ML20213G841
| ML20213G841 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee File:NorthStar Vermont Yankee icon.png |
| Issue date: | 05/08/1987 |
| From: | Murphy W VERMONT YANKEE NUCLEAR POWER CORP. |
| To: | Murley T Office of Nuclear Reactor Regulation |
| References | |
| FVY-87-52, GL-87-05, IEIN-86-099, NUDOCS 8705180480 | |
| Download: ML20213G841 (4) | |
Text
7 a.
VERMONT YANKEE NUCLEAR POWER CORPORATION RD 5, Box 169, Ferry Road, Brattleboro, VT 05301 FVY 87-52 Warren P. Murphy Vice President and Manager of Operations (802) 257 5271 May 8, 1987 U.S. Nuclear Regulatory Commission Washington, D.C.
20555 Attn:
Office of Nuclear Reactor Regulation Mr. Thomas E. Murley
References:
a)
License No. DPR-28 (Docket No. 50-271) b)
Letter, USNRC to All Licensees of Operating Reactor (BWR's) with Mark I Drywells (Generic Letter 87-05),
dated 3/12/87 c)
IE Information Notice 86-99: Degradation of Steel Containments, dated 12/8/86
Dear Sir:
Subject:
Response to Generic Letter 87 Request for Additional Information - Assessment of Licensee Measures to Mitigate and/or Identify Potential Degradation of Mark I Drywells By Generic Letter 87-05 [ Reference b)] and pursuant to 10CFR50.54(f), you requested that each licensee of an operating reactor with Mark I drywell submit a formal response of its review. This letter provides Vermont Yankee Nuclear Power Corporation's response to that request.
Specifically, you requested, under oath or affirmation, responses to the following:
Item 1)
Provide a discussion of your current program and any future plans for determining if the drain lines that were provided at your facility for removing any leakage that may result from refueling or from spillage of water into the gap between the drywell and the surrounding concrete or from the sand cushion itself are unplugged and functioning as designed.
Response
Information Notice 86-99 [ Reference c)] identified a potential problem with drywell corrosion at Oyster Creek. Vermont Yankee began an immediate review of the conditions and their applicabilty to Vermont Yankee's containment. A walk-down was performed by the Operations Department which verified the installation 8705180480 870508
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-a VERMONT YANKEE NUCLEAR POWER CORPORATION U.S. Nuclear Regulatory Commission May 8, 1987 Page 2 of the drain lines (a total of eight 1" PVC drain lines) which lead from the sand region between the drywell shell and the concrete. A visual inspection was also performed which indicated no leakage from any of the eight drain lines.
Vermont Yankee will complete an internal inspection of the drain lines by using a borescope and verify that the drains are not plugged and will perform their intended function. This inspection will be accomplished prior to our 1987 refuel outage, which is scheduled to begin August 8, 1987.
This verification of properly installed drain lines, combined with no other evidence of a fuel pool leak, will provide Vermont Yankee adequate assurance that any potential water leakage into the sand region would not go undetected.
Item 2)
Provide a discussion of preventive maintenance and inspection activi-ties that are currently performed or are planned to minimize the possiblity of leakage from the refueling cavity past the various seals and gaskets that might be present.
Response
The existing refueling cavity design at Vermont Yankee includes fully welded stainless steel / carbon steel construction with a backup barrier channel and seal rupture drain.
In addition, an alarm system is provided to detect any bellows or drain line leakage.
Figure 1 Section A-A of the Oyster Creek drywell to cavity seal (of Generic Letter 87-05) indicates that the source of leaking was a gasket at the cavity drain. The 42' diameter drywell to reactor bellows at Vermont Yankee is sealed with a penetration weld not a gasket.
In addition, as a backup in the event of leakage in the bellows or drain piping, an additional stainless steel water barrier is included as part of the concrete liner to catch any water. A 3" diameter bellows rupture drain welded to the water barrier provides a flow path for any leakage to the equipment drain with an alarm system to notify operators in the event of bellows leakage.
Vermont Yankee will verify that the leak detection instrumentation is operable during the next refuel outage.
Item 3)
Confirm the information listed in Table 1 is correct with regard to your facility.
Response
The information that was originally provided in Table I was preliminary information only. A more detailed review has been completed with the following results.
VERMONT YANKEE NUCLEAR POWER CORPORATION
'U.S. Nuclear Regulatory Commission May 8,.1987 Page 3 Sand Gap Details Drawing Available Yes G191481, Rev. 2 Wall Thickness UT Performed No UT Method /Results Sent to NRC No Gap Material Ethafoam Was Gap Material Removed Yes - See Note 1 NOTE 1:
In order to create the 2" gap, a layer of Ethafoam material was attached to the steel. prior to the concrete pour. To form this 2" gap at Vermont Yankee, 2" thick sheets of Ethafoam were placed between the steel liner and a.040 sheet of Noblock plastic sheeting which kept the concrete from adhering to the Ethafoam.
Concrete was then poured against this in 3' lifts and allowed to set. The Ethafoam sheets were then removed creating the 2" gap.
Upon removal of the Ethafoam, 2" thick by 6" wide strips of polyurethane were placed circumferentially in the top of the opening to prevent objects from entering the gap. This process was repeated for the several concrete lifts necessary to form the shield wall.
Item Mark I Owners Whose Desians Are Such That the Sand Cushion Is Open To Gap Between The Drywell Shell and Surroundina Concrete Provide any plans for performing ultrasonic thickness measurements of the drywell shell plates adjacent to the sand cushion or any other proposed actions to ascertain if plate degradation has occurred.
Since the degradation that has occurred at Oyster Creek is localized, sufficient details should be included to show that the sampling basis for. ultrasonic thickness measurements is adequate in terms of size and test location.
Response
As identified in Reference b), Oyster Creek identified localized degrada-tion as a result of some water leakage into the sand region surrounding the con-tainment shell. This leakage was attributed to the deterioration of a drain line gasket at the drywell to cavity bellows.
Further, due to Vermont Yankee's design for the refuel bellows, we do not believe any water has or will leak into the 2" gap area undetected. Therefore, Vermont Yankee, assuming satisfactory results of its visual inspection of the drain lines, will conclude that no water has leaked into the sand gap area and if any water had it would have exited by way of the eight drain lines provided.
Based on the above discussion, combined with potentially significant ALARA concerns, Vermont Yankee feels ultrasonic testing of the drywell shell is not warranted. However, if our investigations indicate the drain lines were not operating properly or undetected water has i
penetrated the gap area, Vermont Yankee will submit a revised response for your review.
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1 VERMONT YANKEE NUCLEAR POWER CORPORATION U.'S. Nuclear Regulatory' Commission
- May 8, 1987 Page 4 We trust that the above information adequately addresses your request; however, should you have questions or desire additional information, please do not hesitate to contact us.
Very truly yours, VERMONT YANKEE NUCLEAR POWER CORPORATION WfY )
Warren P./ Murphy Vice President anu Manager of Operations
/dm STATE OF VERMONT)
)ss WINDHAM COUNTY )
Then personally appeared before me, Warren P. Murphy, who, being duly sworn, did state that he is Vice President and Manager of Operations of Vermont Yankee Nuclear Power Corporation, that he is duly authorized to execute and file the foregoing document in the name and on the behalf of Vermoni Yankee Nuclear Power Corporation and that the statements therein ere true to the best of his knowledge and belief.
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D Diane M. McCud l
Notary Public My Commission Expires February 10, 1991 NOTARY i
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