BVY-93-112, Provides Results of Insp Activities During 1993 Refueling Outage W/Regard to Rv Cladding & Plans for Future Insps,As Requested in NRC .Indications in Areas of Cladding Inside Rv Head Discovered

Provides Results of Insp Activities During 1993 Refueling Outage W/Regard to Rv Cladding & Plans for Future Insps,As Requested in NRC .Indications in Areas of Cladding Inside Rv Head Discovered

ML20057E882
Person / Time
Site:	Vermont Yankee
Issue date:	10/06/1993
From:	Tremblay L VERMONT YANKEE NUCLEAR POWER CORP.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
BVY-93-112, NUDOCS 9310130315
Download: ML20057E882 (2)

Text

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VERMONT YANKEE NUCLEAR POWER CORPORATION

. Ferry Road Brattleboro. VT 05301-7002

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ENGINEERING OFFICE

%0UAN STREET DOL TOf 4 MA 0170 s .

October 6,1993 United States Nuclear Regulatory Commission BVY 93-112 ATrN: Document Control Desk Washington, DC 20555

References:

a. License No. DPR-28 (Docket No. 50-271)

b. Ietter, VYNPC to USNRC, BVY 92-055, dated April 5,1992

c. Ietter, USNRC to VYNPC, NVY 92-057, dated April 17,1992

d. Ietter, VYNPC to USNRC, BVY 93-066, dated July 1,1993

e. Letter, USNRC to VYNPC, NVY 93-162, dated September 29,1993

Subject:

Reactor Vessel Clad Inspection during the 1993 Refueling Outage Des . Sir:

The purpose of this letter is to provide the results of inspection activities during the 1993 refueling outage with regard to reactor vessel cladding and to provide our plans for future inspections, as requested by your recent letter [ Reference (e)] .

During the 1992 refueling outage, Vermont Yankee performed a reactor vessel head inspection to address concerns raised in General Electric SIL No. 539. This SIL discussed the situation at Quad Cities Unit 2, where cracking was detected in both the stainless steel cladding and the low alloy steel under the cladding of the reactor pressure vessel head. Vermont Yankee discovered indications in areas of cladding inside the reactor vessel head. Additional inspections myealed similar areas of cracking on the reactor pressure vessel flange and an indication at a dryer suppon bracket attachment weld.

As a result of the fm' dings from the 1992 refueling outage, Vermont Yankee performed extensive ultrasonic examination techniques of more than 140 indications and performed manual exploration of a typical " worst case" visual indication to investigate the nature of the indications.

As a result of those investigations, Vermont Yankee concluded that the indications were due to stress corrosion cracking (IGSCC) of the furnace sensitized stainless steel cladding, with no evidence to conclude that the indications compromised the structural integrity of the reactor pressure vessel or vessel head.

'Ihe results of these investigations were submitted to NRC in Reference (b) and presented to  !

representatives of NRC staff in a meeting held on April 8,1992. NRC concurred with these  !

findings via Reference (c). In Reference (b) Vermont Yankee also committed to submit a plan for j future inspections no later than 30 days prior to the next (1993) refueling outage. This inspection j plan was submitted to NRC via Reference (d). j l

The purpose of the follow-up inspection in the 1993 refueling outage was to verify the findings and conclusions of the previous inspection; i.e. that the clad cracking at Vemiont Yankee is due to IGSCC and presents no concern relative to the structural integrity of the reactor pressure vessel assembly. l l g 1 Onn r ,  ;

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United States Nuclear Regulatory Commission October 6,1993 Page 2 Consistent with the statistical sampling approach that was used in the original inspection, Vermont Yankee inspected the following areas:

1. The eight regions of the RPV head flange that were inspected in 1992 were reinspected.

Ukrasonic (UT) inspections from the inside diameter of the head flange were performed to determine flaw depths.

2. The flaw that was panially ground to determine flaw depth was inspected adjacent to the ground area by performing UT from the inside diameter of the head flange.

3. The cirrumferentially oriented flaws at the top of the manually applied cladding area near the flange to dome weld and on the dollar plate were inspected by performing UT from the inside diameter of the head.

4. The dryer support bracket indication was inspected by performing UT from the vessel outside diameter.

These inspections concluded that the cracking continues to be cont 40ed wholly within the stainless steel vessel cladding material, with no evidence of base metal penetration. This confm' ns the technical assessment that was made in 1992.

With regard to our future inspection plans, we intend to revise the Vermont Yankee Inservice Inspection Program to provide for a similar clad inspection once each period for the next two inspection periods. As previously committed in Reference (b), Vermont Yankee will also include a remspecuon of the dryer support bracket in the next two inspection periods.

Should you have additional questions with regard to this issue, please contact this office.

Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION Q

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Leonard A.Tremblay,Jr. 1 Senior Licensing Engineer \

cr: USNRC Region I Administrator USNRC Resident Inspector- VYNPS USNRC Project Manager- VYNPS i