ML20214T989

Safety Evaluation Re Util 870112 Proposed Plans to Inspect Two Overlay Repaired Core Spray safe-ends in Lieu of Replacement During Upcoming 1987 Refueling Outage.Plans Acceptable,Providing That Insp Results Satisfactory

ML20214T989
Person / Time
Site:	Vermont Yankee
Issue date:	05/28/1987
From:	Office of Nuclear Reactor Regulation
To:
Shared Package
ML20214T984	List: ML20214T981 ML20214T989
References
IEIN-84-41, NUDOCS 8706100511
Download: ML20214T989 (2)

Text

F s pmc j y, m[g UNITED STATES y ,y g NUCLEAR REGULATORY COMMISSION

5. ,j WASHINGTON, D. C. 20555 o, a

,0 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATING TO THE REPAIR OF CORE SPRAY SAFE ENDS FOR FACILITY OPERATING LICENSE NO. DPR-28 VERMONT YANKEE NUCLEAR POWER CORPORATION VEPMONT YANKEE NUCLEAR POWER STATION DOCKET NO.: 50-271 1.0 IfiTRODUCTION During the 1980 refueling outage at Vermont Yankee ultrasonic and liould penetrant examinations were perfomed on the core spray buttered nozzle-to-safe-end welds in accordance with I&E Notice 84-41. Cracking was found in the Inconel 182 butter of both core spray nczzle-to-safe-end welds. The cracking was assured to be IGSCC (Intergranular Stress Corrosion Cracking). By letters dated May 5 and June 2,1986, Ven"ont Yankee Nuclear Power Corporation (the licensee) proposed repair of the core spray safe-ends.

The licensee proposed to weld overlay repair both cracked core spray nozzle-to-safe-end welds with Inconel 82. By letter dated June 16, 1986, the NRC staff found the proposed repairs acceptable on an interim basis, but recomended that the licensee seriously consider replacing both cracked core spray safe-ends during the 1987 refueling outage.

By letter dated January 12, 1987, the licensee infonted the staff of their plans to inspect rather than replace the two core spray safe-ends during the 1987 outage.

2.0 EVALUATION The staff has reviewed the submittal dated January 12, 1987, from the licensee l regarding their plan to inspect the two overlay repaired core spray safe-ends I instead of replacing them during the upcoming 1987 refueling outage. The core spray safe-ends were found to be cracked and were overlay repaired during the 1986 refueling outage. In the staff's safety evaluation report (SER) dated June 13, 1986, the staff reconinended that the licensee consider replacing both repaired core spray safe-ends as a permanent means to ensure the structural integrity of the nozzles and the reactor pressure vessel without the need for augmented inspection of the safe-ends. In the licensee's submittal, Vennont 8706100511 870528 PDR ADOCK 05000271 g PDR

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Yankee contended that the replacement of the repaired safe-ends during the upcoming outage is not warranted because the use of the overlays can be justified for many fuel cycles based on a conservative fracture mechanics analysis. We find that the thickness of the repaired overlays meets the staff's requirements for full structural (standard) overlays and the repaired overlays are entering the service of a second fuel cycle. Based on the current staff position, the licensee's proposed plant to inspect the repaired safe-ends instead of replacement is acceptable for the next fuel cycle.

However, we must evaluate the inspection methodology and results to detennine the suitability of the repaired safe-ends continued service through the next fuel cycle.

In a telephone conversation on April 16, 1987, the staff discussed VYNPC's proposed inspection plan for the repaired core spray safe-ends and expressed concern over the adequacy of the inspection. Because of the complex configuration of the repaired core spray safe-ends, the growth and initiation of the cracks underneath the overlay might be difficult to monitor or detect.

VYNPC indicateo that the EPRI reconnended inspection procedures and methodology for overlay examination would be qualified on a full section thickness mockup to ensure the perfonnance of an adequate inspection.

Furthermore, ultrasonic testing personnel qualified at EPRI for both overlay examination and sizing would be used for this examination. Preliminary testing results perfonned on the mockup block had shown that detection of the defects in the Inconel 182 butter and SA508 nozzle materials through the overlay was successful. The licensee also plans to inspect the nozzle transition area and area ad,iacent to the overlay by liquid penetrant to ensure that no cracking occurs due to temper embrittlement or weld shrinkage stresses. The licensee provided details of the proposed inspection of the core spray safe-ends by letter dated Pay 7,1987.

3.0 CONCLUSION

We conclude that VYNPC's proposed plan to inspect the repaired safe-ends, instead of replace them, is acceptable for the next fuel cycle, providing that the inspection results are satisfactory.

Principal Contributor: W. Koo i

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