ML20126C122

Safety Evaluation Authorizing Util to Continue Current Test Method for Interim Period,Based on Util Plans to Develop & Implement Use of non-intrusive Testing Techniques for Check Valves Following 1993 Unit 2 Refueling Outage

ML20126C122
Person / Time
Site:	North Anna
Issue date:	12/04/1992
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20126C109	List: ML20126C106 ML20126C122
References
NUDOCS 9212220379
Download: ML20126C122 (5)

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\...../ SAFETY EVALVATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO THE INSERVICE TESTING PROGRAM RE0 VESTS FOR RELIEF NORTH ANNA POWER STATIONS UNITS 1 AND 2

@CKET NUMBERS 50-338 AND 50-339

1.0 INTRODUCTION

The Code of Federal Regulations,10 CFR 50.55a, requires that inservice testing (IST) of certain ASME Code Class 1, 2, and 3 pumps ed valves be performed in accordance with Section XI of the ASME Boiler nu Pressure Vessel Code and applicable Addenda, except where specific written relief has been requested by the licensee and granted by the Commission pursuant to 10 CFR 50.55a(f)(6)(i) or where the alternative has been authorized pursuant to 50.55a(a)(3)(1) or (a)(3)(ii). In requesting relief, the licensee must demonstrate that: (1) the proposed alternatives provide an acceptable level of quality and safety; (2) compliance would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety; or (3) conformance is impractical for its facility. The NRC guidance contained in Generic letter (GL) 89-04, " Guidance on Developing Acceptable IST Programs," provided alternatives to the Code requirements determined to be acceptable to the staff.

10 CFR 50.55a authorizes the Commission to grant relief from or approve alternatives to ASME Code requirements upon making the necessary findings.

The NRC staff's findings with respect to granting or not granting the relief requested or authorizing the proposed alternatives as part of the licensee's IST program are contained in this Safety Evaluation (SE).

This SE covers Relief Requests V-72 and V-73 for North Anna Power Station, Units i and 2, respectively, as described in Virginia Electric and Power Company's (the licensee) letter dated February 21, 1992. The licensee's program is based on the requirements of the 1983 Edition of the ASME Section XI Code through the Summer of 1983 Addenda. The licensee is requesting interim relief from the Code requirements for testing the main steam line stop check valves in order to have time to develop appropriate closure verification test methods. Similar relief has been requested for the Surry Units-1 and 2 main steam line stop check valves. The licensee intends to evaluate one or more non-intrusive test methods during the next Surry Unit 2 refuelirg outage.

The methods chosen for closure verification of these valves will be used on both the Surry and the North Anna units during subsequent cold shutdowns.

2.0 RElli F RE0 VESTS V-72 AND V-73 The licensee requested interim relief from ASME Code Section XI, IWV-3520

" Tests for Check Valves," requirements for exercising valves during plant operation at least once every 3 months to the closed position. The valves in l

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Relief Requests V-72 and V-73 are non-return main steam line stop check valves. The valves involved are 1-MS-NRV-101 A, B and C for Unit I and 2-MS- l NRV-201 A, B and C for Unit 2. j 2.1 BASIS FOR INTERIM REllEF l l

The licensee currently exercises and verifies these stop check valves closed by driving the valve stem down onto the disk using the valve motor operator, after the main steam system has been isolated, during plant cold shutdown.

The licensee justified cold shutdown testing because full- or part-stroke exercising of these valves quarterly at power could result in a turbine or-reactor trip.

The licensee considered the current method a valid ASME Code closure test for stop check valves based on the staff response to Question #25, conveyed in_ the

" Minutes of the Public Meeting on Generic Letter 89-04," issued on October 25, 1989. However, based on the supplement to the minutes issued on September 26, 1991, which clarified the response to Question #25 with regards to closure verification of stop check valves, the licensee finds the test method is not adequate. Condition "C" of the supplement states, "If prompt closue of these valves on cessation or reversal of flow is required to accomplish a safety-related function, closure must be verified by reverse flow testing or such other positive means as acoustic monitoring or radiography."

The licensee considers reverse flow testing is not practical at power or during cold shutdown. The stop check valve is needed during cold shutdown to ensure double valve isolation of the secondary plant piping from the steam ,

source.

2.2 ALTERNATE INTERIM TESTING The licensee proposes to develop, test and evaluate one or more non-intrusive methods during the 1993 Surry Unit 2 refueling outage. The methods involve application-during the cold shutdown process. The most practical method tested will be selected and implemented at both North Anna units during subsequent cold shutdowns.

During the interim, prior to implementing the new test methods,_ the licensee proposes to continue the current test method every cold shutdown at the North Anna Power Station, Units 1 and 2. The licensee states that the current test of driving the stem onto the disk is adequate to demonstrate the disk is seated in the closed position and free movement of the disk is demonstrated when steam flow is established, at full power, and the disk travels from the seat to the full-open position.

2.3 EVALUATION The main steam non-return valves 1-MS-NRV-101 A, B and C and 2-MS-NRV-201 A, B and C have a safety-related function to prevent reverse flow and limit blowdown to a single steam generator during a postulated steam line break.

i*

l The licensee has requested interim relief from ASME Code Section XI, IWV-3520, " Tests for Check Valves," requirements for verifying valve closure every three months during plant operation.

The licensee currently exercises these stop check valves to the cli sed position during cold shutdown by driving the stem down onto the disi using the valve motor operator. Exercising these valves during plant cold shutdown is justified because closing these valves quarterly during power operations could result in a turbine or reactor trip.

Based on th'e supplement response to Question #25 in "The Minutes of the Public Meeting Held on Generic letter 89-04," issued on September 26, 1991, the licensee must verify closure by reverse flow testing or such other positive means as acoustic monitoring or radiography.

The licensee has requested an interim period to evaluate in-house and vendor non-intrusive test methods capabilities, develop procedures and implement a test program for application during the cold shutdown process. The licensee will test one or more methods during the Surry Power Station Unit 2, 1993 refueling outage and implement the most practical test method, at the North Anna Power Station Units 1 and 2, following the refueling outage of Surry Unit 2. In the interim, the licensee proposed to proceed with the current test method to demonstrate valve closure while free movement of the disk is demonstrated by its travel from the seat to the full-open position with steam flow during ascension to full power.

It would be impractical to exercise these valves full- or part-stroke during power operations because it could cause a turbine or reactor trip. The licensee proposes to develop and determine the practicality of using a non-intrusive method of closure verification testing during the process leading to cold shutdown.

The licensee needs time to develop an adequate test method to verify closure of these valves on cessation or reversal of flow for compliance with Code requirements and NRC guidance. The licensee's proposed interim test to continue the current method to demonstrate valve closure by driving the stem down onto the disk and free movement of the disk demonstrated by travel of the disk from the clued to open position during ascension to full power steam flow provides an acceptable level of quality and safety for an interim period.

2.4 CONCLUSION

S Based on (1) the licensee's plans to develop and implement the use of non-intrusive testing techniques for these valves, (2) consideration of the time involved to develop and implement a non-intrusive monitoring alternative test, and (3) the alternative test method providing an acceptable level of quality and safety for an interim period, the alternative for the licensee to

continue' the current test method for an interim period is authorized pursuant- i to 10 CFR 50.55a(a)(3)(1) provided the licensee implements a non-intrusive test method for these valves following the 1993 Surry Unit 2 refueling outage.

Principal Contributor: F. Grubelich Date: December 4, 1992

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