ML20135E540

Safety Assessment Accepting Mod of RHR & CS Sys Containment Isolation Function Configuration

ML20135E540
Person / Time
Site:	Vermont Yankee
Issue date:	03/03/1997
From:	NRC (Affiliation Not Assigned)
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ML20135E514	List: ML20135E511 ML20135E535 ML20135E540
References
NUDOCS 9703070131
Download: ML20135E540 (5)

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, 2 WASHINGTON, D.C. SegeMcM SAFETY ASSESSMENT BY THE'0FFICE OF NUCLEAR REACTOR REGULATION MODIFICATION OF THE CONTAIMENT ISOLATION CONFIGURATION OF THE CORE SPRAY AND RESIDUAL HEAT REMOVAL SYSTEMS VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET N0. 50-271

1.0 INTRODUCTION

Vermont Yankee Nuclear Power Corporation, has made changes to the isolation j valve configuration for the residual heat removal system and the core spray '

system of Vermont Yankee. These changes were made without prior NRC staff review and approval in accordance with 10 CFR 50.59. The following discussion documents the staff's subsequent assessment of these changes and of the licensee's review of these changes under 10 CFR 50.59 In 1973, the NRC amended 10 CFR Part 50 by adding Appendix J, " Primary Reactor Containment Leakage Testing for Water-Cooled Power Reactors." Based on the requirements of Appendix J, it was concluded that Type C leak testing of these valves was not required because there were no postulated single active failures that would result in losing the 30-day water seals in the RHR and CS injection lines. This position was accepted by the NRC staff in its 1983 safety evaluation of Vermont Yankee's Appendix J 1eak rate testing program.

During a subsequent self assessment of the Vermont Yankee Appendix J 1eak rate testing program, VYNPC determined that Appendix J requirements were not being satisfied on several containment penetrations, including the CS injection line penetrations. This was reported to the NRC on March 1, 1996, in Licensee Event Report (LER) number 96-04 .

As a result, VYNPC installed test connections and attempted to perfom Type C tests on these check valves at the next opportunity during the fall 1996 refueling outage. However, these valves failed the Type C testing because they were not designed to seal at the relatively low pressure differentials used in Type C tests. In lieu of replacing these valves with valves designed to pass Type C test requirements, VYNPC proposed to modify the containment isolation configuration of the RHR and CS systems, pursuant to the change provisions of 10 CFR 50.59, prior to restart from the fall 1996 refueling outage.

During a series of telephone conversations with the NRC staff concluding on October 3,1996, representatives of VYNPC described changes planned in the containment isolation configuration for the RHR and CS systems prior to restart from the fall 1996 refueling outage. The NRC staff requested VYNPC 9703070131 970303 PDR ADOCK OS000271 p PDR

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tc submit a summary of VYNPC's evaluation of these changes. VYNPC submitted

the requested information in a letter dated October 15, 1996. This letter was j supplemented on November 15, 1996. The following assessment of these changes

by the NRC staff is based on the Sformation submitted in these letters.

! 2.0 RACKGROUND

General Design Criteria of 10 CFR Part 50, Appendix A, address requirements i

for the containment isolation function of piping systems that penetrate primary containment. General Design Criterion (GDC) 55, " Reactor Coolant Pressure Boundary Penetrating Containment," defines acceptable configurations j of containment isolation valves (CIVs) for lines penetrating containment and i connected to the reactor coolant pressure boundary. In addition to listing l Specific acceptable containment isolation valve configurations, GDC 55 also provides for satisfying the containment isolation function "on some other i defined basis." t

! Because the RHR and the CS systems penetrate primary containment and are  !

! connected to the reactor coolant pressure boundary, VYNPC applied GDC 55 of

the General Design Criteria of 10 CFR Part 50, Aspendix A. The General Design

Criteria are requirements for plants which have >een more recently licensed

than Veraont Yankee. An acceptable alternative to satisfying GDC 55's "other

defined basis" provision is a configuration consisting of a closed system and i one containment isolation valve outside primary containment for each '

l containment penetration. This alternative configuration is described in l ANSI /ANS-56.2 N271-1976, " Containment Isolation Provisions for Fluid Systems,"

which is endorsed by NRC Regulatory Guide (RG) 1.141, " Containment Isolation Provisions for Fluid Systems," dated April 1978. This standard was modified

, in 1984 but the changes do not affect any conclusions in this assessment.

t l 3.0 EVALUATION i The previous containment isolation configuration on each RHR and CS system i injection line, as described in the Vermont Yankee FSAR, consists of one i manually operated motor operated valve (MOV) outside containment and one check i valve inside containment. In addition, each injection line contains a non-CIV MOV. These valves are the following:

i System / MOVs (Outside Containment) Check Valves (Inside l Division Outboard Inboard CIV QILtainment)

RHR A RHR-25A RHR-27A RHR-46A

) RHR B RHR-25B RHR-27B RHR-46B

CS A CS-IIA CS-12A CS-13A l CS B CS-118 CS-12B CS-138 i

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On a safety injection signal, both MOVs in each injection line receive a

signal to open. The motor operated CIV has remote manual closure capability.

i However, the non-CIV motor operated valve is prevented from closing by the RHR

or CS logic when a safety injection signal is present. In order to retain the

capability to cope with a single failure of the containment isolation function ,

i of these systems, VYNPC has chosen to rely on a single motor operated valve on I i

each injection line and the capability of the RHR and CS systems outside j containment to function as closed systems.

3.1 Evaluation of CS and RHR Systems as Closed Systems 1

l VYNPC's evaluation cites GDC 55, " Reactor Coolant Pressure Boundary )

! Penetrating Containment" which permits a different CIV configuration based on l

! "some other defined basis" and ANS-56.2 ANSI N271-1976, " Containment Isolation Provisions for Fluid Systems," which is endorsed by NRC Regulatory Guide (RG)

1.141, " Containment Isolation Provisions for Fluid Systems", dated April 1978, )

which permits the use of one CIV outside containment and a closed system j

outside containment. RG 1.141 provides the following criteria which must be

! satisfied in order to consider a system to be a closed system outside

! containment, i

j a. The closed system does not communicate with the outside atmosphere.

b. The closed system meets Safety Class 2 design requirements.

! c. The closed system can withstand temperature and pressure equal to the j containment design conditions,

d. The closed system can withstand the loss-of-coolant accident transient.

j e. The closed system meets seismic Category I design requirements.

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f. The closed system is protected against overpressure from thermal expansion of contained fluid when isolated, if required.

g. The closed system is protected against high energy line breaks.

h. The closed system is protected against loss of function from missiles.

1. The closed system is capable of being leak tested.

VYNPC's evaluation of the Vermont Yankee RHR and CS systems against each of the RG 1.141 closed-system criteria is contained in VYNPC's October ~15, 1996,

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letter to the NRC. In its letter, VYNPC noted that the RHR and the CS systems )

are included in Vermont Yankee's leakage reduction program required by Vermont Yankee Technical Specification 6.10, " Integrity of Systems Outside Containment." Based on this and its review of VYNPC's evaluation, the NRC staff concludes that the Vermont Yankee RHR and CS systems outside containment may be considered closed systems as defined in RG 1.141. Although the RHR and CS check valves inside primary containment will no longer function as CIVs, '

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these valves will remain operable with respect to all other required safety-

! related functions, such as pressure isolation. For these reasons, the change in containment isolation configuration for the RHR and CS systems is acceptable.

! 3.2 Evaluation for NRC Prior Approval i

VYNPC forwarded its 50.59 safety evaluation of this change by letter dated

! November 15, 1996. VYNPC applied the criteria in 10 CFR 50.59 to the change

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and detemined that removing the CIV designation from the RHR and CS injection line check valves inside containment:

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a. Does not involve a change to the Vermont Yankee Technical Specifications (TSs) because none of these check valves are listed in TS Table 4.7.2a, I

" Primary Containment Isolation Valves - Valves Subject to Type C Leakage Tests."

b. Does not involve an unreviewed safety question because:

(1) These check valves remain fully capable of performing all of their system and safety-related functions, other than containment isolation. In particular, these valves will continue to function as pressure isolation valves and be inspected and tested as specified by the applicable requirements of Section XI of the ASME Boiler and Pressure Vessel Code. Based on this, the NRC staff concludes that the change does not increase the probability of occurrence of an accident or malfunction of equipment important to safety, or create the possibility for an accident or malfunction of a different type than any evaluated previously in the safety analysis report.

(2) The previous and modified configurations are both acceptable, testable containment isolation valve configurations. The motor operated CIVs outside containment will still be subject to Type C Appendix J 1eakage rate testing. The RHR and CS systems outside containment meet the critaria of Regulatory Guide 1.141 for a closed system and are subject to leakage monitoring as required by the Vermont Yankee TS 6.10, " Integrity of Systems Outside Containment."

Therefore, the modified configuration is equivalent to the previous one. Based on this, the NRC staff concludes that the change does not result in an increase in radiological consequences or a reduction in the margin of safety as defined in the basis for any technical specification. . . ..

Based on the above, the NRC staff concludes that the RHR and CS system containment isolation function configuration change meets the criteria of 10 CFR 50.59 for changes that the licensee can make without prior Commission approval.

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4.0 CONCLUSION

The NRC staff concludes that YYNPC's modification of the RHR and CS system

, containment isolation function configuration is acceptable because it provides a level of protection equivalent to the previous configuration. This equivalence is recognized in an industry standard which has been endorsed by an NRC regulatory guide, as discussed above. In addition, based on its review of VYNPC's submittals describing the change and the associated 50.59 safety evaluation, the NRC staff concludes that the change does not require prior NRC approval .

Principal Contributors: R. Lobel C. Harbuck Dated: March 3, 1997

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