's Test of Buchanan , __

Terminal Blocks for Philadelphia Electric 2 Company............................................. 22 i 3.2.2 Franklin Research Center's Test of Buchanan yg Terminal Blocks for control Products --

Divielon of Amerace Corporation..................... 26 43 3.2.3 Wyle Laboratory's Test of Marathon Terminal EE Blocks for Marathon Special Products................ 27 "2 m

3.2.4 Franklin Research Center's Test of Weidmuller 3 Terminal Blocks for Weidmuller Terminations, gj Inc................................................. 28 jE 3.2.5 Wyle Laboratory's Test of Weidmuller 4:

Terminal Blocks for Washington Public Power j!

Supply System....................................... 28 J

4 m.

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Table of Contents (continued)

- Page 3.2.6 Reports on Nuclear Qualification Tests of Selected Phonix Terminal Blocks.................. 29 3.2.7 Wyle Laboratory's Test of Eight Marathon Terminal Blocks for Commonwealth EdLeon company.............. 31 3.2.8 Westinghouse Electric Corporation's Test of Terminal Block Performance in LOCA Environment...... 33 4.0 Sandia Tests of Terminal Blocks in a Simulated LOCA Environment................................................ 34 4.1 Terminal Blocks Tested..................................... 34 4.2 Test Configuration................................

........ 34 4.3 Major Results..................................... ........ 36 5.0 Tests of Terminal Block Performance at Tem University................................ple ...................... 44 .

5.1 Phase I Tests of Terminal Blocks in a Quiescent Temperature and Humidity Environment....................... 44 5.2 Phase II Tests of Terminal Blocks in an Active Steam, Chemical Spray, and Temperature Environment......... 50 5.3 Characterization of the Amount of Salt De by Fingerprints.......................... posited

.................. 60 6.0 Theoretical Considerations Governing Film Formation and Conduction on Terminal Block Surfaces.....................,...... 63 6.1 Qualitative Discussion of Phenomena........................ 63 6.2 Explanation of the Mode 1................................... 64 6.3 Strengths and Weaknesses of the Mode 1...................... 74 7.0 F%i lure Modes of Terminal Blocks................................ 76 8.0 Examples of Possible Terminal Block Effects..................... 81 8.1 Transmitter Circuits....................................... 81 oe ?

8.2 [' L1 RTD Circuits...............................................

8.3 Thermocouple 86 C. 1l 8.4 Solenoid ValveCircuits......................................

89 P.d 8.5 Motor circuits................................. .. 98 M4 ~^

Circuits.......................................... .. 104 zhj}.

9.0 Possible Methods of Reducing Terminal Block Lea ?. i-.

Currents.......................................kage ................. 107 fjj J q 3lp ,

9.1 Cleaning................................................... 107 5..KN 9.2 > <.7 0 Sealing.................................

9.3 107 Coatings...................................................

................... 108

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Table of Contents (continued) rn 10.0 Assessment Celteria............................................ 112 10.1 Terminal Block Design Considerations..................... 112 10.2 Testing Considerations................................... 113 10.3 System Design Considerations............................. 114 11.0 conclusions.................................................... 117 12.0 References..................................................... 118 i

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List of Figures Fl.ture Page 2-1 Typical Configuration for a One-Piece Terminal Block......... 13 2-2 Typical Configuration for a Sectional Terminal Block......... 14 4-1 Wiring Schematic for the Sandia Phase I Terminal Block Tect.. 35

! 4-2 Wiring Schematic for the Sandia Phase II Terminal Block Test. 36 l

l 4-3 Wiring Schematic for the Transmitter Circuit Tested in the Sandia Phase II Terminal Block Test................... 37 4-4 Terminal-to-Terminal Insulation Resistance for Sandia Phase I Terminal B1ocks.............................................. 38 4-5 Insulation Resistance A for Sandia Phase II Terminal Blocks.. 39 4-6 Insulation Resistance for One Manufacturer I Model A Terminal Block From the Second Steam Ramp to the End

of the Test.................................................. 42 5-1 Experimental Test Setup for Salomon's Phase I Tests.......... 45 5-2 Electrical Circuit for Salomon's Phase I Tests............... 47 5-3 Sketch of Terminal Block Showing Location of Breakdown Path.. 48 5-4 Experimental Test Setup for Salomon's Phase II Tests......... 51 5-5 Electrical Circuit for Salomon's Phase II Tests.............. 52 5-6 Leakage Currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block in the "As-Received" Condition............................... 54 5-7 Leakage Currents at 125 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block in the "As-Received" Condition............................... 55 5-8 Leakage Currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block After Being Washed and Soaked in Distilled Water............. 56 5-9 Leakage Currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block After Being Washed With Distilled Water and Then Handled..... 57 5-10 Leakage Currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block in the "As-Received" Condition and Subjected to 7 Minutes of Finely Atomized Chemical Spray............................ 58

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List of Figures (continued)

Flaure F.nst 5-11 Leakage Currents ' at 45 Vdc as a Function of . Time and

. Temperature for a Manufacturer I, Model A Terminal Block

. Dipped in Saturated Nacl Solution and Dried.................. 59 6-1 Side and Frontal Views of Simplified Geometric Model for Film: Conduction on a Phenolic Substrate Material............. 67 6-2 Predicted Leakege Current Versus Applied Voltage for-Selected Film Widths and Other Parameters as Specified' in Table 6-1................................................. 73 8-1 : Simplified Schematic of a Typical Transmitter circuit in a Nuclear Power P1 ant........................................ 82 8-2 Percent Error in a Transmitter Circuit for Selected i values of Terminal Block Insulation Resistance............... 84 8-3 Total Current Trace of Transmitter Circuit During LnCA simu1stion................................................... 85 8-4 Indicated Pressure as a Function of Transmitter Output

.for a Correctly Operating-Circuit and for a circuit ~

With Terminal Block Insulation Resistance Assumed to be 10 kohns..................................................... 87

8-5 Simplified Block Diagram of a 3-Wire RTD Circuit Showing Parallel Connection Between Terminal Block Insulation Resistance and the Resistance of the RTD Sensing Element..... 88 8-6 Percent Error in the Resistance Measurement of an RfD RTD as a Function of Terminal Block Insulation.

Resistance................................................... 90 8-7. ~ Simplified Schematiclof a Thermocouple Circuit (Figure a) and a Temperature Profile for the Circuit That Night Exist

-During an Accident (Figure b)................................ 92 8-8 Open Circuit Voltage V2 ns a Function of the Spurious Voltage E5 for Selected Values of Ierminal Block Shunt Resistances.................................................. 94

,8-9 Error in the Open Circuit Voltage L.i a Function of the Spuelous Voltage E5 for Selected Values of Terminal Block Shunt Resistances...................................... 95 8-10 Open circuit Voltage V2 as a Function of the Shunt Resistance R5 for Selected Values of Terminal Block Shunt Resistances.................................................. 96

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List of Figures (continued)

Flauro Page f

8-11 Error in the Open Circuit Voltage as a Function of the Shunt Resistance R$ for Selected Values of Terminal Block Shunt Resistances...................................... 97 8-12 Simplified Circuit Schematic for One Possible Solenoid Valve Circuit................................................ 99 8-13 Typical Motor Circuit Connection for a 3-Phase Motor......... 105 8-14 ~ Time-to-Trip as a Function of Percent of Motor Full Load Current for One Type of Directly Heated Binetal Overload Re1ay............................................... 106 9-1 Comparison of Leakage Currents for Red'Glypt" Coated and Uncoated Terminal 81ocks..................................... 110 9-2 Comparison of Leakage Currents for Cycloaliphatic Epoxy Epoxy Coated and Uncoated Terminal Blocks.................... 111

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List of Tables Table. Page '

1-1 Summary of Terminal Block Usage by Plant..................... 6 l 2-1 Typical Radiation Dama'ge Thresholds and Maximum Service Temperatures For Five Insulating Materials Used in Terminal Blocks Found in U.S. Nuclear Power Plants........... 16

'3-1 Comparison of Some Industry LOCA Simulations For j

-Terminal Block Qualification................................. 23 '

5-1 Representative Data for Salomon's Quiescent Environment Bench Tests of Terminal Block Performance.................... 49 5-2 Typical Leakage Current Data from Salomon for One Manufacturer I, Model A Terminal Block Powered at 45 Vdc in a Clean Steam Environment......l.......................... 53 5-3 Final Values of Leakage Current and the Ratio of Final to Initial Values of Leakage Currents for Manufacturer I,

.Model A Terminal B1ocks...................................... 60 5-4 Sample of Data for Measured Residual Salt (Nacl) From One Fingerprint on a 1 cm2 Area of a Phenolic Terminal B1ock........................................................ 62 6-1 Sample Equilibrium Film Parameters Predicted by Film Conduction Mode 1............................................. 72 7-1 Summary of Failure Modes for Terminal Blocks................. 77 8-1 Selected Temperatures (*C(*F)) Indicated by the Type K Thermocouple Circuit Discussed as an Example in This Section...................................................... 98 8-2 Contact Development Table for Control Switches C1 and C2..... 100*

8 Contact Development Table for Limit Switches 21, 22, 23, and 24....................................................... 101

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Acknowledgments I wish to extend by gratitude to all those who contributed to the Component Assessment Program and its evaluation of terminal blocks. Mark Jacobus and Dave Furgal provided especially helpful consultation and moral support throughout the project. Mark also provided many hours of assistance in preparing the documentation. Dr. Robert Salomon of Temple University provided independent verification of experimental results and initiated development of the theoretical considerations presented hurein. Thereafter, Mark Jacobus modified the model and put it in its current form. Gary Johnson of Portland General Electric Company supported the work with input on the circuit analyses. He along with Dr.

Salomon at Temple, and Mark Jacobus, Meet Robertson, Frank Wyant, Dave Furgal, Larry Bustard, and Tim Gilmore here at Sandia carefully sifted through the draft report making many critical and needed comments. Carol Schmidt and Della Vigil worked diligently to prepare the many iterations of the report for publication. And finally, I especially want to thank my NRC program monitor, Ron Felt, for his patience and guidance throughout this project.

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Executive Summary Terminal blocks are used in nuclear power plant Class 1E and non-Class IE circuits inside and outside containment. Applications range fyom low voltage instrumentation and control (I&C) circuits to 480 Vac power circuits. Most terminal blocks are used in the low power I&C circuits. ..

The most prevalently used terminal blocks are General Electric EB series and CR-151 series, Weidmuller SAK types, Westinghouse 542247 types, States Type NT and Type ZWM, and Buchanan NQB series. All of these terminal .

blocks may be found in both inside and outside containment applications.

Approximately 50 percent of the utilities are planning to continue using terminal blocks in Class 1E applications inside containment. Those utilities choosing to continue use of terminal blocks operate mostly older .

plants with a large number of installed terminal blocks. However, some of the newer plants will also use terminal blocks. Alternately, some __.

utilities have chosen to remove all explicit

terminal blocks in Class IE "..,.,

applications inside containment, and others are removing them from selected applications (e.g., transmitter applications) or locations (e.g.,

3 'O' below submergence level). The major trend for new plants is to use f.-

splices insido containment. ;} F ,

yt The two major terminal blocks designs (one-piece and sectional) are ga c in approximately equal usage. Of the 57 distinct models of terminal E Jr.'

blocks tabulated in Section 1.3.3, 32 are of sectional construction and 25 are of one-piece construction. However, one-piece terminal blocks are f34

' ' C' . 4 probably more numerous in absolute terms since they are specified by a V..~

larger' number of plants. To characterize terminal block types as a 2 ;@

percentage of the total population is difficult, since data for the quantity of each type, as well as the total population of terminal blocks,

([

are not readily available. Yf' Since 1977, there have been a number of test programs sponsored by %gg j

both utilities and terminal block manufacturers that have been used to ,fj '

support the qualification of terminal blocks. These tests generally age >

.~,;

the terminal blocks using Arrhenius techniques or the 10*C rule, expose qM.- '

them to a seismic and vibration test, and then conduct a Loss of Coolant .. . . -

! Accident (LOCA) or a High Energy Line Break (HELB) simulation. Functional b ,-

evaluations normally consist of insulation resistance (IR) measurements f .j, l h

and conductor continuity checks following each of the several sequentially , $P.

applied environmental stresses (i.e., thermal aging, radiation exposure, seismic e%i vibration simulation, and LOCA/HELB simulation). Although the F.g}...

2 acc.ortance criteria for the functional tests were not always specifically $;'.

stated, all of the industry test reports reviewed by us indicate that the .e. ;[.' '

~

terminal blocks performed satisfactorily during the functional IR tests .# .', )

subsequent to each type of exposure. In some of these tests, measurements 1. / .j of the variation in terminal block perfermance during these tests were not .

made. In other tests, megohmmeter measurements were made at various ., - A points during the test with the block unpowered. The typical method used M J' f;D n:w::,

The term explicit refers to terminal blocks which are not an integral 3,MS 3

part of larger pieces of equipment such as electrical penetrations or .y M motor operators. g. ..

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to monitor terminal block performance during the LOCA/ HELD simulation was via fuses in the circuits that provided potential to the terminals of the terminal block. These fuses were sized to fall at leakage currents between 1 A and 24 A depending on the test specification. Acceptance criteria during LOCA/HELB simulation were based on the terminal block's ability to carry the specified voltage and current without falling those fuses. During some of the tests, the fuses in the circuits for one or more terminal blocks failed once or twice and were replaced. Sometimes for a given terminal block, the fuse continued to fall; in those cases, the terminal block was removed from the test. The test reports do not specify the number of times that a fuse was allowed to fall or the number of terminal blocks in the test lot that could be removed from the circuit before the terminal blocks were deemed to have failed the test. Using fuses in this manner has two drawbacks: first, the failure of a fuse is only a single point criterion that shows only that leakage currents were at least as large as the rated value of the fuse for the time necessary to fall the fuse; and second, the sizing of the fuses to "large" values l provides no information about low level leakage curetnts. As shown by the analysis of applications that may use terminal blocks, low level leakage currents on the order of mil 11 amperes can affect low powee instrumentation and control circuits. These circuits are the primary terminal block applications, and, therefore, the test acceptance criteria are not, in this respect, germane to most terminal block appilcations.

Surface leakage currents are the primary mechanism by which terminal blocks contribute to I&C circuit degradation. During Sandia's tests of terminal blocks in a simulated LOCA environment (1], insulation resistance at 4 Vde, 45 Vde, and 125 Vdc fell to 102 to 105 ohms from initial values of 108 to 1010 ohms. At 45 Vdc leakage currents were on the order of 0.1 to 10 mA. These values are sufficiently large to affect some 4 to 20 mA instrumentation circuits by 0.3 to 185 percent with a nominal effect of 0.5 to45percentattheirmidrange(12mA). At 4 Vdc insulation resistance ranged from 5 x 103 to 7 x 10 ohms. These values could affect RTD circuits by 0.3 to 9 percent. At 125 Vde, the irs were comparable or slightly higher (1/2 to 1 order of magnitude) than at 45 Vdc. During the cooldown periods to 95'c and during the post-test ambient temperature period, the insulation resistance increased to 106 to 108 ohms, but not to the pre-test levels of 108 to 1010 ohms. This behavior illustrates three points: first, the similarity between cooldown and post-test IR values indicates that the same conduction mechanism is probably occurring during these periods; second IR recovery to a higher value after exposure indicates that a transient phenomenon is responsible for the low IR values during the steam exposure; and third, that some permanent degradation of the terminal block innulation resistance occurs. A conductive moisture film is the most probable explanation for the transient phenomenon. During cooldown periods, the residual heat of the terminal block keeps its temperature and the temperature of the film higher than the temperature of surrounding environment. The film's vapor pressure will exceed the partial pressure of water in the surrounding atmosphere and hence the flim will vaporize, improving the terminal block's IR. Similarly, in post-test environments the film will evaporate and the IR will increase, l

l

I A model of film formation which predicts leakage currents that are consistent with the observed experimental results is presented. This model accounts for Joule heating of the film and the various heat loss mechanisms that exist. Interpretation of the results of the model and the Sandia test results ill indicate that qualification testing at voltage levels above those of actual use may be nonconservative with respect to leakage currents.

All tested terminal blocks performed similarly in a steam environment, though some designs experienced irs consistently lower than other designs. The formation of surface moisture films appears to be mostly independent of terminal block design. Three potential methods for reducing the magnitude of surface leakage currents (cleaning, sealing, and coating) will probably not reduce leakage currents to a level acceptable for I&C appilcations. We must, therefore, conclude that leakage currents observed during LOCA testing of terminal blocks can cause erroneous indications or actions of the low power I&C circuits in which they are a component. Most of the present quellfication tests do not address the primary failure mode (low level leakage currents) and therefore do not demonstrate that terminal blocks will operate properly in I&C circuits.

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}.0 INTRODUCTION I 11.1 Background

~ Terminal blocks are used in nuclear power plant class 1E and.non--

Class- IE circuits inside and outside ' containment. Their past widespread application'in critical circuits and their potential for causing common mode failure. lead to questions concerning their effect.on nuclear plant safety. Notivated by questions arising from the accident at Three Mile Island (THI), the NRC requested that Sandia National Laboratories investigate terminal block performance in TMI conditions. The results of this work by Stuotter (2) indicated that terminal blocks could potentially affect plant safety by undergoing low voltage surface breakdown at voltages between one hundred and five hundred volts. Stuetter also pointed out the highly statistical-nature of terminal block breakdown, and the influence of many complex, nonceproducible parameters.

Therefore, to minimize variability, Stuetzer employed a controlled laboratory environment to investigate terminal block behavior. Most of his work was conducted at 480 Vac and used experimental configurations that were not typical of actual nuclear plant installations. On this basis..the work was attacked as noncepresentative of actual industry practices. The results, however, did raise sufficient concern that a more thorough review of the terminal block issue was deemed necessary.

This document and a companion report (1) present the results of the follow-on study.

1.2 Objectives There were three rather broad objectives to the terminal block review. These were:

(1) Investigate the failure and degradation modes of terminal L

blocks in a configuration that was typical of actual plant:

installations, uses, and conditions.

(2) Assess the impact of the terminal block failure and degradation modes on nuclear power plant circuit performance.

(3) Develop the technical bases for judging the safety significance of terminal blocks.

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1.3 Terminal Blocks in the Nuclear Power Industry

l 1.3.1 'Why Terminal Blocks?

Terminal blocks are used as a method for connecting electrical circuits. They provide a convenient, low-cost method of making cable junctions. They are easily installed and provide provide maintenance and calibration access to the circuit by allowing circuit elements to be quickly and efficiently isolated. They are especially convenient for-maintenance in areas where anti-contamination clothing encumbers personnel. For these and other reasons, the utilities prefer terminal blocks as a means cf making circuit connections, particularly for l

4_

f low-voltage, low-power applications. The arguments against the use of terminal blocks are generally the dynamic regulatory environment and the desire to avoid qualification problems.

1.3.2 Terminal Block Usage The use of terminal blocks is universal throughout the nuclear industry for outside containment applications. Inside containment, terminal blocks are employed widely in older plants and in some newer

( plants, though the current trend for new plants is to une splicos inside containment. Based on a 1981-1982 survey of 25 utilities and data in the e Electric Power Research Institute (EPRI) Equipment Qualification Data Bank (EQDB) and the NRC's EQDB [3,4], approximately 50 percent of the utilities will continue to use terminal blocks in Class 1E applications inside containment. These utilities are pursuing two approaches to retaining terminal blocks: (1) qualify already installed blocks so as to avoid an extensive and costly replacement effort and (2) replace the terminal blocks with ones qualified by a vendor or another utility. Some of the utilities which are replacing terminal blocks with qualified spilces are continuing to use terminal blocks in outside containment applications, and some will continue to use terminal blocks in non-Class '

18 applications inside containment. Some utilities are following a policy of selective terminal block replacement, with a major criteria for replacement being the location of the terminal block relative to submergence level. Plants utilizing splices insido containment are not ;

totally exempt from in-containment terminal blocks in Class 1E -

applications. Many pieces of equipment (e.g., Limitorque valve operators and some electrical penetrations) contain terminal blocks as integral components. These are " implicit" terminal blocks as opposed to the _

" explicit" terminal blocks which the utilities are removing. .

It is difficult, if not impossible, to say that terminal blocks will or will not be used in plants still to be built and/or licensed. The decision between terminal blocks or splices depends somewhat on the preference of the utility and their Architect / Engineer (A/E). Other factors in the decision are the availability of qualified terminal blocks, and the stage of construction. These other reasons tend to be argued in either direction depending on the inclination of the utility and the A/E.

Table 1-1 summarizes the available data on terminal blocks being used in 73 of the 77 operating plants and 17 of the 68 planned or under construction plants.[5] No information was obtained from the other 7 plants. The primary sources of data used to complie these tables were the EPRI EQDB, the NRC's EQDB (3,4] and the survey of 25 utilities. The two data bases derive their major input from the utilities' I&E Bulletin J 79-01B submissions and subsequent updates and contain essentially duplicate information. The EPRI data base, however, has been regularly updated and expanded, whereas the NRC's data base has remained relatively static since 1981. One of the limitations to both data bases is that the inputs are generally limited to the utilities' Class 1E equipment; this limitation is in keeping with the intended objective of the data base, but does not permit a complete characterization of component usage within

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a plant. Further, the location of equipment is only provided as inside or outside containment. No detailed locations are given. As a result l any generic tests of terminal blocks must use generalized, very conservative environments. Little information is available in the data bases to tie down specific applications of the terminal blocks. To l overcome these weaknesses, the survey of 25 utilities was made.

Corporate headquarters or site personnel were contacted depending on the l organization of the utility. The quality of the information was limited l in most cases to the personal knowledge of the people contacted. No physical inspection of facilities was conducted.

TABLE 1-1 Summary of Terminal Block Usage by Plant flant Manufacturer Model Location Beaver Valley 1 Buchanan 0511, 0211 IC Marathon 1500 series Penn Union Series 1000 IC Big Rock Point General Electric EB-25, CR-15NT IC Westinghouse 542247, 805432 IC Weidmuller DK-4, SAKR Braidwood 1 & 2 Marathon 1600 NUC IC Penn Union No Model Number given Browns Ferry General Electric EB-25 1, 2, 3 Brunswick 1 & 2 Curtis Type L IC General Electric EB-5, EB-25, IC/OC CR-151D3 OC

, Wr.idmuller SAK Types IC Byron 1 & 2 '.iara thon 1600 NUC IC Penn Union No Model Number given Calvert Cliffs Buchanan B112 IC 1& 2 Marathon 1600 series IC Weidmuller SAKS IC Westinghouse 542247 IC Comancho ceak Weidmuller SAK6N, SAK10 IC/OC 1& 2 Cooper Buchanan 0514 IC General Electric EB-5, EB-25 IC CR-151A6

TABLE 1-1 (cont)

Summary of Terminal Block Usage by Plant ,

Plant Manufacturer Model Location Crystal River 3 Kulka STB, 7TB States NT OC Davis Besse 1 Stanwick Type G IC D.C. Cook 1 & 2 No Terminal Blocks in IE circuits inside containment Dresden 1, 2 Allen Bradley No model given IC

&3 (to be replaced)

Buchanan NQB series IC (replacements)

Duane Arnold General Electric EB-5 EB-25 (to IC/DC be replaced)

Buchanan NQB series IC (replacements)

Edwin I. Hatch Buchanan 515,212,222 IC 1&2 States ZWM Fermi 2 Weidmuller SAK Types OC Fitzpatrick General Electric EB-5, EB-25 IC Marathon No Model No. given Square D Class 9080 IC Fort Calhoun 1 States M25014 M25016 IC M25018, M25112 (Type NT)

Grand Gulf 1 & 2 Buchanan 0222, 0524 Cinch Jones 8-141 General Electric EB-5 EB-25, CR2960SY139C Ch-151D101 Kulka STB, 7TB, 17TB, 27TB, 600J-J, 601J-J, 602J-J.

603J-J, 604J-J Haddam Neck General Electric EB-25 IC Marathon 6012 Westinghouse 805432 IC Weidmuller SAK Types IC/0C Indian Point 2 Westinghouse 542247 IC

-1

TABLE 1-1 (cont)

Summary of Terminal Block Usage by Plant Plant Manufacturer Model Location Indian Point 3 Westinghouse 542247 IC Joseph M. Farley States ZWM IC 1&2 Kewaunee General Electric EB-5, EB-25 IC Lacrosse Buchanan 218 IC LaSalle 1 & 2 Buchanan NQB series IC Limerick 1 & 2 No Terminal Blocks in IE Circuits Inside Containment McGuire 1 & 2 States ZWM OC Weidmuller AKZ-4 OC Maine Yankee General Electric CR-1518 IC Square D Class 9080-CBI IC (1828-C19) (to be replaced)

Weidmuller SAK Types IC (replacements)

Millstone 1 General Ele tric EB-25 IC l Millstone 2 Weidmuller SAK-4 IC/DC I

Monticello Allen Bradley 1492-CD3 OC General Electric CR-151D3 OC Nine Mile Point 1 General Electric EB-5, EB-25 IC North Anna 1 & 2 Connectron NSS3 IC General Electric EB-5 EB-25 OC Marathon 200, 1500 series OC Thermoelectric Type 32-25 OC Nuclear One 1 & 2 General Electric EB-5 EB-25 Oconee 1, 2, 3 States M25004, M25008, OC M25012 (Type NT)

SLS-8 Oyster Creek 1 General Electric EB series (to be replaced)

Weidmuller SAK4 (replacement) OC/(ICf)

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TABLE 1-1 (cont)

Summary of Terminal Block Usage by Plant Manufacturer Model Location Plant Palisades Weidmuller DK-4 SAKR Westinghouse 805432 IC Peachbottom 2 & 3 General Electric CR-151 series OC Buchanan 2B100 series IC/DC Marathon 1600 series DC Weidmuller SAK Types OC I

Pilgelm 1 General Electric EB-25, CR-151 series Point Beach 1 & 2 Square D 77101, 17710 OC States M25012, M25006 OC (Type NT) 1492-CD3 (nylon) IC Prairie Island Allen Bradley 1&2 Quad Cities 1 & 2 Allen Bradley No model given (to be replaced) IC Buchanan NQB series IC (replacement)

Kolka 7TB IC Rancho Seco Square D Type G, 9080-CBx, IC (1828-C19)

Westinghouse 542247 IC Robert E. Ginna States Type NT OC f

H. B. Robinson 2 General Electric EB-5, EB-25 OC Salem 1 & 2 Buchanan 2B112N IC Cinch Jones Various IC/0C San Onofre 2 & 3 No Terminal Blocks in IE Circuits Inside Containment Seabrook 1 & 2 Weidmuller SAK Types IC/DC Sequoyah 1 & 2 General Electric EB-5, ER-25, CR-151B Westinghouse 805430(?)

Cutler Hammer 10987 General Electric EB-5, OC St. Lucio 1 & 2 CR-151D101

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! TABLE 1-1 (cont)

Summary of Terminal Block Usage by Plant Plant Manufacturer Model Location Surry 1 & 2 Connectron NSS3 OC General Electric EB-5, EB-25 OC Marathon 200, 1500 series OC Thermoelectric Type 32-25 OC Weidmuller SAK Types IC TMI-1 States NT, ZWM IC Weidmuller SAK Types IC Troj an General Electric EB-5, CR-151 IC Square D 828(phenolic) IC Turkey Point General Electric EB-5 OC 3&4 Vermont Yankee Buchanan 0222 Ir States Type NT Iu WNP-2 Weidmuller SAK Types IC Other Weidmuller Products OC General Electric CR-151B, OC CR2960SY139 Yankee Rowe Westinghouse 542247 IC Weidmuller SAK Types Zion 1 & 2 Marathon Pro Type IC EM-215/6000, Pro Type IC EM-41150/6000 1.3.3 Terminal Block Applications Terminal blocks are used predominantly in two types of circuits:

instrumentation and control circuits. Selected plants also employ terminal blocks explicitly in 480 Vac power circuits, but this practice is limited to 10 percent or less of the plants.

The instrumentation circuits are typically RTD circuits, which are low voltage (4 Vdc or less) and low current (1 mA or less), or

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transmitter circuits * (4-20 mA at 24-50 V$c). Control circuits are typically solenoid valve circuits, motor-operator control circuits, or status indication circuits and are normally 120 Vac or 125 Vdc and 1 A to 2 A or less.

The physical location of terminal blocks varies depending on the need to junction cables. Two of the most typical locations are at containment penetrations;and near equipment. At these points, field wiring must be terminated and connected to the penetration or to the instrument or control device pistall.

Electrically, the terminal blocks are typically adjacent to the instrument or control device and are separated only by the resistance of the intervening cable. As will be seen, this means that terminal block faults can be viewed as impedances in parallel with the input of the instrument or control device and their effects can be analyzed as such.

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Due to the susceptibility of transmitter circuits to leakage current, most utilities are now employing splices in these circuits or are planning to change to splices within the near future.

1 2.0 TERMINAL BLOCK LIFE CYCLE

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2.1 Terminal Block Design

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Terminal blocks are considered to be "off-the-shelf" items with designs that have not changed for many years. The two basic types of designs are one-piece and sectional. The primary distinguishing feature of the one-piece terminal block is that the insulating material which forms all of the barriers and the support for all electrical terminals is s single piece of molded insulating material. The number of terminals is fixed by the molding. Mounting plates or channels do not comprise part of the one-piece terminal block design, and the block is typically mounted directly to the enclosure structure.

The primary feature of the sectional terminal block is that each section is an individual unit of insulating material and conductor. Each of these sections may or may not have one inter-terminal barrier as part of each section's molding. If the barrier is separate, it will be held in place by alignment tabs. The sections are mounted on a channel or l

base plate to form a multi-terminal terminal block assembly. The sections are either individually attached to the mounting plate, or they are gang-mounted using a mating dovetail-like arrangement between the sections and mounting channel. Special end-pieces keep the sections from sliding off of the channel.

Figures 2-1 and 2-2 illustrate typical one-piece and sectional terminal block configurations, respectively. The sectional construction has a gap between sections from the top surface of the terminal block to the mounting rail. This gap does not exist in the one-piece terminal blocks. The width of the gap depends on how tightly the end pieces compress the sections together. Given the proper conditions, this gap has the potential to retain a moisture flim that could be a conducting path to ground, d

of the terminal block models reported in Table 1-1, 25 models were identified as one-piece and 32 as sectional. However, in terms of quantity installed, there are probably more one-piece than sectional terminal blocks in use simply because the majority of plants specify one-piece terminal blocks.

All terminal blocks have squared corners, crevices, and other convoluted surfaces which may retain deposits of contaminants and would be difficult to clean. Further, these designs make use of conformal coatings ineffective because a complete coating is difficult to achieve with the many concealed areas.

2.1.1 Terminal Block Materials For the terminal blocks listed in Table 1-1, five insulating materials were identified. phenolic with either a glass or cellulose filler is the primary material used for the insulation (39 of 57 models used this material) and alkyd, melamine, diallyl phthalate, and nylon i

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(five or fewer models each) make up the remainder. These materials are i normally chosen because of cost considerations, moldability, and their -i o

relatively good electrical insulation proporties. Table 2-1 summarizes some of the relevant properties for generic formulations of these 9

materials. Product literature for models which utilize phenolic l insulation indicates a maximum service temperature of 150*C J (302*F).[9,10,11,12,13) This value is in agreement with Table 2-1. Y Qualification tests of terminal blocks for nuclear service

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[14,15,16,17,18,19,20,21] typically age samples between 120*C (248'F) and 9

[ 165*c (329'F) and subsequently expose them to accident pecfiles that K j reach sustained temperatures of 170*C (338'F). The specimens tested e survive these thermal environments showing only minor degradstion. Thus. --

, from'a thermal standpoint, the selection of a phenolic or other polymeric material rated at a 150*C (302*F) service temperature is reasonabic for nuclear application.

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l Radiation sensitivity is influenced by insulator fill material. I

[ Westinghouse Research Laboratories, in reference to Westinghouse terminal _

[ blocks, evaluated the radiation properties of phenolics as follows (22): c; e *

! " Cellulose-filled phenolics...are less radiation i resistant, in general, than unfilled or mineral-filled j l phenolics. Information on paper , paper-laminate, and 2 k linen-filled phenolics indicates that they all begin to degrade at approximately 5 x 105 rada. The most -

radiation sensitive properties, elongation and impact

[' strength, are reduced by 25% at doses from 3 to 8 x p 106 rads. The (cellulore-filled phenolics) will ,

probably exhibit similar behavior. Electrical properties are not affected by doses <.2 x 107 rads."

g One manufacturer experienced a failure of their cellulose filled melamine terminal blocks during radiation and steam testing which is

[ possibly attributable to radiation effects. They experienced cracking of '-

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the terminal block insulation material. The postulated mechanism was that radiation degraded the surface resin material and perhaps opened the 2 structure sufficiently to allow moisture to be absorbed into the filler.

( Subsequently, when the high temperature accident transient was applied, j this moisture vaporized, pressurizing the interior of the insulation in a 1 time frame short enough to prevent pressure equilibration. Hence, the e e material cracked to relieve the stress, s

E The selection of a fill material typically affects the radiation tolerance of a material by plus or minus one to two orders of magnitude F (6) with organic fillers such as cellulose decreasing radiation tolerance and mineral or glass fillers increasing tolerance. The radiation doses

{ quoted in Table 2-1 are for degradation of mechanical properties such as flexural or tensile strength. It has been known for some time that the h electrical properties of many polymeric materials, such as volume resistivity, dielectric strength, and nec resistance, appear to be unchanged by radiation levels which cause extensive physical damage to the material.(23) Thus, with proper selection of fill material (e.g.,

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. Table'2-1 I Typical Radiation Damage Thresholds and Maximum Service Temperatures for Five Insulating Materials Used in Terminal Blocks Found in U.S. Nuclear Power Plants Insulating Radiation Damage Service Temperature

[ Material Threshold (Rads (C)) *C (*F)

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Phenolles

! glass filled -1010 160-190 (320-374) l- cellulose filled 108-109 120-220 (248-428)

Alkyd glass filled 109 . 149-191 (300-376) cellulose filled 108 191 (376)

Melamine (Restn) 108 glass filled 109 204 (399) cellulose filled 107 99-150 (210-302)

Diallyl phthalate

' glass filled 108 204 (399) cellulose filled 107 160 (320)

Nylon 61 105 106 130 (266)

(8) glass), the radiation levels quoted it. Table 2-1 indicate that there will be minimal effect on the insulating materials normally used for terminal blocks by nuclear plant radiation doses-(estimated doses: 5 x 107 rad operating life and estimated 1.5 x 108 rad accident).

The metallic terminals are typically stable to temperature and radiation levels which exceed the aging and accident environments postulated for nuclear power plants. Thus, we wculd not expect degraded performance of the conducting material based on pure radiation and/or temperature effects. There is, however, potential for material .

Interaction problems such as corrosion or galvanic action to occur. The selection of metal coatings and base conductor material should be such that these effects are minimized in both the normal operating environment (e.g., 80-110*F and 10-100f. NN) and the postulated accident environments which include steam and chenleals. One specific example would be to avoid the use of cadmium as plating material'because in a steam-chemical spray environment it may be a reactant in a galvanic reaction.

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1 l 2.1.2 Quality Assurance in Terminal Block Design

The. manufacturer's quality assurance manuals reviewed by us

-[24,25,26] do indicate that design reviews are conducted by the their engineering organizations. The manuals are vague concerning what specifically is reviewed, but they do explicitly cover such items as drawing control, change control, compliance'with applicable standards and regulations, and analysis of tolerances and dimensions. It is not clear whether or not consideration is given to appropriate material selection, i material compatibility, or terminal block designs to reduce leakage currents or contamination. Apparently, some of these considerations are ,

addressed as evidenced by a trend towneds the use of glass-filled l

phenolics, the elimination of cadmium-plated conducting parts in terminal blocks for nuclear applications, and new designs to increase conductor separation. ,

4 2.2. Terminal Block Manufacture 2.2.1 Manufacturing Process i

4' There are several processes applicable to the manufacture of terminal blocks. These include injection, transfer, and compression molding. As long as the Quality Assurance / Quality Control (QA/QC) i programs assure that specified raw materials are used, that molds conform 1 to specification, and that processes and assembly operations function

-correctly, there should be little reason to suspect the manufacture of terminal blocks as contributory to the failure and degradation modes.

i- One potential area may be the use of mold release and the retention of a

1. residue on the insulation surface which could affect performance. Based on our limited experience in procuring terminal blocks from nine

! manufacturers, we found no observable variations or defects and all were in conformance with catalog specifications. For a simple item such as

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terminal blocks, one would expect this type of reproducibility and

quality.

2.2.2 Quality Assurance'in Manufacture I The quality assurance manuals [24,25,26) vary in the thoroughness with which they describe the QA programs applicable-to the manufacturing

, process. Some are sufficiently detailed to outlined the inspection programs which include inspection of the first production unit, last ten I production units, and ten production units per case. The manuals also vary le the thoroughness of their stated raw material segregation, bee:eability, and receiving inspection requirements. Those vendors claiming compliance with 10 CFR 50, Appendix B appear to have good material control, lot traceability, verification that production units match, design, and production line quality control. In general, the QA j applied by the vendors to the manufacturing process appears to adequately '

meets.the requirements for nuclear application.

7 4

l 2.3 Terminal Block Selection, Procurement, and Installation' 2.3.1 Role of Architect / Engineering (A/E) Firms '

The issue of terminal block selection, procurement, and installation was discussed with three (Bechtel, Burns and Roe, and Sargent and Lundy) of approximately tweise A/E firms participating in nuclear plant design.

Though not a large sample in terms of total number of A/E firms' participating in nuclear plant construction, these firms represent slightly more than 50 percent of the 140 planned and operating' plants in' the U.S. Generally, the A/Es function in a key advisory role in deciding whether or not to use terminal blocks and what terminal blocks'to use.

As the funding agency and the licensee, the utility retains final responsibility over the decision, but the policy and practices-of the A/Es bear on the final choice. The A/E firms call out in the design specification when terminal blocks will be used and what makes or models are acceptable. Typically, an A/E might specify a particular make and model with purchasing to be done on an "or equivalent" basis. It is not clear, however, who makes the determination of what constitutes "or equivalent" or what criteria are used to make the determination. No other detailed controls over procurement or selection of terminal blocks are in place. On site, the A/Es do not provide any specific quality assurance function for terminal blocks except as mightEbe provided in site quality assurance plans.

2.3.2 Construction and Installation practices Construction procedures are not normally written by the A/E unless they are also the constructor. The A/Es do, however, review and comment on the construction procedures and thus play an important role in determining how a component will be installed. The installation procedures we have reviewed give minimum clearances for terminal blocks, how cables are to be terminated, how wires are to be labelled, etc.

Terminal block orientation within the enclosure was not mentioned nor was the entry direction for bringing wiring into the box. There is an effort to keep like voltages and applications on the same terminal block. For-example, a single solenoid valve's power, actuation signal and indication signal might typically be on the same terminal block, but a pressure transmitter circuit or an RTD circuit would not also be on that block.

There is also an effort to segregate applications by electrical box. For example, several transmitter circuits may all be on different terminal blocks but within the same enclosure, while terminal blocks in RTD circuits would be in a different enclosure.

The construction procedures are important in determining the installation quality assurance program since they document the basis for inspection and control. Typical quality control checks might include assuring that quellfled terminal blocks are used in Class 1E applications and that installation procedures are followed with respect to spacing,'

circuit continuity, and wiring technique. As evidenced by the utility and A/E surveys, no written procedural check for cleanliness is made except to insure that large foreign objects do not remain in the electrical enclosures.

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Terminal blocks are typically installed !n a National Electrical Manufacturers Association (NEMA) Class 4 enclosure.* However, nelected plants use enclosures fabricated to a company specification which may or may not meet NEMA-4 specifications. Other plants have different NEMA 3 class boxes in use. All new construction that we are aware of employs NEMA-4 enclosures.

The conduit entries are normally made with conduit terminations that have neoprene or other organic material as seals. These entries may penetrate the box from the top, side, or bottom, but typically are top or side entries. There is no provision made to trap and drain condensate in the conduit to prevent it from flowing down the interstitial space between the cable and conduit and entering the box. The sealing of the conduit entry and exit points is utility dependent. Some utilities have scaled them with materials like Room Temperature Vulcanizing (RTV) sealant or Red Glypt"; however, most utilities have not sealed the conduit entries. All but one of the utilities contacted indicated that a 1/4" to 1/2" diameter weep hole is drilled in the bottom of the electrical enclosures. The primary reason for this hole is to permit condensation which accumulates under normal operating environments to drain from the box. The utilities also indicated that the weep hole will allow rapid pressure equilibration during a LOCA steam pressurization of the external atmosphere. To our knowledge, flow retarders are not installed in these holes.

2.4 Inspections and Maintenance 2.4.1 Utility Inspections and Maintenance Most utilities surveyed indicated that no special maintenance or QA activities occur with respect to terminal blocks subsequent to installation. When circuit maintenance is performed, a visual inspection is made. If Class 1E circuits are involved, a check is made to assure proper reconnection of the circuits. No specific check for cleanliness is made. However, one utility that we are aware of, has modified its installation procedures for terminal blocks so that when new terminal boxes are installed or old terminal boxes are modified, the terminal blocks therein are cleaned with deionized water and allowed to air dry.

2.4.2 NRC Inspection Activities The following comments are based on discussions with Region II and Reston IV personnel and a review of NRC Inspection and Enforcement (I&E) inspection procedures.[28] During construction, NRC inspectors review the terminal block qualification documentation and verify whether or

NEMA-4 enclosures are intended for indoor or outdoor use primarily to provide a degree of protection against wind blown dust and rain, splashing water, and hose-directed water.(27] The lid g6sket is normally neoprene and it is incumbent upon the installer to use conduit terminators that maintain the integrity of the box.

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not the blocks are installed in accordance with the way they were i qualified. For example, if the qualification was for non-harsh _i environment areas, then the blocks must be installed in non-harsh y environment areas. They check the enclosures to assure compliance with r the manner in which the blocks were protected during qualification. ]1 With respect to the terminal blocks themselves, there are no f stringent inspection procedures. They do examine the installation to 0 assure that the blocks are correctly installed in accordance with- (

construction procedures, that the terminals and cable terminations are [

tight, that the blocks are not cracked or broken, that the electrical enclosures are dry and nothing is stored in them, and that no stresc is imparted to the blocks by the cable. They also check cleanliness, but :

the degree of cleanliness is a personal judgment decision. NRC/I&E I Inspection procedure 's.063C [28) simply says that af ter installation.. . II

" cable trays, junction boxes, etc. [should be] reasonably free of debris." No specific standards for cleanliness exists other than the a general housokeeping standards, ANSI N45.2.3 and IEEE 336-1977.[29,30) -

These standards address cleanliness only generally and do not reference ;

any specific type of equipment or standard to be applied. IEEE 336

simply refers to ANSI N45.2.3, stating that housekeeping should be in accordance with ANSI N45.2.3. ANSI N45.2.3 sets up zones with different d degrees of cleanliness and access requirements for each. For operational -

plants, no explicit standard addressing cleanliness exists. Only to the -

extent that ANSI N45.2.3 carries over does a standard exist for -

operational plant cleanliness.

The NRC inspectors expect a different degree of cleanliness a depending on the type of equipment in the enclosure. For example, 3 enclocures with relays require a higher degree of cleanliness than i enclosures with simple terminal blocks. Surface dust is almost always present. ?

Inspectors do not regularly inspect terminal blocks in operational plants. However, this does not mean that terminal blocks are never inspected, but rather that they are not an explicit point on an inspection agenda.

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2.5 Summary The above sections highlight that terminal blocks are considered an m "off-the-shelf" component with relatively few requirements that must be 2 met. Their designs have been relatively static for a long period of a time. Their simple, passive nature coupled with the industry's famillerity and traditional use of terminal blocks, has led to a relatively methodical approach in their selection, installation. 3 inspection, and maintenance. QA activities designed specifically to assure adequate and appropriate attention to terminal blocks in these phases of their life cycle have not been diligently pursued, perhaps due r to a lack of consideration about the relative importance of terminal 2 blocks.

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i 3.0 TESTING OF TERMINAL BLOCKS 3.1 Standard Industry Tests All terminal blocks that we are aware of comply with the provisions of UL Standard 1059 (31] or NEMA Standard ICS-4-1977.[32] These standards specify minimum terminal spacing and insulation dissnsions, properties to be considered in material selection, standard temperature rise at rated current, criteria for wire pull out, marking standards, connection types, and dielectric-voltage withstand test criteria. The standards and tests to assure compliance are designed to p? ovide a high grade, industrial application product, which they do. In addition, some vendor catalogs quote that their insulating material fall in one of four flammability categories defined by UL Standard 94.[33] Other tests for tracking index (34,35] or arc resistance [36] are generally not quoted by the terminal block vendors, though original mcnufacturers of the insulating materials may have data available. Reference 7 tabulates electrical properties for many generic polymer materials such as the phenolics, melamines and alkyds used for terminal block insulations.

3.2 Nuclear Qualification Tests Since 1977, there have been a number of test programs sponsored by both utilities and terminal block manufacturers that have been used to support qualification of terminal blocks.[14,15,16,17,18,19,20,21] These tests generally consisted of thermally aging terminal blocks using Arrhenius techniques or the 10*C rule, exposing the terminal block to normal vibration and seismic tests, and then conducting a LOCA/HELB simulation. Functional tests normally consisted of insulation resistance (IR) measurements and conductor continuity checks subsequent to each of the sequentially applied environmental stresses (i.e., theraal aging, radiation exposure, seismic tests, LOCA/HELB simulation.i All industry test reports reviewed by us indicated that the terminal blocks passed the functional IR tests subsequent to each type of exposure. Measurements of the variations in terminal block performance during these tests with the blocks powered were generally not conducted, though many of the tests removed power from the blocks and made megohmmeter measurements during the LOCA simulation. The typical method used to monitor terminal block performance during the LOCA/HELB simulation was via fuses in the circuit providing potential to the terminal block. These fuses were sized to fail at leakage currents between 1 A to 24 A depending on the test _ specification. Acceptance criteria were based on the terminal block's ability to carry the specified voltage and current. During most of the tests, the fuses in the circuits to one or more terminal blocks failed once or twice and were replaced. Sometimes with a given terminal block, the fuse continued to fail; in that case, the terminal block was removed from the test. An important point which is not speciflod in any of the reports was how often a fuse was allowed to fall or how many terminal blocks were allowed to be removed from the test before the test lot was determined to have failed. Only the Washington Public Fower Supply System test of

Weidmuller blocks in a post-LOCA soak environment t18] and the phonix test of their own blocks (19] made definitive measurements of leakage currents during the tests in addition to the fusing techniques.

Using fuses to monitor during-test performance has two drawbacks:

first, the failure of a fuse is only a single point criterion that shows that leakage currents were at least as large as the rated value of the fuse for the time necessary to fail the fuse; and second, the sizing of the fuses to "large" values provides no information about low level leakage currents. As shown by analyses in Section 8, low level leakage currents can affect low power, instrumentation and control circuits.

These circuits are the primary terminal block applications, and, therefore, the acceptance criteria were not, in this respect, germane to the majority of terminal block applications.

Table 3-1 provides a brief comparison and summary of some industry terminal block qualification reports, and the following sections give a more detailed synopsis of each.

3.2.1 Franklin Research Center's Test of Buchanan Terminal Blocks for philadelphia Electric Company [14]

This test series consisted of two phases, A and B. Each is discussed in turn.

In phase A, six Buchanan terminal blocks were evaluated (2 each 2B104 and 4 each 28108). These blocks are similar except for number of terminals (4 and 8). The insulating material for these terminal blocks is a filled phenolic. No further details on the material such as fill material or phenolic formulation were available. Two terminal blocks were subjected to 100 Meads Co-60 gamma radiation and then thermally aged at 136*C (277'F) for 160 hours0.00185 days 0.0444 hours 2.645503e-4 weeks 6.088e-5 months , two terminal blocks were subjected to 50 Heads Co-60 irradiation and not thermally age, and two were neither irradiated nor thermally aged. All terminal blocks were then subjected to a 14-day steam / demineralized water spray (S/D) ehvironment to simulate a LOCA exposure. During the S/D exposure, the blocks were installed in either steel compartments or vented aluminum boxes of philadelphia Electric design; the terminal blocks were energized with 150 Vac and 12.5 A. If more than 1 A of leakage current was required to maintain the specified potential, the specimen was removed from the circuit.

During the LOCA test, four specimens h_d to be deenergized for a 0.9-hour period when suspected flooding of the test chamber occurred; the two other specimens had to be deenergized for a 16-hour period when insulation resistance was low and leakage currents high; and one of these latter two terminal blocks had to be deenergized permanently 4.9 days into the S/D exposure, apparently due to the blockage of the drain hole which permitted liquid to partially submerge the terminal block. IR was measured before and after each sequential test and at selected times during S/D exposure. The circuits had to be deonergized to make the IR meocurements. No failure criteria were promulgated for IR readings.

Initial IR measured 108 ohms or greater at 500 Vdc for all specimens and there was insignificant change after gamma and thermal exposures.

Early in the S/D exposure, the IR for all samples dropped to less than

Table 3-1 Comparison of some Industry LOCA Simulations f or Terminal Block Qualification Megohameter Measurements Lengt h Acceptance (ohns) (500 Vdc unless noted) Special of LOCA Utility / TB No.

During LOCA Post-LOCA Notes Exposure Ref.

Test Lab ID Tested Criteria Power' Ability to carry 150 Vac . < 5 x 104 102 t o 1012 One block removed 14 d 14 Phalauelphta Buchanan from test at 4.9 Phase A-EAectrac/ 2B104 2 specified current at 12.5 A at 50 Vdc specified voltage. days. Others FNC* 28108 4 removed at various times.

150 Vac (5:105 <5:104 One 78 removed from 7d 14 Philadelphia Buchanan Ability to carry Phase B specified current at 12.5 A at 50 Vdc at 50 Vdc to from test after Electrac/ 2B10s 3

< 5:105 5.1 hours1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months .

FRC* Marathon specified voltage.

at 50 Vdc 16u8 2

<5x104 Post-test During LOCA, leakage 7d 15 Ceneric/ Buchanan Maintain potential 120 Va:

1 of 120 V and current 25 A at 10 V to hipot test currents were < 200 mA FMC* NQ8106 to < $ mA f or all NQs112 1 of 25 A. 2x1012 at 500 V terminal blocks kuul06S 1

together.

NQB112S 1 NQO Series 1 Leakage currents 132 Vac, None <53105 Blew 25 A fuse on 30 d 16 I Ceneric/ Marathon 528 Vac specimens.

Wyle 1600 NUC 6 less than 12 A, or 33 A for all 528 V

[$ 18 A , or 24 A. 264 Vac, boxes Removed from test.

3 (Huntsville) 1500 NUC 6 Monitored by fuse. J3 A Blew 18 A fuse on 142 NUC 6 264 vac specimens.

528 vac, 33 A Replaced fuse and continued.

None 2.4x107 to voltage reduced to 29 hr 17 Generic / Weidauller 5 Maintain 600 Vac 600 Vac and 20 A with leakage 20 A 3.5m108 150 V when spray FMC* SAK Types current less than 1 A. at 500 Vdc introduced to Monitored by fuse, maintain leakage current less than 1 A.

FRC = Franklin Research Center

.t >

Table 3-1 (continued)

Comparison of Some. Industry LOCA Simulations for Terminal Block Qualification Megohameter Measurements Le'agth

-Utility /. 78 No. . Acceptance (ohns) (500 Vdc unless noted) Special Test Lab ID Tested Criteria of LOCA

. Power During LOCA Post-LOCA Notes Exposure Ref.

WPPSS/Wyle Weidauller 5 l A Leakage current 600 Vac None 1.2x105 to measured leakage 32 d (Norco) SAK Types 18 Monitored by fuse 20 A 5.0x1010 current during test.

(same Tus as' and discrete time Test was only a post-tested by monitoring of Wendauller,' test LOCA soak. 230*F leakage currerts. and 2G psig,.1004 Ref. 3) ' relative humidity.

No steam.

Generac/ Phonix Wy&e SSK Series. 30 None specified 420 Vac None Reported 2 superheated steam 24 hr 19

- (Norco) Ceramic- units' 20 A periods. No leakage KEK Series exposed 45 Vdc current measurements Ceramic to 24 Vdc of DC circuits.

SSR Series LOCA < 40 mA to Meiamine > 700 mA current K Series-Polyester observed in 420 Vac case (2 Types)

Commonwealth Marathon ' Leakage current 175 Vac None < l . 6 x 106 *

Some periods of 36.9 hr> 20 f3 Edison /Wyle Series 6000 2 less than 10 A. 15 A to 2.2x10I2 superheat in accident su (Huntsville) Series 1600 2 Monitored by fuse. at 500 vac exposure. One block i exceeded 10 A leakage

- Off scale current--shorted to low. Measure- ground, ment with Digitial Multimeter read 3.6 ohns cenerac/ Curtis BT None Specified 600 Vac 8x103 to 2x1010 to Leakage currents = 21 h r 21 kestinghouse canch Jones 5x105 2.3x1011 not monitored 541 during test with Westanghouse blocks powered.

542-247 Marathon 1500

fdC = Franklin Research Center

5'x 104 ohns at 10 Vde, but then recovered to less than 5 x 105 ohms

~at 50 Vdc for the remainder of the S/D exposure. After the S/D exposure, the IR varied from 120 ohms to 10 12 ohms at 500 Vdc. Leakage currents '

were not monitored during the S/D' exposure.

Post-LOCA simulation observations by Franklin Research Center were:

a) 'After gamma radiation (50 Mead or 100 Mead air equivalent dose depending on sample)

Dark deposits on metal parts of tbs b) After thermal aging (136*C (277*F) for 160 h)

Green deposits on TB mounting screws Olly residue inside box Thick, gray, crusty deposits on terminals c) After steam /delonized water exposure (14 days)

Conduit seals marginal

-Box gaskets marginal (EPR rubber)

Marker strips deteriorated Cable insulation split, swollen, stuck together Rust color sediment White and. tan deposits on all metals parts of the tbs Debris from test materials clogging drain holes Phase B of the FRC/ Philadelphia Electric test exposed three Buchanan 2B108 and two Marathon 1608 terminal blocks to 26 Mead (air) gamma

' irradiation and a 7-day steam / demineralized (S/D) exposure. No thermal aging was conducted. As.in Phase A, the blocks were installed in either a steel compartment or vented aluminum boxes of Philadelphia Electric

. design.

Insulation resistance was measured before and after each environment r

and during S/D exposure. Again, the circuits were doenergized to make' l 'the IR measurements. Initial IR at 500 Vdc was greater than 10 9 ohns and no significant change was noted after gamma radiation. During the e

S/D exposure, the IR for all specimens measured less than 5 x 105 ches 4

[- ;at 50 Vdc. The' Phase A test reported IR values as less than 5 x 10

.ohns; the factor of ten discrepancy was not explained.* After the S/D exposure, the IR of one Marathon and one Buchanan terminal block measured less than 5 105 ohms at 50 Vdc. The irs of two Buchanan terminal blocks were not measured after S/D (no reason stated). One Marathon terminal block was deenergized 5.1 hours1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months into the test. After the test, the IR of this block measured less than 5x104 ohms at 50 Vdc. The i .

Different megohameters were used in each test'. They presumably had different lower limit values and hence the irs of the tbs could j have been the same. All that is positively known is that in both Phase A and Phase B the irs went below the range of the meter. l I i L

i

. . , ._- ,. _. ~ . . _ ,_ _

report postulates that the reason for the low IR which aaused the block's removal from the test was the presence of conductive moisture and/or I

deposits on the molding ridges between the energized terminale and the I box. The acceptance criteria for the phase B test as stated in the test plan was "when the... insulation is degraded to the extent that the specimen is no longer capable of carrying the specified current at the specified voltage." A more precise definition of acceptance criteria was not given.

3.2.2 Franklin Research Center's Test of Buchanan Terminal Blocks for Control products Division of Amerace Corporation [15]

Twelve one-piece NQB series terminal blocks and three assemblies of selected NQO sectional terminal blocks were exposed to thermal aging (165*C (329'F), 39.6 days for NQB samples and 121*C (250*F) for 8.3 days for NQO samples), gamma irradiation (200 Mead at 0.56 Mrad /hr, co-60),

vibration aging (10 pairs of acceleration and frequency between 0.03 and 0.74 s's and 3 and 60 Hz with 15-minute dwell at each acceleration-frequency pair), and seismic fragility tests (five 30-second dwells at greater than operating basis earthquake (OBE) levels with a peak acceleration of 5.5 g's between 2.5 and 13 Hz and one 30-second dwell at greater than safe shutdown earthquake (SSE) level with a peak acceleration of 8 g's between 2.5 and 13 Hz). Four of the NQB r cies samples and one of the NQO assemblies were then submitted to a /-day steam and chemical spray exposure.

The terminal blocks were protected by NEMA-4 enclosures. The samples were energized with 120 Vac and 25 A except during the period when IR measurements were made. IR measurements after the thermal aging were greater than 1.4 x 1012 ohms, and after the gamma irradiation they wero greater than 5.1 x 1011 ohms. Similar results were obtained after the seismic and vibration tests. During the steam / chemical spray exposure, the one-piece terminal blocks experienced variations in IR from 3 x 105 ohms at 10 Vdc to 2 x 1012 ohms at 500 Vdc. The sectional terminal blocks experienced IR variations from less than 5 x 104 ohms at 10 Vdc to 1.9 x 109 ohms at 500 Vdc. Though leakage currents were !

not measured for each terminal block individually, nor were they recorded throughout the test, the test report makes the following statement which we assume is based on periodic meter readings: "The leakage / charging I currents which energized the specimens at 120 V were less than 200 mA '

during the dwells at 174*C (346*F). The leakage / charging currents decreased to less than 5 mA for the remaining portions of the steam / chemical spray exposure." The specimens withstood a 5-minute 2200 V high-potential withstand test after the steam / chemical spray exposure.

Acceptance criteria were not specifically mentioned, though reference was made to the maintenance of 120 Vac and 25 A.

l l

3.2.3 Wyle Laboratory's Test of Marathon Terminal Blocks for Marathon Special Products [16]

Three sets of terminal blocks, each consisting of two Series 1600 NUC terminal blocks, two Series 1500 NUC terminal blocks, and two Series 142 NUC terminal blocks were tested. The blocks were protected in NEMA-4 enclosures. The. test sequence was radiation exposure (200 Meads at 0.58 Mead /hr), thermal aging (120*C (248'F) for 18.5 days), vibration aging (0.1 g peak acceleration between 5 to 200 Hz), seismic simulation (5 OBE and 2 SSE) and LOCA simulation.

The planned accident simulation consisted of two 174*C (345'F),

50 psig steam plateaus each of 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months duration, followed by a 42 hour4.861111e-4 days 0.0117 hours 6.944444e-5 weeks 1.5981e-5 months plateau at 163*C (325*F), 83 psig, and a 28-day, 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months plateau at 144*C (291*F), 45 psig. The two initial steam plateaus had initial camps to 196*C (384*F), which lasted momentarily and then retreated to 174*C (345'F) in approximately 2 minutes. It should be noted that the 174*C (345*F), 50 psis condition is 26 C' (47 F*) superheated, while the other two temperature-pressure periods are saturated. Chemical spray was applied throughout the 30-day exposure. Arrhenius techniques were used to compress a one-year accident profile to a 30-day simu)stion. Each set of terminal blocks was powered at different voltage levels. One set was powered at 132 Vac, 33 A; one set at 264 Vac, 33 A; and one set at 528 Vac, 33 A. The acceptance criteria specified that 10 6 ohms was to be the minimum allowable IR for the functional tests and that during the accident exposure the 132 Vac specimens should not exceed 12 A leakage current, the 264 Vac specimens should not exceed 18 A leakage current, and the 528 Vac specimens should not exceed 24 A leakage current.

Functional IR measurem--/.s were made initially and subsequent to each se Tne pre-test baseline measurements ranged from 10guentialexposure.

to 1010 ohms; subse radiation exposure, the irs variedbetween2.4x10guenttot.and 3 x 10 10 ohms; subse aging, IR values varied between 10 11 and1.2x10guenttothethermal 2 ohms. Similar values were'obtained after the vibration and seismic tests. During the first LOCA ramp, the leakage current for the 528 Vac terminal blocks exceeded 25 A and failed the fuse used to monitor the leakage currents.

Also, the 18 A fuse in one of the 264 Vac circuits failed but did not fall a second time after it was replaced. During the second steam ramp, the 25 A fuse in the 528 Vac circuit failed again and the 528 Vac specimens were removed from the test. Leakage currents were monitored daily by using a clamp-on current probe for the specimens that remained in the test, though these readings are not reported other than to say that they were below the acceptance criteria. Also during the accident exposure, a power failure occurred which deenergized all terminal blocks. When power was reapplied approximately 15 minutes later, it was turned on abruptly and all leakage current fuses failed. This same phenomenon was observed in the Sandia tests [1] where rapid changes in applied voltages caused severe drops in terminal block IR. The post-5 accident IR functional tests yielded values.between less than 5 x 10 ohms for the 528 Vac specimens to 1.2 x 10 10 ohms for7 the other specimens. There were, however, a large number of 10 -108 ohm readings which indicated that, in general, the irs did not recover to the pre-accident levels.

. - . _. - -= _ _ _ _ _ _. _ __

a 3.2.4 Franklin Research Center's Test of Weidmuller Terminal Blocks for Weidauller Terminations, Inc. [17]

Five terminal block assemblies each containing five SAK series terminal blocks were tested. The terminal blocks were molded of a glass-filled phenolic material. The-terminal blocks were thermally aged (140*C for 7 days), exposed to 200 Mead (air equivalent) Co-60 gamma dose at less than 1. Mead /hr, vibrationally aged (3 to 60 Hz), and subjected to t

a multifrequency seismic vibration (l'to 40 Hz) which included five i

30-cccond dwells at OBE levels and one 30-second dwell at SSE levels.

The specimens were then divided into two groups and mounted in NEMA-4 enclosures. Each test group was then separately subjected to a 29-hour ;

steam / chemical spray exposure to simulate a LOCA environment. The profile for one group reached a maximum temperature of 246*C (475'F) and 70 psig (89 C'.(161 F*) superheat).and then retreated to 185'c (365'F) after 6 minutes and to 174*C (345*F) after 14 minutes into each of ths peaks. The 174*C (345'F) periods lasted for approximately 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months and were at saturation pressure. After the second 174*C (345'F) period, two additional temperature plateaus completed the profile: 164*C (328'F) for

-9 hours and 156*C (312*F) for 17 hours1.967593e-4 days 0.00472 hours 2.810847e-5 weeks 6.4685e-6 months . 'Again, both of these plateaus

' were at saturation conditions. The peak temperature reached by the

.second group was 232*C (450*F) at 68 psig. The remainder of the profile followed the first group's profile. The terminal blocks were energized 3 during the steam exposure with 600 Vac and 20 A. The acceptance 1

criterion was to maintain a leakage current less than 1 A at the 600 Vac i encegizing level. Monitoring of leakage currents was accomplished by a 1

1 A fuse. For both test groups, it was observed that the 600 Vac potential had to be reduced to approximately 150 Vac at the times when fresh, room temperature solution was sprayed into the test chamber. With potential.at 150 Vac or less the leakage currents remained less than 1 A. The leakage paths appeared to heal themselvas after the i

recirculated spray reached temperatures of approximately 93*C (200*F). 3

IR measuroments at 500 Vdc before the LOCA simulation varied between 1 x 108 and 1.5 x 1010 ohms;8after the LOCA simulation they varied between 4 x 107 and 3.5 x 10 ohms. Two of these terminal block assemblics were subjected to further seismic qualification tests in a subsequent test program.

R3.2.5 Wyle Laboratory's Test of Weidmuller Terminal Blocks for Washington public-power Supply System [18]

4 This test program tested the same five terminal block assemblies subjected to the LOCA simulation discussed in paragraph 3.2.4. These

~

assemblies had been stored by Weidauller at normal office temperatures and humidities in the intervening two years. The test was a post-LOCA soak of the terminal' blocks with intermittent periods of domineralized

water spray. The terminal block assemblies were-protected with the same NEMA-4 enclosures used in the Franklin test. New cabling was installed )

to power the terminal blocks. The test environment did not introduce steam; rather. the chamber was filled with demineralized water to within one foot of the specimens and submersion heaters were used to bring the test chamber and specimens to 110*C (230*F) . pressure was maintained at l

.20 psig which means that the system was approximately 17 C* (29 F*) below j boiling temperature. The relative humidity in the chamber was 100

]

I l

percent. Spray was on one out of every three hours. The terminal blocks were energized with 600 Vac and 20 A. The acceptance criterion'was 1 A leakage current, monitored by a fuse. In addition . leakage currents were monitored throughout the. test by a digital voltmeter and computer setup which sampled each of ten channels (two per terminal block assembly) continuously throughout the test. The sampling rate was not reported, but approximately once every eight minutes a printout of the maximum, minimum and average leakage currents that occurred in the preceding eight minutes was made. The leakage currents for four of the five terminal block assemblies remained 7ess than 0.2 mA throughout the test and for most of the time were less than 0.1 mA. One terminal block assembly failed the 1 A fuse but post-test inspection of the assembly indicated that the failure occurred at the test chamber penetration and not the terminal block. Pre-test IR values were approximately 4 x 10 9 to 5 x 109 ohms at 500 Vdc and post-test IR values were 1 x 10 5 to 1 x 107 ohms. Forty-eight hours after the test, the IR values had recovered to 5 x 108 to 5 x 109 ohms. This recovery is similar to the recovery experienced in the Sandia tests.[1]

3.2.6 Reports on Nuclear Qualification Tests of Selected Phonix Terminal Blocks [19]

These reports summarize qualification tests conducted on terminal

. blocks of European origin. One ceramic type block, one thermosetting insulation type block, and two. types of thermoplastic insulation type blocks were tested. A total of twenty-nine blocks were testei-in the LOCA/HELB simulation. Precise identification of the blocks is given in-the reports but detailed specification of the materials was not provided.

The test sequence was as follows:

a. Pre-test dimensional checks, insulation resistance (at 500 Vdc),

voltage strength (3 kV ras (50 Hz) for 1 minute), and contact (i.e.,-conductor) resistance measurements.

l b. Thermal aging at 140*C (284*F) for 30 days. (Thermal aging parameters based on 10*C rule and assumed ambient operating

[

temperature of 50*C (122*F)).

l Damp heat of 55'c (131*F) and 80 percent. relative humidity for I

! c.

! 48 hours5.555556e-4 days 0.0133 hours 7.936508e-5 weeks 1.8264e-5 months .

d. _ Gamma irradiation with co-60 to 50 Mead (air) Total Integrated Dose (TID) at a maximum dose rate of 0.442 Mead /hr (air).

l-

e. Vibration test. Terminals energized with current loads of 20 mA.

f. Seismic test. Terminals energized with current loads of 20 mA.

g. Second gamma irradiation with Co-60 to 150 Mead (200 Mead cumulative TID) at a maximum dose rate of 0.43 Mrad /hr (air).

t

h. HELB test. The test profile selected for HELB simulation reflects both LOCA and HELB and lasted 30 hours3.472222e-4 days 0.00833 hours 4.960317e-5 weeks 1.1415e-5 months .

I

1

, 1 4- _. . .. .

- ~

e s wr > gm . 3 r

Two initial high temperature steam! phases consisted of. a 2-minute'. ramp to 256*C (493*F), 2 minutes at 256*C (493*F) followed by a_2-minute ramp to 185'C;(365*F), 8 minutes at 185'c (365'F) followed by a 2-minute.reag'to 174*C (345'F) and 2 '

hours,.46 minutes at 174*C (345*F). !The two high1 temperature steam phases were separated-by a.2-hour ramp to 50*C (122*F).

Subsequent to the'second high temperature steam-phase, camps to a 9-hour 164*C (327*F) plateau and an 18-hour 156*C (313*F)

. plateau completed the test. Chemical spray was initiated at' the beginning.of each of the 174*C (345'F) plateaus and continued .

- until the beginninglof_the. ramp.to 50*C,(122*F) ending the first '

high. temperature phase and to the end of the 30-hour test for

. the.second high' temperature phase. The-terminal blocks were energized with one of four schemes:,(1) 420 Vac and 20 A; (2) 420 Vac, no: current; (3) 48 Vde, unspecified current; and (4)

- 24 Vde, unspecified current. . It was not clear from the, reports ,

whether or not leakage currents were monitored throughout the HELB. simulation.-

1

1. Second thermal aging (post-LOCA aging) at 135*C (275'F) for 100

' hours. (parameters based-on.10*C rule and assumed ambient

, . temperature of 70*C (158'F)).

. j. Voltage strength test at 3 kV ras (50 Hz).

~

The main results of the-tests are as'follows:

k

a. IThe.mean' insulation. resistance of all samples in the pre-test

_ condition was 1013 ohms.

b. No pre-test breakdowns at 3 kV were experienced.

c. Contact resistance was on the order of 0'.1 to 0.3 mohns.

. d .' -The'firstLthermal' aging and-damp heat environments did-not affect the physical characteristics of the material. Insulation resistance measurements at the conclusion of each environmental exposure was about a factor of ten greater than the pre-test

, measurements. H e.- No adverse, effects occurred during vibration and seismic testing. During these tests, the terminal blocks were loaded l with a 20 mA current. Circuit continuity was maintained throughout the test.

l

. f. No adverse effects were noted other than slight material discoloration'after either gamma irradiation.

I;

g. Insulation-resistance decreased by an order of magnitude <

to 1012.~ohes subsequent to the HELB environment. Of the 29 terminal block assemblies tested in the HELB simulation, only

, one experienced.an irreversible short circuit. This block was

.made from thermoplastic type insulation and energized with aw9 =-==e'r c. =e,.- e a.1.e-se w.- we e 1 t-4-+---r-e-mm-smT-+'t'+'9t-7 T--Pt'-*t"Mf ~-N *Leyny---.y-"*- r-M--'--T -

T~ + - + ' ---1 M 'M

420 Vac, but no current. A second thermoplastic insulation terminal block assembly energized to 420 Vac and 20 A ,

-experienced a leakage current of greater than 5 A at the l beginning of the second chemical spray period. After <

-replacement of circuit fuses, this assembly successfully I completed the test. Five of the thermoplastic insulation blocks j '

and one of the thermosetting insulation blocks were badly deformed by the HELB test environment. Four of them were so badly deformed that they fell off of their mounting rail due to their own weight.

h. Three kV ras (50 Hz)' voltage strength tests were conducted after the post-HELB thermal' aging. All ceramic terminal blocks passed the voltage withstand tests. The six plastic insulation block assemblies that were badly deformed by the HELB simulation were not subjected to this. test. One of the eight thermosetting insulation blocks-tested failed the terminal-to-terminal test.

Of the seven thermoplastic insulation blocks tested, three failed the terminal-to-terminal tests and one failed the terminal-to-ground test.

No definition of failure or acceptance criteria was provided in the test report. The conclusion drawn from these tests was that only ceramic

terminal blocks should be used for in-containment applications.

3 . 2.' 7 Wyle Laboratory's Test of Eight Marathon Terminal Blocks for Commonwealth Edison Company [20]

This report documents testing performed on Series 6000 and 1600 Marathon fixed barrier terminal blocks. Two assemblies of terminal blocks were tested,'each consisting of three Series 6000 terminal blocks and one Series 1600 terminal block. They were housed in an electrical enclosure manufactured to Commonwealth Edison specifications and connected.in the usual alternating terminal, serpentine type wiring scheme used in other industry qualification tests of terminal blocks.

Okonite 10 AWG Hypalon insulated cable was used to make the. connections.

The test sequence was as follows:

a) Baseline Functional Tests f b) Irradiation to 206 Mead gamma (Co-60)

I

~ c) Functional. Test d) Thensal Aging 'one assembly at 120*C (248'F)' for 466 hours0.00539 days 0.129 hours 7.705026e-4 weeks 1.77313e-4 months (20-year equivalent life) and one assembly at 120*C (248'F) for 932 hours0.0108 days 0.259 hours 0.00154 weeks 3.54626e-4 months (40-year equivalent life) e) Functional Test

, f) Seismic Test-i

g) Functional Test l

i

h) Accident Exposure Simulation I i) Functional Test I

The acceptance criteria for the baseline functional test were to possess an insulation resistance of at least 109 ohms and a resistance through the terminal block / cable conducting path of less than 10 ohms.

For.all of the post-test functionals, the acceptance criteria were to maintain IR greater than 106 ohms and resistance through the conducting l

path less than 10 ohms. During the LOCA simulation, the original acceptance criterion was to maintain leakage currents less than 2 A, but this criterion was changed by commonwealth Edison to 10 A. In the i report. the figure showing the schematic of the electrical circuit shows ammeters set up to measure leakage current along with fuses to limit leakage current. However, no leakage currents are reported in the test documentation.

The accident exposure was originally planned for 34 hours3.935185e-4 days 0.00944 hours 5.621693e-5 weeks 1.2937e-5 months which was based on an Arrhenius calculation to compress a one year accident exposure. The original profile called for two 10 second ramps from initial conditions of 57*C (135'F) and 0 psig to 196*C (384*F) and 50 psis, then retreating after 100 seconds to 174*C (345'F) and 50 psig' for 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months . During the 3 hour3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months exposure for margin and during the first 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months of the accident exposure portion of the profile, chemical spray was to be sprayed at 0.5 gal / min /ft2 . After the first'3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months of the accident exposure portion of the profile, the following conditions were to prevail: 163*C (325'F), 45 psig (28 C* (50 F*) superheat) for 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months , 163*C (325'F), 25 psig (47 C* (E5F*) superheat) for 18 hours2.083333e-4 days 0.005 hours 2.97619e-5 weeks 6.849e-6 months , and finally 163*C (325*F), 20 psig (54 C' (97 F*) superheat) for 10 hours1.157407e-4 days 0.00278 hours 1.653439e-5 weeks 3.805e-6 months .

Due to the inability of the test facility to maintain superheat conditions for such high spray rates, the spray rate was modified to 0.04 gal / min /ft2 for the 3 hour3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months margin peak and the first 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months of ;

the accident exposure. To make up for this deficiency from planned spray rates, at the end of the 163*C (325'F), 45 psis period, a 3 hour3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months period ;

was added at 127 *C (260*F), 45 psis (8 C* (15 F*) subcooled) with spray ,

at 0.5 gal / min /ft2 . The spray was terminated at.the end of this period '

(the 9 hour1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months point of the accident exposure). From the 9 hour1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months point the remainder of the planned profile was run except an extra 2.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months was l added at the end to account for the 3 hours3.472222e-5 days 8.333333e-4 hours 4.960317e-6 weeks 1.1415e-6 months at 127*C (260*F).

The data in the report indicates that the first transient (for margin) had one thermocouple (TC) reading a. maximum of 163*C (325*F) 24 i seconds after introduction of-the steam, while the second and third l thermocouples had reached 141*C (285'F) and 93*C (200*F) respectively at l this time. By 52 seconds, the first TC was reading 141*C (285'F) and the second TC began tracking it. At the 3 minute point, the readings of these TCs diverged from a common value of 121*C (250*F). The third thermocouple was reading 82*C (180*F) at the 3 minute point. All data ceases at the 3.9 minute point and no further data are presented until the second ramp begins.

l 1

H I

Notice of Anomaly 14 in the Wyle test report explains that during the first transient (for margin), the chamber rupture disc burst at 20 psig. At Wyle's suggestion additional time was to be added to each temperature plateau of the main exposure rather than repeating the initial transient. Looking at the temperature profiles achieved, apparently 30 minutes was added to the 174*C (345'F) plateau. The profile actually achieved during.the main exposure was 182*C (360*F) to 210*C (410*F) (depending on thermocouple), 50 psig at approximately 40 seconds elapsed time,-177*C (350*F), 50 psig from approximately 2 minutes to 3.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months elapsed' time, 163*C (325'F), 45 psis from 3.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months to 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months elapsed time, 127'C (260*F), 45 psig from 6 hours6.944444e-5 days 0.00167 hours 9.920635e-6 weeks 2.283e-6 months to 9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months elapsed time, 163*C (325*F), 25 psig from 9 hours1.041667e-4 days 0.0025 hours 1.488095e-5 weeks 3.4245e-6 months to 25 hours2.893519e-4 days 0.00694 hours 4.133598e-5 weeks 9.5125e-6 months elapsed time and finally 163*C (325'F), 21 psig from 25 hours2.893519e-4 days 0.00694 hours 4.133598e-5 weeks 9.5125e-6 months to 36.5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months elapsed time.

At approximately 1 hour1.157407e-5 days 2.777778e-4 hours 1.653439e-6 weeks 3.805e-7 months and 50 minutes into the test (during the 174*C.(345'F), 50 psig, 0.04 gal / min /ft 2 period), Notice of Anomaly 17 reports that a 6000 Series terminal block exceeded 10 amperes leakage current. Inspection showed that it was shorted to ground and so it was removed from the test circuit and the test continued. During the remainder of the test the leakage currents of the other terminal blocks remained below 10 amperes. In the post-LOCA functior.a1 tests, the circult-to-circuit insulation resistance of the terminal block removed from the test was 3.6 ohms. The post-test inspection notes that the area where.the failure occurred could be seen. .The post-LOCA irs of the other terminal block were between 106 and 1012 ohms.

3.2.8 Westinghouse Electric Corporation's Test of Terminal Block Performance in LOCA Environment [21]

This report documents testing performed on Curtis.BT, Cinch Jones 541, Westinghouse 542247 and Marathon 1500 Series terminal blocks. No thermal or vibrational aging was conducted and no seismic simulations or radiation. exposures were reported. The test was an exposure to an unspecified LOCA steam profile of approximately 5 hours5.787037e-5 days 0.00139 hours 8.267196e-6 weeks 1.9025e-6 months , 30 minutes duration. Chemical spray was sprayed for one hour at 0.32 gal / min. It is unclear from the report whether the terminal blocks were mounted in a NEMA-4 enclosure. During the test the blocks were energized with 600 Vac.

No acceptance criteria are stated in the report. IR measurements were taken before, at various times during, and after the steam exposure.

Before and after the exposure the IR values were 10 10 to 1012 ohms.

During the test IR values varied from 8 x 10 3 to 2.6 x 105 ohms. The concluding statement'says that " Although the insulation resistance dacreased more than six orders of magnitude, the terminal blocks...were able to function at 600 Vac throughout LOCA."

1 l

4.0 SANDIA TESTS OF TERMINAL BLOCKS IN A SIMULATED LOCA ENVIRONMENT 4.1 Terminal Blocks Tested Earlier work at Sandia (2) consisted of testing terminal blocks under TMI conditions. This test raised questions regarding terminal block performance but was not conclusive in that there were several areas where test conditions deviated from actually installation conditions. Therefore, to quantify the performance of realistically-installed and protected terminal blocks in a LOCA environment and to investigate terminal block failure and degradation modes, we tested 24 terminal blocks (5 models from 4 manufacturers *) in a simulated LOCA environment.[1] Based on our reviews of the qualification documents, we determined that neither the accelerated aging process nor the seismic testing significantly affected terminal block performance. Thus, we tested terminal blocks in the "as received" condition. To simulate normal handling during installation, no special care was taken during test preparation to prevent the deposit of finger-prints or other normal contaminants on the terminal block surfaces; however, we did not simulate deposits of construction dirt or other sediments which tend to accumulate over time. As such, the terminal blocks were probably in the best initial condition that might possibly exist for terminal blocks installed in the field. The terminal blocks were protected by NEMA-4 electrical enclosures with 1/4" diameter weep holes in the bottom.

Cables entered the boxes from the side through nuclear grade, liquid-tight conduit. To simulate cables entering a conduit from a cable tray system, the conduit was terminated inside the test chamber and was unsealed at both ends.

4.2 Test Configuration The test was divided into two phases. Phase I exposed 12 terminal blocks (three each of four designs) to an 11-day steam-only environment.

Phase II exposed 12 terminal blocks (six each of one design and three each of two other designs) to approximately one day of simultaneous steam and chemical spray followed by five days of a steam-only environment. Both temperature profiles closely followed the PWR temperature profile recommended by IEEE-323-1974, Appendix A.[37] Saturated steam conditions were maintained throughout both test phases. In Phase I, the terminal blocks were connected in an alternating terminal serpentine, similar to the wiring scheme used in industry qualification tests (Figure 4-1). In Phase II, the terminal blocks were connected in a configuration more representative of actual plant connections with one terminal powered and the two adjacent terminals and base plate monitored for leakage currents (Figure 4-2). One terminal block in the Phase II test was connected to a pressure transmitter in a circuit configuration representative of a plant transmitter circuit. This transmitter circuit was included to validate the results obtained from the other circuits and to confirm the analysis of the effects of terminal block degradation on low power circuits. Figure 4-3 shows the transmitter circuit wiring.

Table 1 in Reference 1 identifies the manufacturers I through IV and the Models A through E. That nomenclature is continued in this report, and is extended in Table 5-1 to Manufacturer V Model F.

The, terminal blocks were powered at voltages typical of in-plant applications: 4 Vdc typical of RTD circuits (Phase I test only), 45 Vdc typical of instrumentation circuits, and 125 Vdc typical of control circuits. The terminal-to-terminal leakage currents were monitored in both Phase I and Phase II tests, and the terminal-to-ground (base plate) leakage currents were monitored in the Phase II tests. The data were acquired at discrete time steps by data loggers. The time interval between successive measurements varied depending on the experimental activity being conducted. For example, during steam camps or other transients, monitoring was accomplished as rapidly as possible (about every 6 seconds); during long periods of steady state conditions, the monitoring interval was lengthened to 30 minutes. Based on these data, insulation resistances were calculated for each leakage path on each terminal block. Four channels of leakage current data were monitored continuously by strip chart recorders throughout the test.

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, , t, R o, Figure 4-2: Wiring Schematic for the Sandia Phase II Terminal Block Test (Note the once through connection on the terminal block) 4.3 Major Results Surface leakage currents through conducting surface moisture films are the primary mechanism by which terminal blocks contribute to instrumentation and control circuit degradation. During our tests, the formation of surface films reduced insulation resistance to 102 to 105 ohns from initial values of 108 to 1010 ohms. Figures 4-4 and 4-5 illustrate these changes in insulation resistance for both Phase I and II at various LOCA temperature conditions. At 45 Vde, leakage j currents were on the ceder of 0.1 to 10 mA. These values are i sufficiently large to affect 4 to 20 mA instrumentation circuits by 0.3

.to 185 percent with a nominal effect of 0.5 to 45 percent at the j mid-range of instrument output. At 4 Vde, insulation resistance was I

varied from 5 x 103 to 7 x 10 4 ohms, values which are sufficiently low to affect RTD measurements by 0.3 to 9 percent. At 125 Vdc, the IR values were comparable to the 45 Vdc values and were at times slightly 1 (approximately 1/2 to 1 order of magnitude) higher. Reference 2 reports slightly lower but comparable results for TMI-2 conditions; leakage currents between 0.08 and 0.3 mA are reported therein for terminal blocks protected by an electrical enclosure.

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10*1 MFGIV MFGI MFG 11 MODEL E MODEL A MODEL C Figure 4-5: Insulation Resistance A for Sandia Phase II Terminal Blocks Insulation resistance A is the IR calculated for the A path (see Figure 4-2). Terminal Blocks 1-6 powered at 125 Vde, 1 A and Terminal Blocks 7-12 powered at 45 Vde, 20 mA.

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We experienced one open failure where the leakage currents increased over a 90-minute period to values which contributed to the separation of I the 12 AWG wire supplying power to the terminal block. The separation occurred close to the terminal block-wire junction and was primarily j caused by test induced tensile stresses.[1] l l

During the periods of cooldown to 95"C (203*F) and the post-test I ambient temperature period, the insulation resistance values increased to 106 to 108 ohms but not to the pre-test values of 108 to 1010 ohms.

This behavior illustrates three points: first, the similarity between cooldown and post-test IR values indicates that the same conduction mechanism is probably occurring during these periods; second, IR recovery to higher values after exposure indicates that a transient phenomenon is responsible for the low IR values during the steam exposure; and third, that some permanent degradation of the terminal block insulation resistance occurs. A conductive moisture film is the most probable explanation for the transient phenomenon. During cooldown periods, the residual heat of the terminal block will keep its temperature higher than the surrounding atmospheric temperature. Since the surface film will be close to the terminal block temperature, its vapor pressure will exceed the surrounding atmosphere's pressure, causing the film to vaporize. In the post-test case, the same phenomenon occurs until the terminal b1< ks cool to ambient temperature. Then the normal relative humidity reg' takes over. The permanent degradation of the terminal block IR may e been caused by either carbonization of the terminal block surface or 1er organic materials in the vicinity or by residues of potentially semiconducting mediums such as cadmium sulfide. post-test chemical analysis of three phase II terminal blocks showed the presence of both

+

cadmium sulfide deposits and carbonaceous residues in a graphite-like structure.

There was a noticeable dependence of IR on temperature. The irs at temperatures less than 110*C (230*F) tended to be 1/2 to 1-1/2 orders of magnitude greater than irs at temperatures greater than 110*C (230*F).

All of the terminal blocks tested exhibited similar temperature related performance trends, though there were block-related differences in absolute performance. This result is in agreement with the findings of Reference 2 and the theory of electrolytic conduction (38) which indicates increased conductivity with increased temperature.

Since saturated steam conditions were maintained throughout the test, the temperature dependence could also have been interpreted as a pressure dependence. pressure per se, though, is not the governing factor in film conduction, but it is important in determining the conditions necessary for film formation. Exclusive of contamination effects, if a system is superheated and at equilibrium, films will not form and the performance of the terminal block will be relatively good. Similarly, if the terminal block temperature is above the dew point in an air environment, the same i

condition will exist. Alternately, if the terminal block temperature is below the dew point in an air environment, or if films have formed due to a cool terminal block being surrounded with steam and the system remains at saturation, films will form and remain on the surface of the terminal block.

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During the chemical spray periods of the Sandia Phase II tests, no effect of the chemical spray was observed. This finding was somewhat surprising since we expected the chemical spray to enter the conduit, penetrate.down through the conduit-cable interstitial space, and drip onto the terminal blocks. We hypothesized that the introduction of Na+

and OH- ions to the surface film would enhance the conductivity of the film.' The lack of any observed change in leakage currents initially indicated.to us that the NEMA-4 enclosures with unsealed conduit entrances.provided adequate protection against the intrusion of chemical spray. .To check this result, at the conclusion of the Phase II environmental exposure we conducted a submergence experiment to observe the performance of blocks positively known to be spray contaminated. In this test'three blocks were submerged in a chemical spray and steam condensate solutior and three blocks were left unsubmerged. irs in a ,

steam environment after the submergence were compared. They indicated !

that.there was only slight. difference between submerged and unsubmerged blocks, with the unsubmerged blocks being slightly better. This data coupled with the observation that the Sandia Phase I test results were compatible with the Sandia Phase II results shows that even if spray had penetrated the enclosures'little difference in leakage currents may have been observed. Apparently, the additional conducting lons from the spray may not significantly alter the conductivity of the film. It also-precludes a definite conclusion about the effectiveness of the NEMA-4 i

enclosure in preventing' chemical spray from penetrating to the terminal'

. blocks. However, we believe the NEMA-4 enclosures as they were installed in the Sandia tests are reasonably effective in preventing such penetrations.- This result correlates well with the results reported in Reference 18.

- Figure 4-6 shows the insulation resistance measured during Phase I of the Sandia tests for one Manufacturer I, Model A terminal block. The data begin with the second transient and continues to the end of the test. One of the first things to note is that IR does not remain constant. There are periods when the IR improves dramatically (e.g.,

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just after temperature reduces from 160*C (320*F) to 150*C (302*F) there is an increase in IR from 10 kohms to 63 kohms) and then deteriorates just as dramatically (e.g., following the spike to 63 kohms the IR drops .

back to the 10 kohm region). The introduction of steam is one parameter.

' which causes the IR to drop and as already discussed, changes in temperature caused observable changes in IR. Another important factor is voltage gradients. Whenever power is applied or the voltage. increased suddenly to an otherwise quiescent terminal block the irs were always observed to decrease by large amounts, often to values below the range settings on the recording instruments. Two illustrations of this effect t

are apparent in Figure 4-6: the first is at hour 121 where power was reapplied'after 25 hours2.893519e-4 days 0.00694 hours 4.133598e-5 weeks 9.5125e-6 months without power and the second is at hour 238 where.a-transition from 4 Vdc to 45 Vdc occurred. In both-cases an immediate decrease in IR is apparent, and then over a period of hours, an increase in IR is observed. In the first instance the IR increased eventually to the 65 kohm region. In the second case the recovery was

! back to the 60 kohm region at which point the test was terminated. In

.both cases a period of some 10-20 hours was required to make the recovery. Also note that at the same environmental temperature, the mean IR level at 4 Vdc is less than at 45 Vdc by about a factor of three.

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the Test Temperature trace is for a thermocouple located in the NEMA enclosure with the terminal block. Except for the 4 Vdc period noted, the applied voltage was 45 Vdc.

1

The model in section 6 predicts a nearly constant value of steady state IR as long as the number of conducting ions in the film remains constant. The transient application of potential increases the currente through the leakage paths more than would be expected if the IR was a constant value. At the higher current values, more Joule heating exists and the film temperature increases. More convective and conductive heat transfer occurs, but during the transient period the primary energy loss mechanism is vaporization (and hence thinning) of the film. As.the film thins, the IR slowly increases towards an equilibrium value. Joule heating decreases to a point where it is in balance with convective and conductive heat losses. At this point, net vaporization of the film ceases and a new equilibrium film thickness is established. The approach to equilibrium is a slow process, as evidenced by the rather long time constants observed for recovery of the irs to higher values after application of an increasing voltage gradient.

-. _ _ . . _ _. . .. _._ _ _ _ _ . ~

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.5.0 : TESTS OF TERMINAL BLOCK PERFORMANCE AT TEMPLE UNIVERSITY To provide independent tests of terminal block performance,-Temple University was contracted to perform laboratory bench tests of terminal 4

blocks. ~The tests were designed and directed by Dr. Robert Salomon of j

the Temple University Chemistry Department. The tests at Temple were conducted in two phases. Phase I tested terminal blocks in 100 percent

. relative humidity and at the TMI accident temperature of 86*C (187'F).

~

. Phase II~ tested terminal blocks at somewhat lower temperatures, and used steam as a heat source. Phase II also introduced chemical spray into

, some of the test' environments during selected periods of the test.

i-5.1 Phase I Tests of Terminal Blocks in a Quiescent Temperature and Humidity Environment e

. The Phase'I experiments tested three* models of terminal blocks in 100 percent' relative humidity and 86*C (187'F) with little chance for temperature gradients. The basic premise here was that if temperature

-gradients were-eliminated, then leakage currents would be small since no special preference for initiating moisture condensation would exist.

, Test voltages were 480 Vac, 400 Vac, 300 Vac,-200 Vac, and 100 Vac. The

, -experimental setup used is illustrated in Figure 5-1. A battery jar-was used as the environmental chamber. _The terminal blocks were suspended

from a polycarbonate lid above a water or hcl solution via the electrical j / leads. The leads were connected to adjacent. terminals of the terminal

-block-and if a metal base plate was part of the terminal block design, it Lwas connected to one of these terminals. Thus, the leakage paths were from one terminal to an adjacent terminal or from one terminal to an

' adjacent terminal 'and the base plate. The solution in the battery jar was four inches deep and was either deionized water or a 10 percent by volume solution of HC1. The' solution was stirred vigorously throughout the test by a high speed magnetic stirring device. The motion of the solution also stirred the atmosphere in the battery jar above the solution. Heat was supplied to the system via heating wire wrapped

' around the outside of the battery jar from the bottom, to a level just below the level of ' stationary solution in the jar. The exterior of the battery jar was insulated with fiberglass insulation to reduce any thermal gradients within the jar. In addition, for some of the experiments run in Phase I, an infrared lamp was used to. prevent condensation of moisture en the terminal block. The lamp was positioned such that its rays penetrated the polycarbonate lid and impinged.on the

. terminal block. . Without this light, visible droplets of moisture would i

-condense on the polycarbonate lid; however, at no time, either with or without the infrared lamp, was moisture observed on the terminal blocks.

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.Two of the three models tested were also tested in the Sandia tests.[1]

These were Manufacturer I, Model A, and Manufacturer II, Model C.

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. Figure 5-2 shows the electrical circuit used in Salomon's phase I tests. Initially a princeton Applied Research lock-in amplifier was used to measure the leakage current, but this instrument failed and the

,l resistor-diode-electrometer* circuit shown in Figure 5-2 replaced it.

l The system was calibrated against known resistances, and to protect against giant current surges, the_Variac supplying power to the primary

' side of the transformer was'underfused. The guard ring was tightly i-pressed against the polycarbonate lid and completely encircled one

' electrode feeding through the lid. It was always at a-potential slightly less than the guarded _ electrode. Any possible leakage currents along the surface of the polycarbonate lid were thus returned to the power supply without affecting the measurements of terminal block leakage current.

-Initially the blocks were tested in the "as-received" condition and no special care was taken to clean them. These blocks therefore were contaminated with fingerprints. The leakage currents were measured as a function of time and temperature as the-system moved toward the final system temperature of 86*C (187*F). The experiments lasted from one to

' three hours. Generally-, leakage currents with the delonized water

-solution in the jar were in the micro-ampere region or lower if the infrared-lamp was turned on. The leakage currents;with the hcl solution

-inlthe jar were sometimes slightly higher, but not significantly so since hcl has a high vapor pressure at 86*C--(187'F).

After testing the b' locks in the "as-received" condition, they were soaked briefly (a few minutes) in 1%, 10% (0.26% and 2.6% by weight) and

- saturated Nacl solutions, oven dried at 90*C (194*F) and then reinstalled in the experimental setup. The experimental procedure was than repeated.

The leakage currents generally increase monotonically with the Nacl concentration of the soaking solution. For those blocks soaked in the

! i saturated salt solution, the leakage currents reached the mil 11 ampere

': region before the final system temperature of 86*C (187'F) was reached. ,

In some case, the heavily conteminated blocks experienced a decrease in the leakage current as applied voltage increased. We attribute this-phenomenon to Joule heating of the conducting film which caused drying .

and precipitation of salt and therefore reduced conductivity. There also {

may be-some formation of drybands which would reduced path continuity. .1 One actual breakdown was experienced at approximately 400 Vac for a

terminal block soaked in saturated Nacl solution. . The breakdown path is illustrated in Figure 5-3 and was evidenced by severe blistering of the phenolic material. A summary of some of Salomon's phase I results is i

given in Table 5-1.

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j. The'electrometer was a Keithley Model 610C.

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Table 5-1 1 Representative Data For Salomon's Quiescent Environment Bench Tests of Terminal Block Performance Mfg I Mfg II Mfg V**

Model A Model C Model F Appliec Leakage Leakage Leakage Voltage current Temp Current Temp Current Temp (Vac) _ (mA) ('C) (mA) (*C) (mA) ('C) Contamination 100 U.024 86 0.60 86 0.0084 86 "as-received" 200 0.038 86 0.16 86 0.0071 86 +

300 0.068 86 0.0069 86 1004 RH 400 0.095 86 0.30 86 0.0077 86 480 0.075 86 480 0.032 83 480 0.022 81 0.38 86 0.011 86 ,

100 0.040 86 0.080 86 14 Nacl solution 200 0.010 86 No Msats Made 0.16 86 +

300 0.030 96 0.070 86 1004 RH 400 0.040 86 0.080 86 400 0.070 86 0.060 86 480 0.060 86 0.060 86 480 0.060 85 0.080 82 8 4u0 0.040 84 0.070 78

$ 480 0.030 83 -0.080 76 a

100 0.050 86 0.10 86 10% Nacl solution 200 0.110 86 No Msmts Made 0.060 86 6 300 0.180 8f 0.070 86 1004 RH 400 0.240 86 0.070 86 480 0.250 86 0.080 86 480 0.250 86 0.10 80 460 0.175 80 0.070 70 480 0.070 69 b.060 60 480 0.C50 60 0.023 45 480 0.0090 45 0.021 35 480 0.010 .36 20 9.0 86 Saturated Nacl 40 20. 86 No Msmts Made &

100 60. 86 19.2 86 100% RH 140 20. 86 -

160 30. 86 200 0.70 86 300 200. 86 0.20 86 400 Breakdown

0.17 86 480 0.20 86

Breakdown occurred before reaching 400 Vac. _'

- The nomenclature for terminal block manufacturer and model number established in Reference 1 is extended here.

W

5.2 Phase II Tests of Terminal Blocks in an Active Steam, Chemical Spray, and Temperature Environment In Phase II, seven different models of terminal blocks from four manufacturers were tested. The test arrangement was similar to the one used in Phase I except for the modifications in the lid for steam and chemical spray entrance ports and the use of a commercial temperature controlling bath apparatus instead of a battery jar as the environmental chamber. No infrared lamp was used in the Phase II tests. Figure 5-4 illustrates the experimental arrangement for Phase II tests. The steam was produced from a commercial vaporizer modified with an asbestos wrapped tube leading to the bath controller lid. Deionized water was used in the vaporizer together with a small amount of sodium sulfate as a nonvolatile conductor. Delonized water was used to avoid the potential for volatile impurities being introduced into the terminal block environment. The steam made in this manner was condensed, and the conductivity of the condensate measured. It measured 3 x 10-4 ohm-Icm-1 Steam was delivered to the system at low pressure and at a rate equal to approximately 20 ml of condensate per minute.

Temperature in the chamber was controlled by an auxiliary heater in the bath which supplemented the energy introduced via the steam. The temperature of the system never exceeded 90*C (194*F) in any of the experiments.

The composition of the chemical spray was that specified by IEEE 323-1974 Appendix A.[37] It was introduced into the system by forcing a stream through a small glass nozzle at approximately 20 psig. This stream was intersected with a jet of nitrogen at the same 20 psis. The result was a finely atomized spray in the chamber. The point of intersection for the chemical spray stream and the nitrogen jet was approximately 9 cm from the terminal block, and thus the chemical spray stream did not directly impinge on the terminal block. A polycarbonate lid sealed the bath controller opening. The terminal block was suspended from this lid by the electrical leads just as the Phase I terminal blocks were installed in the battery jar. The electrical wires used glass enclosed leads to penetrate the polycarbonate lid. One of these leads was electrically guarded to prevent leakage currents along the interior surfaces of the chamber from entering into the measurements. The leads were connected to adjacent terminals on the terminal blocks. For those terminal blocks which had a base plate as an integral part of the design, this plate was connected to one of these terminals. Thus, either terminal-to-terminal or terminal-to-terminal and base plate leakage currents were measured. Figure 5-5 shows a schematic of the electrical connections.

[

Twenty-four experimental runs were made using various combinations of terminal block model, spray, and no-spray. When spray was introduced, it was always after the steam had bett on for at least 30 minutes. Table 5-2 summarizes the data obtained from one run with one Model'I, Manufacturer A terminal block. Figures 5-6 through 5-11 give the results of all runs made with this model of terminal block. These plots show

[ three pieces of information: leakage currents as a function of time.

leakage currents as a function of temperature and temperature as a function of time.

I N SPRAY N2 }

RESERVOIR STEAMLINE

//\

l-SPRAY / GUARD RING VAPORIZER g .y , , ,

I ,, - .. l= POLYCARBONATE 4/ BLOCK 1

SPRAY / TERMINAL

& ATOMlZATION

'T BLOCK y WATER LEVEL 7 AUXILIARY HEATER

/

BATH CIRCULATOR Figure 5-4: Experimental Setup for Salomon's Phase II Tests The environment included clean steam and controlled additions of atomized chemical spray at selected times.

l GUARD RING i I

l I

= .

1-POLYC ARBON ATE PL ATE ~ (%%M L\\\%\1 L\\%%\\\\l e a TERMINAL BLOCK

\

B ASE PL ATE- _

O O O O O O (FLO ATIN G) O O O O O y POWER SUPPLY ELECTROMETER O C

:$f. .

i l

l l

1 Figure 5-!: Elactrical Circuit for Salomon's Phase II Tests l

- U '

+

Table 5-2 o

Typical Leakage Current Data From Salomon for One Manufacturer I, Model A Terminal Block Powered at 45 Vdc'in an Clean Steam Environment Neasurement Time Temperature Leakage Current No. (min) (*C) (mA) 1 0 22 0 2 1 70 0 3 2 75 'O.1 x 10-3 4 3 77 0.4 x 10-3

'5 4 77.5 1.2 x 10-3 6 8 80 3.7 x 10-3 7 10 81 5.6 x 10-3 8 15 83 8.0 x 10-3 9 22 85 11.0 x 10-3

'10 25 86 12.4 x 10-3

-11 30 86 15.0 x 10-3 12 55 86 21.4 x 10-3 13 60 86 29.0 x 10-3 Salomon's dcta, not all of which are' presented herein..show several things. First, the data show a secat deal of variability in the magnitude of the leakage currents. Variations between 10-7 A to 10-3 A were noted, with the_latter value being care. Although, the example in Figure .5-10 does not clearly show'the effect, when containment spray was present-the currents were frequently enhanced and often reached the milliampere region. One was as high as 6 mA. The greatest variety of tests were run on the Manufacturer.I, Model A terminal block. Table 5-3 tabulates the leakage currents observed at the end of the test for'these blocks. The environment temperature for these observations was between

- 80*C (176*F) and 90*C (194*F).

Except for the block dipped in saturated Nacl solution and dried, the final leakage currents are the highest values observed during the i 1

test. For similar block conditions, these endpoint. leakage current

- values compare reasonably well with data reported for the Phase I quiescent tests by Salomon. - The "as-received" condition in the Phase I test had values varying from 0.024 s9L at 100 Vac to 0.095 mA at 400 Vac,

while.the Phase II value was 0.029 mA at 45 Vdc. During the Phase I tests, the terminal block which had been dipped in saturated Nacl I solution and dried experienced leakage currents of 9 mA at 10 Vac to 200 mA and breakdown at 400 Vac. ~ For this same block condition, a maximum of only 0.33 mA was observed in the Phase II test. This difference may possibly be attributed to the polarization of the

, electrolytic soletion [61] that occurs in conductive solutions when a de potential is applied.

$ er r- - - y +-y. y -y. ? m v.- * -4m - - - y- - - -s

TEMPERATURE (*C) '

10 30 50 70 90 110 130 I I I I I I l l l l 1 1 I O CURREN vs. TIME A CURRENT vs. TEMPER ATURE -

170 V TEMPER ATURE vs. TIME 32 -. -

160 150

- O A y, 2 8 - -

140 x -

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60 U O A 50 8 - O A -

40 O A 30 7

4O A 0

0 A 10 009 ' 'A ' ' ' I d.8 I I ' I O l 0 20 40 60 80 100 120 140 1 TIME (minutes) l l

Figure 5-6: Leakage currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block in the "As-Received" Condition

' Environmental temperature as a function of time is

j. is also shown.

I I

l

d TEMPERATURE (*C) 10 30 s .- 50 70 90 110 130 l 19 I i i I i i 190 l l 1 l 1 18 -

180

'O CURRENT vs. TIME -

170 17 -

A CURRENT vs. TEMPER ATURE 16 -

160 15 -

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I 379;7 30 l

l 2 -

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10 00 OdOOd.OQ(

l' 0

0 20 40 60 80 100 120 140 TIME (minutes)

Figure 5-7: Leakage currents at 125 Vdc as a Function of Time and

' Temperature for a Manufacturer I, Model A Terminal Block in the "As-Received" Cond1 tion ,

Environmental temperature as a function cf time is also shown. ,

i j:

4 4

TEMPERATURE ('C) 10 30 50 70 90 110 '"130 I I I I I I I I l l l l l 190 45 -

O CURRENT vs. TIME -

160 A CURRENT vs. TEMPERATURE V TEMPERATURE vs. TIME -

170 40 -

160

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30 SV- OO M -

20 0 ' ' ' ' ' ' I I I 0 20 O

, 40 60 80 100 120 140 TIME (minutes)

Figure 5-8: Leakage currents at 45 Vdc as a Function of Time and !

Temperature for a Manufacturer I, Model A Terminal l Block After Bein5 Washed and Soaked in Distilled Water .

1 Environmental temperature as a function of time is also shcwn.

I l l l

l

TEMPERATURE ('C) 10 30 50 70 90 110 130 i i i i i I I 200 i i I I I I 190

, O CURRENT vs. TIME 45 -

A CURRENT vs. TEMPER ATURE -

180 V TEMPER ATURE vs. TIME 170 k- 40 - -

160 0 -

150 C

b35 -

OA -

140 x

OA -

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-V o A 30

(. 7 A O

5- g 20 7

O A -

10 0[O~

d^

20 l

40 I I 60 I I 80 100 120 140 O

TIME (minutes)

Figure 5-9: Leakak Currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal l Block After Being Washed With Distilled Water and Then Handled Environmental temperature as a function of time is also shown.

l -- - ,

TEMPERATURE ('C)

" 10 -30 50 70 90 0 110 130

y. y y , , , , , , , y. 200 g

O CURRENT vs. TIME '

- 190 A CURRENT vs. TEMPERATURE 9 -

V TEMPER ATURE vs. TIME - - 180 170 i i

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20 Oe A i -

10 l O COO-b-OkOk- h^ I I I I I I I I O

o 2o 4o so s0 100 12o 14o TIME (minutes)

Fiture l 5-10: Leakage Currents at 45 Vdc as a Function of Time and and Temperature for a Manufacturer I, Model A Terminal l Block in the "As-Received" Condition and Subjected to I 7 Minutes of Finely Atomized Chemical Spray Environmental temperature as a function of time is also shown.

TEMPERATURE ('C) 10 30 50 70 90 110 130 50 , , , , , , , , , , , i g 200 O CURRENT vs. TIME -

190 A CURRENT vs. TEMPERATURE 45 -

V TEMPERATURE vs. TIME -

180 170 0O O AA A 40 -

OO O 00% A AA -

160 OO MO A O A 150

? 35 - -

140 o O A

" O A w O A 130 a 30 -

O A -

120 E

e 0 w -

110L

$ W z 25 - -

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50 i 10 9

sr -

40 l -

30 0 A 57 -

20 O A 10

! OO I d I I I I I I I I I 120 I I 140 O

l 0 20 40 60 80 100 TIME (minutss) l Figure 5-11: Leakage Currents at 45 Vdc as a Function of Time and Temperature for a Manufacturer I, Model A Terminal Block Dipped in Saturated Nacl Solution and Dried Environmental temperature as a function of time is also shown.

l - _ _ _. - _ _ - _ . ._ - .. . _ -

f Table 5-3 Final Values of Leakage Current and the Ratio of Final to Initial Values of Leakage Current for Manufacturer I, Model A Terminal Blocks

45 Vde-- -

125 Vde-----

I

I f I f f / f' /

(mA) i (mA) i As Received 0.029 290 0.0175 115 Washed & Soaked in 0.0037 60 - -

Distilled Water Washed & Soaked in 0.0038 76 - -

Distilled Water, Handled'

- As Shipped With 0.0055 183 - -

Chemical Spray Dipped in Saturated 0.33 330 - -

Nacl Solution and Dried

If = Final value of leakage current It - Initial value of leakage current Also included in Table 5-3 are the ratios of final leakage current.

I f, to beginning leakage current I I. These ratios give an idea of

the relative change observed during the test. For the most part, this

. change occurred between 35*C (95'F) and 80*C (176'F) and for some terminal blocks it occurred over a much narrower range--nominally 55'C (131*F) to 70*C (158'F). The temperature behavior is readily apparent in-Fidures 5-6 through 5-11 and may contribute to the lower leakage currents observed in these tests versus those observed in the Sandia tests.

Elect.rolytic conductivity is 'known to follow an Arrhenius relationship.[38]. However, the overall behavior results from the influence of the many other factors, especially changes in concentration which affect the conductivity of the film solution.

i l

5.3 Characterization of the Amount of Salt Deposited by Fingerprints ;

In order for a moisture film to be conductive, it must contain I dissociated ions. There are potentially many sources for these ions on the surface of a terminal block. These included surface dust contamination, residue from manufacture and salt from fingerprints. Of

{

1 "these, the most likely;. source is the seit deposited from the fingerprints

-of:those'who handle the terminal block during its life. On this premise, -

a brief experimental determination of the . salt deposited by fingerprints was. undertaken.

All measurements.were made with six Westinghouse #542247 terminal blocks. This terminal block is made from a cellulose-filled phenolic

. insulation material. -The experiment consisted of cleansing the surface to be tested,Ethen masking off a square area 1 cm on a side and touching this : area with.the tip of the index finger. The pressure of the contact was not measured, but was assumed to be typical of an average man picking

_ up

" a terminal block. .Three subjects, A, B, and C participated in the test, which helped average both the amount of salt deposited and the contact pressure.between the fingertip and the terminal block.

To measure the amount of salt deposited, the area was flooded with between 0.3 cc and 0.5 cc of deionized water. This drop was held on the contact area by surface tension. After 30 seconds of contact, the water

was removed with a syringe and a portion was added to a micro conductivity cell. This cell was calibrated against solutions of-accurately known Nacl concentrations. By measuring the sample's conductivity, the concentration of salt was determined, and knowing the sample volume the moles.of salt were calculated. A test of the einse solution's ability to remove.the salt was made by making a second rinse and measuring the residual salt in the second solution. It was found' that the. primary rinse removed virtually all the available salt.

1Nm sets of measurements were made, the first being with dry fingers, the second'with wet fingers. A sample of the results is included in Table 5-4. The greatest contamination occurred for wet ,

fingers (5 x 10-6 moles NaC1/cm 2 ), while the dry fingers left

contaminations approximately two orders of magnithfe less (5 x 10-8 moles NaC1/cm 2),

A measure of the WaCl contamination on a 1 cm2 area of several blocks in the "as-received" condition was made. These measurements varied widely, but were within the range of the dry' finger contamination level. The results from these measurements give an order of magnitude feel for the amount of ions available on " clean" terminal blocks for.

~ dissolution in a moisture film. We use the term " clean" to imply the contamination. level that may be present after installation and assuming loose dust and other contaminants have been removed. We see'in the next section that 10-7 moles of. salt is sufficient to. provide approximately 1.0 mA of leakage current depending on the applied voltage. .

1 i

i f:

a.

l Table 5-4 Sample of Data for Measured Residral Salt (Nacl) From One Fingerprint on a 1 cm2 Area of 'a Phenolic Terminal Block Moles of Nacl Sub3ect Wet (W) or Der (D) -(10-7)

A D 1.1 B D 1.04 A D 0.8 A D 2.0 A D 1.0 A D 1.5 A D -0.56 C D 0.30 C- D 0.22 C D 0.25 C D 0.32 C D 0.26 A W 25 A W 40 A W 34 A W 52 A W 33 A W 28-A W 53 A W 20 A W 50 A W 63 l

l I

A i

6.0 THEORETICAL CONSIDERATIONS GOVERNING FILM FORMATION AND CONDUCTION ON TERMINAL BLOCK SURFACES

[

The model presented in this section'is based on the work of Dr.

Robert'Salomon of Temple University and Mark Jacobus of Sandia. The objective of this-work was to provide a basic understanding of the 12 mechanisms of' film formation and to predict, if possible, the conditions where dryband formation and tracking breakdown will occur. There were two' motivations to develop these theoretical considerations. First', the data'from the Sandia tests' indicated that film formation was the most

' probable explanation for the transient phenomena.and it~was therefore desirable to explain the mechanisms which governed this behavior.

?Second, the formations of drybands due to Joule heating of the moisture

_ film has been proposed by others'[39) as a possible mechanism leading to tracking; breakdown and it was desirable to estimate the potential.for.

this mechanism to be operable at'the voltage and current levels of i instrumentation and control applications.

.The model assumes that the terminal block is initially contaminated i with salt from fingerprints.and there is 100 percent relative humidity in tho' environment surrounding it. The basic premise is that at steady state.the vapor pressure.of the film will equal the partial pressure of the water vapor.in the atmosphere. At 100 percent relative humidity, f this partial pressure is equal to the saturation pressure of water at the ambient temperature.- The model employs a basic relationship for the 1

vapor _ pressure of a 11guld at-two different temperatures which is i derivable from the well known Clausius Clapeyron equation. An additional l factor is1 incorporated into this basic equation to account for the vapor pressure lowering resulting from the presence of a solute (dissolved

' impurity)'in the film. The derivation makes some reasonable assumptions j suchEas the applicability of.the ideal gas equation of state, a large L

molar-volume of vapor compared to the molar volume of liquid, and a j temperature independent heat of vaporization. -The model also usesLdata, i from the International Critical Tables (40)oto predict the conductivity

! of sodium chloride'in water as a function of temperature.

6.1 Qualitative Discussion of phenomena i

Moisture will initially condense on a terminal block surrounded by a steam environment because it will be at a temperature below the saturation temperature of the steam. In the absence of any contamination

- or imposed voltage between the terminals, the film on the block will reach a temperature equilibrium with the surrounding environment. As 4

flong-as the surrounding environment is at 100 percent relative humidity, the film will remain on the surface and'not evaporate.

i If_the surface of the terminal block is contaminated with salt E (e.g., from fingerprints), then the film's vapor pressure will be lowered relative to the vapor pressure of pure water at the same temperature.

.Thus, the film' vapor pressure will be below that of the surrounding water vapor's partial pressure, and water will condense into the film. The

, addition of water dilutes the film, resulting in less flim vapor pressure

> " lowering. The condensation process raises the film temperature because F

the latent heat of vaporization is deposited in the film, while heat transfer back to the surroundings tends to return the film temperature to the ambient temperature. The process of condensing vapor, diluting the film solution, and transferring heat away from the film continues until an infinite dilution is reached. At this point, there is no longer any I film vapor pressure lowering.

When an electric potential is applied, a current flows in the film electrolyte. This current is en additional source of energy to the film, heating it through Joule heating. The film temperature rises accordingly, and the vapor pressure equilibrium point is reached before infinite dilution is achieved. Thuc, the additional energy from Joule heating is the balancing factor which ccspensates for the vapor pressure lowering due to the salt. Disregarding the physical dimensions for the moment, the equilibrium point is a result of the interaction of three parameters: the amount of salt present, the applied voltage, and the external environment's temperature. The amount of salt governs the solution concentration and hence the amount of vapor pressure lowering that occurs. It is also the primary contributor to the film conductivity since it is the source of ions in the solution. The applied voltage determines the amount of current which will flow for a specific solution conductivity and hence is a factor in determining the amount of Joule heating that occurs. The external environment's temperature affects the heat transfer from the film surface slightly by changing the associated convective heat transfer properties. With some geometric assumptions concerning conductive film dimensions and the heat transfer areas, and by specifying the three parameters just discussed, the equilibrium salt concentration, film temperature, and film thickness can be calculated.

Also, as an integral part of the calculation, a leakage current can be determined.

The film thickness is especially interesting since it provides insight to the onset of dryband formation. As stated at the beginning of.

this section, dryband formation is believed to be the initial step in tracking breakdown of a moist surfaces which leads to the permanent degradation of surface resistance even after the film is dried.[39, 41]

6.2 Explanation of the Model 1

A very appropriate and useful model of the phenomena is a steady-state model which calculates the conditions that exist in the film for a given set of parameters. We begin by considering the vapor pressure of 1 the film given by:

l l

I i i i l 1 l l

l l

[

P = P exp OH i f 1 _ 1 [1_ 2n2) Eq. 6-1 R j T, T j_ (

n 1j i

where P y = vapor pressure of film at temperature T (atmospheres)

Po = vapor pressure of pure water at temperature T. (atmospheres)

T. = ambient temperature of external environment (Kelvin)

T = film temperature (Kelvin) 8H = heat of vaporization of water (calories / mole)

R = ideal gas constant (1.987 calories /(mole Kelvin))

n2 = moles of salt dissolved in flim ni = moles of water in film Except for the (1 - 2n2/nt) factor, this equation is derivable from the Clausius Clapeyron equation which describes the relationship between saturation.(vapor) pressures and temperatures. The (1 - 2n2/ "1) factor modifies the expression to account for the vapor pressure lowering which results from the salt dissolved in the film. It is based on the knowledge that the vapor pressure of solutions is lowered to a factor of 1 - E of.the initial value where X is the mole fraction of solute. The "2" arises-from the dissociation of the Nacl into Na+ and Cl- lons.

Hence..for every mole of salt, two moles of ions are generated in the dissolution process. To apply Equation 6-1 to the film model we first express n2, the moles of salt, as:

~

n2 = C*V where C is the concentration of salt in the solution in moles /cc of solution and V is the volume of the film in cc. Po is the saturation pressure of pure water at temperature T, and hence, for 100 percent relative humidity, it is the partial pressure of water vapor in the atmosphere at temperature T .* Thus, the condition of equilibrium between the partial pressure of water vapor in the atmosphere and the film vapor pressure can be expressed as:

Py/Po=1

Note that in the test set up used at Sandia the entire pressure in the chamber was due to steam and hence the water vapor partial pressure was the entire measured pressure. The test set up of Salomon closely achieved 100 percent relative humidity.

~ , _ - , - , , ,- - - - _ _ _ - . - . . - - . - _

Applying this condition to the film and substituting for ng, Equation 6-1 can be rearranged to express salt concentration, C, in terms of tem'perature :

C= # 1 - exp AH 1 _ 1 Eq. 6-2 2MW

, R (T T, j ;

In this equation, the leading coefficient, nt/2V, has been expressed as p/2MW where p is the density of water and NW is the molecular weight of water. Making this change in coefficient assumes that the volume of the solution does not change when the salt is dissolved in the water.

Equation 6-2 provides us with a relationshipebetween the salt concentration in the film, the temperature of the film, and the external temperature. In order to apply Equation 6-2,'it is necessary to know two of these three parameters. Before the solubility limit of salt is reached, the obvious parameters to determine from other means are the two temperatures. T eis normally specified as an environmental condition either in a test or an accident specification. T, the film temperature, can be determined by balancing the energy sources and sinks for the film. To achieve this balancing, consider a simplified geometric model of a film on a phenolic surface pictured in Figure 6-1.

A phenolic substrate material of width, w, and length, 1, and depth, d, is covered on one surface with a film of thickness h. The film is at temperature T and the surrounding environment is at temperature T.. To simplify the calculations the back boundary of the phenolic block is assumed to be at temperature T., an assumption that is not entirely correct, but which seems to work fairly well for the order of magnitude calculations being conducted, qcv is the convective heat lost from the film to the surrounding environment; qcd is the conductive heat lost from the film to the phenolic block. The power, P.

input to the film arises from the leakage current I. Thus:

P = El = E2 /Z where E is the potential across the flim and Z is the resistance of the film. At steady state the temperature of the film will be determined by the balancing of heat loss and heat input. Thus:

E 2 f g - 9cv - 9ed = 0 Eq. 6-3 FILM PHENOLIC 1 =

l=

\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\

4 u

{ 4,, 4 _ o

+ FILM SURFACE _

4cd INSULATED l

BOUNDARIES 4 _

T. T _.

T *-

{' 4= -E- =_

+ ,

+ -

u

\\\\\\\\\\\\\\\\W \\\\\\\\\\\\\\\\'

I hH *-

i : d :l SIDE VIEW FRONT VIEW s

f 1

j Figure 6-1: Side and Frontal Views of Simplified Geometric Model

- for Film Conduction on a Phenolic Substrate Material i

l

i Each of'these terms are. evaluated in turn below. <

First.: consider the power input term, E 2/Z. E is the applied potential .in volts, across the phenolic block. In the case of a terminal block, it is the potential between the poles. 2 is the resistance of the flim in ohns. In the model, the film is considered ~

to be a Nacl salt i solution. To obtain the relationship between Z and film temperature, data 'I from the International ~ Critical Tables [40] was used. This data is

-reported as equivalent conductivity values in em /[(ohmecm)3 mole). By

' definition, equivalent conductivity A, is the conductivity, s, divided-by the concentration. That is:

A = s/C

,It is known that A follows an Arrhenius relationship of the form:

. A = u*exp - EA

. RT _

where u is the temperature independent part of the ion mobility and EA is the activation energy for conduction. Using the International Criticali Table. Data [40] to evaluate u and E A , we find that u = 17800 cm3 /[(ohns*cm) mole] and EA = 3160-calories / mole. R is the ideal gas

constant and T is the solution temperature. Combining the.two above equations yields the f11m conductivity, s:

s = uC*exp - EA

.. RT _ ;

and since s = 1/Z, the power input to the film is:

P = E uC*exp - EA Eq. 6-4 RT _

Equation 6-4 is the desired expression for the first term in Equation 6-3, the power input to the f11m as a result of Joule heating. Noting the value of E A. it is. clear that though a varies;with T, large changes in T are required to' change s significantly. This fact, combined with the knowledge that T will be close to T., is used in the computer implementation of this model to obtain the initial guess of the power input to the f11m.

~68-

The second term in Equation 6-3 is the convective heat loss, gey, given'by:

9cv = h'A(T-T ) Eq. 6-5 ,

where gey:is the heat lost per unit time in watts, h' is the average convective heate transfer coef ficient, in watts /(cm2* Kelvin), A is the heat transfer surface area in cm2 , and T - T, is the difference between the film and ambient temperatures in Kelvin. From the dimensions in Figure 6-1, we see that:

A = tw Evaluating h', however,.is not nearly as straightforward as evaluating A. -First, the expression for h'. depends on the orientation of the heat

- transfer area. ' Since terminal blocks are typically mounted on walls, the

heat transfer area is assumed to be vertical and hence:

h' = Nuek w where Nu is the average Nusselt number, k is the thermal conductivity of the gaseous medium surrounding the heat transfer area in watts /(cm* Kelvin),

and w is the vertical dimension of the heat transfer area in cm. The average Nusselt number for a vertical flat plate is:

Nu = 0.68 + _

0.670 (Ra) 4 _

1+ 0.492 /16 /9

\ Pr j ,

where Ra is the Rayleigh number and Pr is the Prandt1 number. The Frandt1 number is the.dimensionless ratio of the molecular momentum to the thermal diffusivity of the medium surrounding the heat transfer area, and is a measure of how rapidly momentum is dissipated compared to the rate of diffusion of' heat through a fluid. The Rayleigh number is the product of the Grashof number and the Frandt1 number. The Grashof number 1s;used in natural convection and may be interpreted as the ratio of the

buoyancy forces to the viscous' forces. Thus,the Rayleigh number is a

i. measure of relative convective forces on a body compared to the rate of

. heat diffusion. The Rayleigh number is given by the relation:

38 T - T,-w va j.

r where g is the acceleration of gravity in en/sec2, 8 is 2/(T + T.) in Kelvin-1, u is the kinematic viscosity in cm2 /sec, and a is the thermal diffusivity in cm /sec. 2 Combining these equations, we find that the expression for h' is:

g8T-T w

/4 0.6701 I h' = k 0.68 + _

\ V8

) Eq. 6-6 .

1+l I 0.492 I'/ 16 Pr I

/9

.- A / .

Equation 6-6 coupled with Equation 6-5 gives the convective heat loss.

The third term in Equation 6-3 is the conductive heat transfer per unit time, qcd, in watts, qcd is given by:

T-T gcd

d

~

_w here k .is- the - thermal conductivity of the phenolic in watts /(cm* Kelvin),

l

' A is the cross sectional area through which the heat is conducting, and d is the conduction distance. Here T is the film temperature, and T. is the temperature of the opposite side of the phenolic. As mentioned above, for simplicity'we assume that this T.-is the same as the

-temperature of the surrounding ambient environment. This assumption tends to overestimate qcd; however, for the accuracles of this model,

.further refinement is not warranted. Using Equations 6-4, 6-5, 6-6, and 6-7, all of the terms in Equation 6-3 are defined in terms of known or assumed values and the film temperature, T. Assuming an applied potential E, and using appropriate values for the constants T can be easily found. .The solution for T is arrived at using a binary iteration algorithm in the computer implementation of this model. Knowing T, it is now possible to return to Equation 6-2 and solve for the concentration of the salt in the film. This process is a straightforward substitution for T'and T. in Equation 6-2. Then, having determined the salt concentration and knowing the width and length of the film, the flim thickness..h can be found as fo11cws: .l l

C = n2/Y

= n2/twh or rearranging 4

h = n2/twc 4

l _

r -

n ,

n2 is the. number of moles of salt initially assumed to be on the ~

surf ace, . C was just calculated f rom Equation 6-2, ' and 1 and w are the

- assumed dimensions of the conductive film. Though not explicitly given above, the leakage current in the film can be easily'obtained from the computation _of power since voltage and resistance are both available. It 1should be emphasized that the output obtained from the'model is at steady state. .The transient-process of vaporization resulting in the thinning

. of the film is not modeled; we look at the flim after this transient process has occurred.

Table 6-1 gives a sample output from the computer simulation implementing the above model for an assumed ambient temperature of 450 K (177*C (351*F)), an initial salt contamination level of 10-7 moles (approximately one fingerprint), an electrical conduction length of 2 cm..

a' film width of 0.75 cm, and a thermal conduction length through the block of.1.25 cm.'. Figure 6-2 shows the predicted leakage currents as a

-function of voltages for this. set of conditions but with varying film widths. .The change in film widths. increases the peak leakage currents predicted as well as the voltage at which it occurs. In all cases, the peak leakage current occurs-at the point where the. solution is saturated.

Thereafter,-higher voltages cause additional heating and hence additional vaporization'of the film. Since the film is saturated, precipitation of the salt occurs, reducing the number of ions available for conduction and hence lowering the leakage current. At each voltage the balance between Joule heating and convective and conductivo heat losses determines the equilibrium value of leakage current. The wider film widths increase the film volume and the heat loss mechanisms, and hence the enount of heat.

input necessary to achieve equilibrium is increased both when saturation is approached and subsequently when salt precipitates.

, A potentially important implication of these results is that qualification testing which incorporates increased voltage for margin may actually be nonconservative; after:a threshold is reached, the model predicts that the leaka'ge currents will decrease with increasing

~

voltage. "Some experimental support for this type of behavior was observed in the Phase I results of the Sandia tests.[1]

e s

f 4

^

r

-+ ,-w-r , -m., .,,,1n-, ,n.-n.-..,,w,mme,.e,w,,,,,,,-,--m . - - - . - ~ - - - , - - , , , , - - , , ,,--m--.-,-~ man.-~, ,,,.e,,,,,,,,-w--,-..--,,. .w.m ,~

1 l

l l

Table 6-1 -

l Sample Equilibrium Film Parameters Predicted by Film Conduction Model*

Applied Leakage ' Salt Film Film Potential- Current- Concentration ' Temperature Thickness (Vdc) -(mA) (moles /cc) (E) (cm) 5 0.064 0.000044 450.074 1.51E-03 15 0.19 0.00034 450.578 1.94E-04 25 0.32 0.00088 451.496 7.59E-05 35 0.46 0.0016 452.787 4.15E-05 45 0.60 0.0025 454.442 2.66E-05 55 0.74 0.0035 456.461 1.88E-05 65 0.89 0.0047 458.854 1.42E-05 75 1.1 0.0059 461.636 1.12E-05 85 1.0 0.0065** 462.932 8.89E-06 95 0.93 0.0065 462.932 7.12E-06 105 0.84 0.0065 462.932 5.83E-06 115 0.77 0.0065~ 462.932 4.86E-06 125 0.71 0.0065 462.932 4.11E-06 135 0.66 0.0065 462.932 3.52E-06 145 0.61 0.0065 462.932 3.06E-06 Parameters assumed are an initial salt contamination of 1.0E-07 moles, i

ambient environment temperature of 450 K, electrical conduction length of 2 cm, electrical conduction width of 0.75 cm, and a thermal conduction length of 1.25 cm. The thermal conductivity of steam at 450 K is 2.99E-04 watts /(cm* Kelvin) .

I

- Solubility limit of Nacl is ~0.0065 moles /cc.

4 If the salt concentration calculated by the above method exceeds C,, the solubility limit of salt'(~0.0065 roles /cc), a different

-computation procedure is used*, First the salt concentration is set equal to the solubility limit; then, using Equation 6-2,'a film temperature is calculated. Note that once the solubility limit is reached, the film temperature becomes a~ constant, such a condition is e- entirely reasonable since for a saturated solution the maximum vapor i

' pressure lowering has occurred, and thus the film has reached its maximum temperature.

Note that the solubility limit of sait 'is only weakly dependent upon temperature, and hence the model does not incorporate this minor effect.

i 1.2 ,

! 1.1 -

1.0 - ,,t,-

l WIDTH (cm) -

_< 0.9

\

t E -

~ 0.8 -

1 Z -

i w 0.7 -

o.7 s E

l $ O.6 -

i O

, w 0.5 -

o.so-

. y 0 l j O.4 -

4 o.a s-l w J 0.3

~

0.10 l

i 0.1

' ' ' I ' '

0.0 140

' O 20 40 60 80 100 120 1

APPLIED VOLTAGE (V) i t

Figure 6-2: Predicted Leakage Current Versus Applied Voltage for l

Selected Film Widths and Other Parameters as Specified in Table 6-1 4

1

By fixing the film temperature, the convective and conductive heat losses become constant and any additional Joule heating causes further vaporization of water and begins precipitating salt. The film thickness i continues to drop and the potential for dryband formation increases. In i the model, a reduction in the number of salt ions available for conduction occurs due to precipitation of the salt. This effect reduces the rate of Joule heating (leakage current) until it equals the rate of convective and conductive heat loss to the environment. However, in this model the saturation limit may be artificially reached too soon because the film dimensions are fixed. In the real case, we hypothesize that at the lower potential, the salt remains in solution with different film dimensions. At the higher potentials, dry areas may be formed rapidly and a localized voltage gradient may be large enough to support arcing.

In this case surface breakdown, rather than film leakage currents, may be experienced. These latter phenomena have not been modeled directly, but by extrapolating the film conduction model to higher voltages, we see that the film thickness reaches the 10-6 to 10-7 cm range at about 300 volts. These thicknesses are on the order of 1 to 10 molecules which probably means dry bands have formed somewhere in the conduction path.

Thus we might reasonably expect drybands to become an important surface mechanism at or above 300 volts. This conclusion, though not proved by data, is supported by it since the only confirmed breakdown was observed by Salomon at 400 Vac.

6.3 Strengths and Weaknesses of the Model The primary strength of this model is that it offers a plausible explanation for the observed phenomena based on first principles. It only assumes ideal gas behavior and temperature independence of two parameters: the heat of vaporization of water and the solubility limit of salt. With reasonable assumptions for the dimensions of the conduction path, the model predicts leakage current values within the range observed by both Sandia and Salomon. The dimensional dependence of leakage currents (as illustrated by Figure 6-2) may reflect reality since the observed variations in leakage current may be a result of fluctuations in the size of the conducting path. The model works for a saturated steam or a 100 percent relative humidity environment. In fact, it will work with minor modifications as long as the percent relative ,

humidity exceeds the adjustment factor for the vapor pressure caused by {

the presence of a solute in the moisture film. The model also provides a framework that allows an estimation of the relative importance of the various parameters and phenomena involved. For example, the flim i temperature will not be dramatically different from the environment's ;

temperature, and film conduction is not strongly dependent on temperature. Of more importance is the amount of salt (ions) present and the conducting geometry.

l The primary weakness of the model is its inability to simultaneously l predict both high and low temperature data using fixed film dimensions. I This effect may be a result of a change in mechanism or a change in film dimensions at lower temperatures which is not accounted for in the model. Further, the model assumes that a film will always be present whereas this may not always be the case. Salomon's data are about an I

order of magnitude below the values predicted by the model; however, almost all of his data ends with a strong upward trend in leakage current. Since his experiments proceeded only to a specified temperature and were of relatively short. duration, his data may represent only transient behavior. The true steady-state values predicted in the model were perhaps never achieved in his experiments. As already noted, dimensinnal sensitivity exists and it is, therefore, incumbent upon the analyst to choose reasonable dimensions. The fixed dimensions do not al1ow for parallel conducting paths that would change leakage currents and effective irs for a given set of conditions. Finally, the uniform film thickness assumed by the model does not recognize that the film undoubtedly undergoes localized heating and cooling which leads to localized thinning and reforming of the film.

h

I 7.0 FAILURE MODES OF TERMINAL BLOCKS Table 7-1 provides a summary of terminal block failure modes. The three broad categories of failure modes presented therein are gross electrical breakdown, leakage currents, and open circuits. Gross electrical breakdown is one end of the spectrum of leakage currents and is defined as that leakage current which makes the circuit inoperable.

It may be either permanent as in the case where carbonized tracks form on the insulator surface or it may be temporary as in the case where voltage is applied rapidly in the presence of a moisture film and the IR momentarily decreases to virtually zero. Leakage currents imply any level of leakage which does not render the circuit totally inoperable, but does affect the operation in some manner. Leakage currents are the usual precursor to gross electrical breakdown. The dividing line between leakage currents and gross electrical breakdown is not precise and is application dependent. For example, milliampere leakage currents in an instrumentation circuit may make that circuit inoperable, but mil 11 ampere leakage currents in a power circuit are probably acceptable. An open circuit is the final terminal block failure mode. It is simply the breaking of the desired electrical conduction path. Gross electrical breakdown precipitated by leakage currents is one possible mechanism which could lead to an open circuit. A momentary surge of current, or a sustained high level of leakage current in conjunction with stress, corrosion, or other factors may cause the cable or the terminal block or their interface to separate. As reported in Reference 1, we observed one such failure in the Sandia tests of terminal blocks. Another example of an open circuit failure mode is the embrittlement of the metal forming the "U" clip in a sliding link terminal block and subsequent torquing of the screw in the sliding link. This failure mode has previously been studied.[42,43]

-Table 7-1 shows the three basic failure modes and then correlates some relevant mechanisms by which these modes may occur. The term "causes" refers to those conditions which enable the mechanism to proceed. "Causes" may be independent of one another, but more likely they will work synergistically. " contributing factors" are those items which aid and abet, or in some way affect a "cause" or "causes", but are probably not sufficient by themselves to cauee the failure mechanism to proceed. " Effects and/or symptoms" summarize the consequences that the failure mode has on the circuit or the terminal block. Normally, these effects would be observable or at least detectable by the operator.

Table 7-1 Summary of Failure Modes for Terminal Blocks Potential Contributing Effect/

Causes Factors Sympt om Comments Failure Mode Mechanism Voltage Exposure Loss of Circuit Temporary Gross Electrical Low Voltage Surface Environmental Conditions Operability Breakdown Breakdown

High Temperature Time (e.g., low Humidity / Moisture Contaminante Insulation Type resistance path terminal-to- Contaminant Temporary terminal or Volatile / Soluble Surface Contamination Deposition Rate terminal-to-base plate Aging ,

Radiation Normal Accelerated High Leakage Currents and Surface Tracking Non-Volatile Surface corrosion Permanent i

Contamination Products u

Conductive Residue 7

Thermal and/or High Temperature Loss of Circuit Permanent Conducting Path Pryolytic Decomposition Operability of Insulation Exposure to Burning Environment Excessive Cracking of Permanent Structural Failure Temperature Insulation Excessive Thermal Shock .

l Vibration

High voltage breakdown not included due to lack of HV circuits in nuclear applications I

l Table 7-1 (continued)

Summary of Failure Modes for Terminal Blocks Potential Contributing Effect/

Failure Mode Mechanism Causes Factors Syrpton Comments Gross Electrical Conducting Structural Failure Improper Breaucown Path (continued) Maintenance (continued) (continued; Improper Installation Aging sult Insulation Radiation Breakdown Moisture Absorption Cracking Moisture Splitting of Absorption insulation and

-formation of conducting paths e Leakage currents Surface Conduction Surface Contamination Installation Low Frequency Some leakage g Practices Line Noise will always i

occur. The Environmental Maintenance Circuit question is Conditions (e.g., . Practices Crosstalk a matter of High Temperature degree.

Humidity / Moisture, Voltage Level Excessive Leakage of Contaminants) Power Drain a few milli-amperes may Aging Biased be detri-Readings on tal to an Instrument instrumen-Outputs tation circuit, but

' Radiation Access for Gross have no beta-emitting Breakdown effect on isotopes a power circuit.

Table 7-3 (continued)

Summary of Failure Modes.for Terminal Blocks Potential Contributing Effect/

Failure Mode Mechanism Causes Factors Symptom Comments Leakage Currents Surface Conduction Structural' Failure Excessive Cracking of (continued) (continued) Temperature Insulation

~ Excessive Thermal Shock Vibration Improper Maintenance Improper Installation Open Circuit Separation of Loose Terminal Screws Loss of Circuit.

Conductor Operability

Contact Corrosion Chemical Reagents U Moisture / !

i Humidity '!

Structural Failure vibration Cracking of i Conductor Thermal Shock Improper Maintenance Improper Installation Differential Expansion

,y, p ..

Table 7-1'(continued)

Summary of Failure Modes for Terminal Blocks._ ,

' Potential . Contributing Effect/

Failure Mode Mechanism Causes Factors Symptom Comments Open Circuit ' Separation of High Leakage Currents (continued) conductor (continued).

' Failure to Reconnect Careless Main-Terminals tenance Procedures Lack of Quality

-Assurance O.

I se O

4

'h I

J.

T d

b 4

e b

$ h

8.0 EXAMPLES OF POSSIBLE TERMINAL BLOCK EFFECTS 8.1 Transmitter Circuits A pressure transmitter. typically operates with 4-20 mA of current in the instrument loop. At zero pressure, or the low end of the calibrated span, 4 mA.is allowed to flow in the circuit, at full pressure 20 mA is allowed.to flow. The key word here is " allowed." A transmitter essentially functions as a variable resistor in the circuit, limiting the amount of current flowing in its branch of the circuit to a value ;

proportional to the input pressure; it is not a current source. This characterization is extremely simplified, bat it captures the essence of circuit behavior and permits terminal block effects to be analyzed.

Figure 8-1 shows how a transmitter might typically be connected in an actual plant application.

The' transmitter will operate correctly as long as the voltage remains in a specified range. For example, a typical transmitter will operate to specification as long as the voltage across the transmitter

' terminals remains between 15 and 50 Vdc. The loop resistance external to the transmitter (from the current-to-voltage amplifiers, the cable, and the other external resistances) also may vary over a specified range depending on the voltage cupplied to the transmitter. For a typical transmitter, if the power supply voltage is 45 Vde, the external loop resistance may very between 250 and 1,500 ohms. Note from Figure 8-1 that the-potential across the transmitter, AVT , is essentially the potential across the terminal block and therefore would be the driving potential for any terminal block leakage current. AVy can be expressed in terms of the normally constant power supply voltage, V,,

and the voltage drop AV,, across the external loop resistance, Re-AVT = V, - AV, AVT"Vs - R.It Eq. 8-1 where IL is the total loop current. The leakage current, ITB, across l' the terminal block is:

i l

l ^'r I

TB " RTB l where RTB is the-insulation resistance of the terminal block. The L

total loop current, which will be observed in the control room as the transmitter signal, will be the sum of the transmitter output current, Iy, and the terminal block leakage current:

f-I

1 OUTSIDE CONTAINMENT g INSIDE CONTAINMENT l

1 1

I I

' RTB I

i .# +

l C

F" 3 POWER SUPPLY

~ v v -

a l

\ TRANSMITTER 7 II TB \

I I

TERMINAL a I BLOCK I

<L I m m p g RexT RLINE I I

READOUT jS ATION SIGNALS AMPLIFIERS AT 2509 EACH _, -

R.

3 Figure 8-1: Simplified Schematic of a Typical Transmitter Circuit in a Nuclear Power Plant I

-- _. .- .=_ .. - - _ . - .

In = ITB + IT Eq. 8-2 Under normal conditions, ITB will be zero or negligibly small ,

' compared to IT . However, under accident conditions, ITB can become a sizable fraction of Iy, and therefore, becomes a sizable portion of the total loop current sensed by control room instrumentation. The error, e, in the signal will simply be the ratio of the terminal block leakage l

. current to the transmitter signal current. That is:

b Eq. 8-3

e= =

T T Using the above equations, we can express e in terms of V,, R., RTBe and I T:

V,-RIT e= I* ~

I TRTB + Re Figure 8-2 shows a plot for the signal error as a functir7 of transmitter output for common values of V,, R., and several aw,umed.

values of RTB. Note that the error is expressed as a percent of output current (or reading) rather than a percent of calibrated span. This was done intentionally to. illustrate the error that would actually be o

observed'especially at the low end of the transmitter calibration.

The errors can be quite significant when-the terminal block leakage current approaches the values of the transmitter signal or equivalently, when.the terminal block IR approaches the values of transmitter input impedance. At 45 Vde, the transmitter input impedance will vary from approximately 2 to 10 kohns as its output varies from 20 to 4 mA. Hence, i

the terminal blocks may be viewed as a resistor in parallel with the

!. transmitter and..as such, acts as a current divider. Figure 8-3 shows

! the current. trace of total circuit current as a function of time for the I terminal block connected in the transmitter circuit during the sandia test.[1] For the period of time covered by the plot,-the transmitter was

-operating at ~4 mA base signal level. Clearly, the total circuit current observed isein ,greement a with the above analysis. During the cooldown period when the film vaporizes, the transmitter current returns l

to its base current level.

t l

To illustrate the impact of these errors, suppose that'the transmitter in question was a narrow range reactor coolant system (RCS) i pressure monitor calibrated from 1700 to 2500 psi. Thus, each mil 11 ampere of signal corresponds to a 50 psi increment in pressure. The sensed pressure will be based on'the total loop current, I L. Assuming I

l

200 ,

VALUE OF RT s -

160 5 kohms -

10 kohms ~

60 kohms

% ERROR IN 120 -

- 500 kohms -

~

i CONTROL . 5

, ROOM SIGNAL r -

4 i

80

- 'N s -

's,- ,

40 - ,

i --- ---

.. . ~_. . . . . .... . . . . . . . . . . . . r * * *; *

u* " " T ~~~~~

" ,1,' .". 4.

. . . .. m. L. -.- . . *. ". . s

~. -

O

4 6 8 10 12 14 16 18 20 -

TRANSMITTER OUTPUT CURRENT (mA)

Figure 8-2: Percent Error in a Transmitter Circuit for Selected '

Values of Terminal Block Insulation Resistance i

(R, = 1000 Q and V, = 45 Vde) ;

i

I I I I I I 1. I I I I I I 13.7 - -

11.7 - -

17 5 *C _

161

C _

95*C 14 9'C _

9.8 - -

2.7 mA LEAK AGE CURRENT C RC T 7.8 - -

CURRENT (mA) '

i b, 5.9 -

k -

3.9 -

N i TR ANSMITTER B ASE COOLDOWN 19 -

SIGNAL LEVEL PERIOD 0.0 ----- C POWER ON i

l l I I I I I I I I I I I O 30 60 90 120 150 180 210 240 270 300330 RELATIVE TIME (minutes)

Figure 8-3: Total Current Trace of Transmitter Circuit During i

LOCA Simulation

f everything else in the circuit works perfectly, Figure 8-4 shows the i readouts that would be observed in the control room for V, = 45 Vde, I R, = 1000 ohms, and RTB = 10,000 ohms. Note that the minimum reading-is 1886 psi at the minimum transmitter current level of 4 mA.

4 One of the uses for a narrow range pressure monitor is to provide an actuation signal for high pressure injection (HPI). A typical set point would be 1750 psi which is less than the minimum reading of 1886 psi caused by the summing of the 4 mA base current signal of the transmitter and the terminal block icakage current. In fact, any setpoint less than 1886 psi would not be achieved. The result is that one or more of the instrumentation loops required for actuation of HPI by low RCS pressure would not reach their set points, and hence, HPI may not be automatically accomplished; in this situation another means of actuation would have to be implemented. This type of error would also affect the pressure readings observed by the operator. Not only would the readings themselves be in error, but the operator would also be faced with a discrepancy in c'eadings between narrow and wide range gauges.

8.2 RTD Circuits RTD circuits are low voltage, low current circuits. They are not, however, immune to the effects of terminal blocks. An RTD circuit typically operates at 4 Vdc or less with currents in the range of 1 mA or less. The resistance in a typical RTD might vary from 200 ohms to 500 ohms over the full temperature range of the RTD. Figure 8-5 shows in a very simplified block form how an RTD circuit will look using a terminal block to connect the RTD to the remainder of the circuit. The IR of the terminal block is a parallel connection with the RTD resistance. Hence,

~

the bridge or constant current circuit used to sense'the resistance of the RTD is actually sensing the effective resistance, Re gg, of this parallel combination. R,gg is: .

1

~

i R

eff = R TB + RTD and the fractional error e is:

e= " ~

S* ~

R R '

RTD TB RTD l t !

h i

i 2500 i i i i RESPONSE CURVE WITH 10 KG TERMINAL 2300 -

BLOCKIR 9

0[ -

3 INDICATED

/ +0 0

RESPONSE

A\ CURVE FOR PRESSURE 2100 g,,,)

CORRECTLY -

5 OPERATING

((4 CIRCUIT ASSUMPTIONS: _

1900' 1sae f[ R, = 1 K G O

Vs =45 Vdc

, ; Rys=10 KG 1750 ..

8 ' 8 l 1700 4 8 12 16 20 TRANSMITTER OUTPUT (mA)

Figure 8-4: Indicated Pressure as a Function of Transmitter Output for a Correctly Operating Circuit and for a circuit with Terminal Block Insulation Resistance Assumed to be IC kohms

OUTSIDE INSIDE CONTAINMENT CONTAINMENT R TB $R RTD POWER SUPPLY ;;

+

, MSMT.CKT m a

' R .gg Figure 8-5: Simplified Block Diagram of a 3-Wire RTD Circuit Showing Parallel Connection Between Terminal Block Insulation Resistance and the Resistance of the RTD Sensing Element

l 2

4 For a typical 200-ohn RTD which varies in resistance from 200 to 480

- ~ohns over its temperature range, a terminal block resistance cf 10,000 ohns introduces an error in measured resistance of 2.0% at the low end of s the calibration and an error of 4.6% at the high end. Figure 8-6 shows

- the two bounding curves of percent error in measured resistance for a

commonly used 200-ohn RTD as a function of terminal block insulation resistance. For an RCS temperature monitor calibrated from 93*C (200*F) to 399'C (750*F) the 2.0% and 4.6% resistence errors translate to a 4*C (7'F).orror at the low end and a 24*C (43*F) error at the high end.

Since the parallel connection will make the measured resistance less than the actysl RTD resistance, the indicated temperature will always be lower e than the actual temperature.

l To'111ustrate the effect that these errors may have, consider the hypothetical example where the RTD is measuring a temperature of 327'C (621*F) and the pressure is 1800 psia. If the RTD is calibrated-as assumed above, it should have a resistance of.414 ohns at that temperature. A terminal block insulation resistance of 10,000 ohns in parallel with the RTD would give an effective resistance for the pair of 398 ohms or a temperature readout of 309'c (589'F). Thus the displayed

'- temperature would be 18'c (32*F) less than what actually existed. Since ,

the saturation temperature at 1800 psia is 327'c (621*F), the coolant at the RTD could be vaporizing, where as the perceived condition would be

~18 C* (32 F*) subcooled. Thus, even relatively large terminal block irs (e.g., 10,000 ohms compared to 414 ohms for the RTD) can have a j: significant impact on the perceived conditions. The temperature and pressure.in this example are only illustrative; any set of' conditions close to the saturation point could have been chosen with similar

. results. Also, it is important to recognize that an evaluation of accident sequences is necessary to determine the relevance of such misperceptions in coolant condition to accident management.

8.3 Thermocouple Circuits

'Another important temperature measuring device that may employ terminal blocks in the circuit is a thermocouple (TC). One common TC l

circuit design closely approximates a null balance circult; that is, the l

sensing device balances the potential across its input terminals so that L

no current flows through its branch of the circuit. Thus, if the TC circuit is properly designed and installed and is operating correctly the l

potential across the sensing circuit is the open circuit potential. ,

' _ generated as a result of the temperature difference between the measurement j and the reference junction's of the TC. .The presence of moisture films on terminal-blocks-may cause shunt resistances to form between the TC elements l

l.

or'between a TC element and ground. As Moffat (44] points out, the

' introduction of shunt paths into a TC circuit can cause significant effects onLthe output of the TC circuit, that,is, on the potential across the input of the sensing circuit. In order to analyze the effect of these possible t -

shunt resistances and any associated spurious enfs, it is necessary to locate the thermoelectric sources of emf within the circuit relative to the potential shunt resistances and spurious.emfs. Reed [45] has developed a

10 , , , , , , , , , ,

i 9 -- 8 t

TYPICAL 200G RTD -

8 -

} ----RRTD=480G _

j R RTD 2OOO l

PERCENT 6 -

1 -

ERROR IN $

MEASURED RTD 5 g -

RESISTANCE 'g 4 _

\ -

4 3 -

Ns ,-

i 2

\ %

l 1 '

- ~ ~ _ _ _ _- ,

l 0 ' ' ' ' ' ' ' ' ;

O 50000 100000 TERMINAL BLOCK INSULATION RESISTANCE (G)

Figure 8-6: Percent Error in the Resistance Measurement of an RTD as a Function of Terminal Block Insulation Resistance i

i d

functional model of a TC circuit which clearly highlights the location of

[

I enfs in the circuit and permits one to electrically locate the relevant circuit elements for analysis. The key, ingredient in Reed's model is the temperature profile for the entire TC circuit.

g For illustrative purposes consider a typical in-containment thermocouple application such as core-exit thermocouples. The measurement-junction of these TCs will be near the core flow exit point in the reactor ve'ssel. From there, the TCs are typically routed down through the core and exit the reactor vessel from the bottom; shortly after the vessel exit point they may physically junction via a terminal' block or other similar connecting device to TC extension wire which runs through containment to a heated reference junction. At this point -the !

- circuit converts.to a common conductor type such as copper, and' proceeds via a containment. penetration to the sensing circuit (device) located in the control room. . Newer TC circuit designs locate the reference junction outside the containment.

' Figure 8-7 illustrates one possible core-exit thermocouple circuit arrangement and shows a hypothetical, but reasonable, temperature profile for the circuit that might exist during a LOCA. The reference junction for this example is-inside containment. Section 1 represents the thermocouple from the measurement junction to its . junction with extension

wire just outside the reactor vessel. Section 2 represents the run of extension wire from the vessel exterior to the reference junction.

Section 3 represents the circuit from the reference junction through the-measurement circuit-in the control room. Using the method of Reed (45]

and assuming homogeneous wires in each section of the circuit, lumped possible omf sources are shown in Figure 8-7. Et is the net enf-resulting from the temperature difference'between the measurement'and reference junctions. For this example the temperatures of the measurement and reference junctions are assumed to be 550*F and 150*F.

respectively. Thus El -for a Type K thermocouple is 9.036 mV. E2 is

-a possible enf resulting from temperature gradients that'may exist within containment along Section 2 of the circuit; for this example Section 2 of the circuit is assumed to be isothermal since an accident is in progress and the containment temperature and the reference junction temperature will.most likely be the same. Thus, E2 is zero and is not considered '

further inLthis example. E4 and E5 are spurious emfs which may be introduced by the terminal ~ blocks in the shunt paths. These enfs may be l-of galvanic or other origin as discussed in Reference 1. R1 is the l

lumped resistance of the TC' wire in Section 1 of the circuit and R2 is the. lumped resistance of the TC extension wire in Section 2 of the C circuit. For.this example these values are assumed to be 598 ohms and 117:ohns, respectively and were chosen as follows: R1 = (100 feet of I. 0.01 inch diameter Type K TC wire)*(5.98 ohm / double foot) = 598 ohms; L R 2 = (200 feet of 20 AWG Type K TC extension wire)*(0.586 ohms / double foot) = 117 ohns.[46, 47, 48] R4 and R5 are the ohmic resistances of

'the shunts caused by the terminal blocks.

i t

- ~ - , , - - . _ - , , - . _ ~ , .

SECTION 1 SECTION 2 A

SECTION 3 r

v A A v T 1

$ 8 l \

I l \

8 f

Et i NULL E,

4 1g Es f i i BALANCED

/ N, !

l SENSING

% / I I I I CIRCUlf AND Tu g,\ l g, , lNDICATING g, I lyl CIRCulT.

i : \ u Ia 6i ta 6 i !

'd) %W ICNMT d

Iref (a) THERMOCOUPLE CIRCUlf WITH TWO SHUNT PATHS soo -

E

.,sao4 g T,,,

!150 -

^

g I CNMT I

3 5

70 -

i RELATIVE CIRCulT POSITION (b) HYPOTHETICAL TEMPERATURE PROFILE Figure 8-7: Simplified Schematic of a Thermocouple Circuit (Figure a) and a Temperature Profile for the Circuit That Might Exist During an Accident (Figure b)

Figure a shows the circuit with shunt paths located at cable junction points just exterior to the reactor vessel and at the thermocouple reference junction. Figure b shows a potential temperature profile for an accident situation. As a result of the accident T rg and Tenat are shown equal, and therefore, E 2 becomes zero.

l l

l The parameter of interest in Figure 8-7 is V2 , the potential across the sensing circuit input. For a properly operating, null balanced. TC circuit V2 equals E 1. However, the-presence of shunt resistances and spurious'enfs changes V2 , and hence changes the indicated temperature

- in the control room. The error in the voltage across the sensing circuit, e, is:

E -V 2

O e=

E 1

By any one of several methods V2 can be expressed in terms of the.other circuit elements, Et , E4 , ES , R1, R 2, R 4, and RS . The ,

result.is:

RRE+RR54+

4S _

12+ 14* 24 5 Eq. 8-7 2* RR2+RRg4+RR75* 2 4'

45 Examining Equation 8-7, we see that V2 varies linearly with any one of <

)the potentials (E1 ', E4 , or E S) while the other potentials are held constant. Figures 8-8 and 8-9, respectively, show the open circuit voltage, V2 , and the voltage error, e, as a function of the spurious potential E5 . In these- figures, E4 3is assumed to be zero and the l shunt resistances,-R4 'and R$ , are 10 , 10 ,_and 10 5 ohms as noted. 4

~

An interesting point illustrated by these figures is that large shunt resistances (e.g., 105 ohns or more) tend to mitigate the effect of large ,

spurious.emfs'in the shunt paths. For example, if both R4 and R5 are

~ 105 ohns, then the error in the desired 9.036'mV value of V2 for this example varies from +9.7% to'-6.5% (using Equation 8-6) as the. spurious enf The reason for this mitigating effect

.E5 varies from -0.1 Y to +0.1.V.

.is that the large spurious enfs generate significant currents in the' shunt paths (compared to the virtually zero current'in the. properly operating TC circuit).which in turn cause most of the spurious emf to be dropped across the large shunt resistances. Hence, V2.is not affected as dramatically as might be expected since 0.1 V is 11 times the desired 9.035 mV. Of course, changing the relative values of R4 and R5 also affects'the error in V .2 To compare'to the above numbers, if R4 is 104 ohns and l-l R5 _ i s ' 10 5 ohns, then.V2 varies from +13.8% to -1.2% as E5 varies from -0.1:V to +0.1 V. And as' expected, as the shunt' resistances fall, the effect'of the spurious enfs increases. In the limit when R5 is zero, V2 will equal E5- .

I' The effect of varying R5 on V2 and e is illustrated in Figures 8-10 and 8-11, respectively. In these figures the three curves represent ;

'different values of,ES (-0.01 V, 0.0 V, and +0.01 V); R4 is assumed to

!! be 104 ohns. These figures show R$ varying only up to 11000 ohms, but the trend is clear. As R5 increases we see that V2 approaches R4 /(R 1 '+ R 4 )*E t, and if R4 is large compared to R1 , then V2 approaches 1E . As expected, for R$ equal to zero V2 is exactly the l

n ,

j !

1

- :- 4 . . , , - - - -

- - - - . , . . . , _ _~. . - - , , . . , _ _ _ , - . - . - - - - . _ . - ~ . - - ---r . . - , _ , , , . . ._I

1 0.05 -

i .

i . .

i .

i . i i .

0.04 -

0.03 -

0.02 -

0.01 -

l

8 R4 AND Rs = 10 4 7 x R4 AND Rs = 10sn 0.00

-0.01 -

-0.02 - -

8 R4 AND Rs = 10 0

-0.03 -

-0.04 ' ' ' ' ' '

-0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 .0.08 0.10 Es Figure 8-8: Open Circuit Voltage V2 as a Function of the Spurious Voltage ES for Selected Values of Terminal Block Shunt Resistances

6 .

l R4 AND Rs =103 0 5 -

4 -

i ;-

! 3 - -

! E O

cc 2 - -

8 i

$ R4 AND Rs=10 0

! J 1 i <

Z

! oO i b R 4 AND Rs = 10sg i O

< _1 _ _

m u.

-2 - -

l

, -3 - -

-4 -

1 t ! t ! t a ! I E I R ! l ! I j -0.10 -0.08 -0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 l Es Figure 8-9: Error in the Open Circuit Voltage as a Function of the Spurious Voltage E5 for Selected Values of Terminal Block Shunt Resistances

0.010 , .

0.009 - -

0.008 E, - + o.o s/

O.O O 7 -

,s,,,,,

0.006 0.005 - -

0.004 - N Es =-0.01 -

0.003 - -

0.002 - -

O.O O 1 -

f 0.000

-0.001 - -

- b -0.002 - -

-0.00s - -

-0.004 - -

-0.005 - -

-0.006 - -

i

-0.007- - -

-0.008 - -

-0.009 - -

- 0.C ' t - ' ' ' ' '

O 2000 4000 6000 8000 100dO Rs i

Figure 8-10: Open Circuit Voltage V2 as a Function of the Shunt Resistance R5 for Selected Values of Terminal Block Shunt Resistances

___ _ _ _ _ _ _ . _ _ _ _ . _ _ __ m________w

0 0

I 0

0 h e

1 t l

f a

' , oni nm or i e tT 0 c nf I , 0 F uo 0 ae s

8 u sl aa V

1 e

' , gd ae tt l c oe Vl 0 e tS i

0 i urs

, 0 coe 6 i rf c n

C 5a Rt s

n s eei

' - , R pcs One aR et h st ti n 0 su i

0 neh IRS 0

/1 4 rtk onc ruo 0 rhl ESB i

0 ,

=

1

_ 1 s 1 0 E 8 0 0 e i

- , 0 r u

=

s 0 i g

E 2 F O

O.

0

=

s E

- - - - - - - - - 7 0 2 0 8 6 4 -

2 ,0 8 6 4 2 0 2 .

2 2 1 1 1 1 1 O 0 0 O O 0 c -

o0g@ a.4ZOpoyE e

l i

l value of the spurious voltage, E5 Clearly, negative spurious emfs relative to the sign convention shown in Figure 8-7 are more detrimental to circuit performance than positive spurious emfs. It is also clear i that the value of the shunt resistance is a more dominant factor in i determining circuit performance than the value of the spurious emfs.

Since R 4 , R $ E4 , and E5 can vary perhaps continuously over fairly large ranges, a definitive prediction of V 2 is impossible.

Finally, to illustrate precisely what these effects on V2 mean in terms of indicated temperature, a few V2 values predicted by the above example for selected values of R5 and E5 were translated into temperatures. This conversion assumed that the sensing device adds the reference junction compensating voltage to the value of V2 before converting the indication to temperature. These temperatures are summarized in Table 8-1. The assumed values of the other parameters (keyed to Figure 8-7) are noted in the table.

Table 8-1 Selected Temperatures (*C(*F)) Indicated by the Type K Thermocouple Circuit Discussed as an Example in This Section*

(correct temperature indication in all cases should be 288'C (550*F))

___________________---RS( hms)------

5 1000 5000 10000

-0.1 off scale low off scale low 104 (220)

-0.01 90 (194) 221 (429) 247 (476) 0 190 (374) 251 (483) 253 (487)

+0.01 289 (553) 279 (535) 278 (532)

+0.1 1184 (2164) 536 (996) 415 (779)

Values of the other circuit parameters used to derive the results in this table (see Figure 8-7):

1 Et = 9.036 mV E4 = 0.0 V R1 = 598 ohms R2 = 117 ohms 4

R4 = 10 ohms !

8.4 Solenoid Valve Circuits Terminal blocks are commonly installed in 120 Vac and 125 Vdc control circuits for solenoid valves. Figure 8-12 is a simplified schematic showing one possible solenoid valve circuit. Before addressing the effects of terminal blocks, it is important to understand the normal 1

1 -

I 10 A i

i

+

C1 o :: C2 Z12:

' Ryst 120 Vac , /.NT - -- - - f.'. ,:

OR / '

1 125 Vdc s'

'-~~~'

y #

ZZZ2 2:Z3

(

s' ,

RTa t ..;

e

_Z4 R

TB3 ;, SOLENOID '---o O O VALVE

's , STATUS -~

's I INDICATING S

'm LAMPS STATUS PANEL LIGHT 3

1 Figure 8-12: Simplified Circuit Schematic for One Possible Solenoid Valve Circuit i

i l'

operation of this circuit. To begin, assume that the valve is normally {

open and that when energized, it closes. The desired position for operation is open.

The contacts C1 and C2 are control switches in the control room.

These switches can be any one of a number of types, but a common type might be three position momentary contact switches. That is, there is a neutral position which is the rest position for the switch, and there are open and close posillons which must be held by an operator in order for the switch to make contact in that position. Thus, when an operator moves the lever to open and releases it, the switches return to the neutral position. Assume that both C1 and C2 are operated by the same lever. Z1, 22, 23 and 24 are two position limit switches located on the valve itself. L1 and L2 are indicator lamps in the control room and indicate that the valve is not closed and not open, respectively.* S is a status panel light which lights when the valve is in the normally desired position. Tables 8-2 and 8-3 are the contact development tables for this circuit. An "x" means that contact is made in that switch position.

Table 8-2 Contact Development Table For Control Switches C1 and C2

---Switch and Valve position---

Open Neutral Close C1 -

x x C2 - -

x x = contact made

- = contact not made

=

The terms "not open" and "not closed" are used rather than " closed" and "open".because that is the true meaning of the lamp. The "not open" lamp lights when the valve leaves the open position and is thus lit both while the valve is closing and when it is closed. Similarly the "not closed" lamp lights when the valve leaves the closed position and is thus lit both while the valve is opening and when it is open. If both lamps are lit simultaneously, then "not open" ar.d "not closed" are both true which means that the valve is changing state. If only one lamp is lit, then it means that the valve is either open ("not closed")

or closed ("not open").

-100-

Table 8-3 Contact Development Table for Limit 0 witches 21, Z2, 23 and 24

Valve position---------

Open Intermediate Close 21 - -

x 22 x x -

Z3 x - -

24 - x x x = contact made

- = contact not made If the valve is open, we see from Tables 8-2 and 8-3 that C1, C2, 21, and 24 are open. Only 22 and Z3 are closed which means L1 and S are lit and the indication is that the valve is open (see footnote on "not open" and "not closed) . If the operator now wants to close the valve, he moves the lever for C1 and C2 to the "close" position. Both C1 and C2 make contact and, because 21 is still open, power is applied to the valve via C2. The valve begins to close; 23 trips open extinguishing S and 24 trips closed lighting L2. Both L1 and L2 are now lit, and hence we know the valve is changing position. If the operator releases the lever before the valve is fully closed it will return to the full open (nonenergized) position since Z1 is not yet closed and C2 is open when in the neutral position. When the valve reaches the fully closed position, Z1 and Z2 change state. 21 closes so that when the operator releases the switch lever, power to the valve will be applied through C1 and 21; 22 opens turning L1 off. The sequence happens in reverse when opening a closed valve. The operator moves the switch lever to open, thus opening C1; C2 was already open. power to the valve is lost and it begins to open. As it does, 21 and 22 change state. 21 opens to ensure that power will not be reapplied when C1 is released to the neutral position. 22 closes, lighting Ll. When the valve reaches fully open, 23 and Z4 change state. Z3 closes, lighting S, and 24 opens turning L2 off.

The dots in Figure 8-12 indicate circuit nodes which are physical junctions to field wiring near the valve. These may very likely be adjacent terminals on a terminal block. Three possible terminal block leakage paths have been indicated on Figure

12 by dotted resistors.

Each may have a detrimental effect on the operation of the solenoid circuit. First, consider RTB1, a leakage path between the always powered node of Z2, 23, and 24, and the solenoid valve. This leakage path bypasses the valve control switches C1, C2, and 21. The effect of this leakage current could be the inadvectent energizing of the valve when a steam environment quickly envelopes the terminal block. If RTB1 is small enough, a leakage current sufficient to power the valve may

-101-

i occur. If the valve in question is a 17.4 watt, de service valve, then the steady state resistance of the valve is:

1 Ry =

" = 900 Q i 1

-In actuality, because of the finite value of RTR1, the entire power. supply potential will not be dropped across_the solenoid valve.

The minimum voltage to actuate the valve is approximately 90 Vdc [49] and hence the current necessary for this condition is:

I, = 00 = 0.1 A If at least 90 volts must drop across tho solenold' valve, then a maximum of 35 volts can drop across R TBl. Using. the 0.1 A current requirement to operate the valve, we see that:

R * '

TB1 " 1A Thus, a transient terminal block insulation resistance of 350 ohms would cause the valve to close when it was intended to be open. Industry qualification tests experience leakage currents sufficiently large to indicate that such low IR values are possible. Further, low values of IR would be most likely to occur under. transient. conditions (see Figures 4-6 and 8-3). The question here is whether or not such low values of Ik would prevail for a period sufficiently long to complete the closing of the valve. Sandia test results indicate that the answer is probably yes, because solenoid actuation is fairly rapid and the low values of terminal block IR' prevailed for seconds to minutes after their onset.

Next consider the leakage path designated by RTB2 This path is~a leakage path by limit-switch 22 and the net result could be a false lighting of indicating lamp L1. Analogous paths, not shown in Figure 8-12, would erroneously light lamps L2 or S. The current and voltage required to light L1 will undoubtedly vary from design to design, but two cases might be considered as examples. In the first case, the lamp is in a series connection as shown in' Figure 8-12. A typical 125 Vdc lamp for such an application might require a minimum of 110 Vdc to operate.[50]

The lamp itself might.typica!.ly.have a resistance of 2000 ohns'and hence the current necessary would be:

I * = 0.055 A Lamp 0Q

-102-i

l-Thus, the terminal block insulation resistance would have to be:

TB2 " 0 5 A" Again, this value of IR is not unreasonable for transient conditions though sustained values at this low level are unlikely.

The second lamp configuration would replace the actual 1sinps with a relay which would turn separately powered lamps on or off. Thus L1, L2, and S would be the pick-up coils for these relays. Such relays might typically have a pick-up voltage of 75 percent of the rated voltage and a coil resistance of 13000 ohms. The required current therefore would be:

(0.75)(125 V) = 0.0072 A I 7 , '

relay 13000 Q l

The voltage drop across the terminal block could be at most 25% of 125 Vdc or 31 Vdc and hence:

bB2

O O2A Thus, a much larger terminal block IR would permit false operation of the indicating or status lamps if they were switched on and off by a relay. Any value of RTBp less than 4300 ohms would cause the lamps to falsely illuminate for the assumed type of relay.

The final fault shown in Figure 8-12 is RTB3 This path leaks by the valve itself and would cause a problem only if the leakage current became large enough to make the circuit fuse fail. For the worst case with a 17.4 watt de valve energized and all three lamps illuminated, the current in the circuit would be:

I = +3+ = 0.327 A max 125 V 2000 Q if.the circuit were fused at 10.A. then 9.673 A would have to leak around the valve to cause the fuse to fail. With the valve remaining energized at 125 V, fuse failure would occur at a terminal block IR of:

= 30 TB3

7 A

-103-

i iEE

-2 This value is essentially a dead short; however, if the circuit were fused at 1 A, fuse failure would occur at a terminal block IR of 186 ohms. These low IR values are not impossible to achieve, but for any i sustained period seem improbable. Momentary high leakage currents may 1 cause the fuse to open. At these high leakage current levels, one must -=

also be concerned with the power being dissipated by the terminal block m and the effect such power dissipation may have on permanently degrading g the block's surface.

2

-m I

' In summary, the above discussion indicates that terminal blocks may -

interfere with the proper operation of a solenoid valve circuit when the s terminal block's insulation resistance decreases to about the 4 kohin level. At this value of terminal block IR, indicating lamps may falsely _f light depending on how they are wired into the circuit. At a few hundred ohms of insulation resistance, the valve may falsely energize and at a -f f

few ohms of insulation resist'nce the leakage current may be large enough [

to fall circuit fuses. Being slightly conservative, we may conclude that @{

at IR values above 5 kc; s. terminal blocks probably do not affect the operation of solenoid valve circuits.

y j

8.5 Motor circuits i

Consider the case where a terminal block is used to connect a motor -3 to a motor control center (MCC). A typical connection might look like g Figure 8-13. The terminal block leakage path is indicated as a fault resistance, RTB, between lines.

j In this esse the leakage current does g not affect the motor directly, but rather would affect the thermal "I overload protection devices and the circuit breakers. The amount of =

leakage current that would be significant would depend on the settings of these devices. Figure 8-14 shows time-to-trip as a function of percent 3!

of Motor Full Load Current [51) for one type of directly heated bimetallic overload relay.

There are many manufacturers of such devices. 3 both bimetallic type and magnetic type, and the selection of time-to-trip "

characteristic curves are extremely varied. Thus, the following !l=

discussion is only representative of the type of concerns that may be a -

problem; each application must be analyzed individually. -

i probably the most sensitive case is for small 1/2 hp or 1/3 hp ==

motors which draw ~1 A at full power. From Figure 8-14 we see that 200 g*

percent of motor full load current requires approximately 40 seconds to trip the overload pr aection relay; at 500 percent the time to trip is "

down to 3 seconds. These overload currents correspond to ~2 A and y

~5 A currents for the small 480 Vac motors, or leakage currents of T

~1 A and ~4 A. These values of leakage currents have been observed Y in industry qualification tests of terminal blocks. Sandia and industry g

test data suggest that it is possible to have these leakages for periods I of time sufficiently long to trip the overload protection devices, and g hence, the line-to-line faults caused by terminal blocks may cause them N to trip. Acceptable levels of leakage current are those which do not -~5 exceed the excess current capacity of the overload protection for the 9 time necessary to trip the device and do not dissipate damaging amounts j of power on the terminal block surface. Small, low current motors are 2

a s-

-104-O

480 Vac MCC E

) ) CIRCUlf BRE AKER RELAY

THERM AL OVERLO AD E ( ( PROTECTION DEVICES I

h

RsT TERMIN AL BLOCK i .smA-u, ,

MOTOR i

r Figure 8-13: Typical Motor Circuit Connection for a 3-Phase Motor i

" the most susceptible motor applications because with larger sizes, the 7

full load current is higher and larger leakage currents are required to

- trip the protection devices. However, industry qualification tests have

[ reported failures of 25 A fuses used to monitor leakage currents and therefore even circuits for larger motors may be affected.

[ The limiting condition for a terminal block to open a circuit

- breaker is the set point of the circuit breaker. This value is typically

? well above the motor full-load current and hence the terminal block i leakage currents would have to be very large to trip a breakar. Unless

- the terminal block was nearly shorted, such would not be the case.

E However, if the motor is off and then switched on, the transient i application of voltage to the terminal block will cause much higher than i

average leakage currents. The high transient leakage current coupled

[ with the motor starting current may reach values large enough to trip the

[ breaker.

5 k

In summary, terminal blocks in motor circuits may be a problem, not b to the motor itself, but rather to the circuit that supplies power to the 3

motor. The most sensitive devices in the circuits are the thermal i-overload protection devices and the most sensitive situations are where L they protect small horsepower motors. Also, the tripping of circuit

[

breakers may be a problem on motor start-up. The effect of a tripped

[

overload protection device or a tripped breaker would depend on the L function of the motor, the ability of the operator to recognize that a 5 protection device or breaker had tripped, and his ability to prevent the E problem from recurring.

E E -105-

[

E

- . - . . , = _ . . . s,m _ . .

10,000 i i l l 1 1 -

1000 --

7 e .

n.

$100 e

7 o

4 -

3_ -

H -

10 -

3 I I I I I I i 100 200 300 400 500 soo 700 800 I

PERCENT MOTOR FULL LOAD CURRENT Figure 8-14: Time-to-Trip as a Function of Percent of Motor Full l' Load Current for One Type of Directly Heated Bimetal Overload Relay (51]

-106-

9,0 POSSIBLE METHODS OF REDUCING TERMINAL BLOCK LEAKAGE CURRENTS Three possible methods were considered candidates for reducing surface leakage currents in moisture films: cleaning, sealing, and coating. Each is discussed in turn.

9.1 Cleaning I

cleaning of terminal blocks was a possible remedy for terminal block performance suggested by Stuetzer in his earlier work.(2) Specifically, he stated that "a very highly contaminated block, cleaned [with steam ano subsequently washed with alcohol) and sealed with RTV... regenerated completely and functioned like a new block." Stuotzer reported leakage currents of approximately 0.7 mA for this cleaned block and the new blocks that he tested. These results are entirely consistent with the results reported in the later Sandia tests.[1] Reference 1 also reports j

that one new terminal block was cicaned prior to testing by soaking i sequentially in clean baths of freon, deionized water and freon. No improvement in the performance of this terminal block compared to the new, uncleaned blocks was noted. This result was somewhat surprising since we expected the cleaning to remove salts and other sources of ions for film conduction. Stuetzer's data supports this finding since his cleaned block performed essentially the same as his new blocks.

The fact that cleaning is not as effective as originally hoped for should not actually be surprising. Terminal blocks are extremely convoluted surfaces with covered cavities and many small crevices that are not easily accessed. In the sectional designs the interface between adjacent sections is not accessible without disassembly of the terminal block unit. For these reasons a thorough cleaning of a terminal block unit, even in a laboratory environment, is difficult to achieve. In a field environment it may be practically impossible to achieve and maintain cleanliness. The observed performance of a cleaned, new terminal block in Sandia tests indicates that cleaning does not reduce leakage currents to levels that will not affect instrumentation and control circuits. Note that this statement does not imply that routine cleaning should not be performed as a part of preventive maintenance.

9.2 Sealing Terminal blocks are typically installed in NEMA-4 enclosures. An obvious questior. is whether these enclosures can be sealed to prevent the steam environment from surrounding the terminal blocks. As the enclosures now exist with weep holes and conventional conduit / cable entries, the practical answer is probably no. The biggest problem would be the conduit entries. To effectively seal the interstitial space i between the cables and the conduit against steam intrusion would require a penetration into the NEMA-4 boxes similar to a containment penetration. Using a silicone compound such as RTV may stop condensed moisture, but achieving a reliable vapor seal in all possible conduits would be unlikely.

l

-107-

Given that the electrical enclosure could be sealed successfully, another set of questions arises. First is.the question of structural .

integrity of the box. Rapid external pressurization may. collapse the box i i

around the terminal blocks. In tests of new NEMA-4 enclosures without l

' weep holes or conduit entries, external pressurization with nitrogen gas l to 20-35 psid deformed the boxes sufficiently so that they leaked and l equilibrated pressure. These pressure levels are below the design basis I containment pressures specified in IEEE 323-1974 Appendix A.[37]

i Another question is the phenomenon of cable " piping" observed dering Sandia and industry qualification tests. In these tests, a compression fitting around a cable forms a pressuce barrier between the test chamber and the environment. In cable " piping", differential pressure drives moisture along the cable between the insulation and the conductor from

, the high pressure end to the low pressure end. If the terminal blocks are hermetically sealed in the NEMA boxes, this differential pressure condition could be set up in reverse during an eccident' situation.

Moisture would then be driven along the cables directly onto the terminal 1 blocks. Such a condition would be extremely undesirable.

4 It would be difficult, if not impossible to practically achieve total enclosure sealing. Evan if it could be achieved, another set of questionable effects such as NEMA enclosure strength and cable " piping" would arise. Thus, sealing the enclosures does not appear to be a viable

solution.

9.3 Coatings Conformal coatings for terminal blocks were investigated as a means of sealing the exposed conductors. Several classes of coating materials were looked at including polyamides, silicones, polyurethanes,-epoxies, and proprietary materials. The coatings were judged according to their moisture permeation, dielectric strength, heat resistance, strippability,

' and applicability. Based on these criteria, two materials were chosen as likely candidates for coating terminal blocks. These were Red Glypt" insulating varnish which has been available for some time, and a new class of epoxy, cycloaliphatic epoxy, which has recently become commercially available'. The advantage of both of these materials is that they.are one part systems and easily applied.

Red Glypt" dries by exposure to tir and its maximum operating

~ temperature is quoted in the manufacturer's catalog as 121*C (250*F). To test its ability to function at higher temperatures, copper substrates l

were coated with Red Glypt"'and then baked for 10 to 180 minutes at 160*C (320*F). .The higher temperatures did not affect the resistivity of the material, however, it became quite hard and some creep was observed.

In order to test the importance of film uniformity on resistance, other

'- samples were coated by brushing Red Glypt" on to them with no attempt j being made to achieve a uniform coating. At 500 V applied potential,'one 1 sample experienced periodic breakdowns and another sample experienced corona discharge. No breakdowns were observed on samples coated uniformly.

These'b eakdowns illustrate the importance of uniform coating since the s

material'is too viscous to flow and provide a pinhole free film, l

-108-

..,n., , , , - , - , -- , - - - - - - - - - - , - - ,- , , ,a , ,

The cycloaliphatic epoxy is cured by exposure to ultraviolet light rather than by using an amine curing agent as is required for common epoxy materials. This makes field application reasonably easy. It also has reasonably good electrical properties measured at 150*C (302*F) and maintains these properties up to ~180*C (356*F) which envelopes the IEEE 323 design basis temperatures.

i To test the effectiveness of these two materials, four terminal blocks were coated with them, two with Red Glypt" and two with the epoxy. . To' achieve a good costing, the metallic conducting parts of the terminal blocks were removed from the insulating material and otherwise concealed surfaces were coated. Such a procedure probably would not be possible.in a field application. Wires were attached in a serpentine configuration identical to the~ electrical connections reported for the Phase I Sandia test.[1] Continuity though the desired conducting paths was verified and surface coatings were applied so that no electrical continuity existed between the adjacent terminals and cable terminations.

These four terminal blocks were installed in a NEMA-4 enclosure along

-with two uncoated terminal blocks-which acted as test controls. All terminal blocks were of the same make and model. These terminal blocks were exposed to a saturated steam LOCA simulation profile which approximately followed the temperature profile recommended by IEEE-323-1974, Appendix A.[37]

Figures 9-1 and 9-2 show the leakage currents of the Red Glypt" and epoxy coated terminal blocks, respectively, as a function of time.

The control block leakage current traces are also included for comparison.

- Basically'the coated blocks performed like the uncoated blocks. These results point to the fact that complete coatings were not achieved, and ,

that leakage paths existed. Post-test examination and diagnostic tests showed that the primary connection point between the metallic conductors and the phenolic insulation was the screw which attached the conductors to the paenolic. In fact, the mating threads of the phenolic insulation were carbonized into a powder which appeared to enhance the connection.

between the metallic conductors and the insulation surface. The threaded mating surface of the screws, though originally coated, were not coated at the end of the test. Reinserting them into the phenolic probably l

removed the coating from.the screw surface. The results of this. test

i. - indicate that coatings applied under laboratory conditions do not achieve t a significant improvement in terminal block performance. A field application would most likely be less perfect; hence we must conclude l.

- that conformal coatings, short of a complete potting, do.not provide the i desired improvement in terminal block performance.

A coating which was not investigated or tested is a spray of a silicone-based fluid. Silicones are extremely hydrophobic and may

- inhibit film formation for some period of time. Such a coating would not j be permanent and would require routine recoating to maintain its protective quality. Further, the inrush of steam may strip the siliccae from the surface and render it ineffective. It may also have detrimental

. effects such as enhanced agglomeration and retention of dust and dirt.

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-0.05 0.00 0.05 0.10 0.15 0.20 RELATIVE TIME (hrs)

Figure 9-1: Comparison of Leakage Currents for Red Glypt" Coated

. and Uncoated Terminal Blocks

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10 0 CONTROL 1 EPOXY CO ATED Q10-1 b

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Figure 9-2: Comparisen of Leakage currents for Cycloaliphatic 1

Epoxy Costed and Uncoated Terminal Blocks

10.0 ASSESSMENT CRITERIA c .

The question asked at the outset of this effort was what are the

. failure and degradation modes of terminal blocks and what are their-

~effect on system performance. The answer, of course, is not simplelar

- straightforward. It depends on many complex and interacting factors.

This report.and the report of the Sandia tests of terminal blocks [1]

. provide an insight into the performance of terminal blocks. This report -

also illustrates some simple analyses which can be performed to define the effect of terminal blocks in various applications. It is not the-

intent of this study to judge the safety significance lof terminal blocks, but~rather to provide'the'necessary technical bases to make a safety -l judgment. The following paragraphs summarize the conclusions about

. terminal blocks which we believe are supported by the data obtained and-the analyses made. Engineering judgments and recommendations are clearly noted as such.

10.1 Terminal Block Design Considerations

The two basic dez.gns of terminal blocks (sectional and one piece) do not appear to be '.-adically different in their performance in a LOCA

- environment. Although some sectional blocks did perform comparably to the one-piece blocks, other sectional blocks performed noticeably worse

- (one or two orders of magnitude) during the LOCA simulation.[1] The materials from which' terminal blocks are commonly made (phenolic and ceramic) do not appear to dramatically affect their performance during a LOCA environment. .This' result arises because the primary mechanism for degrading terminal block performance (film formation) is somewhat

~

independent of the underlying insulation material of the terminal block.

~

However, some difference in film formation and continuity may result from differences in the surface wettability characteristics 9f the insulating 4 material.-

'Though we did not include radiation in-any of the Sandia tests, evidence from industry indicates that it is' good engineering Practice to

' choose a fill material for the phenolic, such as-glass or mineral which is as radiation. resistant as possible. Cellulose, a commonly used filler

-material, has a lower radiation resistance than glass or mineral fillers and may contribute to failure modes such as cracking or crazing or water absorption. These phenomena were'not examined in the Sandia tests.

Terminal blocks are, by their very nature, convoluted surfaces with

- inaccessible cavities and interfaces. -For example, a hole may exist below the conducting plate to accommodate.the screw which attaches the

- lug terminating the wire to the terminal block; or, in sectional designs the interface between adjacent sections is not accessible without

disassembly of the terminal block unit. 'For these reasons, a thorough

, cleaning of the terminal block surface, especially in an' installed plant situation,Lmay be difficult if not impossible to achieve. Sandia's test-of a " clean," one-piece terminal block further indicates that for our cleaning method (soaking in freon and detonized water), little improvement in performance over'that of new, but' uncleaned' blocks can be expected, i

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-112-r 4

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Thus, for common terminal block designs with highly convoluted surfaces, and inaccessible cavities and interfaces, cleaning may not be an effective method of reducing low level leakage currents thct exist during exposure to.a steam environment. Proper cleaning cannot make the situation worse, but it is doubtful that it will reduce leakage currents to a level acceptable for most instrumentation and contro1' applications.

TLe large, positive impact on terminal block performance that was

'riginally believed to accrue from cleaning was not observed in the Sandia tests.

During the Sandia tests, relatively large emfs (0.01 mV to 0.5 V at

~0.1 mA) were observed to be generated within unpowered test units.*' A possible explanation for these emfs is oxidation-reduction reactions between dissiellar metals at the interfaces of the terminal block terminals, the ring-lugs, and the cable conductors. The addition of high temperature, conducting moisture films provides the electrolyte necessary for these reactions to occur. Cadmium sulfide was found as a residue on the terminal blocks at the conclusion of the Sandia tests, suggesting the possibility of galvanic reactions.** Emfs may have significance to low power circuits such as'thermocouples and points to a design / installation need for using metals with like oxidation potentials and system components which will not form potentially detrimental compounds under accident conditions.

10.2. Testing Considerations The primary objective in testing components for nuclear power applications is to determine their performance in adverse accident environments. -Using data obtained from these tests, analysis can determine the effect of component performance on the systems. Thus, qualification testing of components has two objectives: (1) demonstrate that.the. equipment will perform its function in an accident situation; and (2) provide data that characterizes the component's performance in an accident situation. Though easily stated, achieving these objectives 13

'less than telvial. At a minimum, sufficient knowledge about the equipment's required functions must be known so that relevant data can be collected and relevant. acceptance criteria formulated. Also, knowing the function of the equipment allows one to put the failure modes into perspective. Test methods must be adequate to detect failure modes if they exist and to monitor the performance of the equipment.

The test unit consisted of the electrical cable, crimp type ring-lugs and the terminal block.

- The cadmium source was the plating on a 1/4-20 nut used to attach the enclosure mounting plate to the NEMA-4 enclosure studs. The sulfur was hypothesized to be from the sodium thiosulfate added to the chemical spray solution or from the cable jacket material. The occurrence of CdS points to a system consideration in assembling the terminal block-NEMA-4 enclosure unit: even an innocuous nut or bolt somewhere in the unit may affect the performance of the unit in an accident environment.

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. . . . .. _- ~ - - . .. .-

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'L

~

The primary application of terminal blocks in the nuclear power

'in,dustry is in instrumentation and-control circuits. Therefore, generic'

, testing should be geared to this spp11 cation. -

For these applications l2 leakage currents on the order of a fraction to a few mil 11 amperes can y- become significant to the operation of a circuit. Thus, test apparatus should be designed to obtain such data; the common practice of measuring leakage current with a 1 A or-larger valued fuse provides no information about leakage currents less than 1 A. Industry test reports indicate

-numerous failures of these fuses. It'is necessary to obtain low level-F leakage current data if analyses of the effects of terminal blocks are to be made. If on-off power cycling is anticipated in the operation of a circuit (e.g., a motor circuit), then the ability to measure transient, high level leakage currents and their duration should be part of the test. l i.

Because film formation followed by Joule heating of-the film may lead to film vaporization, highet potentials may actually lead to higher film resistances. Thus, the testing of terminal blocks at increased potentials for margin may actually be less conservative in terms of measuring-terminal block performance than testing at actual use potentials.

I Test environments must be such that they include the pressure-q temperature conditions expected-to be present in the. predominant accident sequences. .This consideration is important since pressure in concert with temperature govern the conditions necessary to form and. sustain a-moisture film. Tests which maintain superheat throughout the test are inappropriate unless.superheat is expected throughout all possible

,. accidents. Thus,-the practice of using Arrhenius techniques to compress l accident exposures by elevating. temperatures into superheated regimes

, does not test terminal blocks in saturated steam and condensing steam i environments. _The saturated environments are commonly accepted as a i predominant long-term accident environment. - Further, the use of-Arrhenius techniques to accelerate aging and accident simulations is

. based on the time-temperature superposition phenomenon of polymer chemical degradation; it has nothing to 'do with the primary failure mode of. terminal blocks--film formation and conduction through these films.

In. general, test methods and procedures must be germane to the l application, and'they must provide data for analyses of the effects of component performance _on-system performance. To accomplish this goal, an understanding of'the' failure and~ degradation modes is required.

10.3 -System Design Considerations Terminal blocks will affect the operation of instrumentation and contro1' circuits. proper utilization of terminal blocks is therefore a critical question in nuclear plant applications. For high impedance circuits such as transmitters and thermocouples, terminal blocks can ~

2 significantly change the sensed output of the circuit. A graphic illustration of.the effect was presented in Figure 8.3. RTD circuits are

! 'also important since they are the primary temperature monitoring device i

for the primary coolant system and the containment building. Valve l

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. circuits are not as susceptible as RTDs or high impedance circuits, especially from an operability point of view, but the existence of power b on a terminal block close to a valve may falsely provide power to valve

' indication lights. The results would be erroneous valve position

. indications to'an operator in the control room. Motor circuits are

! 'relatively immune to the effects of degraded terminal block operation, except to the extent that' leakage currents may.cause thermal overload protection' devices or circuit breakers to trip. Unfortunately, these effects will occur at the time when operators are under pressure to respond to_a_ plant transient and are inundated with alarms. They will i most likely be performing activities of a higher priority than determining that circuit breakers have tripped or thermal overload i protective devices have-actuated. Thus, terminal blocks may affect motor j circuit operation, though not directly.

f . _ The question of terminal block failure is one of relative magnitude of the'effect. ' Clearly, if terminal blocks are to be used, then analyses

~ specific to the application are. required to insure that the circuit >

operation is not' detrimentally affected.

t The current method of terminal block installation appears to be as good as can be practically achieved. The NEMA-4 enclosures with a weep j 4-hole in the bottom protects the blocks from direct impingement of Ll chemical spray and permits condensation to drain from the enclosure.

-Based on the results of Sandia chemical _ spray and submergence data, the presence of spray external to the electrical enclosure does not

significantly affect terminal block performance. A logical measure to 4 prevent condensed moisture and spray from penetrating the interstitial space between the_ cable and conduit and then dripping onto the terminal block would be to; bring the cables into the enclosure.from the side or bottom. Top entry of cables into the enclosure would not prevent moisture from dripping onto'the terminal blocks.

Hermetically sealing the terminal block enclosures is'probably an 1

impractical-solution. The chances of achieving good-seals around all the cables where they enter.the NgMA-4 enclosure or where the cables enter conduit is remote. Further, the NEMA-4 enclosures do not have good.

+

ability to withstand external pressurization for long periods. Depending on the pressurization rate, the~ maximum differential pressure that can be

tolerated is 20 to 35 psid. Hermetically sealing the' enclosures also creates a condition where, due to differential pressure, moisture can be driven along_the cables between the' conductor and' insulation into the terminal block enclosure. Since the cable insuistion continues right up to-the terminal block, the moisture could be' driven onto the terminal

.. block. This " piping" phenomenon is commonly observed in'both Sandia and i - industry tests of cables and terminal blocks where unspliced cables

. penetrate test chamber boundaries. Therefore, hermetic sealing of terminal block enclosures is not advised, nor is it easily achieved.

i

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-115-(-' .+ 3 - - - . . ,. . , _ . .~,.7o ,,,y ,,,.m,, ,_,.,~,._,_._..g,,

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Coatings were initially believed to be a feasible solution to terminal block leakage problems. However, as with hermetic sealing, achieving a good conformal coating, especially for already installed terminal blocks, will be almost impossible. The test run at Sandia to test two possible coatings showed no observable difference or delay between leakage currents observed on coated terminal blocks and uncoated l blocks. Thus, we do not believe that coatings are a viable means of j limiting terminal block leakage currents.

)

In conclusion, leakage currents observed during LOCA testing of terminal blocks can cause erroneous indications and/or actions in low l power instrumentation and control circuits. Possible solutions such as cleaning, sealing, or coating do not appear to have the desired corrective effect, and hence two possible courses of action are apparent: (1) analyze for the effects of terminal blocks in circuits and account for these effects circuit design; or (2) remove terminal blocks from instrumentation and control appilcations. If the first option is chosen, then qualification activities should monitor leakage currents at levels appropriate to the application.

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E L

11.0 CONCLUSION

S

1. Theiprimary application of. terminal blocks in the nuclear power l industry'is instrumentation and contro1' circuits.

2. " Terminal blocks receive minimal quality' assurance attention in selection, installation, inspection and maintenance activities.

3. Most industry qualification tests do not continuously monitor l

>for low level leakage currents during LOCA simulation tests of l

' terminal blocks. Without quantitative knowledge of these leakage' currents,_ adequate analyses of'their effects on instrumentation and control circuits cannot be. performed.

Surface moisture films are the most probable explanation for

4. . degradation-in' terminal block performance during exposure to a

steam environment. Because the existence of moisture films is 4

- highly dependent upon environmental conditions, test l environments must realistically reflect the predominantly expected accident environments. For example, superheated test conditions may not accurately represent the terminal blocks'

-performance.

'5. The use of voltage levels above actual use conditions in qualification tests of terminal blocks may be nonconservative with respect to the measurement of low level leakage currents which:are the primary degradation mode of terminal blocks.

'6. Terminal block leakage current in a steam environment may

^ degrade performar.ce of instrumentation and control circuits to an extent sufficient to cause erroneous indications and/or actions.

7. Cleaning will probably not reduce leakage currents to a level l acceptable for most instrumentation and control applications.

The large, positive impact on terminal block performance that was originally believed to accrue from cleaning was not observed. 'Further, terminal block leakage currents were not significantly reduced by the application of either of two coatings tested.

i I

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4 W

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14". fFranklin Research Center _" Qualification Tests of Terminal Blocks Tand Spilce-Insulating Assemblies in a Simulated Loss of Coolant JAccident= Environment, Phase A and Phase B,"~ FRC Reports F-C5022-1 and F-C5022-2,.0ctober 1978 and November 1978. Prepared for Philadelphia Electric Company.

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Weidauller Terminal Blocks for Washington Public Power. Supply System,"' Wyle Report.58687, Norco. CA, Junef29,~1982. Prepared' for'WPPSS and Weidauller Terminations, Inc.

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. Terminal Blocks, consisting of thel following test reports:

a) ~Bundesanstalt fur Materialprufung. Berlin, Test Reports .

3.42/444 and'3.43/444-1

.b) Instituto National des Radioelements, Fleurus, Belgium. Test Report Q. N. 21 and Q. N. 24 c)' ~ Societe pour le Perfectionnement des Materials et' Equipments

'Aerosportlaux,'Velizy-Villacoublay France,' Test Reports .

LV24633 and LV14711/1-d) Wyle Laboratories, Scientific Services.and Systems Group, Norco ~ '

' ' Facility, California ~, Test Report 58610

20. Wyle Laboratories, " Nuclear Environmental Test Program on Four 0-Z Godney Conduit' Sealing Bushing Assemblies Two'0-Z Gedney Conduit l

Sealing Bushing /NAMCO Limit Switch Assemblies, and Two Marathon j- ,

Fixed Barrier Terminal Block Assemblies," Wyle Report.45611-1,

_Huntsville, Alabama, February'24,,1982. Prepared for Commonwealth

. Edison Co.-

i.

~ 21. ' Westinghouse Electric Corporation, " Test Report on the Effect of a LOCA on the Electrical Performance of Four Terminal Blocks,"

t PEW-TR-83. . September 13, 1977.-

l 22.. iWestinghouse Electric Corporation, Letter from J. P. Boyd to F. W.

Chandler of TVA, dated March 9, 1978,

Subject:

- " Data for

. Westinghouse Terminal Blocks."

s- ~ I' c - -

r i

-119- j i

l l

l

23. Durez Division, Hooker Chemical, File E39252 Extracted from i reprints APEX 167 and 261, Office of Technical Services, U. S.

Department of Commerce, Washington, DC, 2/5/62. i

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Reapproved 1978. American Society of Mechanical Engineers, United

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Washington, DC 20037.

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Mechanical Engineering, Stanford University. Prepared for ISA 29th International Insteunent Symposium, May 2-5,1983.

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t

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, . _ _. ... _ _ _ _ . . _ . .__..- _ .._ ~ _ _ . _ . _ _ _ _ ,

l

i l

1

47. Scientific Engineering and Manufacturing Company, "Sempac Metal l Sheathed, Mineral Oxide Insulating Materials,".11505 Varowen Street. l North Hollywood,'CA 91605. l

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b

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-124-u

l Imatran_Voima Oy Kraftwerk Union AG Department R361 Electrotechn. Department P.O.-Box 138 Hammerbacherstrasse 12 + 14 D-8524 Erlangen SF-00101 Helsinki 10 WEST GERMANY FINLAND ~

Atta: I. Terry Attn: B. Regne11 K. Koskinen Kraftwerk Union AG Institute of Radiation Protection Section R541 Department of Reactor Safety Postfach: 1240 P.O. Box 268 D-8757 Karlstein 00101 Helsinki 10 WEST GERMANY Attn: W. Siegler FINLAND-Attn: L. Reiman Kraftwerk Union AG Instituto de Desserollo y Diseno Hammerbacherstrasse 12 + 14 Ingar --Santa Fe Postfach: 3220 D-8520 Erlangen Avellaneda 3657' WEST GERMANY C.C. 34B 3000 Santa Fe Attn: W. Morell REPUBLICA ARGENTINA Attn: N. Labath Motor Columbus Parkstrasse 27 Japan Atomic Energy Research Institute CH-5401 Takasaki Radiation Chemistry Baden Research Establishment ~ SWITZERLAND Watanuki-machi Attn: H. Fuchs Takasaki, Gunma-ken JAPAN National Nuclear Corporation Attn: N. Tamura Cambridge Road K. Yoshida Whetstone T. Seguchi Leicester LE8 3LH ENGLAND Japan Atomic Energy Research Institute Attn: A. D. Hayward J. V. Tindale Tokai-Mura Naka-Gun Ibaraki-Ken NOK AC Baden 319-11 Beznau Nuclear Power Plant l CH-5312 Doettingen

! JAPAN _

Atta: Y. Koizumi SWITZERLAND Attn: O. Tatti l

l_ Japan Atomic Energy Research Institute Osaka Laboratory for Norsk Kabelfabrik Radiation Chemistry 3000 Drammen 25-1 Mii-Minami machi, NORWAY Neyegawa-shi Attn: C. T. Jacobsen L

Osaka 572 JAPAN Nuclear Power Engineering Test Center Attn: Y. Nakase 6-2, Toranomon, 3-Chome Minato-ku No. 2 Akiyana Building Tokyo 105 JAPAN Attn: S. Maeda

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4 Ontario Hydro Alabama Power Co.

700 University Avenue P.O. Box 2641 Toronto. Ontario M5G 116 Flintridge Blog B301 CANADA Birmingham, AL 35291

'Atta: R. Wong- Attn: M. Lalor B. Eukreti l

Amerace Corporation-Oy Stromberg Ab- 2330 Vauxhall Road-Helsinki Works Union, NJ 07083 1

Box 118 Attn: M. Marszalowicz i FI-00101 Helsinki 10 l FINLAND Carolina Power & Light Co.

Atta: 'P. Paloniemi P.O. Box 1551 Raleigh, NC 27602-Rappini Attn: T. E11eman

- ENEA-PEC J. L. Harness Via Arcoveggio 56/23 Bologna. Combustion Engineering ITALY 1000 Prospect Hill Road Attn:- Ing. Ruggero Windsor, CT 06095 Attn: J. Glasman

- Rheinisch-Westfa11scher Technischer Uberwachunge-Verein e.V. Detroit Edison Postfach 10 32 61 2000 Second Avenue D-4300 Issen 1 Detroit, MI 48226 WEST GERMANY Attn: R. J. Seguin Atta: R. Sartori Duke Power Company Sydkraft- P.O. Box 33189 Southern Sweden Power Supply Charlotte, NC 28242 21701 Malmo Attn: B. Coley

- SWEDEN

- Atta: 0. Grondalen EDS Nuclear, Inc.

350 Lennou Lane UKAEA Walnut Creek, CA 94598 Materials Development Division Attn: C. Sellers

. Building 47~

AERE Harwell EG&G Idaho, Inc.

OION 0111 ORA P.O. Box 1625 ENGLAND Idaho Falls, ID 83415 Atta: D. C. Phillips Attn: A. Williams

- United Eingdom Atomic Energy Authority Farwell & Hendricks, Inc.

Safety & Reliability Directorate P.O. Box 209 Wisshaw Lane Milford, OH 45150 Culcheth Atta: J. R. Hendricks

- Warrington WA3 4NE ENGLAND Marathon Special Products Atta: M. A. H. G. Alderson P.O. Box 468 Bowling Green, OH 43402 Wese42 University Atta: H. Black Department of Electrical Engineering 4-1 Ohkubo-3, Shinjuku-ku Tokyo

- JAPAN

' Atta:- E. Yahagi

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.Phonix Terminal Blocks. Inc. Yankee Atomic Electric Co.

1900 Greenwood Street 1671 Worcester Road Narrisburg, PA 17104 Framingham, MA 01701 Atta: D. B. Springer Atta: D. Hansen Portland General Electric 1820 R. E. When 121 SW Salmon Street 2155 J. E. Gover

-Portland, OR 97204 2155 O. M. Stuotzer Atta: G. L. Johnson (2) 6400 A. W. Snyder 6410 J. W. Hickman Rochester-Gas and Electric Corp. 6417 D. D. Carlson 89 East Avenue 6420 J. V. Walker Rochester, NY 14649 6430 N. R. Ortis Attn G. S. Link 6440 D. A. Dahlgren 6442 W. A. Von Riesemann Stone and Webster Engineering Corp. 6445 J. H. Lineberger 245 Summer Street 6445 L. D. Bustard Boston, MA 02107 6445 c. M. Craft (25)

.Atta: H. V. Redgate 6445 D. T. Furgal 6445 M. J. Jacobus Temple' University 6446 L. L. Bonzon Department of Chemistry 6446 F. V. Those Philadelphia, PA 19122 6447 D. L. Berry Atta: R. E. Salomon 6450 J. A. Reuscher 3141 C. M. Ostrander (5)

The States company 3151 W. L'. Garner 4271 Bronze Way 8424 M. A. Pound Dallas, Texas 75237 Atta: W. C. Wright TRW Cinch Connectors 1500 Morse Avenue Elk Grove Village, IL 60007 Atta: R. M. Pontone VEPCO/OJRP-5 P.O. Box 26666

. Richmond, VA 23261 Atta: G. Smith Washington Public Power supply System

' 3000 George Washington Way Mail Drop 981F Richland, WA 99352 Atta: C. Zeamer Weidauller Terminations Inc.

821 Southlake Boulevard

. Richmond, VA 23235 Atta: J. H. Tyler Westinghouse Hanford Co.

P.O. Box 1970 Richland, WA 99352 Atta: P. Cannon v

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e l

t i me coa r =wwee - .4.ea.,e, r,oC , vs. =e . ,saw maccom.aus u a muctamaovatonv consisission s'8 BIBUOGRAPHIO DATA SHEET D Ses smstauCTs045 0m 7, s ogvgast 3 T47L8 amD $weisTLS 3 Leave 36a44 AN ASSESSMENT OF TERMINAL BLOCKS IN THE NUCLEAR POWER INDUSTRY e Datt agapat cow. gtsp wogise itam o awt-Oaise July 1984

oa" "'oa55 'o Charles M. Craft .osv. . ..

g Septemler 1984 7 PSP 8 0# sm0 083&Ni2 Af EON hawl aseD Masking ADDm8 55 ## sit <eise tap Cese, 4 PROJECT T AS4 WQA4 WN T hwWSt4 Sandia National Laboratories . e i oa Ga a~i ~e....

Division 6445 P.O. Box 5800 A-1327 Albuquerque, New Mexico 87185 10 SPomSOas9G OmGANidateON %Awt AND uaigie G aDDmES$ traesverte Cases tt.Tv'tOsattomf Division of Facility Operations Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission . . .. oo co. . . o .,,,, e. .

Washington, DC 20555 12 SuP*61wtwtam,motts 13 4437maci (J00 stores or vees The primary application of terminal blocks in the nuclear power industry is ir.strumentation and control (I&C) circuits. The performance of these circuits can be degraded by low level leakage currents and low insulation resistance (Ih) between conductors or to ground. Analyses of these circuits show that terminal blocks, when exposed to steam environments, experience Icakage currents and low surface IR levels sufficient to affect some I&C applications.

Since the mechanism reducing surface IR (conductive surface moisture films) is primarily controlled by external environmental factors, the degradation of terminal block performance is mostly independent of terminal block design.

Testing shows that potential methods of reducing surface leakage currents will not reduce them sufficiently to prevent terminal blocks from affecting I&C circuits. Therefore, terminal blocks can cause erroneous indications or actions of the I&C circuits in which they are a component. Most of the present qualification tests of terminal blocks do not address the issue of low level leakage carrents, and hence do not demonstrate that terminal blocks will operate properly in I&C circuits.

l a i

.. .oco . .. 6...... u . o o ei.ca..,ou . . .,,, .z y, .

Unlimited i

e to SECumity Chall'8sCafiom f Fae es,es

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UNC

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n Sandia National Laboratories Abuqurqp, New Moico BM M date: January 11, 1982 to: Distribution s

SNL/IEHQ, T-7, 19 l

b Q ~ Qh from: D. M. Jeppesen, 4445 E. A. Salazar, 4445 subjam Equipment Selection for the NRC Equipment Qualification Research Test Program Ref: Memo, Z. R. Rosztoczy to G. W. Reinmuth and D. F.

Sullivan, dated 11/19/81, same subject.

On January 5, 1982, D. M. Jeppesen and E. A. Salazar met with W. Booth and K. Desai of NRR/DE/EQB to formalize equipment selections for the NRC Equipment Qualification Research Test program sponsored by NRC/RES. The objective of this program is to develop confidence in current equip-ment test methodologies and to better understand equipment behavior. Based on existing NTOL audit experience and on industry equipment qualification test progr ams, the EQB prepared a list of equipment, focusing on priority and j concern, which Sandia might use in the test progr am. The list, outlined in the referenced memo, was discussed in detail with emphasis on specific rather than generic equipment. It was agreed that:

)

l Item (1) Asco Solenoid Valves - Would require no Sandia involvement. Franklin Research Laboratories will per form all tests.

Item (2) Joy / Reliance Fan Motors - These are a series that include a large var iety of sizes. Sandia will investigate these components to determine if one size, adaptable to our test f acilities , is representative of all or most sizes.

The decision to proceed with these tests will be based upon Sandia's findings and will be mutually agreed upon by Sandia, NRR and RES.

i A5 i.. . _ . .

~ . .

Memo to Distribution January 11, 1982 Item (3) G.E. Penetration - Sandia is to procure and test this component. If for some unknown reason G.E. Penetrations are not available, Sandia shall procure Anphenol Penetrations and proceed with tests.

Item (4) RTDs - Sandia is to procure and test Pyco, RdF, and Rosemount RTDs.

Item (5) Pressure Switches *.

Item (6) Coaxial Cables *.

Mr. Desai requested additional time to review further the merits of testing these two items. An answer would follow shortly.

On January 7,1982, Mr. Desai informed us that Sandia should include as Items (5) (Static-o-Ring, Barton, and Barksdale) "

and (6) (Okonite and Kerite) in this test program.

With these agreements, Sandia will proceed with the test composition definitions and will initiate the necessary purchase requisitions as quickly as possible so that pro-curement times may be minimized. We extend our thanks to Messrs. Booth and Desai for their time and interest in this regard. )

Distribution:

USNRC 3. R. Rosztoczy USNRC D. F. Sullivan USNRC G . W. Reinmuth USNRC W. C. Booth USNRC K. D. Desai 4440 G. R. Otey .

4445 L. O. Cropp, File 7.4 4445 L. L. Bonzon 4445 E. E. Minor 4445 D. M. Jeppesen 4445 E. A. Salazar

+

ML20127A108

Text

SUBJECT:

7 P

RESPONSE

11.0 CONCLUSION

Subject:

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