ML20205L967
| ML20205L967 | |
| Person / Time | |
|---|---|
| Issue date: | 04/07/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20205L961 | List: |
| References | |
| NUDOCS 9904150027 | |
| Download: ML20205L967 (7) | |
Text
~,
U.S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLtEAR REACTOR REGULATION SAFETY EVALUATION OF "BWRVIP VESSEL AND INTERNALS PROJECT. BWR LOWER PLENUM INSPECTION AND FLAW EVALUATION GUIDELINE (BWRVIP-47)."
EPRI REPORT TR-108727. DECEMBER 1997
1.0 INTRODUCTION
1.1 Background
By letter dated December 30,1997, as supplemented by letter dated March 3,1999, the Boiling Water Reactor Vessel and Intemals Project (BWRVlP) submitted the Electric Power Research Institute (EPRI) proprietary report TR-108727, *BWR Vessel and Interr.als Project, BWR Lower Plenum inspection and Flaw Evaluation Guidelines (BWRVIP-47)," for NRC staff review. The BWRVIP-47 report presents generic guidelines for the inspection of components in the lower plenum region of BWR vessels. Components addressed include control rod drive (CRD) housing and stub tube, control rod guide tube and orificed fuel support, and in-core housing, guide tube and dry tube assemblies. Shroud support legs and core delta pressure systems / standby liquid control system (SLC) are addressed in separate guidelines. The BWRVIP-4 ' guidelines provide recommendations for non-destructive evaluation (NDE) methods, inspection locations, and inspection frequencies. The BWRVIP-47 report also recommends acceptable methods for mraluating the structuralintegrity significance of flaws that are detected during these examinations. The intent of the BWRVIP-47 guidelines is that BWRVIP members will adopt the inspection recommendations as a replacement for General Electric (GE) Safety Information Letters (SILs).
1.2 Purpose The staff reviewed the BWRVIP-47 report to determine whether its guidance will provide acceptable levels of quality for inspection and flaw evaluation (l&E) of the subject safety-related 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 Organization of this Report Because the BWRVIP-47 report is proprietary, this safety evaluation (SE) was written so as not to repeat proprietary information contained in the report. 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-47 report is given in Section 2 of this SE, with a detailed evaluation in Section 3. The conclusions are summarized in Section 4. The presentation of the evaluation is structured according to the organization of the BWRVIP-47 report.
j i
9904150027 990407 PDR TOPRP EXIEPRI i
4 C
PDR ENCLOSURE i
j
e s
2 2.0
SUMMARY
OF BWRVIP-47 REPORT The BWRVIP-47 report addresses the following topics:
Component Descriotion and Function - The various lower plenum components are j
described in considerable detail by a series of illustrations along with brief descriptions of each component's function'and materials / welding characteristics. Differences among the various models of BWRs (BWR/2, BWR-3-5, and BWR/6) are identified.
I Susceptibility Factors -The various types of material degradation mechanisms (fatigue, e
l stress corrosion cracking, age embrittlement) that could impact lower plenum components l
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 components.
Potential Failure Locations and Safety Consecuences - Each of the lower plenum components are addressed from the standpoint of inspection history, future susceptibility l
to degradation, and consequences of failures in terms of component functions and plant safety. Based in these qualitat;ve considerations, the BWRVIP-47 report makes recommendations as to the need for inspections for each of the lower plenum components.
Backaround and insoection Historv-Data on service related failures of components are summarized. The major sources of such data are the various GE SILs and Rapid Information Communication Service information Letters (RICSILs). Another source of data is the reported findings from inspections of lower plenum components performed at I
plants in the U.S. and Spain. Inspection requirements are evaluated according to the following four criteria: 1) the potential consequences of a failure plant safety,2) the ability of leak monitoring to detect degradation as a complementary measure to inservice inspections, 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 l-high level of confidence that no degradation mechanisms are active for the components of concem.
1 BWRVIP Insoection Guidelines - The guidelines recommend the specific locations, NDE methods, and inspection frequenc!es for examinations of lower plenum components. The i
recommended NDE methods are limited to visual examinations, with reference made to the BWRVIP-03 report (Reference 3) for detailed requirements for implementing these
' visual examinations. The BWRVIP-47 report recommends only a limited number of inspections for the lower plenum components, based mainly on the relatively good service experience to date that indicates no evidence of generic cracking. The relatively small safety consequences of structural failures and the ability of leak delection to provide an early indication of structural degradation are also cited to justify the recommended level of inspection. The plant-specific recommendations focus on a one-time baseline inspection at each BWR plant, with no periodic re-inspections being required unless i stified by evidence of the actual occurrence of degradation. The scope of sample inspections is expanded to address similar components if flaws are found, i
g
.o 3
Loads - This section briefly states that the loads used in fracture mechanics evaluations to address the effects of detected flaws on structuralintegrity should be based on the plant design and licensing basis. The various types of loads (e.g., pressures, seismic, etc.) of concem are listed.
Consideration of Shroud Reoair-The discussion of flaw evaluation methodologies is limited in the BWRVIP-47 report. It is ackriowledged that the number of component geometries and potential cracking configurations is very large. Detal!s of the evaluation procedures would need to be developed on a plant-specific case-by-case basis, with the methodologies currently addressed by ASME Section XI serving as examples of acceptable bases for the evaluation of flaws.
3.0 EVALUATION The inspection guidelines provided by the BWRVIP-47 report are comprehensive in dealing with a large number of lower plenum components as candidates for inservice inspection.
Differences in the design and operating experience for the various types of BWR reactors (BWR/2, BWR/3-5 and BWR/6) are reviewed and taken into account as part of the inspection strategy. The guidelines limit the inspections to visual methods, but take steps to ensure that future visual examinations will be performed with an enhanced level of effectiveness compared to examinations performed in the past. Implementation of the recommendations are intended to ensure an enhanced inspection relative to the examinations now required by ASME Section XI, but will replace or eliminate examinations recommended by GE in past SILs or RICSILs.
Industry-wide implementation is intended to provide operators of BWR plants with improved knowledge of the initiation and progress of materials degradation within the lower plenum region.
With the exception of issues described below, this review finds that the guidance provided in the subject report to be acceptable.
The recommendations of the BWRVIP-47 report focus inspections on welds, with special i
atter. hon given to detecting evidence of stress corrosion cracking. Inspectior3s are to be performed in two phases, beginning with a " baseline" inspection of a selected set of locations.
The number of inspected welds and components for this baseline inspection of lower plenum components is divided into three categories, focusing on the locations most likely to experience degradation and/or components whose failures could most impact plant safety.
The proposed baseline inspections does not address many components that have been examined in the past, and justifies the reduced level of inspection on the basis of favorable operating experience and/or lack of significant consequences associated with the anticipated failure modes.
Upon completion of this initial baseline inspection, as currently proposed, the BWRVIP-47 report does not require any of the lower plenum components to be subject to re-inspection, unless flaws are found in the baseline inspection. It is stated that additional recommendations for re-inspection will be developed at a later date, which would permit the inspection strategy to be influenced by future plant operating experience and by insights gained from the industry-wide program of baseline inspections.
l l
k' l
l*.
4 l
The inspection guidelines provided in the BWRVIP-47 report recommends a " baseline" inspection and re-inspection of 1) the CRD guide tube sleeve-to-alignment lug weld,2) the CRD guide tube body-to-sleeve weld and the guide tube, and 3) fuel support alignment pin to-core plate weld. The guidelines recommend that the inspections be either modified VT-1 (1 mil wire resolution) or VT-3. For other locations within the lower plenum (CRD housing / stub tube / guide tube / fuel support assemblies and the in-core housing / guide tube / dry tube assemblies) the guidelines recommend no additionalinspections based on good field history, significant inspection experience, detectability through leaks, and minimal safety implications.
For the baseline inspections access to the lower plenum is not required. The inspection of the same location during different outages does not count towards satisfying the minimum population requirements identified in Table 3.2-1 of the BWRVIP-47 report. Also included in Table 3.2-1 are recommended time intervais for these minimum population requirements. The BWRVIP has identified itself as the recipient of all BWR fleet inspection information so that they can perform analysis of this data to identify any generic cracking behavior that might necessitate adjustments to the current inspection recommendations.
The staff believes that an initial baseline inspection should be comprehensive, and ir;clude all components that are practicable to inspect, based on tooling available. Further, the staff believes that a re-inspection so,hedule and scope, based on the performance and results of the initial baseline inspections, should be addressed. The staff requests that the BWRVIP address these in a revision to the BWRVIP-47 report.
Issues 2.3.3.2 and 2.3.2.1 Primary Pressure Boundarv Welds Some of the welds in the CRD housing assembly (welds CRDH-2 and CRDH-3) and the in-core housing (weld ICH-1) are part of the primary system pressure boundary. The BWRVIP-47 report recommends no inspection of these welds, because 1) no indications have yet been found in these welds, and 2) the BWRVIP-47 evaluation does not identify safety consequences for failure of these welds, it is stated on page 2 38 that welds CRDH-2 and CRDH-3 are ASME Section XI pressure boundary welds, and that examination requirements are specif.Jd by the Code. On the other hand, the BWRVIP-47 report does not include inspection of these welds in the recommended Inspection strategy of Section 3.2. The report should provide clarification regarding the inspections that will be performed under the requirements of ASME Section X'.
Issue 3.2.1 Reauirements for Visual Examination and Altemative inspection Technoloaies The BWRVIP informed the staff during a public meeting on December 17,1998, that committee members are working on revisions to the BWRVIP-47 and -03 reports, and plan to make the EVT-1 a visual exam capable of achieving a % mil wire resolution. This change would be an improvement, and would be consistent with the requirement in BWRVIP-03 for core shrouds, which uses a % mil wire resolution standard. Based on this, the NRC staff requires no further actions to resolve issues 3.2.1 a and b, which are included below to document the commitments.nade by the BWRVIP to address the staff's concems.
Issue 3.2.1 a) Imolementation Recuirements for Visual Examination
l
- s..
5 in the BWRVIP-47 guidelines, two inspection methods are recommended for visual examinations. The two methods are the modified VT-1 and VT-3. The implementation requirements and definitions of these two methods can be found in the BWRVIP-03 report, which is being revised to reflect the issues in the staff's SE dated June 8,1998. The requirement identified in the BWRVIP-47 report for the modified VT-1 calls for a visual system capable of achieving a 1-mil wire resolution. In discussions with the BWRVIP members 1
working on the revisions to the BWRVIP-47 and BWRVIP-03 reports, the planning is to make i
the modified VT-1 capable of achieving a %-mil wire resolution and calling it enhanced VT-1 (EVT-1). This c.ange would be an improvement and would be consistent with the requirement in BWRVIP-03 for core shrouds, which uses a % mil wire resolution standard.
There is no mention of the detailed requirements in the BWRVIP 47 report for assuring that an effective visual examination can be conducted other than a note stating prior to the use of the above inspection methods, the utilities should assess whether cleaning would be required in order to obtain meaningful / reliable results. Specifics are needed for many of these parameters such as how clean does a component have to be in order to conduct an effective EVT-1 examination. These requirements are to be covered in the revised BWRVIP-03 report, and should be appropriately addressed in a revision to this report.
A visual examination can be very effective in finding degradation. However, the current versions of the BWRVIP-03 and -47 reports do not provide adequate detail to insure that I
effective visual inspections will be performed. These revisions will need to provide sufficient guidance for inspection equipment, procedures, and inspector training / skills to insure that a reliable inspection will be performed or that inspectors, equipment and procedures in combination will demonstrate their effectiveness through a performance type of test.
Issue 3.2.1 b) Altemative inspection Technolooies in the information complied in Table 3.1-1 of BWRVIP-47, most of the inspections that were conducted used VT-1, VT-2 or VT-3. The exceptions to inis include the inspections at.
Dresden, Unit 3 in August 1995 using a VT-1 (with 1 mit sensitivity), Duane Amold used a VT-1 (1-mil sensitivity)in 1988 and at Nine Mile Unit 1 that used UT in 1997. The most likely degradation mode of the maierials and alloys used in the lower plenum is lGSCC.
IGSCC during early propagation tends to be a crack that is tight where it breaks the surface.
Much of the inspection history has been created using techniques that are looking for leaks, broken off pieces of material, or cracks that have large crack opening dimensions. If IGSCC cracking exists in some of these lower plenum components, more sensitive VT or other techniques (UT, ET) are needed in order to reliably detect them.
Issues 3.2.2 Baseline insoection - Access to Lower Plenum The second paragraph of Section 3.2.2 states that "the recommended inspections do not.
require access to the lower plenum area." The list of criteria listed in Section 3 of the BWPVIP-47 report as the basis for the inspection strategy does not include the criteria of accessability. The staff requests that the BWRVIP provide additionalinformation related to access to, and the inspection of, the lower plenum components, and the criteria for developing an inspection strategy for this area.
{>.
s issue 3.2.4 Re-insoection The recommendation stated in BWRVIP-47 Section 3.2.4 is that no additional inspections are required beyond the baseline inspections that are to be performed during a twelve year period.
However, the report also states that the baseline inspection results will be reviewed by the BWRVIP and, if deemed necessary, re-inspection recommendations will be developed at a later date. The purpose of ISI is to ensure that any flaws which develop during service can be detected and evaluated, and that unacceptable components are repaired or replaced to maintain safety, as well as to identify any possible generic type defects that were unforeseen at the design stage so that timely corrective actions can be taken. Because of the material susceptibility and uncertainties related to tensile stresses and environmental conditions, there is a need to conduct additional inspections in a timely manner to insure that these components are not degrading unacceptably after the baseline inspections have been completed. The staff will continue to interact with the BWRViP regarding the need for re inspections, and will monitor the performance and results of the baseline inspections.
Issue 5.0 Flaw Evaluation Methodolooles Section 5.0 of the original BWRVIP-47 report failed to provide specific guidance on methodologies appropriate for the components of the lower plenum. The report acknowledged the wide range of components in the lower plenum, and stated that detailed flaw evaluation methodologies cannot be provided. However, by letter dated March 3,1999, the BWRVIP proposed revisions to Section 5.0, replacing it in its entirety in order to address the below concems which were discussed with the BWRVIP during a December 17,1998, public meeting.
Section 5.0 assumed that component-specific evaluation methods will be developed in the future as needs arise to deal with specific components and types of degradation. The reference to the Mhodolmy of ASME Section XI was found to be too general, in that Section XI has specific Meria and Waluation approaches for flaws in vessels and piping, but does not address the various types of lower pienum components to be inspected. The proposed expansion of Section 5.0 provided in the March 3,1999, letter defines basic criteria for flaw evaluation, such as material properties, fracture mechanics methods, operating conditions and loads to be considered. However, the methodology and criteria specified did not contain j
sufficient specificity to close this issue; therefor, plant-specific evaluations will need to be evaluated on a case basis by the staff. If the BWRVIP desires to provide more specific criteria in a revision to the BWRVIP-47 report on a generic basis, the staff will review its acceptability.
4.0 CONCLUSION
S The staff has reviewed the BWRVIP-47 report and finds that the guidance of the report is acceptable for inspection and flaw evaluation of the subject safety related core intemal components, except where the staff's conclusions differ from the proposed guidance, as discussed above. The staff requests that the BWRVIP review and resolve the issues raised above, and incorporate the staff's conclusions into a revised BWRVIP-47 report. Please inform the staff in writing at to this resolution.
i
.t l*
- e.
7
5.0 REFERENCES
1.
Letter from BWRVIP with submittal of the report "BWR Lower Plenum inspection and Flaw Evaluation Guidelines (BWRVIP-47)," EPRI TR-108727, December 30,1997 2.
BWR Vessel and Intemals Project, "BWR Lower Plenum inspection and Flaw Evaluation 9,uidelines (BWRVIP-47)," EPRI TR-108727, December 1997 3.
BWR Vessel and Intemals Project, " Reactor Pressure Vessel and intemals Examinations Guideline (BWRVlP-03)," EPRI Report TR-105696, October 1995 4.
- BWR Vossel and Intemals Project, Vessel intemals inspection Summary," April 1997 5.
Baker, A. and J. Van Hoomissen, "BWR Core Shroud inspection Program," presented at EPRI Vessel & Intemcis Inspection Conference, San Antonio, TX, July 11-15,1994 6.
Lindberg, J. T., "BWR Reactor Pressure Vessel Intemals inspection Challenges for the Future," presented at EPRI Vessel & Intemals inspection Conference, San Antonio, TX, July 11-15,1994 7.
Ortega, J., "lSi of CRDH Penetrations la PWR and BWR Vessels: Field Experiences."
presented at EPRI Vessel & Intemals inspection Conference, San Antonio, TX, July 11-15,1994 8.
Coaster, D., *CRDM Reactor Head Penetration inspection," presented at EPRI Vessel &
intemals inspection Conference, San Antonio, TX, July 11-15,1994 9.
Atkinson, l.,"TOFD Defect Sizing for CRDM Penetration Adapters," presented at EPRI Vessel & Intemals inspection Conference, San Antonio, TX, July 11-15,1994
- 10. Gonzalez, E., Barroso. J. S. and A. Wilke, "in-service Inspection on SWR Vessel Stub Tubes with UT Array System," presented at the EPRI Reactor Pressure Vessel Inspection Conference, Olympic Valley, CA, June 4-6,1996
- m. e