ML20235M002

Resolution of Confirmatory Item Non-Class 1E Signal to Class 1E Circuit Interface:South Texas Project 1 & 2, Technical Evaluation Rept

ML20235M002
Person / Time
Site:	South Texas
Issue date:	06/30/1987
From:	Nolan A EG&G IDAHO, INC., IDAHO NATIONAL ENGINEERING & ENVIRONMENTAL LABORATORY
To:	NRC
Shared Package
ML20235L994	List: ML20235L992 ML20235M002
References
CON-FIN-D-6019 EGG-NTA-7728, TAC-63500, NUDOCS 8707170019
Download: ML20235M002 (18)

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' 1 INFORMAL REPORT n

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• TECHNICAL EVALUATION REPORT

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RESOLUTION OF THE CONFIRMATORY ITEM

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., ..'l DISCLAIMER 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 employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party.'s use, of 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.

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l EGG-NTA-7728 l TECHNICAL EVALUATION REPORT 1

RESOLUTION OF THE CONFIRMATORY ITEM NON-CLASS 1E SIGNAL TO CLASS 1E CIRCUIT INTERFACE:

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SOUTH TEXAS PROJECT-1 AND -2 l l

Docket Nos. 50-498/50-499 i

A. E. Nolan )

i Published June 1987  :

4 Idaho National Engineering Laboratory EG&G Idaho, Inc.

Idaho Falls, Idaho 83415 Prepared for the U.S. Nuclear Regulatory Commission Washington, D.C. 20555 Under DOE Contract No. DE-AC07-761D01570 FIN No. D6019

CONTENTS ABSTRACT ...................................................... ii FOREWORD ...................................................... iii

SUMMARY

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, 1. INTRODUCTION / BACKGROUND .................................. 1

2. DISCUSSION AND EVALUATION ................................ 2

3. CONCLUSIONS .............................................. 9

4. REFERENCES ............................................... 10 l

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ABSTRACT The Confirmatory Item, "Non-Class 1E Signal to Class 1E Circuit Interface," listed in Section 7.1.4, Specific Findings, of Safety Evaluation Report (SER) NUREG-0781, "Related to the Operation of South Texas Project, Units 1 and 2," was reviewed to determine if the non-Class 1E equipment would prevent safety-related systens from performing their required functions. Results of the review are summarized in this report.

Docket Nos. 50-498/50-499 TAC No. 63500 ii

i FOREWORD .

l This report is supplied as part of the "SER Chapter 7 Review for South Texas 1 and 2" conducted for the U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation, Division of Engineering and Systems Technology, Instrumentation and Control Systems Branch, by the Idaho )

National Engineering Laboratory, EG&G Idaho, Inc., Rockville Office.

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' t The U.S. Nuclear Regulatory Commission funded the work under f authorization B&R No. 20-19-10-11-3, FIN No. D6019.

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Docket Nos. 50-498/50-499 TAC No. 63500 iii

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SUMMARY

A technical evaluation of the acceptability of the interfaces between non-Class 1E equipment and Class 1E safety systems was performed by representatives of the Idaho National Engineering Laboratory, EG&G Idaho, Inc., Rockville Office, and the U.S. Nuclear Regulatory Commission staff.

-1 Houston Power & Light, the applicant for the South Texas Project, submitted a list of 16 instances in .which non-Class 1E equipment supplies control signals to safety-related systems to the NRC staff for review. 1 The staff chose five representative cases from the list on which to perform a detailed evaluation. This detailed evaluation determined that.

the non-Class 1E equipment would not have an adverse effect on the safety- f system with which it interfaced. The results of the evaluation also state that the applicant should docket the modification made to the circuitry of the toxic gas detectors.

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TECHNICAL EVALUATION REPORT l RESOLUTION OF THE CONFIRMATORY ITEM NON-CLASS 1E SIGNAL TO CLASS 1E CIRCUIT INTERFACE l SOUTH TEXAS PROJECT-1 AND -2 I. INTRODUCTION / BACKGROUND  !

l On July 17, 1978 (Ref. 1), Houston Light and Power (HL&P) Company, the applicant for South Texas Project (STP), Units 1 and 2, transmitted a

. Final Safety Analysis Report (FSAR) to the NRC staff as part of their application for an operating license (0L), Chapter 7 of the STP FSAR describes the instrumentation and control systems used to operate the l reactor in a safe manner that ensures no undue risk to the health and safety of the public. These systems are designated as Class 1E safety-related systems.

During the staff's review of the FSAR, the staff raised a concern I that, in some instances, non-qualified Class 1E equipment was being used to supply control signals to the Class 1E safety-related control circuits. This concern is documented as a Confirmatory Item in Section l 7.1.4, Specific Findings, of Safety Evaluation Report (SER) NUREG-0781, "Related to the Operation of South Texas Project Units 1 and 2," dated l

April 1986 (Ref. 2). The concern is also discussed in Section 7.3.2.12 of ]

l the SER.

The staff also identified concerns dealing with isolation devices.

l These concerns address the use of fuses, Struthers-Dunn (S-D) relays, and Magnetic current transformers (cts) as isolation devices. The use of fuses l as isolation devices is discussed in greater detail in Case No. 3 of this i -

report. The use of S-D relays and Magnetic cts as isolation devices at STP is discussed in Case No. 6 of this report.

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2. DISCUSSION AND EVALUATION The applicant responded to the interface concern by identifying 16 cases in which Class 1E control circuits are supplied with non-Class 1E

. signals. Of the 16 cases, the staff selecte'd 5 representative cases for further review. The following cases were reviewed:

1. Control Room Envelope Heating, Ventilation, and Air Conditioning

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(HVAC) 4

2. Component Cooling Water (CCW)' Pump Logic

3. Essential Cooling Water (ECW) Traveling Water Screens

4. Reactor Coolant System Power-Operated Relief Valves (PORVs)

5. Feedwater Isolation Valves By letter dated May 13, 1985 (Ref. 3), the applicant forwarded a Class 1E to non-Class 1E interface summary. The purpose of the summary was to show that the non-Class 1E control signals.did not degrade the capability of the Class 1E control circuits to perform their safety-related function.

1. Case No.1 - Control Room Envelope HVAC Isolation Damper The Control Room Envelope HVAC receives signals from redundant toxic gas detectors and from redundant smoke detectors. If the output signal of any one of the'four detectors exceeds a high setpoint, a control signal is generated shich will close the control room isolation dampers. The safetyLinjection signal will also close the . isolation dampers, or they may be closed via a manual control switch located in the control room.

These' dampers isolate the control room environment in the event of high concentrations of toxic chemical or smoke in the outside air.

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The reviews of the submittals have determined that the toxic gas detectors were not seismically qualified. Discussions with the applicant disclosed that Class 1E qualified detectors for this application are not commercially available. The iogic diagram showed that, should either a detector or the power fail, the failure might not be detected for.the period between operability verifications that is specified in the Technical ,

Specifications.

An applicant report, pursuant to 10 CFR 50.55(e), which is I dated January 20, 1987 (Ref. 4), stated that the toxic gas detector actuation and alarm circuits are to be modified such that the toxic gas detectors fail in a safe manner (i.e., upon a loss of power or seismic event that results in detector failures, the isolation dampers will receive a close signal). The report also stated that the toxic gas detectors are part of the STp Technical Specifications (TS). The TS surveillance requirements should detect any component failure through the performance of required functional tests.  ;

1 Based on the review of the applicant's commitment to modify l 1

the toxic gas detector circuitry to a " fail safe" mode of j operation and on the TS surveillance requirements, it is concluded that the use of non-seismically-qualified Class 1E detectors will not prevent the Control Roora Envelope HVAC system from performing its safety-related function. The applicant has 1 committed to complete the required equipment modification l discussed above before fuel load.

2. Case No 2 - Component' Cooling Water-pumo Logic 1 The Component Cooling Water (CCW) System is an auxiliary heat removal system whose components (i.e., pumps, heat exchangers, and valves) are used for safe shutdown of the plant and to l maintain the plant in the safe shutdown condition. The CCW pumps can be started manually from either a local or remote location.

An automatic start occurs following either a safety injection 3

signal or a Standby Train Start signal or at the completion of the Auto Start signal sequence. The pump logic design includes a CCW flow switch and a surge tank level switch that protect the CCW pumps from loss of suction pressure. These switches are not seismically qualified.

The applicant determined that, under earthquake conditions, some or all of the CCW pumps could be tripped off line by spurious actions of the switches. The applicant submitted a revised final report, pursuant to 10 CFR 50.55(e) (Ref. 5), j which stated that the corrective action taken was to remove both of the non-seismically qualified switches from the CCW pump logic. The applicant reasoned that existing safety-grade l instrumentation will alert the operator to the status of the surge tank hvel and CCW system flow. Alarms will provide )

adequate warning time for the operator to take action and prevent  ;

i damage to the CCW pumps.

The review of CCW pump logic diagram Drawing No.

5R-20-92-42040, Rev. 5 (Ref. 6), showed that the two switches had been removed from the pump logic. Therefore, the applicant's corrective action has removed the non-qualified equipment and is acceptable. (There was no review of the adequacy of alarms and i operator action.)

3. Case No. 3 - Essential Cooling Water Systems, Traveling Water Screens The Essential Cooling Water (ECW) system is designed to supply cooling water to safety-related systems. The cooling water is taken from the Essential Cooling Pond (ECP), which is supplied by the Main Cooling Reservoir (MCR). The MCR draws water from the Colorado River and, as a back-up source, from the t plant's fresh water supply system. The water from the ECP may contain debris that could damage the ECW pumps or clog the heat exchanger tubes. To minimize the entrance of debris l 4 l

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T into the ECW system, a traveling water screen is installed upstream of each ECW pump. The traveling water screens are I provided with a wash control system that will automatically start i and stop the traveling screens as they become filled with j debris. The status of the screens is monitored by sensors that sense a high differential water level across the screen and by a l high screen wash pressure, which is sensed at the output of the screen wash booster pump. The screens may be operated manually, if the screen wash booster pump is running, or started

. automatically by the safety injection actuation signal.

The drawings associated with the ECW traveling water screens, j Drawing No. SR-28-9Z-42079, Rev. 4 (Ref. 7) and Drawing No.

9E-EWO5-01, Rev. 7 (Ref. 8), show that the differential level switch and the static pressure switch are non-Class 1E switches.

These switches are isolated from the Class 1E motor control 1

circuit with 1 amp series redundant fuses. By letter dated i March 27, 1987 (Ref. 9), the applicant forwarded to the staff the justification for using fuses as isolation devices.

i The applicant stated that the design philosophy for incorporating fuses as isolation devices is described in the South Texas Project FSAR, Paragraph 8.3.1.4.4.13 (6). The staff reviewed the FSAR paragraph, and in SER paragraph 8.3.3.3.4 they accepted the applicant's design philosophy. The applicant's design calls for redundant fuses in series with each of the non-Class 1E switches. The fuses are coordinated with the

. up-stream circuit protection devices protecting the Class 1E 480 VAC MCC bus. The fuses will be soldered into their fuse holders to ensure that the fuses will not be replaced inadvertently with a higher rated fuse. In addition, the Failure Modes and Effects Analysis (FMEA) performed by the applicant shows that, should one of the traveling screens fail, two 50% trains are still available.

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The staff finds-that the use of. fuses in th'is particular case-is acceptable. The ECW system.is not prevented from performing its safety function, and the operating ECW pumps remain protected.

4. Case No 4 - Reactor Coolant pressurizer power-Operated gelief Valves (p0RVs)

. The review of the reactor coolant pressurizer PORV logic diagram, Drawing No. 5R-14-9Z-42160 (Ref. 10), shows that the automatic circuitry that opens and closes the PORVs is not qualified for Class 1E' service. Two non-qualified 1E bistables receive pressurizer. pressure inputs and generate the high pressure signal that opens the PORVs. However, the applicant does not take credit for the p0RVs in their accident analyses.

Since the applicant's analysis shows that automatic control of the PORVs is not required for the safe shutdown of the plant, it is concluded that the use of the non-qualified IE bistables is acceptable.

5. Case No. 5 - Main Feedwater Isolation Valves The main feedwater (MFW) isolation valves are hydraulically operated, fail-closed valves that are normally open. Valve closure protects the containment from overpressurization and prevents excessive cooldown-of the reactor vessel following a steamline break accident. The' isolation valves can be closed.

automatically by the safety injection signal' ,.a high steam generator (SG) water level, and the excessive cooldown protection 1

circuit. They can also be closed manually from the control room.

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l The review of MFW Isolation Valves Logic Diagram No.  !

SS-13-9Z-40116, Rev. 8 (Ref. 11), showed three non-Class 1E l i

interfaces with the Class 1E; control circuit of the isolation  !

valves. The non-Class IE interfaces are as follows:

o Test switch circuit o ' Anti-waterhammer circuit l 1

o Steam generator (SG) water level and pressure sensors The test switch circuit is used to stroke test the valves. j

• This is is a non-safety-related function. The anti-waterhammer. 1 circuit is not safety related and consists of' temperature sensors and alarm units. The SG water level and pressure transmitters are Class 1E instruments feeding a non-Class 1E bistable. This- I non-Class 1E bistable interfaces with the anti-waterhammer logic circuits. All three circuits are isolated from the Class 1E control circuit through relay isolation devices.

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Since all three non-Class IE circuits are isolated from the.

l Class 1E circuit with acceptable isolation devices, it .is concluded that this non-Class IE to Class 1E interface is acceptable.

6. Case No. 6 - Supplemental Isolators' Test Report During a site audit on January 28-30, 1987, the staff raised concerns regarding the use of Magnetics isolation current transformers (cts) and Struthers-Dunn (S-D) relays. These two )

devices are used as isolation devices in Main Control Panel .c CP-003. The applicant responded to these concerns by letters  !

dated February 19, 1985 (Ref. 12) and May 8, 1987 (Ret. 13).  ;

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The Magnetics isolation cts are used for non-Class 1E diesel generator (DG) current metering. They isolate the cts monitoring the 4160 VAC bus from the main control panel. These Magnetics isolation cts have been reviewed and accepted by the staff in the i STP SER, paragraph 8.3.3.3.4.  ;

1 The S-D relays are used to isolate the 125 VDC Class IE power from the DG engine control panel and to isolate the SG preheater l

. bypass valves from the non-Class 1E valve position indicating lights.

The applicant pointed out that the S-D relay in question,. ]

i (Model No. 219XBX242NE, rated for 125 VDC service) is similar to S-D relay Model No 219XBXP, rated for 120 VAC service. The two  !

relays are constructed from the same material, with the differences being that the Model No. 219XBX242NE relay is built l to higher quality standards and has an improved coil design. The DC relay has improved contact-to-coil isolation characteristics.

S-D relay Model No. 219XBXP has been tested for use as an I isolation device. The test results were previously reviewed and accepted by the staff, as noted in Reference 14.

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The Magnetics isolating current transformer is acceptable for use as an isolation device. The S-D DC relays, which are similar to the AC version of the relay (previously accepted by the NRC) and have improved isolation characteristics, are acceptable for use as an isolation device at STP. l B

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3. CONCLUSIONS 1

Case No.1 - The approval of the use of non-seismically qualified j toxic gas detectors for Control Room HVAC isolation damper control is f based on the applicant's commitment to modify the circuitry such that i 1

a loss of power or a seismic event will automatically cause the dampers to close. l

. Case No. 2 - The approval of this case is based upon the applicant's  !

removal of the non-qualified switches from the Class 1E circuitry.

Case No. 3 - The applicant received specihl permission from the staff to employ redundant fuses as isolation devices. The approval applies to this case only.

Case No. 4 - The approval of this case is based on the fact that the PORVs are not required for the safe shutdown of the plant. As such, I a Class 1E control circuit is not required.

Case No. 5 - The approval of this case is based on the use of acceptable isolation devices between the non-Class 1E circuits and the Class 1E circuits that control the MFW isointion valves.

Case No. 6 - The isolation devices described in this case are acceptable for the isolation of Class 1E circuits from non-Class 1E circuits, redundant circuits, and divisional' circuits.

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4. REFERENCES

1. Letter, HL&P to NRC transmitting HL&P's application for license, dated July 17, 1978.

2. NUREG-0781, " Safety Evaluation Report Related to the Operation at South Texas Project, Units 1 and 2," dated April 1986.

3. Letter, M. R. Wisenburg (HL&P) to G. W. Knighton (NRC), " Notes from Review Meetings with Instrumentation and Controls System Branch," dated May 13, 1985.

. 4. Letter, J. H. Goldberg-(STP) to U.S. NRC, " Final Report Concerning Toxic Gas Detectors," dated January 20, 1987.

5. Letter, J. H. Goldberg (STP) to R. D. Martin (NRC), " Revised Final Report Concerning Potential Failure of Non-Seismic CCW Tank Level Flow Switches, " dated July 22, 1986,

6. Drawing No. SR-20-9Z-42040, Rev. 5, " Component Cooling Water Pumps Logic Diagram."

7. Drawing No. SR-28-9Z-42079, Rev. 4, "ECW Traveling Water Screens Logic Diagram."

8. Drawing 9E-EWO5-01, Rev. 7, " Elementary Diagram, Essential Cooking Water, Traveling Water Screens 1A, 1B, and IC."

9. Letter, M. R. Wisenburg (HL&P) to U.S. NRC, "Use of Fuses as Isolation Devices," dated March 27, 1987.

10. Drawing No. SR-14-9Z-42160, Rev. 5, " Reactor Coolant Pressurizer Power Relief Valves Logic Diagram."

11. Drawing No. SS-13-9Z-40116, Rev. 8, " Main Feedwater Isolation Valves Logic Diagram."

12. Letter, M. R. Wisenburg (HL&P) to U.S. NRC, " Class IE/Non-Class IE Control Circuit Interfaces," dated February 19, 1985.

13. Letter, M. R. Wisenburg (HL&P) to U.S. NRC, "Information Concerning Struthers-Dunn Relays and Magnetic Current Transformers Used as Isolation Devices," dated May 8, 1987,.

14. Letter, F. Rosa (NRC) to M. Srinivasan (NRC), " Hope Creek Generating Station - Review of Isolation Devices that Interface with the SPDS," dated January 24, 1986.

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3. TITLL AND SUefitLE J LE AV4 SLANGL Technical Evaluation Report Resolution of the Confirmatory Item Non-Class'1E Signal to- _

Class IE' CircuitInterface: South Texas Project-1 and -2 -

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. June', 1987 S. DATE RtPORT ISSUED A. E. Nolan .. . MONTH nAa

., . June l 1987

8. PROJECTIT ASEtWORIL UN#1 NUMetR

7. FERPORMING ORGAN 64 Af TON NAME AND MAILING ADDR&B5 f t.wsenale Cass EG&G' Idaho, Inc. . . , ,,,,,,,,,,,,,,,,Q,,,,,

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11428 Rockville Pike, Suite 410 Rockville, MD 20852 lla, TYPE OF REPORT 14 SPON50 RING ORGANI4ATION NAM 6 AND MAILING A00RSEmle ecerle Cases Instrumentation & Control Systems Branch Informal Office of the Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, DC 20555 12 84'PPLEMtNT ARY NOTis

13. ASSTR ACT t,200 worse er wees The Confirmatory Item, "Non-Class IE Signal to Class'1E Circuit Interface listed in Section 7.1.4, Specific Findings, of the Safety Evaluation Report (SER)

NUREG-0781, "Related to the Operation of South Texas- Project, Units 1 and 2," was reviewed to ' determine if the non-Class 1E equipment would prevent safety-related systems from performing their required functions; Results of the review are summarized in this report.

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