ML20082N577
| ML20082N577 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 09/03/1991 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 91-392, GL-89-10, NUDOCS 9109090246 | |
| Download: ML20082N577 (7) | |
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YlHOINI A I$1.l:CTillC ANil l'OWI:lt COktl'ANY lif ollHONH,Yllf ulNIA UllWUl September 3, 1991.
United States Nuclear Regulatory Commission Serial No.:
91 392 Attention: Document Control Desk NL&PffAH: R4
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Washington, D.C. 20555 Docket Nos.: 50 338 50 339 License Nos.: NPF 4 NPF 7 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY NORTHERA POWER STATION UNITS 1 AND 2 HRC GENERIC LETTER 8910 INSPECTION Rf1PONSE TO INSPECTION REPORT NOS. 50 338&339/91 09 We have received and reviewed the NRC Inspection Report Numbert. 50 338/91 09 and 50 339/9109 dated July 2,1991, which documents nine areas of NRC concern about our Motor Operated Valys (MO4) Program and compliance with Generic Letter 8010 (GL 8910). Our responses to these concerns are attached.
As discussed during the inspection, all evaluations will be completed and the results-Incorporatad into the MOV programs, as applicable.
The program will be fully implemented with the refueling outage currently scheduled for completion in December,1994.
!! you have any further questions, please contact us.
Veiy truly yo
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L W. L. Steydrt Senior VR:e President Nuclear Attachment CG0033 i
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Dochet IJos,: 60 330 & J39 SerialiJo.:
91 392 Page 2 of 2 pc: U. S. Nuclear Regulatory Cornmission Region 11
- 101 Marietta Street, N. W.
Suite 2000 Atlanta, Georgia 30323 Mr. M. S. Lesser NRC Senior Resident inspector North Anna Power Station 4
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RESPONSE TO NRC GENERIC LETTER 8910 INSPECTION INSPECTION REPORT NOS. 50 338/9109 AND 50 339/91 0_9 i
HRC COMMENT Scope:
This special, announced inspection examined the program developed in response to NRC Generic Letter (GL) 8910. " Safety Related Motor Operated Valve Testing And Surveillance." The inspection was the first of two or more that will be conducted for each nuclear plant in accordance with NRC Temporary Instruction 2515/109, issued i
January 14,1991.
Results:
The inspectors determined that the licensee's program was generally satisfactory and consistent with the recommendations of GL 8910, which was committed to by the licensee in a letter to the NRC dated December 26,1989. The program was in an early stage of implementation. The licensee indicated it would be completed within the schedule recommended by the GL.
Strer,gths were noted in the program relative to training, an 18 month frequency of preventive maintenance and olagnostic testing, and promptness in addressing the special case motor-operated butterfly valves.
Though the program was generally satisfactory, several matters of potential concern were identified. These matters are listed below.
l-(1) NRC Concern:
l The four Residual Heat Removalinlet isolation valves were excluded from the program based on the limited duration that these motor operated valves (MOVs) l are energized. The exclusion of these MOVs did not appear warranted because l
of their important function to isolate the reactor coolant system from low pressure i
plaing. The licensee intends.to reassess the need to include these MOVs in its l
G 8910 program.
Hesponse:
U The Residual Heat Removal (RHR) inlet isolation valves were included in the MOV program at North Anna with minimum and maximum differential pressure and thrust calculations performed on them. The thrust sett:r,p have been set on -
the-valves-as required using diagnostic equipment and wiii-continue to be c
diagnostically tested during corrective and/or preventive maintenance. The L
valves will not be locluded in the differential pressure testing portion of the program for the following reasons:
l The valves are in their safety position, closed, and their breakers de-f energized during normal operations.
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Attachment:
Page 1 of 5
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R$spon53 to GL 8910 inspiction IR 50 338 & 339 / 9109 Electricalinterlocks prevent the valves from opening 1f the Reactor Coolant System (RCS) pressure is >418 psig.
When the suction valves are open, the RHR system is protected from
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overpressurization by the RHR pump suction line relief valves which willlift at i
467 psig.
Because the RHR system is en'irely located inside the containment, a rupture of the RHR system piping would result in a Loss of Coolant Accident (LOCA) which would be confined to the containment, it would not be an interfacing i
system LOCA outside of the Containment (Event V LOCA) and would be bounded by our accident analysis.
Therefore, because 1) these valves are not required to operate for accident mitigation, 2) they are in their safety position, closed, and their breakers de-energized during normal operations, and 3) system configuration makes it i
impractical to perform design differential pressure testing, we will not be including the RilR suction MOVs in the differential pressure testing portion of the MOV Program.
(2) NRC Concern:
In response to Ques %n 16 in Supplement 1 to GL 8910, the NRC staff discussed various factors that might increase the thrust required to operate a valve and stated that these factors should be addressed by licensees. At North Anna, the t
licensee had includeo only differential pressure in its design basis reviews. The licensee intends to consider flow in establishing MOV test conditions and in the written evaluations of the test results. Consistent with its commitment to GL 89-10, the licenseo should also address other design basis parameters outlined in Supplement 1 to GL 8910.
Response
Our program currently considers flow and other elements relevant to design basis review and subsequent testing, as discussed in Supplement 1 to GL 8910. Flow will be considered when establishing MOV differential pressure test conditions and will be documented and discussed where possible.
Consideration of additional factors roletant to design basis review and differential pressure testing is ongoing and develcping with the knowledge base of Industry in addressing this generic concern.
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Attachment:
Page 2 of 5
Response to GL 8910 Inspudion IR 50-338 & 330 / 9109
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(3) NRC Concern:
I Recently published industry test data indicates the valve factors used by the licensee in analytical determinations of MOV thrust may yield non-conservative results. The licensee plans to evaluate industry information and to incorporate i
that informailon where appropriate.
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Response
We will continue to evaluate Industry information regarding analytical modeling of i
I MOV behavior and incorporate appropriate changes.
We will also ver!fy analytical modeling through testing where practical.
(4) NRC Concern:
No provisions had been made in the program to correct analytical thrust determinations for the " rate of loading" effects. which can reduce available thrust at high differential pressure conditions.
Thu licensee intends to evaluate available information on rate of loading effects (such as from MOV diagnostic equipment vendors) and to quantify those effects for incorporation in to their MOV sizing and switch setting evaluations.
Response
We are currently evaluating " rate of loading" effects on vaive behavior in orderio determine the most efficient methodology for quantifying and including th9 phenomena into the MOV program.
(5) NRC Concern:
The degrading effects of high ambient temperature on the output of the MOV moto(s had not been considered. The licensee plans to evaluate ongoing industry efforts with respect to such temperature effects and to revise its determination of available torque and thrust if necessary.
Response
We intend to evaluate the high ambient temperature effects on motor performance with the publication of the Limitorque report addressing this issue and willincorporate appropriate changes in the MOV program as warranted.
1 A"achment: Page 3 of 5
Respons1 to GL 8910 Inspecho' IR 50-338 & 339 / 91-09 (6) NRC Concern:
j The licensee's written evaluation of NRC Information Notice 90 72 (November 28, 1990), " Testing of Parallel Disc Gate Valves in Europe," appeared inaccurate, Specifically, the evaluation implied that the licensee's GL 8910 program had been reviewed and approved by the NRC staff. The evaluation also stated that its thrust calculations for parallel disc gate valves assumed a valve factor of 0.3, when a less conservative factor of 0.2 is actually used. Finally, the evaluation of the information notice did not address instances when design basis testing is not practicable and the capability of the MOVs will need to be verified by analytical means. The licensee stated that they will revise the evaluation of the information notice.
-Response:
We have revised our evaluation of NRC IN 90 72 as discussed during the inspection to include 1) a revision of the stated friction factor from 0.3 to 0.2,2) a removal of the statement implying our program had been approved by the NRC, and 3) addressing the issue of written evaluations for those valves that will not be differential pressure tested. However, we ha"o confirmed that our original conclusions remain valid.
(7) NRC Concern:
The licensee is enanging from MOVATS to VOTES equipment for their MOV diagnostic testing and will need to ensure that differences in the thrust measurements provided by the two, including equipment inaccuracies, are properly considered in determining torque cwitch settings and available thrust margin. The licenseo plans to address such differences in the MOV diagnostic equipment, and to incorporate those results where appropriate.
Response
We have taken steps to reconcile the differences between the two diagnostic technologies and to incorporate those differences where appropriate. We will remain involved in Industry activities addressing the apparent differences among all diagnostic technologies. We have procedures in place to provide guidar;ce for incorporating necessary corrective measures.
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Attachment:
Page 4 of 5 1
nesponso to GL 8910 Inspection IR 50 338 & 339 / 91-09 (8) NRC Concern:
The licensee has an ongoing evaluation of recent failures of motor operated butterfly valves in the Service Water system. These failures occurred because the need to increase torque requirements to accommodate reversed valve installation had not been considered. The licensee intends to document its assessment of reportability of this issue in accordance with 10 CFR Part 21.
Response
Virginia Electric and Power Companv documented the evaluation of this event and the determinution that no significant safety consequences resulted from this event in our voluntary report dated May 31,1991 (Serial Number 91229).
(9) NRC Concern:
After the initial testing of MOVs under differential pressure and/or flow, the licensee plans to use static (no differential pressure or flow) diagnostic testing to ensure MOV capabilities are rnalntained. The inspectors' questioned whether this is sufficient. However, licensee personnel stated that they were satisfied that the static testing will reveal any significant changes. However, the licensee was l
reminded that GL 8910, item C, Recommended Action provides guidance if a i
performance test is conducted where design basis differential pressure and flow can not practicably be performed. The inspectors stated that the acceptability of the static testing will be assessed for individual MOVs in future inspections.
Response
We perform post maintenance testing, periodic maintenance testing or post modification testing in a conservative and reasonable manner. We will evaluate any future guidance on testing and incorporate changes in the testing requirements where necessary.
All evaluations will be completed and the results incorporated into the MOV programs, as applicable,in accordance with the schedule provided with our response to Generic Letter 89-10. The program will be fully implemented with the refueling cutage currently scheduled for completion in December,1994.
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