ML18153B221
| ML18153B221 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 02/06/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18153B220 | List: |
| References | |
| NUDOCS 9502090056 | |
| Download: ML18153B221 (5) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555--0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION REQUESTS FOR RELIEF
1.0 INTRODUCTION
FOR VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION, UNIT 2 DOCKET NO.: 50-281 The Technical Specifications for Surry Power Station, Unit 2, state that the inservice inspection 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 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 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 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 interval, subject to the limitations and modifications listed therein. The 1980 Edition, with Winter 1980 Addenda, of Section XI is the applicable edition of the ASME Code for the Surry Power Station, Unit 2 Second 10-year inservice inspection (ISI)
Interval. The comportents (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.SSa(g)(S), 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 9502090056-950206 1 PDR ADOCK 0500028 p
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, 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.
In a letter dated July 12, 1994, the licensee, Virginia Electric and Power Company (VEPCO), proposed an alternative examination to the requirements of the American Society of Mechanical Engineers {ASME) Boiler and Pressure Code,Section XI.
VEPCO 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 IO-Year System Hydrostatic Testing for Class 1, 2, and 3 Systems" pursuant to 10 CFR 50.55a{a)(3) for IO-year hydrostatic testing on Class 1, 2, and 3 systems.
2.0 EVALUATION 2.1 Licensee's Request This submittal is requesting approval pursuant to 10 CFR 50.55a(a){3) for interim use of Code Case N-498-1, "Alternative Rules for IO-Year System Hydrostatic Testing for Class 1, 2, and 3 Systems" for the upcoming Surry Unit 2 outage.
2.1.1 Licensee's Component Identification Class 1, 2, and 3 systems subject to hydrostatic testing.
2.1.2 ASME Code,Section XI, RequirementsSection XI, Table IWB-2500-1, Category 8-P {for Class 1), Table IWC-2500-1, Category C-H (for Class 2), and Table IWD-2500-1, Categories 0-A, 0-8, and 0-C
{for Class 3) contain the requirements for system hydrostatic and leakage testing. The Code requires system hydrostatic testing once per IO-year interval at or near the end of the interval.
2.1.3 Licensee's Proposed Alternative Testing The licensee proposed to use the alternative contained in Code Case N-498-1, a system leakage test, in lieu of hydrostatic testing, for Class 1, 2, and 3 Systems.
2.1.4 Licensee's Basis for Relief The licensee submitted the following reasons for relief:
Surry Unit 2 is scheduled to complete its second interval, IO-year inservice inspections during its next refueling outage, which is currently scheduled to begin January 14, 1995.
Code Case N-498-1 now provides an alternative to the Class 3, as well as the Class I and 2 (N-498} hydrostatic test Code requirements (ASME Section XI 1980 Edition, Winter 1980 addenda}.
Planning requirements 2
associated with this outage requires that advance approval for use of Code Case N-498-1 be obtained in lieu of the normal Regulatory Guide 1.147 revision process.
Hydrostatic tests are historically difficult to perform, frequently requiring extended test duration, while non-safety related issues such as maintenance boundary valve isolation problems are resolved. This adversely affects exposure accumulated by test personnel and system tag-out duration.
Code Case N-498-1 provides increased testing flexibility, allowing testing to be performed at nominal operating pressure, therefore, significantly reducing the number of test blocks, system tag-outs, and corresponding boundary valves required to complete testing.
This flexibility is accomplished while maintaining an acceptable level of safety and quality by the ASME Code consensus process.
Code Case N-498-1 will continue to provide assurance of component structural integrity as intended by the ASME Code and, as such, it is requested that interim use of the Code Case be approved for the upcoming Surry Unit 2 outage.
2.1.5 Evaluation Information prepared in conjunction with ASME Code Case N-498-1 notes that the system hydrostatic test is not a test of the structural integrity of the system but rather an enhanced leakage test. That this was the original intent is indicated in a paper by S.H. Bush and R.R. Maccary, "Development of In-Service Inspection Safety Philosophy for U.S.A. Nuclear Power Plants," ASME, 1971.
Piping components are designed for a number of loadings that would be postulated to occur under the various modes of plant operation. Hydrostatic testing only subjects the piping components to a small increase in pressure over the design pressure and therefore does not present a significant chal-lenge to pressure boundary integrity since piping dead weight, thermal expansion, and seismic loads, which may present far greater challenge to the structural integrity of a system than fluid pressure, are not part of the loading imposed during a hydrostatic test. Accordingly, hydrostatic pressure testing is primarily regarded as a means to enhance leakage detection during the examination of components under pressure, rather than as a measure to determine the structural integrity of the components.
VEPCO 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 IO-Year System Hydrostatic Testing for Class 1, 2, and 3 Systems" in lieu of IO-year hydrostatic testing of Class 1, 2, and 3 systems.
The NRC previously approved Code Case N-498, "Alternative Rules for IO-Year System Hydrostatic Testing For Class I and 2 Systems" in RGI.147.
The rules for Code Class 1&2 in N498-l are unchanged from N-498.
The staff found N-498 acceptable because the alternative provided adequate assurance and because compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
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e Revision N-498-1 encompasses Class 3 components and specifies requirements for Class 3 that are identical to those for Class 2 components.
In lieu of IO-year hydrostatic pressure testing at or near the end of the IO-year interval, Code Case N-498-1 requires a visual examination (VT-2) be performed in conjunction with a system leakage testing using the 1992 Edition of Section XI, in accordance with paragraph IWA-5000.
Currently, licensees incur considerable time, radiation dose, and dollar resources carrying out hydrostatic test requirements. A significant amount of effort may be necessary (depending on system, plant configuration, Code class, etc.) to temporarily remove or disable code safety and/or relief valves to meet test pressure requirements.
The safety assurance provicled by the enhanced leakage gained from a slight increase in system pressure during a hydrostatic test are offset or negated by the following factors: having to gag or remove code safety and/or relief valves, placing the system in an off-normal state, erecting temporary supports in steam lines, possible extension of refueling outages, and resource requirements to set up testing with special equipment and gages.
Class 3 systems do not normally receive the amount and/or type of Non-Destructive Examinations that Class I and 2 systems receive. While Class I and 2 system failures are relatively uncommon, Class 3 leaks occur more frequently and the failure mode typically differs. Based on a review of Class 3 system failures requiring repair for the last 5 years in Licensee Event Reports and the Nuclear Plant Reliability Data System databases, the most common causes of failures are erosion-corrosion (EC), microbiologically induced corrosion (MIC), and general corrosion. Licensees generally have programs in place for prevention, detection, and evaluation of EC and MIC.
Leakage from general corrosion is readily apparent to inspectors when performing a VT-2 examination during system pressure tests. The industry indicates that experience has demonstrated that leaks are not being discovered as a result of hydrostatic test pressures propagating a preexisting flaw through wall. They indicate that leaks in most cases are being found when the system is at normal operating pressure.
Giving consideration to the minimal amount of increased assurance provided by the increased pressure associated with a hydrostatic test versus the pressure for the system leakage test and the hardship associated with performing the ASME Code required hydrostatic test, the staff finds that compliance with the Section XI hydrostatic testing requirements results in hardship and/or unusual diffi~ulty for the licensees without a compensating increase in the level of quality and safety. Accordingly, the licensee's proposed alternative, use of Code Case N-498-1 for Code Class 1, 2, and 3, is authorized for Surry Power Station, Unit No. 2, pursuant to I0CFRS0.55a(a)(3)(ii).
VEPCO's alternative is authorized until such time as the Code Case is published in a future revision of Regulatory Guide 1.147. At that time, if the licensee intends to continue to implement this code case, the licensee is to follow all provisions in Code Case N-498-1, with limitations issued in Regulatory Guide 1.147, if any.
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3.0 CONCLUSION
The staff evaluated the information provided by the VEPCO in support of its request for relief. Based on the information submitted, the alternative for hydrostatic testing contained in the licensee's proposal is authorized pursuant to 10 CFR 50.55a(a}(3}(ii} as compliance ~ith the specified hydrostatic testing requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
Contributor:
K. Battige D. Tamai, NRR 5