ML20247E608

Discusses Jet Pump Riser Circumferential Weld Insps Results. Flawed Welds Will Be Reinspected During Next Refueling Outage & Further Evaluated.Repts Re Insp Results,Encl

ML20247E608
Person / Time
Site:	Vermont Yankee
Issue date:	05/04/1998
From:	Reid D VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20247E613	List: ML20247E608 ML20247E622 ML20247E635 ML20247E652
References
BVY-98-67, NUDOCS 9805180400
Download: ML20247E608 (2)

Text

. 9 VERMONT YANKEE M

NUCLEAR POWER CORPORATION 185 Old Ferry Road, Brattleboro, VT 05301-7002 (802) 257-5271 May 4,1998 BVY 98-67 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555

References:

(a) Letter, VYNPC to USNRC," Vermont Yankee's Plans For the 1998 and 1999 Refueling Outages Regarding Reactor Vessel Internals," BVY 97-123, dated September 30,1997 (b) Letter, USNRC to VYNPC," Plans for the 1998 and 1999 Refueling Outages Regarding Reactor Vessel Internals- Vermont Yankee Nuclear Power Station (TAC No. M A0107)," NVY 98-44, dated March 25,1998

Subject:

Vermont Yankee Nuclear Power Corporation Liccase No. DPR-28 (Docket No. 50-271)

Jet Pump Riser Circumferential Weld Inspections in Reference (a) Vermont Yankee provided the NRC with its Reactor Vessel Internal Inspection plans for the 1998 and 1999 refueling outages. In Reference (b) the NRC acknowledged these plans and requested that Vermont Yankee perform a best efrort inspection of the jet pump riser circumferential welds during the 1998 refueling outage, in preparation for the 1998 refueling outage, Vermont Yankee contracted for the design and deployment of a new tool to volumetrically inspect all thirty (30) jet pump riser circumferential welds using ultrasonic testing (UT) techniques. Inspection techniques were qualified and were to be performed in accordance with the BWRVIP Guideline-41, "BWR Jet Pump Assembly inspection and Flaw Evaluation Guidelines." The subject welds are numbered RS-1 (thermal sleeve to riser elbow), RS-2 (elbow to riser), and RS-3 (riser to transition piece).

During the current outage, twenty six (26) of the thirty (30) subject welds were UT inspected.

Due to interferences, four welds (one RS-1 weld and three RS-3 welds) were inspected using modified VT-1 inspection techniques. The welds were cleaned prior to visual inspection.

The UT inspections identified a flaw indication in four of the RS-1 welds. Attachment 1 provides excerpts of the final inspection report and includes data for flawed welds N2B-RS-1, N2C-RS-1, N211-RS-1, and N2K-RS-1. The flaws were sized at 2.82",2.82",0.84", and 2.82" respectively.  ;

In addition to the identified flaw sizes, a flaw measurement uncertainty of 0.191" was added to j each end of the flaws for the evaluation process. Flaw lengths and locations were reviewed in ,

detail and verified for accuracy for each weld. l A " Flaw Handbook" has been developed by General Electric for Vermont Yankee to identify the l critical flaw size for each of the jet pump circumferential welds (Attachment 2). It was \\

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• VERMONT YANKEE NUCLEAR POWER CORPORATION BVY 98-67 / Page 2 determined that the RS-1 welds could contain a flaw as large as 16.41" long and still satisfy structural integrity requirements. A 16.41" flaw at end-of-cycle equates to a 5.4" flaw at startup, taking into account maximum possible flaw growth as a result of intergranular stress corrosion cracking and fatigue.

Additional conservative calculations were performed relative to the detected flaw length.

Allowing for measurement uncertainty it was also determined that a flaw of 3.21" length could (worst case) grow to 4.40" over the next operating cycle (Attachment 3). Using the guidance of BWRVIP-41, leakage through the maximum calculated crack was calculated and appropriately integrated into the affected analysis.

- The detected flaw lengths and conservatively projected flaw growth over the next operating cycle are therefore well within the envelope of acceptability for continued operation with regard to structural integrity and corresponding leakage.

Based upon the above and the attachments provided, it is demonstrated that jet pump riser integrity and performance is not compromised. It is anticipated that these flawed welds will be reinspected during the next refueling outage and further evaluated.

We trust that the enclosed information is responsive to your concerns. If you have any questions on this transmittal, please contact Mr. Thomas B. Silko at (802) 258-4146.

I Sincerely, VERMONT YANKEE NUCLEAR POWER CORPORATION Donald A. Reid Senior Vice President, Operations Attachments cc: USNRC Region 1 Administrator USNRC Resident Inspector- VYNPS l USNRC Project Manager- VYNPS l Vermont Department of Public Service

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