ML20217F342

SER Accepting Plans for 1998 & 1999 Refueling Outages Re Reactor Vessel Internals for Plant

ML20217F342
Person / Time
Site:	Vermont Yankee File:NorthStar Vermont Yankee icon.png
Issue date:	03/25/1998
From:	NRC (Affiliation Not Assigned)
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ML20217F334	List: ML20217F330 ML20217F342
References
NUDOCS 9803310359
Download: ML20217F342 (4)

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UNITED STATES g NUCLEAR REGULATORY COMMISSION

• WASHINGTON, D.C. seess 4001 SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION REGARDING REACTOR VESSEL INTERNALS INSPECTION AND REPAIR ACTIVITIES DURING THE 1998 AND 1999 REFUELING OUTAGES VERMONT YANKEE NUCLEAR POWER CORPORATION VERMONT YANKEE NUCLEAR POWER STATION DOCKET NO. 50-271 1

1.0 INTRODUCTION

By letter dated September 30,1997, Vermont Yankee Nuclear Power Corporatum (the licensee) submitted its inspection plans for the Vermont Yankee Nuclear Power Station (VY) spring 1998 and fall 1999 refueling outages for NRC staff review and approval. The licensee intends to use the recommendations of several Boiling Water Reactor Vessel and intemals Project (BWRVIP) guidelines in the performance of intemal component examinations and evaluationa 6Jring the upcoming refueling outages.

2.0 EVALUATION The licensee provided its evaluation of several reactor pressure vessel (RPV) intemal components. The NRC staff review of the licensee's submittal follows.

Core Shroud The licensee stated that an ultrasonic inspection of the VY circumferential welds was completed in the spring of 1995, and as a result of that inspection a full circumferential weld repair, consisting of four tie rods, was performed in the fall of 1996. In conjunction with the repair, ultrasonic and oddy current inspections of the repair design reliant welds was also performed during the fall 1996 outage. The design reliant welds consist of portions of eight vertical welds, six ring segment welds and portions of welds H8 and H9 at the jet pump baffle plate. The licensee reported that no cracking was found in any of these welds. Further, the licensee stated I that the 1996 vertical and ring segment weld inspections will meet the BWRVIP guidelines for reinspection of BWR core shrouds (BWRVIP-07) for a complete baseline inspection of repaired shrouds, as revised. The licensee stated that during its spring 1998 outage that it will perform the first cycle inspection of all four tie rods, which will consist of a visual examination. The staff finds the above to be acceptable.

Shroud Buoport 1

in the fall of 1996, the licensee performed ultrasonic and oddy current inspection of welds H8 and H9 and no cracking was found. The BWRVIP is drafting shroud eupport inspection and flaw i evaluation guidelines; however, the licensee states that the VY fall 1996 inspection meets the current BWRVIP draft guidelines for a baseline examination. The staff finds this acceptable for the upcoming outage, but notes that the licensee may need to revise its plans based on the staff's review of the BWRVIP report, when submitted.

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2-Core Sprav Piping The licensee stated that it performed ultrasonic inspection of 39 core spray piping circumferential

. welds and visual inspection of 5 circumferential welds that were not accessible for the ultrasonic inspection during its fall 1996 outage, which represented 100 percent of the accessible core spray piping welds, and that these inspections met the requirements of the BWRVIP Core Spray

Intemals inspection and Fisw Evaluation Guidelines (BWRVIP-18) for a baseline examination.

Two non-pressure boundary mechanical welds, where the core spray piping penetrates the core shroud, were found to have indications of possible intergranular stress corrosion cracking ~

. (lGSCC). The flaw analysis evaluated several possible conditions of the core spray piping, '

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including the limiting case where all four mechanical collar welds were completely failed.

' The staff evaluated the licensee's analysis and authorized operation through the end of Cycle 19

. without performing weld repairs. Operation beyond Cycle 19 would depend on the satisfactory evaluation of the reinspection results or by implementing acceptable repairs during the next

refueling outage. The licensee stated that it will role.spect the five wolds that were inspected visually in the fall 1996 outage during the spring 1998 outage, and will visually reinspect the two core spray piping welds that exhibited possible cracking. Further, the licensee stated its intention to fully replace the core spray piping system intemal to the reactor vessel (excluding the spargers) during its 1999 refueling outage, and , as such, does not plan to repair the cracked core spray pipe collar welds unless the reinspection warrants such a repair. The staff finds this to be acceptable Core Soray Spargers The licensee has been following the requirements of IE Bulletin 8013 for the inspection of core spray spargers. Beginning with the spring 1998 outage, the licensee intends to follow the guidance of the BWRVIP Core Spray Intemals inspection and Flaw Evaluation Guidelines (BWRVIP-18). The staff finds this position to be acceptable, but notes that the staff's review of the BWRVIP 18 report may necessitate modifications to the licensee's re-inspection schedule or may require other actions.

Too Guide The licensee stated that it had completed GE SIL No. 588 inspection recommendations in the fall 1996 refueling outage and will continue to perform examinations as recommended by GE SIL No.

554. They will perform visual inspections of top guide beams as they become accessible during the normal course of refueling operations. Further, the licensee intends to install top guide wedges during the fall 1999 refueling outage and will acquire the necessary dimensional information during the spring 1998 retuoling outage. Because the licensee intends to install top

j. guide wedges in 1999, it does not plan to perform any supplemental inspections of the top guide alignment hardware in 1998, except as in preparation for the 1999 refueling outage.

. The BWRVIP Top Guide Inspection and Flaw Evaluation Guidelines (BWRVIP-26) were published in December of 1996 and would require for VY a VT-1 inspection of welds in two

- adjacent alignment assemblies every other cycle and a visual inspection every other cycle of rim weld locations made accessible during normal refueling activities. The licensee stated that the

' welds in question are virtually inaccessible for visual inspection, and that a "best effort" visual examination (similar to a VT-3 examination) of two of the alignment assemblies was performed

3-in 1996. Further, the licensee stated that ultrasonic inspection of these welds was investigated and, while accessibility to some of the welds is improved, the majortty would still not be accessible, even from allemative surfaces. Additionally, there are no vendor tools that currently exist or are in development to provide better access for either ultrasonic or visual inspection.

Finally, the BWRVIP inspection Committee has not yet provided guidance on the examination of the above top guide components. Based on the above, the staff concludes that the proposed course of action is acceptable.

Core Plate The licensee stated its intentions to install core plate wedges during the fall 1999 refueling outage which would preclude the need for inspection of the core plate rim hold-down bolts, as is required by the BWRVIP Core Plate inspecticn and Flaw Evaluation Guidelines (BWRVIP-25),

' which is still under staff review. Since the licensee intends to install core plate wedges in 1999, it does not plan to perform any inspection on the core plate in 1998, except as in preparation for

. the 1999 refueling outage. GE SIL No. 588 inspection recommenda'Jons were completed during the fall 1996 refueling outage. Based on the above, the staff concludes that the proposed course of action is acceptable.

Jet Pump Assemblies The licensee stated its intention to perform inspections of the jet pump assemblies during the 1998 or 1999 outage in accordance with the BWRVIP Jet Pump Assembly inspection and Evaluation Guidelines (BWRVIP-41), which is presently under staff review. The current BWRVIP draft guidelines require a 50% sample of the high priority welds (essentially all of the circumferential welds in the riser, mixer, diffuser and adaptor pieces) at the nex1 refueling outage.

There are approximately 190 of these welds at VY. In accordance with recommendations in NUREG/CR-3052, VY also intends to perform ultrasonic inspection of the jet pump hold-down beams during the 1998 refueling outage.

Since several plants have detected cra:: king in jet pump riser circumferential welds, inspection of these components should be of highr priority to the licensee, and the staff requests that a best-effort inspection be performed during the 1998 outage, with followup during the 1999 outage.

Standbv Linuld Control Svstem The licensee stated its intention to follow the BWRVIP Standby Liquid Control System inspection and Flaw Evaluation Guidelines (BWRVIP-27) and inspect the nozzle-to-safe end weld extemal to the vessel _if a technique is developed in time for the 1998 refueling outage.

The staff notes that at VY the standby liquid control system safe end is low carbon (0.019%)

stainless steel material, and thus not considered to be susceptible to IGSCC. However, the staff encourages that this inspection be peformed.

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3.0 CONCLUSION

The NRC staff concludes that the proposed actions, as described above, are acceptable. Based on the above, the NRC staff has concluded that there is reasonable assurance that plant

. operation in this manner poses no undue risk te the health and safety of the public.

The NRC staff Is presently reviewing several BWRVIP documents, and, while the NRC staff has not identified any major deficiencies in the BWRVIP's technical assessments, neither has the NRC staff made a determination as to their overall acceptability. Therefore, if concoms are found during the review of the several BWRVIP reports and the licensee follows the BWRVIP guidance, the NRC staff may request that the licensee also address these concems on a plant-specific basis.

Principal Contributor: C. E. Carpenter Date: Ma rch 25, 1998 d

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