ML20212J966
| ML20212J966 | |
| Person / Time | |
|---|---|
| Issue date: | 09/29/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20212J956 | List: |
| References | |
| NUDOCS 9910060060 | |
| Download: ML20212J966 (5) | |
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i U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION SAFETY EVALUATION OF BWRVIP VESSEL AND INTERNALS PROJECT. BWR TOP GUIDE INSPECTION l
AND FLAW EVALUATION GUIDELINES (BWRVIP-26)
EPRI REPORT TR-107285. DECEMBER 1996 1
1.0 INTRODUCTION
1.1 ' Backaround i
By letter dated December 27,1996, as supplemented by letter dated December 19,1997, the Boiling Water Reactor Vessel and Internals Project (BWRVIP) submitted the Electric Power Research Institute (EPRI) proprietary Report TR-107285, "BWR Vessel and Internals Project, BWR Top Guide inspection and Flaw Evaluation Guidelines (BWRVIP-26)," December 1996, for NRC staff review. The supplementalinformation was in response to the staff's request for additional information (RAI), dated March 14,1997. The BWRVIP 26 report provides generic guidelines intended to present the appropriate inspection recommendations to assure safety function integrity of the subject safety-related reactor pressure vessel (RPV) internal components. It also provides design information on the top guide, geometries, weld locations, j
1 and potential failure locations for the several categories of boiling water reactors (BWR/2 through BWR/6).
4 By letter dated May 18,1999, the staff forwarded its initial safety evaluation (SE) of the BWRVIP-26 report to the BWRVIP. This SE had several open items, repeated below, and i
requested that the BWRVIP address these issues in a timely manner. By letter dated August 5, 1999, the BWRVlP responded to the open items in the staff's initial SE.
1.2 Puroose The staff reviewed the BWRVIP-26 report, as supplemented, to determine whether its revised guidance addressed the open items in the staff's initial SE, and if it will provide acceptable levels of quality for inspection and flaw evaluation (l&E) of the subject safety-related reactor pressure vessel (RPV)' internal components. The review considered the consequences of component failures, potential degradation mechanisms and past service experience, and the ability of the proposed inspections to detect degradation in a timely manner.
1.3 Oraanization of this Reoo.rt Because the BWRVIP-26 report, as revised, is proprietary, this SE was written so as not to repeat proprietary information contained in the report or its revision. The staff does not discuss in any detail the provisions of the guidelines nor the parts of the guidelines it finds acceptable.
A brief summary of the contents of the BWRVIP-26 report is given in Section 2.0 of this SE, with a detailed evaluation in Section 3.0. The conclusion is summarized in Section 4.0. The presentation of this evaluation is structured according to the organization of the BWRVlP-26 report.
ENCLOSURE 9910060060 990929 PDR TOPRP EXIEPRI C
m 2.0
SUMMARY
OF BWRVIP-26
- The BWRVIP-26 report addresses the following topics in the following order:
Comoonent Descriotion and Function - The various top guide configurations are o
described in detail by a series of illustrations along with brief descriptions of each configuration's function and characteristics. Differences among the various models of BWRs (BWR/2, BWR/3-5 and BWR/6) are identified.
Susceptibility Factors - The various types of material degradation mechanisms (fatigue, o
stress corrosion cracking, age embrittlement) that could impact lower plenum components i
are described. Materials, stress, and environmental factors are described in general terms, and followed by specific references to actual occurrences for each degradation mechanism relative to plant operating experience for particular mechanisms and compenonts.
Potential Failure Locations and Safety Consecuences - Each of the top guide o
configurations are addressed from the standpoint of inspection history, future susceptibility to degradation, and consequences of failures in terms of component functions and plant safety. Based on these qualitative considerations, the BWRVIP-26 report makes recommendations as to the need for inspections of each top guide configuration.
Backaround and Insoection Historv-Data on service related failures of components are o
summarized. The major sources of such data are the various GE SILs and Rapid Information Communication Service information Letters (RICSILs). Inspection requirements are evaluated according to the following four criteria: 1) the potential consequences of a failure to plant safety,2) the ability to detect degradation,3) field cracking history as a means to identify the most likely locations for material degradation, and 4) the extent to which results from prior inspections provide a high level of confidence that no degradation mechanisms are active for the components of concem.
BWRVIP insoection Guidelines - The guidelines recommend the specific locations, NDE o
methods, and inspection frequencies for examinations of top guide configurations. The recommended NDE methods are limited to visual examinations, with reference made to the BWRVIP-03 report for detailed requirements for implementing these visual examinations. The BWRVIP-26 report recommends only a limited number of inspections for the top guide, based mainly on the relatively good service experience to date that 1
indicates no evidence of generic cracking. The relatively small safety consequences of structural failures is cited to justify the recommended level of inspection.
Loads - This section describes the loads used in fracture mechanics evaluations to o
address the effects of detected flaws on structural integrity. The various types of loads (e.g., pressures, seismic, etc.) of concern are listed.
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3.0 NRC STAFF EVALUATION The staff's May 18,1999, initial SE provided two open items. The BWRVIP, in its letter of
. August 5,1999, addressed these items, which are discussed below.
3.1 lasue 3.1.2, Examination Methods
'The staff's May 18,1999, initial SE stated:
The BWRVIP informed the staff during a public meeting on December 17,1998, that committee members are working on revisions to the BWRVIP-03 report, and plan to make the enhanced visual inspection method (EVT-1) a visual exam capable of achieving a %
mil wire resolution. The BWRVIP-26 report currently requires only a VT-1 examination,
'which is less capable than the EVT-1 in detecting cracking. The NRC staff finds that all inspections recommended in the BWRVIP 26 report should be performed to at least EVT-1 standards.'
BWRVIP's August 5,1999, Response:
During th's Staff's review of BWRVIP-18, it was agreed that the BWRVIP would simplify the visualinspection criteria by eliminating two of the visualinspection techniques. This was described in detailin the BWRVIP's written response to the NRC's Safety Evaluation on VIP-18. Specifically, the BWRVIP stated "In response to the NRC's comment on the number of visual methods, the BWRVIP will delete the CS VT-1 examination technique from BWRVIP-18 and the MVT-1 technique from the other l&E guidelines. The EVT-1 method will be specified as the primary technique to be used when fine, tight IGSCC is a primary concern. In other locations, VT-1 or VT-3 will be used as appropriate." As required by BWRVIP-03, the EVT-1 method does require a % mil wire resolution and the BWRVIP has not knowingly committed to replacing all VT-1 inspection methods with an EVT-1 inspection method, in BWRVIP 26 both the VT-1 and EVT-1 methods are specified based on the appropriateness of the method. VT-1 is specified for the following locations for the following reasons:
(1)' Alianer oins and sockets for BWR/3.4 without wedoes (Locations 2 and 3)
For this location, an inspection needs to assure that gross failure of the aligner pin hardware has not occurred. Thus, VT-1 inspection is adequate.
(2) Hold-down assemblies for BWR/2-4 devices (Location 8)
These bolts are spring loaded. Therefore, if cracking occurs, the resulting displacement of the bolt would easily be found by VT-1.
Any additionalissues associated with the quality of the VT-1 or EVT-1 insoection methods have been addressed and resolved as stated in the NRC's Final Safety Evaluation of the "BWR Vessel and intemals Project, Reactor Pressure Vessel and Intemals Examination Guidelines (BWRVIP-03) Revision 1" dated July 15,1999.
Staff's Evaluation:
The staff finds that the BWRVIP's response adequately addressed this item.
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1 3.2 lasue 3.2.2, inspection Recommendations by Locations 1
The staff's May 18,1999, initial SE stated:
The BWRVlP 26 report does not require an initial one-time baseline inspection of the top guide at each BWR plant. The NRC staff finds that an initial baseline inspection of the top guide, inclusive of all locations, should be performed, and that a plant-specific analysis which determines that the BWRVIP 26 recommended inspection frequency is adequately j
dispositioned, be completed and maintained by each licensee.
BWRVIP's August 5,1999, Response:
The NRC appears to be addressing two issues, (1) baseline inspection of those locations that require inspection and (2) baseline inspection of those locations that the BWRVIP has determined to not require inspection.
(1) For those locations requiring a VT-1 or EVT-1, the inspection frequency is every other cycle. Therefore, the baseline is accomplished as part of the initial inspection.
For those locations requiring a VT-3 every ten years it is assumed that these inspections are a continuation of inspections performed as part of either ASME Section XI or the General Electric SILs that have recommended comparable inspections. The document l
will be clarified to require a baseline before beginning the 10-year inspection interval if inspections comparable to a VT-3 have not been performed.
(2) In developing inspection recommendations for the top guide (and all other internal components), the BWRVIP first evaluated whether the failure of a particular location (e.g., weld, bolted connection, etc.) could cause a degradation in plant safety. If the failure affects the ability of the plant to safely shut down, an inspection of that location is required, if there are no failure cor: sequences, then no inspections are required for i
that component. This strategy is adequad to ensure plant safety and has been accepted by the st'ff for other core intamals evaluated by BWRVIP. Performing a
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baseline inspectiot, of locations, which if failed, have no affect on plant safety, would require an unnecessary increase in outage time in addition to the cost associated with developing and qualifying additional inspection tooling. Consequently, the BWRVIP does not agree with the NRC suggestion that all locations on the top guide l
be inspected in a comprehensive baseline inspection.
_ Regarding re-inspection, utilities have committed to implement the BWRVIP guidelines in l-
- total unless they notify the NRC to the contrary. Consequently, utilities have also committed to the re-inspection frequencies defined in the Guideline.
Staff's Evaluation:
The staff finds that the BWRVIP's response adequately addressed this item.
4.0 CONCLUSION
S The staff has completed its review of the BWRVIP-26 report, as revised, and finds that the licensee's implementation of the revised guidelines will provide an acceptable level of quality for l
1-examination of the safety-related components addressed in the BWRVIP-26 document.
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