ML20237D225
| ML20237D225 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 12/15/1987 |
| From: | Heitner K Office of Nuclear Reactor Regulation |
| To: | Calvo J Office of Nuclear Reactor Regulation |
| References | |
| TAC-61601, TAC-62198, NUDOCS 8712230117 | |
| Download: ML20237D225 (21) | |
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UNITED STATES
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WASHINGTON. D. C. 20555
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December 15, 1987 o
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Docket No. 50-267 MEMORANDUM FOR:
Jose A. Calvo, Director Project Directorate - IV Division of Reactor Projects - III, IV, V and Special Projects FROM:
Kenneth L. Heitner, Project Manar,er Project Directorate - IV Division of Reactor Projects - III, IV, V and Special Projects
SUBJECT:
SUMMARY
OF MEETING TO DISCUSS CONTROL R00 DRIVE MECHANISM (CRDM) TEMPERATURE REQUALIFICATION AND POSITION INSTRUMENTATION, DECEMBER 4, 1987 (TAC N05. 61601 AND 62198)
The purpose of this meeting was to discuss the licensee's latest proposals for these licensing actions.
The licensee's previous proposals for these areas have been evaluated by the staff in letters dated December 24, 1986, and July 31, 1987.
The attendees at this meeting are listed in Enclosure 1.
Positi.on Instrumentation The licensee presented a preliminary review of the current control rod position l
instrumentation. The presentation material is in Enclosure 2.
The presenta-i tion incluced a failure mode analysis of the present instrumentation.
This l
analysis showed that the current rod-in and rod-out limit switches were strong candidates for replacement.
The problems with the current design of the rod position potentiometers were also highlighted.
The licensee stated that improved instrumentation had been selected as follows:
The rod-in and rod-out limit switches would be replaced by proximity sensors, and The rod position indication potentiometer would be replaced by an improved potentiometer.
Both items would be able to withstand the temperature, humidity, radiation, and pressure environment of the CRDM.
The licensee stated that their intent was to submit a new failure mode analysis report. This report would clarify that there was corrosion failure of the rod-in and rod-out limit switches.
It would also indicate that there were no credible failures (and need to replace) the slack cable limit switches.
There was also not a problem with the proximity switch targets mechanically inter-fering with the position potentiometer shafts.
The staff noted that the licensee had not addressed other important criteria for the new instrumentation. The staff stated that the new instrumentation should clearly have service life equal to or exceeding that of the current instrumentation.
Otherwise, the reactor operation could be constrained by inoperable control rod instrumentation.
(The staff also notes that other factors, such as accuracy and long term drift, should be considered.)
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3 CRDM Temperature Requalification i
The licensee reviewed the key steps in his proposed program for CRDM I
m temperature requalification (see Enclosure 3).
They are as follows:
Evaluate the projected maximum CRDM service temperature.
The licensee has developed a methodology for correlating the CRDM motor l
temperature with reactor temperatures and coolant flow parameters.
These include the orifice position setting for each refueling
'j region.
Projected maximum temperatures for Cycle 4 are about 300 F in Region 12 and 275 F in Region 30.
However,.the licensee noted that some reductions could be achieved by reducing overall core flow and deliberately mismatching region outlet temperatures.through orifice adjustments (within the limits of LC0 4.1.7).
There was also some uncertainty about the validity of th'e correlations at high power, which could result in lower temperatures.. Some possijdlity existed that CRDM temperature requalification would not be n(eded.
Evaluate the CRDM system for acceptability at the higher temperature.
This would include an evaluation of the materials of construction at higher temperature.
The methodologies would be similar to those used to " qualify" materials under 10 CFR 50.49.
Specific accepted methodologies would be used for special cases, such as CRDM drive motor insulation.
Perform an integrated systems test of an entire CRDM assembly.
The purpose of this test would be to evaluate potential synergistic and system effects of increased temperature, and Evaluate the role of the preventive maintenance program in assuring system performance in the event the " qualified" component life is reduced by the elevated temperatures.
This could include more frequent maintenance of CRDMs exposed to higher temperatures Future Actions The licensee proposed to submit a proposal for new rod position instrumentation in April 1988, and'for CRDM temperature requalification in March 1988. The staff commented that the licensee should give care 1ul attention to applicable and related regulatory requirements and guidance.
This included:
10 CFR 50.62 GL 83-28 and related licensee submittals and staff evaluations, SRP 3.11, 4.5.1, and 4.6, The October 16, 1984 Assessment Report, and
/
Subsequent Safety Evaluations on the CRDMs and CRDM position instrumentation.
j Kenneth L. Heitner, Project Manager I
Project Directorate - IV Division of Reactor Projects - III, IV, V and Special Projects
Enclosure:
j As stated i
cc:..See next page DI)TRIBUTION
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t-Enclosure I 1
ATTENDEES I
NRC/PSC Meeting 41 December 4, 1987 i.
1 NAME ORGANIZATION i
Rick Burrows PSC/ Plant Engineering Ed Pitchkolan PSC/Special Projects
. s M. E. Niehoff.
PSC/NED l,
Greg Bates-PSC/NED Jim Heriderson.
PSC/NED it J. R. Reesy
- PSC/NED J. L. Mauck 6RC/NRR/ICSB Ken Heitner NRC/NRR/PD-IV Sam Chesnutt PSC/ Licensing M. H. Holmes PSC/ Licensing C,4Eomberger PSC/ Licensing j.
Don Warembourg PSC/NED Frank Novachek PSC/NPD s
A S
ENCLOSURE 2 Normal Operating Parameters 1 - Cable length % 240" from Fully Retracted to Full-In Limit.
2 - Cable length $ 190" from Full-Out to Full-In Limit.
3 - From Fully Retracted to Full-In g 10 turns on 2-gang potentiometer.
4 - At Full-In 2 each Limit Switches are actuated - wired in series.
Actuated by Cam.
5 - At Full-Out 2 each Limit Switches are actuated - wired in series.
Actuated by Cam.
6 - On loss of a Rod (Cable Breaks) 2 N/C Limit Switches are actuated by counter balancing spring.
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l PRGE I FRILURE ANRLYSIS TREE 1
COMPLETELY PRRTIALLY NORMAL ACTURTED I
I SLIDE JAM SEAL OPEN SEAL CLOSED.
SmFT JAM ROLL OTHER ROLLER CONTACTS I
I MECHANICAL _
ELECTRICAL p.L-IN/FLLL-OUT LIMIT SWITCH l
NOTES FAILURE MODE EFFECTS ANALYSIS l
1 - NOT A FRILURE (INTENDED R - INDICRTING LIGHT ILLUMINATED, l
FLNCTION)
REMAINS SO RFTER LOSS OF STIMULUS 2 - NOT A CREDIBLE FRILURE MODE B - MECHANICR. FRILURE OF AN (NO CIRCUIT RVRILABLE)
UNPREDICTABLE NRTURE WILL OCCUR 3 - NOT R CREDIBLE FRILURE MODE C - NO INDICATING LIGHT ILLUMINATED
{
(BASED ON MRTERIRLS 303&440SS)
UPON ACTLFITION - NOT BY JUDGEMENT 4 - NOT, BY JUDGEMENT, A CREDIBLE A CREDIBLE FRILURE - SEE
'4' FRILURE MODE (SNAP RCTION D - INDETERMINATE - A OR B BRSED SWITCH) SEE
'C' ON PRECISE POINT OF JAM 5 - NOT A CREDIBLE FRILURE MODE
.(BRSED ON STRUCTURAL AND MECHANICAL RUGGEDNESS OF SWITCH) 1 l
4 i
Based on Failure Analysis What Can Fail?
Explain what would caus'e failure.
Pg.1 - A - Full-In/ Full-Out Switch fails mechanically 'by jamming the shaft in the completely actuated position.
Cause - Shaft Failure Investigate cause of shaft failure.
==
Conclusions:==
Shaft fails due to high lateral forces caused by Cam ' angle
>15" (recommended max per Mfr).
Failure' is by erosion, -deposition of eroded metal, corrosion until
' space between shaft and housing is filled and will not allow free movement.
To verify:
(1) Contact manufacturer for concurrence;.-(2)
Check for corrosion / erosion / deposition on only 1 side of shaft (side opposite Cam approach)
Verify as required.
Pg.1 - B - Same as "A"
above except position at. which final failure occurs.* Cam may fail.*
Pg.1 - D - Same as "A"
above, except position at which final failure occurs.
Pg. 1 - C - Full-In/ Full-Out Switch fails electrically by sealing the contacts in the closed position.
Not credible.
Cause - High. inductance discharge from relay coil.
A commitment for testing of surge suppressors is in place.
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4 mcc a FRILURE RNRLYSIS TREE M
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'n" SLIDE SEAL OPEN SERL CLOSED l
OTHER SHRFT CONTACTS I
l MECHANICAL ELECTRICAL l
SLRCK CONTROL ROD CRBLE LIMIT SWITCH NOTES FRILlJRE MODE EFFECTS ANRLYSIS 1-NOT A FRILURE (INTENDED R-NO INDICRTING LIGHT ILLUMINATED FUNCTION)
UPON RCTURTION - NOT BY JUDGEMENT 2-NOT A CREDIBLE FRILURE MODE R CREDIBLE FRILURE - SEE
'4' (NO CIRCUIT RVRILRBLE)
B-INDICRTING LIGHT REMAINS 3-NOT R CREDIBLE FRILURE ILLUMINATED. THE ONLY WRY MODE CUPON LOSS OF ROD TO REMOVE THE STIMULUS IS CRBLE, SPRING RPPLIES TO RE-RPPLY THC WEIGC OF EOURL FORCE TO RN RRER THE CONTROL ROD, VIA THE
-1/4" e) - LF A JRM OCCURRED CRBLE. SHOLLD THIS FRILURE RFTER LOSS OF ROD CABLE OCCUR, IT WOULD BE RESOLVED IT WOULD BE REPLACED BY SWITCH REPLACEMENT DURING REFURBISFt1ENT DURING REFURBISHMENT TESTING.
TESTING. SEE
'B' SEE
'3' 4-NOT, BY JUDGEMENT, A CREDIBLE FRILURE MODE (SNRP RCTION SWITCH) SEE
'A' 5-NOT R CREDIBLE FRILURE MODE (BRSED ON STRUCTURAL RND l
MECHRNICAL RUGGEDNESS OF SWITCH) l l
)
i Based on Failure Analysis What Can Fail?
Explain what would cause failure.
Pg. 2 - A - Slack cable Limit Switch fails electrically by sealing the contacts in the closed position.
Not judged a credible fail ure.
Cause - High inductive discharge from relay coil.
A commitment for testing of surge suppressors is in place.
Pg. 2 - B - Slack cable Limit Switch fails mechanically by jamming the shaft in the completely actuated position.
Not a
credible failure.
Cause - None known.
1
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PAGE 3 FRILURE ANRLYSIS TREE BOLT RING COVER BOLTS MOUNT CLRMP FACE PLATE CONDUCTOR BETWEEN UPPER BODY
& LOWER SLIDES COUPLING I
a sumg Sax g g
JAM JAM SUPPORT CONDUCTOR COIL COIL J
UPPER LOWER SLIDE CARRIRGE COIL
/
l HIPER (SLIDE)
RESIST CE SHAFT BERRINGS OPEN SHORT MECHANICAL ELECTRICAL CONTROL ROD POSITION POTENTIOMETER
Page 3.1-Notes 1 - Not a Failure (Intended Function) 2 - Not a Credible Failure (Failure of some other type required to provide stimuli for this failure).
Failure of this type for both analog and digital portions of a single potentiometer simultaneously is-not considered credible.
3 - Not a Credible Failure (due to the Structural / Mechanical ruggedness of the Part).
4.- Not a Credible Failure (due to the materials used [non-corroding, presumed a type of magnetic stainless], lubrication, low speed, limited number of operations, and limitations of load applied).
5.
Based on operating experience, no known failures of these parts have occurred.
6 - No 'known failure modes (Strictly a mechanical support [ bobbin] for winding the conductor coil of the potentiometer.
7 - Not a-Credible Failure Mode -(Neither mechanical [ wear] or Electrical
[ opening or_ shorting] can occur due to the limited length of conductor and its installed configuration.
The conductor is made up of approx.
40 strands which produce an extremely flexible AWG 26 (approx. by measurement). 'Its length is such that in the installed configuration, this jacketed conductor does not come into contact with the conductor coil of the potentiometer and thus cannot be worn or shorted.
)
i
6 Pg. 3.2 Failure Mode Effects Analysis A - When the upper wiper (slide) jams (at the top or bottom of the slide carriage) due to being driven beyond its design range, system failure is imminent.
One potential failure is the wiper guide (a part of the wiper) is broken, rendering the slide inoperable or at best unpredictable.
This failure is particularly likely to occur when the potentiometer is driven very slowly beyond its design limits.
When the potentiometer is driven at scram speed (8 turns in approx.
150 seconds, approximately 3.2 rpm), the failure mode is far more likely to be Failure Mode "B".
(See Note below.)
B - When the potentiometer is driven beyond design limits, at or near scram speed, the failure mode is most likely to be breakage of the body (housing), the drive coupling, or the drive coupling pin.
The resul t is approximately the same as in failure mode "A"
in which the slide is inoperable or unpredictable.
(See Note below.)
NOTE: In the event of failure modes "A" or "B",
the output and thus the indication in the Control Room becomes unpredictable.
Since the 2-gang potentiometer is 2 independent potentiometers, the following may occur:
1 - Each portion may perform adequately.
2 - One portion may be accurate while the other is inaccurate (linearly or non-linearly).
3 - Both portions may perform identically though inaccurately.
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e Pg. 3.3 Failure Mode Effects Analysis i
C - When moisture is introduced into a potentiometer, as in depressuri-zation following a moisture ingress event, an oxide may result.
Any uninsulated copper used in the support coil may react electrically with the conductor coil and produce copper oxide.
This failure mode is considered unlikely in most potentiometers; yet it has been observed on a limited scale.
The result would be to increase the resistance between the wiper and the conductor coil.
This would result in erroneous indication in the Control Room.
This failure mode may be capable of correction by drying the helium environment prior to depressurization.
It is also possible that operation of the potentiometer may remove the oxide once it has formed, correcting to some degree the erroneous indication.
e l
Based on Failure Analysis-What Can Fail?
Explain what would cause failure.
Pg. 3 - A'- Control Rod. Position Potentiometer. fails mechanically by jamming the upper wiper resulting in wiper damage.
Cause. - Control Rod Drive Mechanism (CRDM) is overdriven (forced beyond the intended design' limit) in. an attempt to actuate non-working Limit switches.
An administrative procedure now controls this action to limit this type of damage.
Pg. 3 - B - Control Rod Position Potentiometer fails mechanically by
. jammirg the upper wiper resulting in body or coupling damage.
Cause - Same as "A" above.
Comment same as "A" above.
Pg. 3 - C - Control Rod Position Potentiometer fails electrically by producing copper oxide and thus' changing the resistance of the potentiometer.
This results in erroneous indication in the Control Room.
Cause - Electrolysis induced by bare copper and other metals in a moi st ' envi ronment.
Apparently, the added current of the circuit aids in the electrolysis.
1 - Contact manufacturer for concurrence.
2 - Verify visually.
Contacted and verified as required.
I l
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Scope of Review for Replacement Products For Position Transmitters (sample)
Encoders Optical Bidirectional BCD
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Magnetic Position Transducers j
Motors Steppers Potentiometers Selsyns Off-the-Shelf Custom Design Companies Contacted (sample):
Microswitch Litton Autotech Bailey Controls General Electric Westinghouse Beckman Many others 1
t For Full-In/ Full-Out Position Sensing Switches Roller (Perpendicular to Contact Bar)
Roller (Longitudinal with Contact Bar)
Non-roller type with slide actuation Sensors Infrared Magnetic Proximity - various types including Eddy current killed oscillator for sensor
- integrated Full-In/ Full-Out/ Position Transmitters i
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Selected Replacement Components 1.
For Rod-In/ Rod-Out Proximity Sensor Eddy Current Killed Oscillator by Microswitch Prototype #X82383-FW A remotely mounted transmitter receiver is used with this component.
See Note below.
2.
For Position Indication 2-gang Potentiometer by Beckman Prototype #7239-2966-0
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See Note below.
Note: All items designed to operate within the following parameters:
Temp 300 F min.
=
Humidity Approx. 100%
=
Radiation 1 Rad per Hour
=
Pressure 845 psi.
=
All parameters encountered simultaneously.
1
-1 ELc W e d PROPOSED PLAN FOR REQUALIFICATION OF CRDM's The following integrated plan has been developed for requalification of the CRDMs. The plan consists of-the following phases: (1) evaluate temperature profiles obtained from operational data and programs in the area of the CRDM assemblies to establish _ the temperature to be used for' qualification basis; (2) document age-related qualifications of-the CRDMs in.accordance with the approved FSV EQ program through evaluation using EQ DOR aging criteria; (3) for components which.nay possess insufficient qualified life at the elevated
. qualification temperature, perform a failure-modes-and-effects analysis to determine the consequences of component failure during. accident,and
' post-accident operation; and (4) perform a type test of a complete CRDM assembly
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to resolve outstanding concerns, including rod position indication, synergistic effects,. moisture ingress, and. operation at elevated temperature. NRC. Standard Review Plans 3.11 and 4.6 will be reviewed and applicable concerns identified in these SRP's will be incorporated into the integrated CRDM requalification progran. Although various phases of this approach have been performed piecemeal to document qualification of the CRDMs, it is PSC's position that this integrated plan will provide a complete qualification approach for qualifying the CRDM's. FSV's EQ program has been audited and approved by the NRC and
. utilizes a standardized methodology for qualification of these assemblies.
The following paragraphs provide' additional information related to each of the areas to be investigated.
1 (1). DOCUMENTATION OF QUALIFICATION TEMPERATURE:
l Analyze and document available data on the maximum expected motor
-temperature for which the CRDMs should be qualified. Document (1) recent
. actor temperatures while operating at power, (2) the program'used to estimate maximum temperature, and (3) assumptions used in this program which will require monitoring / review when additional operating data is available. The purpose of the program and analysis is to provide the basis for the qualification temperature to be used in the determination of~
qualified life.
(2) DETERMINATION OF QUALIFIED LIFE:
The qualification will be based on application of the FSV EQ program, which has been reviewed and approved by.the NRC, to the qualification of the CRDM's. Qualification will be tailored specifically for the CRDM environment and expected operational requirements The program will have to address the following points as a minimum:
a.
description of the applicability of DOR since this component is located inside the PCRV while other EQ items are located outside the PCRV in the Reactor or Turbine Buildings.
b, description of " mild" environment for the CRDMs; define mild and determine worst case accident and post-accident operating environment.
c.
evaluate post-accident operability requirements for these components to ensure that, if required to operate, evaluation of the post-accident environment is performed as well as identification of any appropriate testing requirements.
d.
identify the functional, operational, and design requirements for the CRDMs to ensure that these characteristics are used as the basis for type testing of the CRDM assembly.
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qualified life will be established using standard DOR methodology through use of material analysis. Due to the age of the CRDMs, use of this methodology should be acceptable; full thermal aging by type test is not required since it is not required of similar vintage EQ related equipment and the CRDMs are installed in a mild environment.
(Type testing is recommended to be performed but is intended to resolve non-aging, synergistic concerns identified by the !!RC in their submittals to PSC.)
(3) TAILURE MODES AND EFFECTS ANALYSIS (TMEA):
In addition to determination of the qualified life for degradable components of the CRDM, a TMEA will be needed to justify use of components which are determined to have insufficient qualified life at the elevated temperatures expected.
If any such components are identified, the THEA will determine the consequences of failure of these components or parts.
If failure can be proven to cause no adverse effect on the ability of the CRDM to operate or safely shutdown, no action would be required.
If, however, the part has inadequate qualified life and its failure has unacceptable consequences, then the recommendation should be made to limit the reactor power level such that an acceptable temperature can be achieved or replace the component prior to the end of its useful life.
(4) TYPE TESTING:
Several pre-1985 documents from the NRC to PSC identify the need to perform type-testing of the CRDM assembly.
(See attached page for major comments.)
Due to the uncertainty of the results obtained during the last CRDM type test, it is deemed to be prudent to retest the CRDMs to demonstrate suitable performance; the retest will include operability of the rod position indication, operation following moisture ingress, and operation at elevated temperatures. The intent of this test is to demonstrate the operability of the CRDM and to demonstrate that synergistic effects will not adversely affect performance of the CRDMs; it is NOT the intent of this type test to establish the qualified life of the CRDM components.
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SUMMARY
OF SIGNIFICANT NRC CORRESPONDENCE I
RELATED TO THE CRDM QUALIFICATION ISSUE G-82384:
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" Synergistic effects such as tolerance accumulation, wear induced j
misalignments, lubricant redeposition, differential thermal expansion etc.,
mandate reliance on total assembly qualification tests rather than on analysis or tests of individual components."
G-84392:
"The licensee should determine whether compensating design and/or operational modifications are needed to minimize moisture ingress to the CRDM cavities and minimize temperatures in the vicinity of the rod drives.
In the event that temperatures recorded during plant operation prove to be higher than those for which the assembly was initially qualified, perform requalification testing of a CRDM assembly."
Critical comments received from the NRC in the SER for the CRDH Temperature Requalification (G-86664) include the following:
"The licensee did not develop functional, operational, and design specification based on the environment that the CRDOA's would be expected to operate in. The licensee's submittal did not provide acceptance criteria developed from the functional, operational and design specification against which to evaluate the test results.
The tests were not performed under conditions that are representative of conditions in FSV (i.e., tests were performed with dry helium, while moisture is potentially present in the FSV reactor especially if there is a moisture ingress event). The licensee did not provide information on the mechanical and electrical properties of the materials in the CRDOAs as a function of temperature, humidity, pressure, and radiation. The test was performed for a very limited time (i.e., 14 days at 300 F).
The licensee's submittal did not explain how the data would be extrapolated to the length of time the CRDOA's would be required to operate at elevated temperatures.
In conclusion, G-86664 stated:
"the revised submittal should include or consider such items as functional, operational and design specifications, acceptance criteria, material specifications, material properties, test specifications, test operating procedures, test data, and the necessary supporting analyses.
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