ML20136H301
| ML20136H301 | |
| Person / Time | |
|---|---|
| Site: | Callaway  |
| Issue date: | 03/13/1997 |
| From: | Schnell D UNION ELECTRIC CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-96-05, GL-96-5, TAC-M97027, ULNRC-3548, NUDOCS 9703190109 | |
| Download: ML20136H301 (8) | |
Text
._
I901 Chatiteau Arentje Post Office Box 149 St Iouis. Missouri 63166 314 554 2650 gy Donald F. SchneII Etscnuc
- y~~'t m
March 13, 1997 U.
S. Nuclear Regulatory Commission ATTN:
Docume.c Control Desk Mail Station P1-137 Washington, D. C.
20555-0001 Gentlemen:
ULNRC-3548 TAC No, M97027 CALLAWAY PLANT DOCKET NUMBER 50-483 PERIODIC VERIFICATION OF DESIGN-BASIS CAPABILITY OF SAFETY-RELATED MOTOR-OFERATED VALVES
References:
- 1) ULNRC-2964 dated February 18,1994
- 2) NRC Generic Letter 96-05 dated September 18, 1996
- 3) ULNRC-3487 dated November 6, 1996
- 4) NRC Letter from K. M.
Thomas to D.
F.
Schnell dated November 29, 1996
- 5) ULNRC-3507 dated December 12, 1996 4
- 6) Union Electric letter from M. A.
Reidmeyer to Marc Huber dated April 15, 1994 This letter provides supplemental information regarding Union Electric's MOV periodic verification program, as discussed in our response (Reference 5) to the NRC's request of November 29, 1996 (Beference 4),
and constitutes our 180-day response to Generic Letter 96-05.
In Reference 1, Union Electric committed to a periodic MOV verification program that includes evaluations of industry and NRC activities, including 190081 those related to long-term MOV performance.
Changes necessary to maintain the periodic verification program f
are evaluated and incorporated into the program as g
needed.
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).147 )Il h,
J A 9703190109 970313 PDR ADOCK 05000483i
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Through the continuous monitoring and j
evaluation of industry and NRC activities relating to j
j long-term MOV performance,-we have concluded that no changes are needed to the Callaway periodic verification program to maintain-it as a suitable, valid _and effective program for assuring operability of safety-related MOVs.
Callaway's MOV program ensures j
l that changes in performance are properly identified and j
accounted for.
The Attachment provides a synopsis of
{
i-Union Electric's evaluation of. industry activities, 1
l relating to periodic verification of MOV operability, that have occurred since Callaway's close-out of j-Generic Letter 89-10.
l We consider all actions requested in Generic j
Letter 96-05 to be closed for Callaway Plant.
If you have any questions concerning this letter, please 3
contact us.
Very truly yours, Donald F. Schnell CDN/
Attachment
.. _ _.... _... ~. _ _.
i a
1 STATE OF MISSOURI )
)
SS 4
CITY OF ST. LOUIS )
I Donald F.
Schnell, of lawful age, being first duly l
j.
sworn upon oath says that he Senior Vice President-Nuclear and an officer of Union Electric Company; that he has read d
the foregoing document and knows the content thereof; that i
he has executed the same for and on behalf of said company with full power and authority to do so; and that the facts therein stated are true and correct to the best of his j
knowledge, information and belief.
a 1
2 By
/
'~ ~
Donald F.
Schnell-4 Senior Vice President Nuclear
):
-SUBSCR BED nd sworn to before me this
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- day of '/' Mt u -
- 1997, t
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V~
() V (/
i BARBARA J. PFAFF.
3 NOTARY PUBUC-STATE OF MISSOURI MY COMMISSION EXPIRES APRIL 22.199Z F
ST. LOUIS COUNTY f
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cc:
.M. H.
Fletcher Professional Nuclear Consulting, Inc.
19041 Raines Drive Derwood, MD 20855-2432' Regional Administrator U.S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive Suite 400 Arlington, TX 76011-8064 Senior Resident Inspector Callaway Resident Office U.S. Nuclear Regulatory Commission 8201 NRC Road Steedman, MO 65077 Kristine M. Thomas (2)
Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission 1 White Flint, North, Mail Stop 13E16 11555 Rockville Pike Rockville, MD 20852-2738 Manager, Electric Department Missouri Public Service Commission P.O. Box 360 Jefferson City, MO 65102
Attachment to ULNRC-3548 Evaluation of Industry Activities Relating to Periodic Verification of MOV Operability The following discussion addresses Union Electric's i
evaluation of industry activities conducted with regard to periodic verification of MOV operability since close-out of Generic Letter 89-10.
1.
We reviewed the Electric Power Research Institute MOV i
performance prediction program and the associated NRC 1
safety evaluation on the EPRI program.
The EPRI program results identified:
a
- a. Concerns relating to possible non-conservative results i
from traditional methods for predicting gate valve performance, the effect of varying edge radii on disk 1
seats and guide slots, and the effects of manufacturing processes and controls on valve performance.
Since Union Electric does not utilize the traditional calculation i
methods to predict the required thrust / torque for operation of gate, globe and butterfly valves under design basis conditions, concerns about these traditional methods do not adversely impact the Callaway MOV program.
Union Electric's approach has been to conduct in situ differential pressure tests of the majority of the safety-1 related MOVs (103 of 148 MOVs, Reference 1, Chapter 2).
For the limited number of MOVs on which DP tests could not i
be performed, the required thrust / torque values were determined using bounding values based upon DP testing of i
similar valves of the same manufacturer and type (Reference 1, page 4-4),
- b. A concern regarding stellite friction coefficients increasing proportionally with the number of differential-pressure valve strokes, stabilizing rather quickly in hot water conditions and decreasing as differential pressure increases.
Union Electric addressed the phenomenon of changing friction coefficients by DP testing valves after years cf service and with a margin allowance in valve set-up (Reference 1, page 4-13). DP testing of MOVs to accommodate age-related changes in valve performance is based upon margin allowance (Reference 1, page 4-12).
The phenomenon of a decrease in friction coefficient as DP increases was also incorpcrated during development of the 3 Following the submittal of Reference 1, two non-DP tested MOVs were removed from the plant, therefore reducing the total number of MOVs in the program from 150 to 148 1
Page 1 of 4
e MOV program and has been used partly as the basis for establishing the validity of limited extrapolation of DP test results to design basis differential pressure conditions (Reference 1, page 4-1 and Reference 6, response to NRC question #7).
The Callaway MOV program provides for DP testing following work evolutions that might affect differential pressure thrust requirements, including periodic DP testing to accommodate age-related changes in valve performance, j
- c. A concern regarding performance of gate valves under blowdown conditions.
This concern has a very limited scope at Callaway because of the pressurized water reactor design utilized.
The differential pressure thrust requirements for MOVs that might be called upon to operate under blowdown conditions were determined based upon DP testing of identical valves.
The DP testing was performed at higher differential pressures than required of the valves subject to blowdown conditions.
Additional allowances were added to the aforementioned thrust requirements to accommodate operation under blowdown conditions.
In addition, excess capacity is available to operate against these potential thrust requirements.
Regardless of these assurances of operational capability, Union Electric will continue to monitor industry publications for any additional information relative to these MOVs.
- d. A concern regarding rate-of-loading effects (load sensitive behavior) wherein static thrust output may be reduced by up to 30% under dynamic conditions.
Rate-of-loading effects were acknowledged during development of the Callaway MOV program, from preliminary industry findings, and incorporated in the Callaway MOV program as submitted for Generic Letter 89-10 (Reference 1, page 4-4).
Union Electric has reviewed the findings from the EPRI program and determined that the information does not invalidate the methodology used to accommodate rate-of-loading effects in Union Electric's MOV program.
Accordingly, it is concluded that no action as a result of these findings from the EPRI program (other than reviewing industry experience) is necessary to assure the continuing effectiveness of the current Callaway periodic verification program.
2.
We reviewed information derived from the preparation of a code case by the American Society of Mechanical Engineers Page 2 of 4
i I
j on an MOV periodic verification program that could be used as an alternative to stroke-time testing.
A review of ASME Code Case OMN-1 by Union Electric has i
concluded that the Callaway MOV program satisfies the L
requirements and intent for periodic verification of safety-related MOV operability.
Therefore, no action as a result of the provisions of Code Case OMN-1 is necessary to assure the continuing effectiveness of'the current Callaway periodic verification program.
The ASME code case provides for' extended diagnostic test intervals of up to ten years for MOVs with sufficient margins.
In accordance with the provisions of our MOV program, based l
upon experience gained at Callaway, and in parallel with the provisions of Code Case OMN-1,.MOVs that meet designated performance levels now have periodic verification testing performed every 4 cycles or six years.
Union Electric also is investigating the utilization of the MOV
. diagnostic testing performed for Generic Letter 89-10 compliance in conjunction with one year /one refuel cycle MOV exercising to meet in-service testing requirements.that are currently focused on the quarterly stroke-time testing of ASME Section XI.
If we determine this to be feasible, a relief request to the ASME Section XI requirements will be submitted at a future date.
3.
Information derived from tests sponsored by the NRC on the aging of valve material samples was reviewed.
A review of available test results regarding aging of valve material samples by Union Electric has' concluded that the Callaway MOV program remains valid and effective.
As stated in the response to Item 1, the Callaway MOV program is based upon differential pressure testing performed after several years of "in-service time".and includes provision of margin.
This approach accommodates the time-related friction coefficient changes observed in both the NRC-sponsored tests and the EPRI I
predictive performance test experience.
The finding that indicates the tendency for lower friction coefficients at elevated load levels is also consistent with EPRI predictive performance test experience, and, as stated in the response to Item 1, is utilized as part of the basis for establishing the validity of limited extrapolation of DP test results to design basis differential pressure conditions.
Therefore, no action as a result of the NRC-sponsored valve materials aging testing is necessary to assure the continuing effectiveness of the Callaway periodic verification program.
Page 3 of 4
_ = _ _ _.. _. _. _. _.
l 4.
We reviewed the Callaway MOV program to assure the proper consideration of the attributes characterizing effective periodic verification programs as identified in Generic Letter 96-05, Attachment-1.
A review of the Callaway program for periodic verification of safety-related MOV operability concluded that the program includes all safety-related MOVs covered in the Generic Letter-89-10 program, provides adequate confidence that safety-related MOVs will remain operable until the next scheduled test, provides for monitoring and evaluation of valve performance, j
1 and provides for adjustment of the program as appropriate in response to experience gained and industry findings.
The Callaway program does not consider risk significance of I
specific MOVs, and Union Electric has no plans in the immediate j
future to incorporate relative risk significance as a factor in determining differing testing requirements for safety-related MOVs.
As a result of the extensive differential pressure testing. performed at Callaway and the resulting DP thrust values being based on actual requirements rather than calculated values, the stress levels applied to the MOVs are i
reduced from those pctentially applied if DP testing had not i
i been performed.
Union Electric has determined that the stress 4
levels applied to all safety-related MOVs are acceptable.
i Testing the less risk-significant MOVs in the same manner, and at'the same intervals, as more risk-significant MOVs imposes no potentially adverse effects.
Hence, Union Electric has thus i
far elected not to vary the testing of specific MOVs based upon l
risk significance.
I In summary, the Callaway periodic verification program has considered but does not incorporate the utilization of risk significance as a determining factor for setting specific MOV l
testing intervals, and incorporates all the remaining i
attributes identified as characteristic of an effective program.
i Page 4 of 4
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