ML20248L760
| ML20248L760 | |
| Person / Time | |
|---|---|
| Issue date: | 06/08/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20248L753 | List: |
| References | |
| NUDOCS 9806110342 | |
| Download: ML20248L760 (12) | |
Text
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U S. NUCLEAR REGULATORY COMMISSION OFFICE OF NUCLEAR REACTOR REGULATION DIVISION OF ENGINEERING SAFETY EVALUATION OF EPRI REPORT TR-106740. JULY 1996.
"BWR VESSEL AND INTERNALS PROJECT. BWR CORE SPRAY INTERNALS INSPECTION AND FLAW EVALUATION GUIDELINES (BWRVIP-18)"
1.0 INTRODUCTION
1.1 Background
By letter dated July 26,1996, as supplemented by letter dated October 8,1997, the Boiling Water Reactor Vessel and Internals Project (BWRVIP) submitted the Electric Power Research Institute (EPRI) Proprietary Report TR-106740, July 1996, "BWR Vessel and intemals Project, BWR Core Spray Intemals inspection and Flaw Evaluation Guidelines (BWRVIP-18)," for staff review and approval. The staff requested additional information (RAl) in a letter dated January 22,1997, and the BWRVIP provided it's response in a letter dated October 8,1997.
The BWRVIP-18 report contains generic guidelines for the inspection and reinspection of the core spray piping and spargers it describes piping and sparger locations, categories of plants for which inspection needs would differ, and flaw evaluation procedures to determine allowable flaw sizes. The intent of the subject document was, when approved by the NRC, to replace the guidance in IE Bulletin 80-13, " Cracking in Core Spray Spargers," dated May 12,1980, for use in providing adequate assurance of core spray integrity. The staff notes that IE Bulletin 80-13 requested licensees to inspect their core spray spargers and the segment of piping between the inlet nozzle and the vessel shroud during each refueling outage. These inspections have been successful in identifying cracking and flaws in the core spray piping and spargers.
In addressing the examination methods and the flaw evaluation, the BWRVIP-18 guidelines referenced the following BWRVIP reports:
(1)
" Reactor Pressure Vessel and Intemals Examinations Guidelines" (BWRVIP-03), EPRI Report TR-105696, October 1995, Section 6; (2)
"BWR Core Shroud inspection and Flaw Evaluation Guidelines,"GE Report No. GENE-523-113-0894, Revision 1, March 1995, (3)
" Guidelines for Reinspection of BWR Core Shrouds," (BWRVIP-07), EPRI Report TR-105747, February 1996; and, (4)
" Evaluation of Crack Growth in BWR Stainless Steel RPV Intemals" (BWRVIP-14), EPRI Report TR-105873, March 1996.
The staffs safety evaluation reports (SERs) for References 2 and 3 were issued on June 16, 1995 and September 15,1997, respectively. The BWRVIP-03 and BWRVIP-14 reports are currently under staff review and the use of their guidelines requires NRC approval on a case-by-case basis, until such time as the staff issues SERs granting generic usage.
ENCLOSURE 9806110342 990608 PDR TOPRP EXIEPRI C
Pn
2 The BWRVIP-18 report guidelines allow for plant-specific analysis to be performed for a given weld location. These plant-specific analysis are not addressed in the scope of this report, and NRC approval must be obtained on a case-by-case basis, until such time as they are approved for general usage by the staff.
1.2 Purpose The staff reviewed the BWRVIP-18 report to determine whether its guidance would provide l
adequate assurance of the structuralintegrity and function of the BWR core spray piping and sparger system.
I 1.3 Organization of the Report Because the BWRVIP-18 report is proprietary, this SE was written so as not to repeat information contained in the report. The SE gives a brief summary of the general contents of the report in Section 2 and the detailed evaluation in Section 3. The SE does not discuss in any detail the proprietary provisions of the guidelines, nor does it discuss in detail the parts of the guidelines it finds acceptable. The staff's cor'clusions and issues that the staff requests the BWRVIP resolve are summarized in Section 4.0. The staff has structured its evaluation according to the organization of the BWRVIP-18 report.
2.0
SUMMARY
OF BWRVIP-18 REPORT The BWRVIP-18 report addresses the following topics in the following order:
Core Spray Piping Design and Susceptibility Information Susceptibility Factors Design of Typical Core Spray Assemblies inspection Strategy e
Examination Methods BWRVIP " Baseline" Inspection and Reinspection Plant Categories Piping Locations Sparger Locations
- Geometry-Critical Plants
- Geometry-Tolerant Plants
- Other Locations
- Reporting of Inspection Results Loading
- Significant Loads for Core Spray Line and Sparger Piping
- Load Combinations
- Consideration of Shroud Repair
- Stress Analysis Methodology Evaluation Methodologies
- Piping and Sparger Locations
- Bracket Locations
3 The BWRVIP-18 report also contains appendices on (A) Core Spray Piping and Sparger Flaw Evaluation Example, (B) Seismic inertia Analysis Considerations, and an appendix (C) to demonstrate this report's compliance with the technicalinformation requirements of the license renewal rule,10 CFR Part 54. Appendix C is not esaluated in this SER, but is under separate review.
3.0 STAFF EVALUATION The inspection guidelines provided in the BWRVIP-18 report are comprehensive, covering
" baseline" inspection and reinspection of core spray piping, spargers, brackets and repair components inside the reactor vessels for various types of BWR reactors (BWR/2, BWR/3-5 and BWR/6). The guidelines allow the piping inspection to be performed either by visual or ultrasonic examination, and the inspection of the spargers and brackets to be performed by visual examination. The proposed inspection is focused on the weld areas that are most susceptible to IGSCC, with areas that the BWRVIP have determined as not susceptible to IGSCC not needing inspection. For the
- baseline" inspection, all accessible weld locations are required to be inspected. The exception of this is when an ultrasonic examination is performed on welds made of 304L/316L materials; then, a reduced scope of such welds is allowed. The proposed frequency and scope of reinspection of these locations depend on the type of materials (i.e.,
304/316 vs. 304L/316L), crevice condition (i.e., creviced vs noncreviced), safety consequences, inspection history (i.e., tee box-to-pipe welds), previous inspection results and methods of inspection (i.e., visual vs. ultrasonic). The staff finds that much of the guidance provided in the subject report is acceptable since it incorporates industry-wide inspection experiences and is consistent with the guidelines in the IE Bulletin 80-13, with the exception of the issues discussed below. The staff requests the BWRVIP resolve these issues and revise the subject document in accordance with the staff's conclusions.
Issue 3.1 Surface Cleanina and imo!ementation Requirements for Visual Examination in the BWRVIP-18 guidelines four (4) different kinds of visual examination methods (Enhanced VT-1, CS VT-1, VT-1 and VT-3) can be used for the inspection, depending on the location and safety consequences of the welds. The guidelines state that the implementation requirement and definitions of these inspection methods can be found in BWRVIP-03, however, some of the implementation requirements and definitions are in the course of being developed. The staff notes that only the Enhanced VT-1 inspection method is covered in the BWRVIP-03 report.
Since the BWRVIP-03 report is still under NRC review, it would take some time to establish additional guidelines for the other three visual examination methods. In the absence of the specified guidelines, the staff has concluded that all the requirements, including the equipment, procedure and personnel qualification established for the Enhanced VT-1 method, needs to also apply to the CS VT-1, VT-1 and VT-3 visual examination methods, with the exception of the required optical resolution capability which is different for the various visual examination methods.
In the BWRVIP-03 report, it is stated that the waiver of surface cleaning prior to the performance of visual examination (VT) should be demonstrated on the worst area to show that the oxidized sediment or debris will not mask the surface defects from being detected. The BWRVIP's response to the staff's RA!, regarding the need for surface cleaning prior to visual examination stated that the specified visual examinations neither mandate nor preclude cleaning, which is not consistent with the guidelines in the BWRVlP-03 report as stated above. The staff has concluded that the BWRVIP-03 guidelines pertaining to the surface cleaning prior to visual examination need to be applied to all methods of visual examinations and the subject guidelines need to be restated in full in the BWRVIP-18 report to er.sure a meaningful visual inspection will be performed.
1 4
On page 3-9 of the report, for the inspection of the nozzle welds (S3) using CS VT-1, it stated that at the CE VT-1 does not require any time consuming cleaning. On page 3-11 of the report for the inspection of Piping and Sparger Brackets, it stated that the inspection method for the piping bracket welds and bolts is CS VT-1 method without cleaning. These statements need to be modified to be consistent with the guidelines in the BWRVIP-03 report regarding surface cleaning.
Issue 3.2 Reinspection of Core Sorav Pipino Welds The proposed industry reinspection strategy for uncracked piping welds is focused on reinspection of creviced welds. Except for the tee box-to-pipe welds, the BWRVIP is proposing to inspect all non-creviced welds on a rotating sample basis. The BWRVIP proposes to inspect j
25 percent of those non-creviced welds during each inspection. The staff finds the reduced inspection frequency for 304L/316L non-creviced welds acceptable because no cracking of these welds have been reported. However, the staff does not agree that the proposed schedule for non-creviced welds in susceptible material is appropriate since much of the sparger and intemal piping that has cracked is non-creviced. The basis for the staff's conclusion is presented in the paragraph that follows:
It is well documentad that the creviced condition will accelerate the initiation of cracks in welds susceptible to IGSCC. However, there are other conditions which are equally effective in accelerating the initiation of cracks in welds, (e.g., the effect of surface cold work resulting from weld root or surface grinding and the presence of fit up stresses due to cold pulling of the piping sections during installation). If these conditions are present in the non-creviced welds, early initiation of cracking may occur, depending on its severity. The first reported cracking event in the core spray intemal piping was the cracking of a noncreviced piping weld (upper elbow weld to horizontal header pipe) at Brunswick, Unit 2, in June 1978. By examining the events pertaining to the cracking of the core spray piping in Table 3-1 of the BWRVIP-18 report, the staff l
notes that the first seven events, which occurred from June 1976 through July 1993, are all l
cracking of noncreviced welds. These events consists of cracking of one upper elbow weld, two extra welds and four tee box-to-pipe welds. The first cracking of a creviced weld was not reported until October 1993. For all the reported cracking events for non-creviced welds in Table 3-1 up to March 1992, there were cracking of seven tee box-to-pipe welds, six elbow welds and two extra welds. Dresden Unit 2 reported the cracking of several core spray piping welds including two elbow welds during the last refueling outage. This event was not listed in Table 3-1, since the outage occurred after the submittal of the report. Based on the reported cracking events in Table 3-1, it is apparent that the cracking of non-creviced welds is quite extensive.
Based on the above, the staff concludes that the non-creviced 304/316 welds need to be inspected to the same extent and frequency as the creviced welds.
Issue 3.3 Inspection of Core Soray Soarcers (1) Geometry-Tolerant or Geometry-Critical Plants The BWRVIP-18 report categorizes BWRs as either geometry-tolerant or geometry-critical with respect to the core spray spargers. The BWRVIP-18 document proposes the following reinspection guidance, following the baseline inspection, for geometry-tolerant and geometry-critical plants.
Geometry critical plants:
inspect the identified core spray sparger locations every cycle.
Geometry tolerant plants:
inspect the identified core spray sparger locations every two cycles.
l l
5 in response to the staff's RAI as to which BWRs are considered to be geometry tolerant plants, the BWRVIP stated that "...all US BWRs which inject LPCI exclusively through the jet pumps are considered geometry-tolerant plants for post-LOCA core cooling purposes provided that the following conditions are met:
1.
At least one LPCI pump is available to inject in the unbroken recirculation line.
2.
Water level to the jet pump suction elevation outside the shroud is maintained.
3.
Core spray injection in a nearly uniform pattem is assured. This requirement is met as long as the core spray flow is not confined to a highly local region. Since precise, uniform core spray is not required, some leakage from potential cracking in the sparger is acceptable as long as it is not excessive to the point where core spray flow is confined only to a local region."
These conditions apply to BWR/3s and BWR/4s, except Hope Creek and Limerick Units 1 and 2.
BWR/2s do not have jet pumps and BWR/5-6 and three BWR/4s (Hope Creek and Limerick Units 1 and 2) inject LPCI inside the shroud which inhibits the steaming rate by subcooling the coolant around the submerged fuel. The BWRVIP also stated that "BWRs that have been classified as geometry tolerant plants can become geometry critical under certain circumstances that lead to the violation of the three requirements described above orif there is a change to a fuel type that requires core spray."
The BWRVIP-18 report stated that the determination of a plant's proper geometry-critical /-
tolerant category requires a plant specific analysis. In response to the staff's RAI requesting a description of the plant-specific analysis that might be performed to determine whether a plant is geometry critical or geometry tolerant, the BWRVIP stated that "otherjet pump BWRs can be demonstrated to be geometry-tolerant if the ECCS injection inside the shroud is demonstrated to apply to all fuel assemblies. One way this can be demonstrated is to show that ECCS injection inside the shroud will fill the volume such that the overflow of water will spill into all fuel assemblies. This overflow can provide sufficient post-LOCA core cooling without steaming or uniform core spray. This type of analysis is not cycle dependent; however, it would be fuel type dependent as the filling of the volume is dependent on fuel assembly geometry." The staff notes that there are no requirements for the plant-specific analysis to be submitted to the staff for review and approval, in the staff RAI, the staff asked for the basis of the definitions of geometry tolerant and geometry critical. In response, the BWRVIP stated that the basis for geometry tolerant and geometry criticalis the NRC approved GE LOCA Licensing Topical Report NEDO-20566A, Section Ill. The staff reviewed the NRC SERs related to the GE ECCS Evaluation Model. From this review, it appears that the evaluation of steam effects on BWR core spray distribution was done to confimi the spray cooling heat transfer coefficient of 1.5 Blu/hr-ft - F which was used in the GE ECCS 2
Evaluation Model. In a letter dated March 20,1983, the staff concluded the following:
1.
All of the core spray sector steam tests conducted in the U.S. and abroad indicated that the minimum spray bundle flow is greater than 1 gpm, which test data have demonstrated is sufficient flow to justify the assumption of the spray cooling heat transfer coefficient of 1.5 Btu /hr-ft' *F which is used in the GE ECCS Evaluation Model.
2.
New analyses performed by GE have shown that for the limiting BWR/3, BWR/4 and BWR/5 cases with core spray assumed to drain through peripheral channels to increase the reflood rate as observed in the Lynn tests, the calculated peak clad temperature did
6 i
not exceed the 10 CFR 50.46 limit of 2200*F with no credit taken for the spray cooling effect.
3.
Recent test data show that even without any of the core spray water flowing through 8x8 fuel bundles, steam cooling alone would result in a significantly greater convective heat 2
transfer coefficient that the 1.5 Btu /hr-ft *F assumed in the GE ECCS Evaluation Model.
Based on this review, the staff concluded that even if core spray cooling is not available, fuel I
safety limits would not be exceeded. However, the staff did not conclude core spray was not necessary. This is based on the fact that core spray is an important component of the ECCS and provides a defense-in-depth function for recovering from accident scenarios. Additionally, the BWRVIP-06 report considers the core spray piping and spargers to be high priority items for development of inspection and flaw evaluation guidelines from a safe shutdown perspective.
The BWRVIP-18 report does not consider common mode failure of multiple cracked intemal components, but only individual component failures.
From an analysis viewpoi'it, core spray is also relied upon in worst case net positive suction head (NPSH) and ECCS strainer clogging scenarios, jet pump riser cracking and/or disassembly, and core shroud cracking. The intent of the BWRVIP-06 report was to develop inspection and evaluation guidelines which will assist utilities in identifying potential cracking locations before the component fails. However, the guidelines presented in the BWRVIP-18 report appear to reduce the frequency of current inspections of the core spray sparger and nozzle welds. This appears contrary to the safety priority for the core spray spargers in BWRVIP-06.
Additionally, the staff notes that not all BWRs use GE fuel and GE LOCA Methodology.
Therefore, in addition to the technical arguments given above, for plants not utilizing GE fuel and LOCA methodology, the analysis is not germane.
Based on this review, the staff has concluded that it is not appropriate to use the concept of geometry tolerant and geometry critical for the purposes of reducing the inspections of the core spray sparger or nozzle welds. This conclusion is based on the following factors:
1.
The inspections to date per NRC Bulletin 80-13 and GE SILs have been beneficial in identifying cracking in core spray piping and spargers.
2.
The basis for determining which plants are geometry-tolerant is founded on an analysis of the spray cooling heat transfer coefficient used in the GE ECCS Evaluation Model which was not developed for core spray sparger cracking. This basis would not apply to BWRs that do not utilize GE fuel and GE LOCA Methodology.
3.
The core spray spargers are an integral part of the defense-in-depth of the ECCS.
Reductions in inspection frequencies for the core spray spargers are not prudent from a safety consequences perspective.
Therefore, the staff has concluded that, when performing inspection of core spray spargers, all BWR plants need to be treated as geometry-critical plants.
(2) Inspection of Core spray Nozzle Assembly We' 't3 The BWRVIP-18 report discusses the inspection o: u,e core spray nozzle assembly weld, S3, which attaches the spray nozzles to the core spray sparger. The BWRVIP-18 reinspection guidance for these welds is a rotating 25 percent sample every cycle. This guidance applies to both geometry critical and geometry tolerant p its.
7 The staff notes that the BWRVIP-18 report stated inat for geometry critical plants, the nozzle welds, S3, would have little impact on overall core spray performance. The staff's RAI asked whether this statement was supported by analysis or test data. In response, the BWRVIP stated that as long as sufficient ligament remains at S3, which would assure that the nozzle is attached to the sparger, core spray injection to the local fuel bundle is maintained and ECCS performance is assured. The BWRVIP continued to state that "...the core spray flow available to each bundle is based on test data. The impact of postulated missing, or plugged, single core spray nozzles has been analyzed by GE in the past and found to be acceptable. These evaluations used the same technica! approach as that used to evaluate test data with respect to the interaction and contribution of various nozzles to the core spray flow available to bundles in different regions of the core." However, the BWRVIP did not provide any basis in either their initial submittal or their supplementary RAI response that the proposed 25% inspection would provide adequate assurance of the required minimum core spray flow at all time to each fuel bundle. Therefore, the staff concludes that all nozzle welds need to be inspected during each scheduled inspection.
Issue 3.4 Leakaae Considerations The BWRVIP-18 report provides guidance on leak rate calculation methods and leakage acceptance criteria for the core spray piping and the core spray spargers. In the past, utilities have performed calculations of leakage rates using either standard fluid equations or specially developed computer programs. The guidance provided in the BWRVIP-18 report on leak rate calculation methods does not differ from common industry practice and is acceptable.
However, the staff notes that the amount of leakage calculated and its acceptability is plant specific and dependant on the capacity of the individual plant's ECCS and fuel design. This applies to leakage acceptance criteria of the core spray piping and the core spray spargers. The staff notes that, for core spray spargers, the BWRVIP-18 report stated that "in a geometry-tolerant plant, any leakage through cracks in the spargers is expected to have n, impact en peak cladding temperature (PCT). For such plants, there is essentially no limit on the leakage through the sparger cracks, as long as the core spray water is delivered inside the shroud." Based on the above discussion of the geometry tolerant concept, the staff does not find this guidance to be acceptable. The staff concludes that all leakage needs to be considered in the LOCA analysis and evaluated for plant-specific acceptability.
Issue 3.5 Flaw Evaluation (1) Crack Length in Uninspectable Areas The guidelines stated that if the extent of the cracking on the accessible side is "x" percent of the accessible length, then it is assumed that "2x" percent of the inaccessible lengths are cracked.
This is not acceptable to the staff because it is not supported by data and analysis. The guidelines also stated that, attematively, a statistical approach similar to that adopted in BWRVIP-07 or an equivalent approach may be used. This approach appears to have merit but the BWRVIP has not provided the data and analysis to support the approach. The staff has concluded that the uninspectable areas need to be conservatively assumed to be completely cracked for the purpose of flaw evaluation. This conclusion is consistent with the staff position in all previous safety evaluations.
(2) Estimation of Flaw Length Based on Visual Examination To estimate the limiting crack length at non-creviced locations when only visual examination was performed, the guidelines stated that the flaw should be assumed to be through wall, and the assumed flaw length should be the visual length on outside diameter (OD) plus four times the
8 wall thickness. This is based on the consideration that the OD and inside diameter (ID) cracking l
are not expected to be significantly different. The staff finds that neither pertinent test data nor field cracking experiences are provided in the BWRVIP-18 report to support the guidelines.
Furthermore, an aspect ratio of a flaw depends on many factors in addition to crevice condition.
The other conditions that will affect the intensity of OD and ID cracking are: (i) the magnitude and distribution of stress intensity factor (K) in the wall thickness and length directions and, (ii) the number of crack initiation sites. These conditions are difficult to evaluate because it involves significant uncertainties. Therefore, the staff concludes that supplemental UT needs to be performed to determine the limiting flaw length at both creviced and non-creviced locations.
(3) Inspection Uncertainties The inspection uncertainties in measuring the flaw length by UT or VT needs to be considered when performing the flaw evaluation. The value of the uncertainties used in flaw evaluation needs to be demonstrated on a mock up. This requirement needs to be stated in the BWRVIP-18 report when discussing flaw evaluation.
Issue 3.6 Otheritems (1) BWRVIP " Baseline" Inspection (page 3-3)
To clarify the baseline inspection requirements, a summary statement of the proposed inspection requirements pertaining to inspecting all accessible piping, sparger or attachment welds using various inspection methods needs to be added.
(2) Inspection of Hidden Weld P9 (page 3-11)
The guidelines stated that the inspection of the hidden weld P9, connecting the shroud pipe and the sparger tee box in BWR/3-5 plants is not needed as long as the collar welds P8a and P8b can provide the structural margin needed to react the loads at the shroud. However, recently, some collar welds were found to be extensively cracked in a number of plants, which raised the concem regarding the structuralintegrity of weld P9. The P9 welds need to be inspected when extensive cracking is found in the corresponding collar welds in order to ensure the proper functioning of the core spray piping system. The staff has concluded that the inspection of weld P9 needs to be required when cracking of collar welds are found.
(3) Reinspection Frequency for Plants with 12-Months Cycles in figures 3-3 and 3-4, the "*** note stated that plants with 12-month cycle can double the number of cycles shown. The BWRVIP did not provide, in the either BWRVIP-18 report or the supplementalinformation provided in response to the staffs RAI, an adequate technical justification for allowing an essentially 50 percent increase in inspection period. For example, since the majority of BWRs are operated with an 18-month cycle, it is prudent to adjust the inspection frequency on that basis. Therefore, if the stated inspection frequency is once every two cycles, then, for a plant with a 12-month fuel cycle, it can be reinspected every three cycles instead of"** 4 cycles.
(4) Reporting Requirements for Inspection Results, Flaw Evaluation and Repair Design The staff agrees with the BWRVIP's justification in its response to the staffs RAI that the submittal of the flaw evaluations and repair designs prior to restart is not warranted, since the BWRVIP has submitted inspection, flaw evaluation, repair and replacement criteria to the NRC for approval and that members have committed to either follow those criteria or provide their
g--
9 altemative to NRC for approval. However, the reporting of inspection results, flaw evaluation and repair designs need to be submitted within 60 days after plant startup. This is consistent with the reporting requirement imposed on licensee for similar activities resulting from core shroud inspection. In addition, the licensee needs to continue to report any cracking to the appropriate NRC Regional office within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of identification.
1 (5) Comparison of IE Bulletin 80-13 and BWRVIP-18 Inspection Requirements The staff has reviewed the inspection recommendations in IE Bulletin 80-13 and the BWRVIP-18 report (assuming it will be modified with the staffs comments incorporated). The inspection guidelines (as modified) in the BWRVIP-18 report would be comprehensive and adequate in comparison with that provided in IE Bulletin 80-13. The staff concludes that the inspection of core spray piping and spargers based on the modified guidelines in the BWRVIP-18 report will provide an acceptable level of quality and will provide adequate assurance of the structural q
1 integrity of the core spray piping and sparger welds. The staff concludes BWRVIP-18, if modified I
to reflect the staffs comments, are an acceptable attemative to the inspections requested in IEB 80-13.
The staffs conclusion is based on the following considerations.
(1) Scope of Inspection l
The IE Bulletin 80-13 requires a visual inspection of the Core Spray Spargers and the segment of piping between the inlet nozzle and the vessel shroud. In addition to the scope as specified in IE Bulletin 80-13, the BWRVIP-18 also requires the inspection of all bracket welds. However, the scope of BWRVIP-18 inspection will focus on the inspection of welds and its adjacent area of heat affected zones (HAZ). The base material of the piping and spargers away from the weld will not be inspected. This is acceptable because the base materials are in a solution annealed condition which is not susceptible to IGSCC. With more than fifteen years' inspection in accordance with IE Bulletin 80-13, IGSCC has not been found in the base material of the piping and spargers.
(2) Frequency of Inspection The BWRVIP-18 report stated that the inspection of the core spray piping welds can be i
performed either by ultrasonic examination (UT) or visual examination (VT). However, the spargers will only be inspected by visual examination because of UT accessibility problem.
When visual examination is performed, reinspection is required every fuel cycle, similar to that of IE Bulletin 8013. When UT is performed on the piping welds, the reinspection is required every l
two fuel cycles. UT is a volumetric examination method which is capable of detecting cracks
'l initiated from the weld ID surface as well as the OD surface. Therefore, UT is considered to be capable of detecting cracking in earlier stages than VT and is encouraged to be used to supplement the VT examination whenever feasible. The proposed inspection frequency for UT of
{
core spray piping welds is consistent with the frequency specified for the inspection of piping welds on the primary pressure boundary (recirculation piping system) in GL 88-01. Since the core spray piping inside the reactor vessel is not a primary pressure boundary piping, the
- proposed inspection frequency for ultrasonic examination is considered conservative and, therefore, is acceptable.
(3) Methods of Inspection in the BWRVIP-18 report, two kinds of visual examination methods (Enhanced VT-1 and CS VT-
- 1) are used for the inspection of core spray piping and sparger welds, depending on the safety m.
10 consequences of the weld location. The CS VT-1 method is capable of achieving a 1 mil wire resolutien, which is similar to that specified in IE Bulletin 80-13. The enhanced VT-1 method is a better method than CS VT-1, capable of achieving % mil wire resolution. Therefore, the performance of inspection in accordance with the BWRVIP-18 report will provide reliable results l
as superior inspection methods (enhanced VT-1 or UT) are used in the inspection.
(4) Reporting Requirements IE Bulletin 80-13 requires that, when cracks are identified, an evaluation needs to be submitted to the NRC for review and approval prior to retum to operation. In the BWRVIP-18 report, this reporting requirement is not referenced; however, it does apply to the situation when the performance of flaw evaluation and repair design uses methodology and criteria which are not covered in the NRC approved BWRVIP topical reports In the early 1980's when the subject Bulletin was issued, there were no NRC approved methodology and criteria for the flaw evaluation or repair design, and each evaluation or design needed to be reviewed on a case-by-case basis. With the issuance of the NRC approved generic guidelines in the BWRVIP topical reports for flaw evaluation and repair design, the staff considers that it is not necessary to submit the report prior to plant start up when the evaluation or repair design was performed in accordance with the NRC approved guidelines. However, the BWRViP-18 report needs to indicate that a report which will include the inspection results is required to be submitted to the NRC within 60 days after plant start up as discussed above in issue 3.6 (4).
4.0 CONCLUSION
S The staff has reviewed the BWRVIP-18 report and finds that the guidance of the BWRVIP-18 report is acceptable for inspection of the subject safety-related core spray intemal components except where the staWs conclusions differ from the proposed guidance, as discussed above.
The staff also finds that the BWRVIP-18 report can be used to replace the guidance in IE Bulletin 80-13, when the stars conclusions are incorporated. This finding is based on information submitted both originally and in response to the stars RAI that clarified the guidance in the l
BWRVIP-18 report. The staff has concluded that licensee implementation of the guidelines in J
BWRVIP-18, with modifications to address the staFs conclusions above, will provide an acceptable level of quality for examination of the safety-related components addressed in the BWRVIP-18 document. The staff requests that the BWRVIP review and resolve the issues raised in the enclosed SE, and incorporate the stats conclusions into a revised BWRVIP-18 report. Please inform the staff in writing as to this resolution. These items are summarized below for clarity, issue 3.1 Surface Cleanina and implementation Requirements for Visual Examination 4
The BWRVIP-03 guidelines pertaining to the surface cleaning prior to visual examination
=
need to apply to all methods of visual examinations and the subject guidelines need to be restated in full in the BWRVIP-18 report to ensure that a meaningful visual inspection will be performed.
All the implementation requirements, including the equipment, procedure and personnel qualification established for the Enhanced VT-1 method in the BWRVIP-03 report, need to also apply to the CS VT-1, VT-1 and VT-3 visual examination methods with the exception of the required optical resolution capability, which is different for the various visual examination methods.
11 issue 3.2 Reinspection of Core Sorav Pipino V' dds The non-creviced 304/316 welds need to be inspected to the same extent and frequency as the creviced welds, issue 3.3 Inspection of Core Sorav Soarners When performing inspection of core spray spargers, all BWR plants need to be treated as geometry-critical plants.
All nozzle welds (S3) need to be inspected during each scheduled inspection.
Issue 3.4 Leakane Considerations All leakage need to be considered in the LOCA analysis and evaluated for plant-specific acceptability.
I lssue 3.5 Flaw Evaluation The uninspectable areas need to be conservatively assumed to be completely cracked for the purpose of flaw evaluation.
Supplemental UT needs to be performed to determine the limiting flaw length at both creviced and non-creviced locations.
The inspection uncertainties in measuring the flaw length by UT or VT need to be included when performing the flaw evaluation.
Issue 3.6 Other items To clarify the baseline inspection requirements, a summary statement of the proposed inspection requirements pertaining to inspecting all accessible piping, sparger or attachment welds using various inspection methods need to be added.
The inspection of weld P9 needs to be required when cracking of collar welds is found.
For plants with a 12-month fuel cycle, if the stated inspection frequency is once every two cycles, such plants can be reinspected once every three cycles instead of 2 cycles.
The reporting of inspection results, flaw evaluation and repair designs need to be submitted within 60 days after plant startup.
4 5.0~
REFERENCES 1.
BWR Vessel and intemals Project, "BWR Core Spray intemals inspection and Flaw Evaluation Guidelines (BWRVIP-18)," EPRI TR-106740, July 1996.
~ 2.
Letter dated January 22,1997, from C. E. Carpenter, Jr., USNRC, to C. Terry, BWRVIP,
" Proprietary Request For Additional information - Review of BWR Vessel and Intemals i
Project Reports, 'BWR Core Spray intemals inspection and Flaw Evaluation Guidelines l
(BWRVIP-18),' and ' Core Spray Piping and Sparger Repair Design Criteria (BWRVIP-19)'
i (TAC NOS. M96219 and M96539)."
)
l
1 l
12 3.
Letter dated October 8,1997, fiom V. Wagoner, BWRVIP, to USNRC, "BWRVIP Response to NRC Request for Additional Information on BWRVIP-18."
4.
Memorandum dated March 29,1983, from R. J. Mattson, USNRC, to T. Speis, USNRC, "Close-out of TAP-A-16, Steam Effects on BWR Core Spray Distribution (TACS-40066)."
5.
IE Bulletin 80-13, " Cracking in Core Spray Spargers," USNRC, May 12,1980.
6.
Letter dated October 5,1995, from J. T. Beckham, Jr., BWRVIP, to USNRC, " Safety Assessment of BWR Reactor Intemals (BWRVIP-06)," EPRI TR-105707.
7.
Reactor Pressere Vessel and Intemals Examinations Guidelines (BWRVIP-03), EPRI Report TR-105696, October 1995, Section 6.
8.
BWR Core Shroud inspection and Flaw Evaluation Guidelines, GE Report No. GENE-523-113-0894, Revision 1, March 1995.
9.
Guidelines for Reinspection of BWR Core Shrouds (BWRVIP-07), EPRI Report TR-105747, February 1996.
- 10. Evaluation of Crack Growth in BWR Stainless Steel RPV Intemals (BW'RVlP-14), EPRI Report TR-105873, March 1996.
Technical Contacts:
W. H. Koo, EMCB K. A. Kavanagh, SRXB J. R. Rajan, EMEB i
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