ML20211Q673

Safety Evaluation Accepting First 10-yr Interval ISI Program Plan Request for Relief from ASME Code Case N-498

ML20211Q673
Person / Time
Site:	South Texas
Issue date:	09/09/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20211P794	List: ML20211P787 ML20211Q673
References
NUDOCS 9909150117
Download: ML20211Q673 (4)

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j. NUCLEAR REGULATORY COMMISSION WASMNGTON, D.C. 30es&c001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION FIRST 10-YEAR INTERVAL INSERVICE INSPECTION PLAN REQUEST FOR RELIEF FROM ASME CODE CASE N-498 (RR-ENG-31)

STP NUCLEAR OPERATING COMPANY l SOUTH TEXAS PROJECT. UNITS 1 AND 2 DOCKET NOS. 50-498 AND 50-499

1.0 INTRODUCTION

The inservice inspection (ISI) of the American Society of Mechanical Engineers (ASME) Code i Class 1,2, and 3 components shall be performed in accordance with Section XI of the ASME l Boiler and Pressure Vessel Code and applicable addenda as required by 10 CFR 50.55a(g),

except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).' The regulation at_10 CFR 50.55a(a)(3) states that altematives to the requirements of paragraph (g) may be used, when authorized by the NRC, if (i) the proposed alternatives would provide an acceptable level of quality and safety or (ii) compliance with the i specified requirements would result in hardship or unusual difficulties without a compensating increase'in the level of quality and safety.

Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1,2, and 3 components (including supports) shall meet the requirements,'except the design and access provisions and the

- preservice examination requirements, set forth in the ASME Code,Section XI, " Rules for Inservice inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that inservice examination of components and system pressure tests conducted during the first 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The applicable ASME Code,Section XI, for the South Texas Project, Units 1 and 2, first 10-year ISI interval is the 1983 Edition through Summer 1983 addendum. The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b) subject to the limitations and modifications listed therein and subject to Commission approval.

Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission in support of that determination and a request made for relief from the ASME Code requirement. After evaluation of the determination,

. pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose alternative requirements that are determined to be authorized by law, will not endanger life, j

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s 2 property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed.

By letter dated July 6,1999, South Texas Project Nuclear Operating Company submitted a request for relief from the requirements of ASME Section XI, Code Case N-498," Alternative Rules for 10-year Hydrostatic Pressure Testing for Class 1 and 2 Systems,Section XI, Division 1," which has been adopted in Regulatory Guide 1.147, Revision 11. " Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1," for the reactor vessel head vent line beyond the first isolation valve that is normally isolated from reactor coolant system (RCS) pressure.

The licenses has stated that pressurization of the line between the two isolation valves to full RCS pressure during a system leakage test required under Code Case N-498 would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Pursuant to 10 CFR 50.55a(a)(3)(ii), the staff has evaluated the information provided by the licensee in granting relief from the requirement of the Code Case N-498, for the Class 1 portion of reactor vessel head vent line between the isolation valves.

2.0 DISCUSSION 2.1 Comoonents for Which Relief is Reauested The reactor vessel head vent line,1 inch in diameter, designated as RC1(2)048BB1 downstream of and including isolation valve RC0132, classified as ASME Code Class 1.

2.2 Code Reauirement ASME Code Case N-498 allows use of a system leakage test (IWB-5221)in lieu of a hydrostatic test. Code Case N-498 requires that the boundary subject to test pressurization during the system pressure test extend to all Class 1 pressure-retaining components within the system boundary.

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2.3 Licensee's Reauested Relief from Code Reauirement 1 The' South Texas Project requests relief from system leakage testing at full RCS pressure of 1 the Class 1 portion of piping in the reactor vessel head vent system beyond the first isolation J valve and extending to the second closed valve at the boundary extremity that is normally i isolated from RCS pressure.

Under this relief, the pressure-retaining boundary during the 10-year hydrostatic test shall correspond to the RCS boundary, with both isolation valves in the normal position, that is required for normal reactor operation. VT-2 examination shall, however, extend to and include the second closed valve at the boundary extremity. This portion of the Class 1 boundary will be VT-2 inspected at a stabilization pressure achieved based on seat leakage from the first isolation valve.

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w h~ .-37 2.4 Licensee's Basis for Relief from Code Reauirements (as stated)

' Inservice leak testing of ASME Code Class 1 components is required in order to satisfy Code Case N-498. However, the South Texas Project has concluded that

" compliance with the Code requirements to apply Reactor Coolant System operating pressure to test the subject' components beyond the first isolation valve imposes significant hardships without a compensating increase in the level of quality and safety.

Testing the subject components at Reactor Coolant System operating pressures would require preparation of a special test procedure because the test would place the plant in a lineup that has not been previously used or evaluated. An associated blind flange normally installed in the line would have to be disassembled and the affected Class 1 line pressurized using a hydrostatic test pump. Resulting hardships are as follows:

, ' Special valve lineups for these tests add unnecessary challenges to maintaining system configuration.

Tests performed inside the radiologically restricted area increase the total exposure to plant personnel modifying and restoring system lineups and removing contaminated test equipment.

f-System leakage tests expose components to conditions above their normal operating pressure and temperature, j .

- Use of a single blind flange for isolation from the reactor containment j building environment could result in uncontrolled leakage from these l systems and potential damage to permanent plant equipment.

Use of a single blind flange for isolation could pose a significant personnel safety hazard.

3.0 EVALUATION t

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The staff has reviewed the licensee's relief request and basis for the hardship to the licensee in performing system leakage test in accordance with the requirement of Code Case N-498 for the Class 1 portion of reactor vessel head vent piping that is normally isolated from RCS pressure during operation. The component is the portion of piping downstream of the first isolation valve which extends to and includes the normally closed second isolation valve in the head vent system. This component is located inside the containment and.has no function in regard to containment isolation. When a system leakage test is performed at operating pressure and temperature with the first isolation valve closed, the portion of piping beyond the first isolation valve extending to the second isolation valve is normally at a much lower pressure than the RCS pressure, if the licensee were to perform the system leakage test up to and including the Class 1 boundary extremity by opening the first isolation valve, this would result in single valve protection of the reactor coolant boundary and may result in inadvertent loss of RCS inventory if i the second isolation valve allows sufficient leakage. Furthermore, there is no test connection to pressurize the piping between the isolation valves, and pressurizing this segment of piping to

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' RCS pressure would require a separate hydrostatic test pump using a special test procedure with a comphx valve lineup. This evolution would be performed inside the bioshield, and it would result in high radiation exposure to test personnel.

- The staff has evaluated compensatcry factors that provide reasonable assurance of pressure boundary integrity. The licensee performs a system leakage test during each refueling outage j

~ for Class 1 systems in Mode 3 at normal operating pressure / temperature. Any leakage past the first isolation valve would pressurize the segment of piping for which relief is being sought. The 1 licensee also performs a VT-2 visual examination of the subject piping including the boundary isolation valves. In addition to the pressure testing, an !nspection for boric acid leakage is also ,

performed for the subject components during each refueling outage to ensure leak tight {

integrity of the components. These components, however, function to provide redundant I protection if the line downstream of the first isolation valve were to fail, the first isolation valve l

. will continue to provide pressure boundary protection and any seat leakage past the valve will j cause the containment airborne activity to increase, which can be detected by the airborne activity leak detection system.

The staff, therefore, has determined from the above considerations that compliance with the requirement of Code _ Case N 498 during system leakage test of the subject line downstream of l J the first isolation valve would cause hardship without a compensating increase in the level of l quality and safety. l

4.0 CONCLUSION

I l The staff concludes that the pressure-retaining boundary of the reactor vessel head vent line during the 10-year hydrostatic test shall correspond to the RCS boundary, with both isolation valves in the normal position for reactor startup/ operation. The VT-2 visual examination shall, however, extend to and include the second closed valve at the boundary extremity. This portion of the Class 1 boundary will be VT-2 inspected at a stabilization pressure achieved based on l

! seat leakage from the first isolation valve. In regard to the system leakage test of the portion of the Class 1 piping downstream of the first isolation valve, compliance with the requirement of Code Case N-498 would cause hardship or unusual difficulty without a compensating increase in the level of quality and safety. Therefore, the licensee's alternative in RR-ENG-31 as discussed above is authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for the first 10-year j inspection interval for South Texas Project Units 1 and 2.

Principal Contributor: P. Patnaik Date: September 9, 1999 >

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