ML18101A596
| ML18101A596 | |
| Person / Time | |
|---|---|
| Site: | Salem, Hope Creek  |
| Issue date: | 03/17/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML18101A595 | List: |
| References | |
| RTR-REGGD-01.147, RTR-REGGD-1.147 NUDOCS 9503240199 | |
| Download: ML18101A596 (6) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555--0001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION INSERVICE INSPECTION REQUESTS FOR RELIEF FOR PUBLIC SERVICE ELECTRIC AND GAS COMPANY SALEM NUCLEAR GENERATING STATION, UNITS I AND 2 HOPE CREEK GENERATING STATION DOCKET NOS. 50-272. 50-3II. AND 50-354 I.O INTRODUCTION The Technical Specifications for Salem and Hope Generating Stations state that the inservice inspection and testing of the American Society of Mechanical Engineers (ASME} Code Class I, 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 IO CFR 50.55a(g}, except where specific written relief has been granted by the Commission pursuant to IO CFR 50.55a (g}(6}(i}.
Part 50.55a(a}(3} of Title IO of the Code of Federal Regulations 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 IO CFR 50.55a(g}(4}, ASME Code Class I, 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 lnservice 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 IO CFR 50.55a(b} on the date I2 months prior to the start of the I20-month interval, subject to the limitations and modifications listed therein. The applicable edition of Section XI of the ASME Code for:
(I} Salem, Unit I, Second IO-year inservice inspection (ISI}
interval is the I983 Edition with the Summer I983 Addenda, (2} Salem 2, second IO-year ISI interval is the I986 Edition, and (3} Hope Creek, first IO-year ISI interval is the I983 Edition with the Summer I983 Addenda.
The components (including supports} may meet requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in IO CFR 50.55a(b),
subject to the limitations and modifications listed therein and subject to Commission approval.
~ -~
--9503240199 950317 PDR ADOCK 05000272 P
PDR 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 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 October 19, 1994, the licensee, Public Service Electric and Gas Company (PSE&G), proposed an alternative examination to the requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Code,Section XI.
PSE&G 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" pursuant to 10 CFR 50.55a(a)(3) for 10-year hydrostatic testing on Class 1, 2, and 3 systems; and requested approval for the implementation of the alternative rules of ASME Section XI Code Case N-524, dated August 9, 1993, "Alternative Examination Requirements for Longitudinal Welds in Class 1 and 2 Piping,Section XI, Division l," pursuant to 10 CFR 50.55(a)(3).
2.0 EVALUATION 2.1 Code Case N-498-1 2.1.1 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 B-P (for Class 1), Table IWC-2500-1, Category C-H (for Class 2), and Table IWD-2500-i, Categories D-A, D-B, and D-C (for Class 3) contain the requirements for system hydrostatic and leakage testing. The Code requires system hydrostatic testing once per 10-year interval at or near the end of the interval.
2.1.3 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 Basis for Relief
.The licensee's October 19, 1994, letter provided the following basis for use of Code Case N-498-1:
"PSE&G has reviewed the referenced Code Cases and concurs with the ASME assessment that the use of both Code Cases would provide an acceptable level of quality and safety."
2.I.5 Evaluation/Conclusions Information prepared in conjunction with ASME Code Case N-498-I 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, I97I.
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.
PSE&G requested approval for the implementation of the alternative rules of ASME Section XI Code Case N-498-I, dated May 11, I994, "Alternative Rules for IO-Year System Hydrostatic Testing for Class I, 2, and 3 Systems" in lieu of IO-year hydrostatic testing of Class I, 2, and 3 systems.
The licensee may already use N-498, "Alternative Rules for IO-Year System Hydrostatic Testing for Class I, and 2 Systems" since use of Code Case N-498 for Class I and 2 systems was previously approved by the NRC in Regulatory Guide I.I47, Rev. II.
The rules for Code Class I and 2 in N-498-I 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.
Revision N-498-I 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-I requires a visual examination (VT-2) be performed in conjunction with a system leakage test in accordance with paragraph IWA-5000.
Currently, licensees incur considerable time and radiation dose 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 provided 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 1 and 2 systems receive. While Class 1 and 2 system failures are relatively uncommon, Class 3 system 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 convnon 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 pre-existing 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 difficulty 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 systems, is authorized for Salem Nuclear Generating Station, Unit Nos. 1 and 2, and Hope Creek Generating Station, pursuant to 10CFRS0.55a(a)(3)(ii).
PSE&G 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.
The staff evaluated the information provided by PSE&G 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) for Class 1, 2, and 3 systems as compliance with the specified hydrostatic testing requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
2.2 Code Case N-524 2.2.1 Comoonent Identification Longitudinal Welds in Class 1 and 2 Piping
L l
( 2.2.2 ASME Code Section XI Second Interval Requirements The 1983 Edition through Summer 1983 Addenda, and 1986 Edition, Table IWB-2500-1, Category B-J, Table IWC-2500-1, Category C-F requires surface and volumetric examination of the longitudinal welds.
2.2.3 Proposed Alternative Examination.
The licensee proposes to apply Code Case N-524 as alternative rules for the examination of longitudinal welds in Class 1 and 2 piping..
2.2.4 Licensee's Basis for Request The licensee's October 19, 1994, letter provided the following basis for use of Code Case N-524:
'"PSE&G has reviewed the referenced Code Cases and concurs with the ASME assessment that use of both Code Cases would provide an acceptable level of quality and safety."
2.2.5 Evaluation/Conclusions The ASME Section XI Code (1989 Edition) requires one pipe diameter in length, but no more than 12 inches, be examined for Class 1 longitudinal piping welds.
Class 2 longitudinal piping welds are required to be examined for a length of 2.5t, where t is the thickness of the weld.
These lengths of weld are measured from the intersection of the circumferential weld and longitudinal weld.
The licensee's proposed alternative, Code Case N-524, limits the volumetric and surface examination requirements of the longitudinal weld to the volume or area contained within the examination requirements of the intersecting circumferential weld.
Longitudinal welds are produced during the manufacturing process of the piping, not in the field as is the case for circumferential welds.
The Code contains requirements on characteristics and performance of materials and.
products, and specifies the examination requirements during the. manufacturing of the subject longitudinal piping welds.
In addition, there are material, chemical, and tensile strength requirements in the Code.
The manufacturing process that is specified by the Code provides assurance of the structural integrity of the longitudinal welds at the time the piping is manufactured.
The preservice examination and initial inservice examinations have provided assurance of the structural integrity of the longitudinal welds during the service life of the plant to date.
The experience in the United States has been that ASME Code longitudinal welds have not experienced degradation that would warrant continued examination beyond the boundaries required to meet the circumferential weld examination requirements.
No significant.loading conditions or known material degradation mechanisms have become evident to
~
6 -
date which specifically relate to longitudinal seam welds in nuclear plant piping. If any degradation associated with a longitudinal weld were to occur, it is expected that it would be located at the intersection with a circumferential weld.
This intersection is inspected in accordance with the provisions of.Code Case N-524.
In addition, there is a significant accumulation of man-rem associated with the e~amination of longitudinal welds, especially in Class 1 piping.
The staff concludes that continued imposition of the Code examination requirements for longitudinal welds constitutes a hardship without a compensating increase in safety.
Code Case N-524 is presently under review by the NRC staff and should be published in a future revision of Regulatory Guide 1.147 for general use by licensees. Accordingly, the licensee's proposed alternative to use Code Case N-524 is authorized for Salem Nuclear Generating Station, Units 1 and 2, and Hope Creek Generating Station ~ursuant to 10 CFR 50.55a(s)(3)(ii) until such t~me as the code case is included in a future revision of Regulatory Guide 1.147.
At that time, the licensee is to follow all provisions in Code Case N-524, with limitations issued in Regulatory Guide 1.147, if any, if the licensee continues to implement this relief request.
Principal Contributor:
K. Battige Date:
March 17, 1995