ML20085M407
| ML20085M407 | |
| Person / Time | |
|---|---|
| Site: | Limerick  |
| Issue date: | 06/21/1995 |
| From: | Hunger G PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| GL-88-01, GL-88-1, NUDOCS 9506290177 | |
| Download: ML20085M407 (4) | |
Text
Station Support Department GL 88-01 j
~~F.
PECO ENERGY
- = e"~ c-a "v Nuclear Group Headquarters 965 chesterbrook Boulevard Wayne, PA 19087 5691 June 21,1995 Docket Nos. 50-352 50-353 Ucense Nos. NPF-39 NPF-85 l
U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555
Subject:
Umorick Generating Station, Units 1 and 2 Generic Letter 88-01, "NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping" Gentlemen:
By letter dated August 2,1988, PECO Energy Company provided its initial response to Generic Letter (GL) 88-01, *NRC Position on IGSCC in BWR Austenitic Stainless Steel Piping," which addressed the specific actions identified in the GL pertaining to Intergranular Stress Corrosion Cracking (IGSCC) in the area of piping and safe end weldments at Umerick Generating Station (LGS), Units 1 and 2. This initial response was later supplemented by letters dated April 28, 1989, May 30,1989, and September 11,1989.
By letter dated March 6,1990, the NRC issued a Safety Evaluation Report (SER) and supoorting l
Technical Evaluation Report (TER) documenting its review of our responses to GL 8841 for l
LGS, Units 1 and 2. In this SER, the NRC found the information in our responses to be l
acceptable with the exception of five (5) areas for which additional information was requested.
In particular, the NRC questioned whether we planned to perform Ultrasonic Testing (UT) on welds in the Reactor Water Cleanup (RWCU) system beyond the outboard primary containment isolation valves. The NRC requested that we provide the appropriate justification to support our position that the RWCU welds outboard of the primary containment isolation valves are inaccessible; otherwise, these welds should be examined in accordance with the guidance specified in GL 88-01, GL 88-01 stipulated that welds be categorized according to the piping material's susceptibility to IGSCC, and that an inspection schedule be established to examine the welds based on this categorization. The outboard RWCU piping welds for Unit 2 were designated as Category A, l
which required that 25% of the weld population be examined every 10 years, and at least 12% of I
the welds in six (6) years. However, the Unit 1 outboard RWCU system piping welds were l
categorized as Category G, which required that all of the welds (i.e.,100%) be examined during the next refueling outage, with the possibility of re-categorizing the weld population based on the results of the UT.
I 9506290177 950621 PDR ADOCK 0500 2
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June 21,1995 Page 2 In response to the NRC's request, we provided the necessary justification to support our position that the outboard RWCU system piping welds were inaccessible in a letter dated June 8,1990. Our response indicated that the RWCU system piping welds beyond the outboard primary containment isolation valves were located in high radiation areas, and most welds would require the erection of scaffolding, insulation removal, and surface preparation in order to perform the UT. This would result in significant personnel radiation exposure which was contrary to keeping radiation exposure "As Low As Reasonably Achievable." In addition, we indicated that alternate measures were currently in place to ensure the integrity of the LGS RWCU system. Specifically, the portion of the RWCU system piping outboard of the primary containment isolation valves was included in the ISI Pressure Testing Program being implemented at LGS. As a result, the RWCU system is pressure tested and visually examined in accordance with applicable ASME Section XI Code requirements.
The NRC later responded, as documented in a letter dated October 22,1990, that the IGSCC inspection program proposed for the Unit 1 RWCU system welds outboard of the primary containment isolation valves was unacceptable. The basis for the NRC's conclusion was that the RWCU system generally has the most aggressive environment with regard to IGSCO, and should be examined. However, the NRC recognized our concern regarding the high levels of radiation exposure expected during the preparation and UT of these welds and permitted a reduction in the number of welds that required examination during each refueling outage. The NRC indicated that beginning with the Unit 1 Fourth Refueling Outage, and during each refueling outage thereafter for the remainder of the First Ten-Year ISI interval, only 5% of the Unit 1 RWCU system weld population outboard of the primary containment isolation valves needs to be examined during each refueling outage. However, during subsequent Ten-Year ISI intervals for Unit 1, the sample population of RWCU system welds outboard of the primary containment isolation valves requiring examination should be increased to 10%.
Furthermore, in the October 22,1990 letter, the NRC also documented its review of the IGSCC inspection program for the Unit 2 RWCU system. The NRC acknowledged that the RWCU system piping outboard of the primary containment isolation valves had been replaced with piping material considered to be resistant to sensitization and IGSCC. The Unit 2 RWCU piping is included in the ISI Pressure Testing Program and the system is pressure tested and visually examined in accordance with applicable ASME Section XI Code requirements. Therefore, the inspection program proposed for the Unit 2 RWCU system welds outboard of the primary containment isolation valves was found acceptable by the NRC.
Subsequently, on February 4,1992, the NRC issued Supplement 1 to GL 88-01 to all Boiling Water Reactor (BWR) licensees to provide attematives to some of the NRC staff positions delineated in GL 88-01; specifically, those positions pe-taining to the examination of RWCU system piping outboard of the primary containment isolation valves. In this GL supplement, the NRC agreed that the radiation levels associated with the RWCU system piping outboard of the primary containment isolation valves are very high, and that the piping is designed to be isolable and is generally classified as nonsafety-related piping. However, the service-sensitive stainless steel RWCU system piping is subject to the most aggressive environment with respect to IGSCC.
Therefore, the NRC concluded that until the actions relevant to GL 89-10, " Safety-Related Motor-Operated Valve Testing and Surveillance - 10 CFR 50.54(f)," are completed by licensees, at least 10% of the RWCU system piping weld population outboard of the primary containment iso!ation valves should be inspected during each refueling outage to ensure structural integrity of the piping.
June 21,1995 Page 3 By letter dated July 28,1994, PECO Energy in; (med the NRC that the actions pertaining to GL 89-10 had been completed for LGS, Unit 1. Furthermore, by letter dated December 21,1994, we informed that NRC that the actions associated with GL 89-10 for LGS, Unit 2, would be addressed during the Third Refueling Outage (1,e., January - February 1995), which have been subsequently completed. Therefore, the capability of the RWCU system primary containment isolation valves to perform their intended isolation function is assured.
Pursuant to GL 8841 Supplement 1, Alternative Staff Position (2) dated February 4,1992 PECO Energy requests that the NRC approve a revision to the GL 8841 inspection program for LGS, Units 1 and 2, to eliminate 1) the need to perform UT of the Unit 1 RWCU system piping welds outboard of the primary containment isolation valves, and 2) the need to conduct ISI pressure testing for Unit 2 on the RWCU system piping outboard of the primary containment isolation valves. Our justification for eliminating the UT and system pressure testing is provided below.
1)
The 5% UT IGSCC inspection program established for the Unit 1 RWCU system piping welds outboard of the primary containment isolation valves has been performed during the previous two (2) refueling outages, in which approximately 20 welds have been examined. As a result of these examinations,ng IGSCC was detected. Furthermore, the ISI and IGSCC examinations performed for the RWCU system welds inboard of the primary containment isolation valves detected ng IGSCC at these weld locations. Since no IGSCC has been detected in the RWCU system welds, after five (5) cycles of operation, failure due to IGSCC is not considered imminent. The ISI and IGSCC examinations will continue to be performed on the safety-related portions of the RWCU system piping and should be sufficient to monitor the integrity of the entire system.
2)
In the event that an IGSCC failure would occur, we anticipate that this failure would occur as a " leak-before-break." There are several activities currently in placs to ensure that any leakage would be detected. These activities include: 1) continuous flow balance monitoring of the RWCU system; and 2) continuous temperature monitoring of the RWCU system equipment rooms and related areas. In the event that a leak occurred in the piping outboard of the primary containment isolation valves, the appropriate portions of the RWCU system piping could be isolated, and repairs could be initiated. The safety implications of a " leak-before-break" scenario in the RWCU system piping outboard of the primary containment isolation valves are considered to be minimal, since this portion of the RWCU system piping is isolable, and any repairs og be made while continuing plant operation.
3)
The RWCU system is designed to and is capable of automatic isolation in order to contain postulated losses of reactor coolant. The ability of the RWCU containment isolation valves to perform this isolation function under design basis conditions was verified in accordance with GL 89-10. The isolation function will continue to be subject to periodic verification of capability within PECO Energy's commitment to GL 89-10 testing and the additional tests quired by our ASME Section XI ISI Program. Since the RWCU system will automaticahy iso! ate and the outboard portion of the system (i.e.,
piping downstream of the primary containmemt isolation valves) does not perform a safety-related function, failure of this piping will not adversely impact the accident analysis discussed in Chapter 15 of the LGS, Units 1 and 2, Updated Final Safety Analyses Report (UFSAR).
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June 21,1995 Page 4 -
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' We' consider it important to strees that significant man-Rom has already been empended -
in performing the examinations on the non-ealety related portions d the RWCU systems.
Based on exposure data gathered from these previous examinations, we estimate that an additional eight (8) man-Rom will be involved in performing the next scheduled UT for T
the Unit 1 welds within the scopo d the 5% weld population. The exposure to perfomi J
the piping examinations as part of the ISI Pressure Testing Program is estimated to be an additional two (?) man-Rom each time this examination is performed for the Unit 2 -
welds We conservatively estimate the total exposure over the life of the plant to be in the order of 275 man-Rom for examinations of non-safety related RWCU piping in summary, these UT and pressure tests have a minimal effect on improving plant safety and present a significant burden in the form of high radiation exposure and significant cost in performing the examinations.. We have determined through examination, that the RWCU system piping does not represent a potential of imminent falure. Adequate programs and automatic system actuation functbns are in place to ensure that the implications of a fagure of RWCU system piping outboard d the primary containment lenimilan valves would not impact plant safety. In addition, since we have completed the actions pertaining to GL 89-10 for LGS, Units 1 and 2, we consider that the concems associated with IGSCC in RWCU system piping have been adequately addrweed in accordance with guidance delinosted in GL 8841 and Supplement 1.
We would appreciate the NRC's approval of this request by December 15,1995, in order to eliminate the need to perform these examinations during the upcoming Sixth Refueling Outage (IR06) for LGS, Unit 1, currently scheduled to begin in January 1996, and 611 subsequent LGS Units 1 and 2, refueling outages.
If you have any questions or require additional information, please do not hesitate to contact us.
9 Very truly yours,
.N.
4, G. A. Hunger, J.
Director-Licensing cc:
T. T. Martin, Administrator, Region 1. USNRC N. S. Perry, USNRC Senior Resident inspector, LGS l
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