ML20207E747

Safety Evaluation Granting Request Re Reduction of IGSCC Insp of Category D Welds Due to Implementation of HWC to License DPR-35

ML20207E747
Person / Time
Site:	Pilgrim
Issue date:	05/27/1999
From:	NRC (Affiliation Not Assigned)
To:
Shared Package
ML20207E738	List: ML20207E735 ML20207E747
References
GL-88-01, GL-88-1, NUDOCS 9906070131
Download: ML20207E747 (3)

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UNITED STATES

.s# - NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. asseMoM SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REDUCTION OF IGSCC INSPECTION OF CATEGORY D WELDS DUE TO IMPLEMENTATION OF HYDROGEN WATER CHEMISTRY BOSTON EDISON COMPANY (BECo)

PILGRIM NUCLEAR POWER STATION DOCKET NO,50 293

1.0 INTRODUCTION

By letter dated September 4,1998, Boston Edison Company (the licensee, BECo) submitted a request for N.RC approval of a reduced inspection frequency regarding the intergranular stress corrosion cracking (IGSCC) inspection to be performed at Pilgrim Nuclear Power Station (PNPS) during the upcoming refueling outage (RFO) 12. RFO 12 began on May 8,1999. Due to the implementation of hydrogen water chemistry (HWC) at PNPS, the licensee proposed to inspect all IGSCC Category D welds every four fuel cycles instead of every two fuel cycles per l Generic Letter (GL) 88-01,' Specifically, the licensee requested schedule relief for the examination of 11 IGSCC Category D welds in the recirculation piping system. The affected Category D welds are 1012-inch inlet nozzles to safe-end welds and 128-inch outlet nozzle to safe end welds. Wolds in reactor water cleanup, residual heat removal and core spray systems )

are not included because electrochemical corrosion potential (ECP) measurements are not performed in these systems.

2.0 EVALUATION The staffs position in GL 88-01 allowed a reduced IGSCC inspection frequency when a fully effective HWC is maintained. To provide the industry with guidelines for implementing HWC and receiving inspection credit, the BWR Owners' Group (BWROG) issued a topical report in April 1991, NEDC-31951P, " Implementation of improved Water Chemistry and Technical Basis for Revised Piping inspection Schedules." The staff reviewed the subject topical report and found

that some of the BWROG proposed criteria were not adequately justified and required some

. modifications.' The staff-approved criteria for an acceptable HWC program and a reduced  ;

. Inspection frequency are provided in the staffs safety evaluation (SE) dated January 10,1995.

In a response to the staffs SE, the BWROG submitted to the NRC Supplement 1 to Topical Report NEDC-31951P. Supplement 1 proposed alternative criteria for an acceptable HWC program. PNPS is the lead plant to apply for IGSCC inspection relief referencing Supplement 1 to NEDC-31951P, dated April 1998. '

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Enclosure

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The licensee implemented continuous HWC in cycles 9,10,11, and in current cycle 12. During cycles 9 and 10, ECP was measured externally from the autoclave in the crack arrest verification system (CAVS). During cycle 11 and in current cycle 12, the in-situ ECP probe was installed at the suction decontamination flange to the "A" loop recirculation pump. Due to the i effect of radiation the in situ ECP measurements were not available during the latter portion of fuel cycle 11. Hydrogen is injected into the feedwater when the reactor power exceeds 40 percent. The hydrogen is injected at a rate of 32 scfm at 100 percent reactor power. The licensee has benchmarked several operational parameters against the in-situ ECP measurements which include: (1) feedwater hydrogen injection rate, (2) reactor recirculation dissolved oxygen, (3) reactor recirculation dissolved hydrogen, and (4) main steamline radiation levels. The HWC availability, based on ECP measurements in cycle 11 and in the current cycle (from 4/97 ta 8/98), is reported to be 86.7 percent and 92.9 percent, respectively, if the same level of HWC availability is maintained during the remainder of the current cycle, the average HWC availability for the 2 cycles (11 and 12) would be 89.8 percent which is slightly below the staff-approved 90 percent HWC availability.

The staff has reviewed the licensee's HWC program and has determined that the licensee has implemented an HWC program at PNPS which meets the criteria proposed in Supplement 1 to NEDC-31951P. Based on the staffs initial review, the proposed criteria in Supplement 1 may need some modifications. Furthermore, the licensee-proposed schedule for inspecting all 11 Category D welds in the recirculation system every 4 refueling cycles does not meet the guidelines provided in the NRC staffs SE dated January 10,1995. The current agreed upon schedule is 50 percent every 2 fuel cycles when effective HWC is implemented. This inspection frequency is endorsed by the BWROG in Supplement 1 to NEDC-3159P.

The staff notes that the licensee's HWC program implemented at PNPS is very close to meeting the criteria stipulated in the staffs SE dated January 10,1995. In particular, the licensee has performed in-situ ECP measurements in recent cycles (cycle 11 and in the current cycle) and the HWC availability exceeds 90 percent in the current cycle. Therefore, the staff is granting the licensee a one-time reduced inspection frequency. This would allow the licensee to inspect 25 percent of the referenced 11 Category D welds in the recirculation system during the upcoming refueling outage.

3.0 CONCLUSION

i Based on its review of the licensee's submittal, the staff concludes that the licensee-proposed inspection for all 11 Category D welds in the recirculation system every 4 fuel cycles is not '

acceptable because the proposed schedule does not meet the guidelines provided in the staffs SE dated January 10,1995. The current staff-approved frequency is 50 percent every 2 fuel cycles. This schedule is endorsed by the BWROG in Supplement 1 to NEDC-3159P. This frequency of inspection was approved in the staffs SE although three items remain open. The staff has not yet completed its review of Supplement 1 and, therefore, any further action will be incumbent upon the licensee after the Supplement i review is complete. However, by considering the in-situ ECP measurements performed in recent cycles (cycle 11 and in current 4 cycls) and that the HWC availability exceeds 90 percent in the current cycle, the staff has ,

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l determined that the licensee may inspect the refereneca il Category D welds in accordance i with a reduced schedule of 25 percent for the upcoming refueling outage. The staff is  ;

granting this request because it expects thadee HWC average availability will be sufficient based on the performance to date. It should be noted that this is a one-time inspection relief.

For seeking inspection relief for these welds beyond the upcoming refueling outage, the licensee should follow the guidelines in the staffs safety evaluation dated January 10,1995, or the safety i evaluation of Supplement 1 to NEDC-3159P when it becomes available. Inspection credit for j HWC is also a topic that will be considered in the overall review of the inspection frequencies 1

-contained in NUREG 0313, Revision 2. This is part of an action with industry to, if justified, reduce the burden of the augmented inspection. ,

Principal Contributor: W. Koo i Date: hy 27,1999 l l

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