ML20195J268

Safety Evaluation of Topical Rept TR-108726, BWR Vessel & Internals Project,Lpci Coupling Insp & Flaw Evaluation Guidelines (BWRVIP-42). Rept Acceptable for Insp of safety- Related LPCI Coupling Assemblies,Except Where Staff Differ

ML20195J268
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Issue date:	06/14/1999
From:	NRC (Affiliation Not Assigned)
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NUDOCS 9906180155
Download: ML20195J268 (5)

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[ U.S. NUCLEAR REGULATORY COMMISSION i

OFFICE OF NUCLEAR REACTOR REGULATION SAFETY EVALUATION OF BWR VESSEL AND INTERNALS PROJECT, LPCI COUPLING INSPECTION l

AND FLAW EVALUATION GUIDELINES (BWRVIP-42)

EPRI TOPICAL REPORT TR-108726 l

1.0 INTRODUCTION

l 1.1 Backaround By letter dated December 11,1997, as supplemented by letter dated September 8,1998, the l Boiling Water Reactor Vessel and intemals Project (BWRVIP) submitted both the proprietary and non-proprietary versions of the report,"BWR Vessel and Intemals Project, BWR LPCl inspection and Flaw Et sluation Guidelines (BWRVIP-42)," for staff review and approval. The NRC staff requested additionalinformation (RAl)in a letter dated April 14,1998, and the BWRVIP responded to the RAI by letter dated September 8,1998.

The BWRVIP-42 report contains generic guidelines to BWRVIP members on inspection and flaw evaluation of low pressure coo.' ant injection (LPCI) couplings. These guidelines considered degradation susceptibility, degradation mechanisms, loads, and inspection  !

strategies for LPCI couplings. The intent of the report, when approved by NRC, is to provide an acceptable level of quality and inspection and flaw evaluation guidance to BWRVlP members that can be used to assure adequate BWR LPCI coupling integrity when meeting the specified acceptance criteria.

1.2 Puroose The staff reviewed the BWRVIP-42 report to determine whether its guidance would provide an acceptable level of quality for inspection and flaw evaluation to provide assurance of the structuralintegrity and function of the LPCI couplings.

1.3 Oraanization of the Reoort Because the BWRVIP-42 report is proprietary, this safety evaluation (SE) was written to ensure that proprietary information was not compromised. The SE gives a brief summary of the general contents of the report in Section 2.0 and the detailed evaluation in Section 3.0 below. Because of proprietary information concerns, the SE does not discuss in any detail the provisions of the guidelines nor the parts of the guidelines that the staff finds acceptable.

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SUMMARY

OF BWRVIP-42 REPORT l The BWRVIP-42 report addresses the following topics in the following order.

o LPCI Couclino Desion and Suscentibility Information - The LPCI coupling assemblies are '

described in detail by a series of illustrations and differences among the various models of BWRs (BWR/4, BWR/5, and BWR/6) are identified. The various types of LPCI coupling susceptibility factors and material degradation mechanisms (e.g., intergranular stress corrosion cracking, IGSCC, which has factors that include environment, materials and stress state; fatigue by flow induced vibration and/or thermal cycling; and, aging embrittlement) that could impact the LPCI couplings are described in general terms.

Potential failure locations are addressed frora the standpoint of inspection priority, ,

suscept:bility to degradation, and consequences of failures in terms of component l functions and plant safety.

o insoection Strateov - The BWR/IP-42 report recommends the specific locations, NDE methods, and inspection frequencies for examinations of the LPCI coupling assemblies.

The report also describes the inspection basis and methods, the recommended baseline inspection scope, the reinspection frequency, scope expansion, and reporting of inspection results.

o Loads and L_ pad Combinations - The various types of loads (e.g., pressures, seismic, etc.)

l of concern are listed and load combinations are described. Consideration for shroud repairs is also detailed.

o Flaw Evaluation Methodoloaies - This section presents methods which can be used to determine if observed flaws are acceptable from the structuralintegrity and leakage points of view. It describes flaw evaluations for the elbow / elbow extension welds and other weld locations and a leakage evaluation.

The BWRVIP-42 report also contains an Appendix A,"BWR LPCI Coupling Demonstration of Compliance with the Technical Information Requirements of the License Renewal Rule (10 CFR 54.21)." Appendix A is not evaluated in this SE report, but will be evaluated under a separate review.

3.0 STAFF EVALUATION i The BWR LPCI coupling is an essential component of the emergency core cooling system (ECCS)in newer BWR/4s, BWR/5s and BWR/6s. The LPCI coupling is designed to provide a l flow path between the reactor vessel nozzle thermal sleeve and the core shroud at the top guide elevation. The main function of this system is to restore and maintain the required water

! levelinside the core shroud following a postulated loss of coolant accident (LOCA). The LPCI coupling is not used during normal operations.

1 The inspection guidelines provided by the BWRVIP 42 report are comprehensive in dealing with the LPCI coupling assemblies as candidates for inservice inspection. Differences in the design and operating experience for the various types of BWR reactors (BWR/4, BWR/S and BWR/6) are reviewed and taken into account as part of the inspection strategy. The l

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guidelines utilize visual inspections methods, and take steps to ensure that future visual f examinations will be performed with an enhanced level of effectiveness compared to examinations performed in the past. Industry-wide implementation is intended to provide l operators of BWR plants with improved knowledge of the initiation and progress of materials I-degradation within the LPCI coupling assembly.

The BWRVIP-42 report assigned inspection priorities for the different LPCl weld locations as high, low and/or no inspection depending on the potential safety consequences, including leakage from the failed location. The BWRVIP-42 report stated that a failed location is considered to have safety consequences if it would impair safe operation or safe shutdown of the plant. Leakage is a concem due to the potential bypass of LPCI flow into the annulus during a recirculation line break.

Based on these criteria, three locations were categorized as high inspection priority for BWR/4 and 5 plants, and seven locations were categorized as high inspection priority for BWR/6 l plants. The staff notes that the remaining weld Ircations were prioritized as low and/or no l

' inspection required. These potential failure locations would need other welds or multiple locations to fail concurrently to cause safety or functional concem. The BWRVIP needs to address inspection scope expansion to include these " low and/or no inspection required"

' locations based on the inspection results of examined sites Based on the above and with the noted caveat, the staff finds the inspection prioritization of the potential failure locations acceptable.

l The BWRVIP-42 report provides guidance on evaluating the potentialleakage from a cracked LPCI coupling. The staff notes that any leaks from the LPCI coupling into the RPV annulus is potentially unavailable for core cooling during an event when LPCI operation in required.

Depending on the amount of LPCI bypass leakage, LPCI leakage could result in an increase in peak cladding temperature. The BWRVIP-42 report recommends a plant-specific LOCA analysis to determine acceptable amount of LPCI bypass leakage. When determining total bypass leakage, leakage from all sources should be considered in the plant-specific analysis.

.The staff finds this guidance to be acceptable.

l The loads and load combinations for periorming flaw evaluations are presented in Section 4.0 of the report. This section describes the various applicable loads and load combinations (including "New Loads") which need to be considered in determining the primaryand secondary stress levels for the various operating conditions. Any plant-unique loads and load combinations shall also be considered, as applicable. Notwithstanding the recommendations in this section, the loads and load combinations used in analysis should be consistent with the plant design and licensing basis.

l The applicable significant loads to be included in this evaluation are:

o Normal Load (Dead weight + Water) o Differential Pressure Loads -

o Seismic Loads o Fluid Drag o Safety / Relief Valve Discharge Hydrodynamic Loads o Loss-of-Coolant (LOCA) Accident Hydrodynamic Loads

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o ThermalLoads f o Flow Induced Vibration Loads a

l Flow-induced vibration load due to leakage flow through the coupling shall be considered. The attemating stress intensity amplitude due to vibratory loads which are continually applied during normal reactor operation shall be limited to +/ 10,000 psi to prevent fatigue damage. If plant- specific attemating stress amplitude is larger, then the larger value should be used in the plant specific fatigue evaluation and a smaller value may be used if it can be justified. ,

Even though several of the load combinations specified by the reactor intemals loading i combinations and acceptance criteria are applicable to the LPCI coupling, based on the i

previous analysis performed and documented to qualify the LPCI coupling for these . loads, the critical, goveming primary load combinations can be narrowed down to a limited number, as shown above. Any plant-unique loads and load combinations shall also be considered based on the licensing basis, as applicable. I i

The loads and load combinations as discussed above, are consistent with industry practice, regulatory guidelines, and previously-accepted safety evaluations by the staff for similar applications, and are therefore, acceptable.

With the exception of issues described below, this review finds that the guidance provided in  !

the subject report to be acceptable. 1 issue 2.2 Potential Failure Locations (inaccessible Welds)  :

The BWRVIP inspection Committee is conducting a study to improve access to welds that were described as inaccessible in the BWRVIP-42 report. The staff will review and evaluate the BWRVIP study before making a determination on the subject of inaccessible LPCI coupling welds. .

Issue 3.3 Visual Inspection The specific inspection methods recommended in the BWRVIP-42 report relies on the methodologies described in the BWRVIP-03 report, dated October 1995, with the conclusions and exceptions as stated in the staff's SE dated June 8,1998. The staff has received Revision 1 to the BWRVIP-03 report, dated March 31,1999, which is intended to address the issues raised in the staff's SE. The staff will review and evaluate the BWRVIP-03, Revision 1, before making a determination on the acceptabili.y of this report for the subject components.

4.0 CONCLUSION

The staff reviewed the BWRVIP-42 report and RAI response and found that the guidance contained therein is acceptable for inspection of the safety-related LPCI coupling assemblies, except where the staff's concems differ from the proposed guidance, as discussed above.

The staff has concluded that license implementation of the guidelines in BWRVIP 42, with modifications to address the staff's concems above, will provide an acceptable level of quality for examination of the safety related components addressed in the BWRVIP-42 document.

The staff requests that the BWRVIP review and resolve the issues raised in the enclosed SE,

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l-5 and incorporate the staff's concems into a revised BWRVIP-42 report. Please inform the staff in writing as to tais resolution.

5.0 REFERENCES

1. Terry, C., BWRVIP, to USNRC, "BWR Vessel and Intemals Project: BWR LPCI Coupling Inspection and Flaw Evaluation Guidelines (BWRVIP-42)," EPRI Report TR 108726, December 11,1997.

2. Carpenter, C.E., USNRC, to C. Terry, BWRVIP, " Proprietary Request for Additional Information - Review of *BWR Vessel and Intemals Project, BWR LPCI Coupling inspection and Flaw Evaluation Guidelines (BWRVIP-42)" (TAC No. MA1104)," April 18, 1998.

3. Wagoner, V., BWRVIP, to USNRC, "BWRVIP Response to NRC Recuest for Additional Information on BWRVIP-42 (Reference Project 704)," September 8,1998.

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