ML20237D493

Safety Evaluation Approving Request to Use ASME Section XI Code Case N-498-1 at STP

ML20237D493
Person / Time
Site:	South Texas
Issue date:	08/21/1998
From:	NRC (Affiliation Not Assigned)
To:
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ML20237D483	List: ML20237D481 ML20237D493
References
NUDOCS 9808260234
Download: ML20237D493 (5)

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l SAFETY EVALUATION BY THE OFFICE OF NUCl FAR REACTOR REGULATION OF THE FIRST TEN-YEAR INTERVAL INSERVICE INSPECTION PROGRAM PLAN REQUEST TO USE ASME SECTION XI CODE CASE N-498-1 STP NUCLFAR OPERATING COMPANY SOUTII TEXAS PROJECT. UNITS 1 AND 2 (STP)

DOCKET NOS. 50-498 AND 50-499

1.0 INTRODUCTION

The Technical Specifications for STP state that the inservice inspection (ISI) and testing of the American Society of Mechanical Engineers (ASME) Code Class 1,2, and 3 components shall be performed in accordance with Section XI of the ASME 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).10 CFR 50.55a(a)(3) states that alternatives to the requirements of paragraph (g) may be used, when authorized by the Nuclear Regulatory Commission (NRC), if (i) the proposed alternatives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Pursuent 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 ten-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) on the date twelve months prior to the start of the 120-month intervci, subject to the limitations and modifications listed therein. The applicable edition of Section XI of the ASME Code for STP during the first ten-year ISI intervalis the 1983 Edition through the Summer 1983 Addenda. 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 9808260234 980821 PDR ADOCK 05000498 G PDR

2-altemative requirements that are determined to be authorized by law; will not endanger life, 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 June 2,1998, STP Nuclear Operating Company (the licensee) requested approval for the implementation of the ASME Section XI Code Case N-498-1, dated May 11, 1994," Alternative Rules for 10-Year System Hydrostatic Testing for Class 1,2, and 3 Systems,Section XI, Division 1," pursuant to 10 CFR 50.55a(a)(3)(i) in lieu of the requirements of Table IWD-2500-1 applicable to Code Class 3 components for STP.

The staff has reviewed and evaluated the licensee's request and the supporting information to use Code Case N-498-1 as an alternative to the Code requirements for both units of STP.

2.0 DISCUSSION Recuest for Authorization to Imolement Alternatives to Code Requirements Contained in Code

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Case N-498-1. Alternative Rules for 10-Year System Hydrostatic Testina for Class 1. 7 and 3 SvstemsSection XI. Division 1

, System /Comoonent Affected by Use of Code Case ASME Code Class 3 Components Code Requirement Affected bv Use of Code Case Table IWD-2500-1 requires that a system hydrostatic test of all Code Class 3 pressure retaining components be performed every 10 years. ASME Code Class 3 generally includes those system components or portions of systems important to safety that are designed to provide cooling water and auxiliary feedwater for the front-line systems.

Ucensees' Basis for Use of Code Case Hydrostatic pressure testing of ASME Code Class 3 components is required in order to satisfy the referenced Code. However, the South Texas Project has concluded that such Code Hydrostatic testing requirements impose significant hardship, while adding marginal (if any) value without a compensating increase in the level of quality and safety.

Hydrostatic testing performed under the referenced Code subjects the components to a relatively small increass in pressure over the nominal operating pressure and is not intended to present a significant (potentially destructive) challenge to the pressure boundary integrity.

Accordingly, hydrostatic pressure testing is primarily regarded as a means to enhance leakage detection during examination of components under pressure, rather than a measure of the structuralintegrity of the components.

Furthermore, system leakage tests at nominal operating pressure are conducted at a minimum of once each inspection period per inspection Program B for Code Class 3 systems. Leaks w_______-__-___________--_ . _ - _ _ -

may also be identified during routine system walkdowns by plant operators and system engineers.

1 Hardships associated with hydrostatic testing performed in accordance with the referenced Code are as follows:

o Hydrostatic pressure testing frequently requires significant effort in preparation and performance. Since the testing is of questionable benefit, the required resources could be better spent in activities that more effectively assure plant safety and reliability.

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

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

In addition, hydrostatic tests have the added potential to initiate leak paths at mechanical connections (e.g., valve packing and gland, flange joints).

Licensees' Prooosed Alternative to Code Requirements Code Case N-498-1 is proposed as an alternative to Subsection LWD for leak testing of Code Class 3 components. ASME Code Case N-498 has been approved for use previously and is listeo in Regulatory Guide (RG) 1.147," Inservice inspection Code Case Acceptability ASME Section XI Division 1," Revision 11. This approval of Code Case N-498 allows the South Texas Project to conduct in-service leak testing of Code Class 1 and system pressure testing of Code Class 2 components at nominal operating pressure in lieu of hydrostatic testing. Approval of Code Case N-498-1 will allow system pressure testing of Code Class 3 components similar to what is currently permitted for Code Class 2 components.

To implement the alternative rules of Code Case N-498-1, the following rules apply; o A system pressure test shall be conducted at or near the end of each inspection interval or during the same inspection period of each inspection interval of Inspection Program B (paragraph IWA-2410).

o The boundary subject to test pressurization during the system pressure test shall extend to all Class 3 components included in those portions of systems required to operate or support the safety system function up to and including the first normally closed valve, including a safety or relief valve, or valve capable of automatic closure when the safety function is required.

o Prior to performing the VT-2 visual examination, the system shall be pressurized to nominal operating pressure for at least four hours for insulated systems and ten

4 minutes for noninsulated systems. The system shall be maintained at nominal operating pressure during performance of the VT-2 visual examination.

o The VT-2 visual examination shall include all components within the boundary identified above, o Test instrumentation requirements of IWA-5260 are not applicable.

This proposed alternative to the Code requirement will provide reasonable assurance that flaws will be discovered.

3.0 EVALUATION The licensee has requested approval for the implementation of the alternative rules of ASME Section XI Code Case N-498-1 dated May 11,1994," Alternative Rules for 10-year System Hydrostatic Testing for Class 1,2, and 3 Systems," in lieu of 10-year hydrostatic testing of l Class 1,2, and 3 systems. Use of Code Case N-498 for Class 1 and 2 systems was previously approved by the NRC in RG 1.147, Rev.11. The rules for Class 1 and 2 in N-498-1 are unchanged from N-498. The staff found the use of N-498 to be acceptable since the alternative provided reasonable assurance of operational readiness, and compliance with the specified Code requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Code Case N-498-1, however, encompasses Class 3 components and specifies requirements for Class 3 that are idertical to those for Class 2 components. In lieu of the 10-year hydrostatic pressure testing at or near the end of the 10-year interval, Code Case N-498-1 requires that a visual examination (VT-2) be performed in conjunction with system leakage testing in accordance with paragraph IWA-5000. Class 3 systems do not normally receive the amount l and/or type of non-destructive examinations that Class 1 and 2 systems receive. While Class 1 1 and 2 system failures are relatively uncommon, Class 3 leaks occur more frequently and the failure mode typically differs. The most common cause of failures in Class 3 systems are i erosion-corrosion, microbiologically induced corrosion, and general corrosion. Licensees  ;

generally have programs in place for prevention, detection, and evaluation of these degradation i mechanisms. Industry experience further demonstrates that leaks are seldom discovered as a result of hydrostatic test pressure driving a pre-existing flaw through-wall, rather, they are found in most cases at normal operating condition.

Licensees incur considerable time and radiation dose to conduct a hydrostatic test in comparison to a system leakage test for a minimal amount of increased assurance provided by a slightly higher pressure associated with hydrostatic test of Class 3 systems. Therefore, the staff finds that compliance with the ASME Section XI hydrostatic testing requirements as opposed to system leakage test of Class 3 systems, results in hardship and/or unusual difficulty to licensees without a compensating increase in the level of quality and safety.

4.0 CONCLUSION

The staff has evaluated the information provided by the licensee in support of its request for relief to implement Code Case N-498-1 as an altemative to the 10-year system hydrostatic test required by the applicable ASME Code,Section XI. The staff has determined that the proposed testing in accordance with the rules of Code Case N-498-1 provides reasonable assurance of operational readiness, and compliance with the Code requirement would result in hardship without a compensating increase in quality and safety. Therefore, licensee's proposed altemative to use Code Case N-4981 in lieu of the Code-required 10-year hydrostatic test, is authorized, pursuant to 10 CFR 50.55a(a)(3)(ii) for STP during the first inspection interval.

The use of Code Case N-498-1 is authorized for the first inspection interval until such time as the code case is approved by reference in RG 1.147. At that t:me, if the licensee intends to continue to imp nent this code case, the licensee is to follow all provisions in Code Case N-498-1 with limitations issued in RG 1.147, if any.

Principal Contributor: P. Patnaik Date: August 21, 1993 1

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