ML20212A664

Safety Evaluation Authorizing Relief Request RR-V-16 for Third 10 Yr Interval Inservice Testing Program

ML20212A664
Person / Time
Site:	Hatch
Issue date:	09/13/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20212A643	List: ML20212A641 ML20212A664
References
NUDOCS 9909170090
Download: ML20212A664 (3)

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4. UNITED STATES g ,y NUCLEAR REGULATORY COMMISSION

'* WASPINGTON, D.C. 20555-0001 i

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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION' i .

H RELATED TO THE THIRD TEN YEAR INTERVAL INSERVICE TESTING PROGRAM l SOUTHERN NUCLEAR OPERATING COMPANY.'INC.

EDWIN l. HATCH NUCLEAR PLANT. UNITS 1 AND 2 l

l DOCKET NUMBERS 50-321 AND 50-366 j l

1.0 INTRODUCTION

l- The Code of Federa/ Regulations (10 CFR) Section 50.55a, requires that inservice testing (IST)

l. of certain American Society of Mechanical Engineers (ASME) Code Class 1,2, and 3 pumps

- and valves be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code (the Code) and applicable addenda, except where alternatives have been authorized or relief has been requested by the licensee and granted by the Commission pursuant to paragraphs (a)(3)(i), (a)(3)(ii), or (f)(6)(i) of 10 CFR 50.55a. In proposing ,

alternatives or requesting relief, the licensee must demonstrate that: (1) the proposed altematives 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; l

or (3) conformance is impractical for its facility. Section 50.55a authorizes the Commission to l ' approve alternatives and to grant relief from ASME Code requirements upon making the

. necessary findings. NRC guidance contained in Generic Letter (GL) 89-04, " Guidance on Developing Acceptable Inservice Testing Programs," provides alternatives to the Code requirements determined acceptable to the staff. Further guidance is given in GL 89-04, Supplement 1, and NUREG-1482, " Guidelines for Inservice Testing at Nuclear Power Plants."

The third ten year interval program for IST of pumps and valves at Edwin I. Hatch Nuclear Plant, Units 1 and 2, began on January 1; 1996, and will end on December 31,2006. In accordance with the proposed alternative of Relief Request RR-G-1, which was approved in a

- letter dated August 29,1995, the applicable Codes used in the Hatch IST program are the

~ASME Operation and Maintenance (OM) Code-1990 for pumps and valves, with the exception l . of relief valves. The applicable Code for relief valves is the ASME OM Code-1995.

! Relief Request RR-V-16 was submitted by the licensee in a letter dated May 18,1999. The staff's findings with respect to authorizing alternatives and granting or denying the proposed )

l relief request is given below. j V .

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l 2.0 RELIEF REQUEST RR-V-16 l

l The licensee proposes an alternative to the requirements of Appendix I, paragraph I 1.3.6 for four rupture discs in the high pressure coolant injection (HPCI) system. The Code requires that l

Class 2 and 3 nonreclosing pressure relief devices (rupture discs) be replaced every 5 years, unless historical data indicates a requirement for more frequent replacement. The licensee proposes to replace the rupture discs at least once every 6 years.

2.1 Licensee's Basis for Reauestina Relief The licensee states:

The subject rupture discs are supplied by Continental Disc Corporation. Southern Nuclear Operating Company requested the supplier to perform cyclic testing, to destruction, of a disc that had previously been installed in the HPCI system at Plant Hatch.

The test disc was installed in an appropriate disc holder and flange assembly which simulated the installed configuration. The rupture disc assembly was cycled from full vacuum to 70% of the ambient burst pressure (219 psig). The cycle testing was conducted at ambient room temperature. Since a rupture disc is a differential pressure relief device, cycling conditions were achieved by placing a constant 15 psig pressure on the downstream side.of the rupture disc and cycling the upstream pressure from zero to 70% of the ambient burst pressure plus 15 psig. The 15 psig added to the upstream cycling pressure compensates for the constant 15 psig pressure on the down stream side. An electronic counter recorded each cycle. The test disc completed 2,788 cycles before failure occurred. The rupture disc burst in the normal fashion as with disc of this design.

The HPCI system is tested monthly at a maximum. Monthly testing results in approximately 72 tests during the operating cycles (i.e.,72 months). To meet the Code 5-year replacement frequency, the disc must be replaced every 3* refueling outage or after approximately 54 HPCI system tests. Therefore, a change from replacement every 54 months to every 72 months is insignificant when compared to the expected life of the disc as proven by the number of cycles required for the disc rupture by vender testing.

Plant Hatch operates on an 18-month fuel cycle. Replacement every 6 years results in replacement every 4* refueling outage whereas a 5-year replacement results in replacement every 3* refueling outage. Extension of the replacement frequency by 1 year will coincide with the fuel cycle for Plant Hatch. As proven by the vendor testing, the subject rupture discs have adequate margin for operation beyond the requested 6-year replacement frequency. Therefore, an adequate margin of safety is provided and the requested relief is warranted by 10CFR50.55a(a)(3)(i). )

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4 2.2 Alternative Testina The licensee proposes:

The subject rupture discs will be replaced at least once every 4* refueling outage.

3.0 EVALUATION The licensee requests relief from the requirements of Appendix 1, paragraph 11.3.6 for the following rupture discs in the HPCI system: 1E41-D003,1E41-D004,2E41-D003, and 2E41-D004. The Code requires that Class 2 and 3 rupture discs be replaced every 5 years,

, unless historical data indicates a requirement for more frequent replacement. This corresponds to the licensee replacing the discs every 35 refueling outage. The licensee proposes an alternative in which the rupture discs would be replaced every 6 years, resulting in their replacement every 4* refueling outage.

Cyclic testing of a previously installed rupture disc was performed for the licensee by Continental Disc Corporation. During testing, the rupture disc was cycled from full vacuum to 70% of the ambient burst pressure. Failure occurred after the disc was cycled 2,788 times.

. This cyclic testing is a conservative simulation of the pressure differential experienced by the rupture discs during monthly testing of the HPCI system. During monthly testing, the normal pressure exerted on the rupture discs is 50 psig, which corresponds to approximately 25% of the ambient burst pressure.

The licensee proposes a 6-year replacement frequency for these rupture discs. At this frequency, the discs would be exposed to 72 HPCI system tests or cycles. This is significantly less than the 2,788 cycles needed for failure of the test disc to occur. Therefore, the proposed alternative provides an acceptable level of quality and safety.

4.0 CONCLUSION

The proposed alternative to the requirements of Appendix I, paragraph I 1.3.6 for the four rupture discs in the HPCI system is authorized pursuant to 10 CFR 50.55a(a)(3)(i). The alternative provides an acceptable level of quality and safety and is authorized for the remainder of the third 10-year interval for Edwin 1. Hatch Nuclear Plant, Units 1 and 2.

Principal Contributor: M. Kotzalas Date: September 13, 1999

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