B12527, Responds to Request for Addl Info Re Generic Ltr 87-05, Assessment of Licensee Measures to Mitigate &/Or Identify Potential Degradation of Mark I Drywells. Daily Visual Insp Performed for Water Leakage in Torus Room,Per Procedure

Responds to Request for Addl Info Re Generic Ltr 87-05, Assessment of Licensee Measures to Mitigate &/Or Identify Potential Degradation of Mark I Drywells. Daily Visual Insp Performed for Water Leakage in Torus Room,Per Procedure

ML20214D250
Person / Time
Site:	Millstone
Issue date:	05/12/1987
From:	Mrockza E, Mroczka E NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM)
References
AO6437, B12527, GL-87-05, GL-87-5, NUDOCS 8705210253
Download: ML20214D250 (4)

Text

• e General Offices

• Seiden Street Berhn Connecticut 9 E' sY nSNcowa= P.O. BOX 270

= =8 *a'sa mma c HARTFORD. CONNECTICUT 06141-0270 L ' J %7'.'["Jg"'",C (20 0 665-5000 May 12,1987 Docket No. 50-245 A06437 B12527 Re: 10CFR30.54(f)

U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20535 Gentlemen:

Millstone Nuclear Power Station, Unit No.1 Response to Request for Additional Information -

Assessment of Licensee Measures to Mitigate and/or Identify Potential Degradation of Mark I Drywells (Generic Letter 87-05)

Generic Letter 87-05(l) requested information from BWR owners regarding their intended actions to determine if drywells at their facilities have degraded by a corrosion mechanism similar to that which occurred at the Oyster Creek Nuclear Generating Station from 1980 to 1986. Northeast Nuclear Energy Company (NNECO) is hereby providing the requested information concerning Millstone Unit No.1.

ITEM 1 Provide a discussion of your current prograin aiid any future plans for determining 11 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

Current Program - A daily visual inspection is performed for water leakage in the torus room area according to Operations Procedure 1-OPS-10.09, " Plant Equipment Check Log."

(1) R. M. Bernero letter to All Licensees of Operating Reactors, Applicants for Operating Licenses, and Holders of Construction Permits for Boiling Water Reactors (BWRs) with Mark i Drywells (Generic Letter 87-05), dated March 12,1987. *>{

8705210253 870512^ \

PDR ADOCK 05000245 P PDR

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U.S'. Nuclar Regulat:ry Ccmmission B12527/A06437/Page 2 '

May 12,1987 Future Program - A detailed visual inspection will be performed during the 1987 refueling outage on the eight 1-inch drain lines to verify the following items:

o Plastic or metal pipe o Perforated cap or screen on pipe end o Sand contained within pipe o Perform a remote visual inspection using a borescope to inspect pipe internals if not filled with sand.

o Perform additional air testing as deemed necessary based on the results of above inspection items.

ITEM 2 Provide a discussion of preventative maintenance and inspection activities that are currently performed or are planned to minimize the possibility of leakage from the refueling cavity past the various seals and gaskets that might be -

present.

Response

. As. part of the Preventative Maintenance Management System, the pre-refuel -

requirements preparation package specifies that the reactor to drywell and the drywell to refueling, cavity ' bellows leak detection flow switches shall be functionally tested.

Presently, th'e reactor vessel to drywell bellows and the. drywell to reactor

- building bellows have a leak detection system which will alarm in the control.

. room in the event of a water leak.

As part . of Operations Procedure 1-OPS-10.09, a daily visual inspection is performed for water leakage in the torus room. This daily inspection -of the drain lines has shown no evidence of water leakage into the torus room. This is based on the absence of water marks and/or stains on the torus or torus room 3

' floor in the area of the 1-inch drain lines.

ITEM 3 Confirm the information listed in Table 1 is correct with regard to your facility.

Rfsponse The information listed in TA.ble 1 is correct with respect to Millstone Unit No.1.

In order to clarify the "yes" answer to the question in Table 1 of "was the gap material removed?," the fol*owing information is provided: In order to create this gap, typically a layer of foam material was attached to the steel prior to the concrete pour. To form the concrete shield wall at Millstone Unit No.1,2-inch

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• i U.S'. Nucl::ar Rcgulatory Commission B12527/A06437/Page 3 May 12,1987 thick sheets.of Ethafoam were placed over the steel liner and covered with a plastic sheet. .The concrete was then poured over this and allowed to set. The Ethafoam sheets were then removed creating the 2-inch void space. Upon removal of the Ethafoam, 2-inch thick by 6-inch deep sheets of polyurethane were placed 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 4 Mark I Owners Whose Designs Are Such That the Sand Cushion Is Open to Gap Between the Drywell Shell and Surrounding 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

During the 1987 refueling outage, ultrasonic thickness measurements will be taken on the drywell shell plates adjacent to the sand cushion. A representative sample will be taken based on MIL-STD-105D, " Sampling Procedures and Tables for Inspection by Attributes." Using the assumption that about fifty-four samples will be done in an effective dose rate field of 20 millirem per man-hour, af ter decontamination of piping and pumps in the area, the man-rem for just the inspection process is estir,ated to be a little under 10 man-rem. NNECO considers this to be signehennt, while representing the appropriate balance between obtaining data on drywell integrity and minimizing man-rem expenditures.

The above discussion constitutes NNECO's response to Generic Letter 87-05.

Should you have any questions concerning this matter, please feel free to contact my staff. .

Very truly yours, NORTHEAST NUCLEAR ENERGY COMPANY M m/

E.yMrockza f/

Senior Vice President cc: W. T. Russell, Region 1 Administrator J. J. Shea, NRC Project Manager, Millstone Unit No.1 T. Rebelowski, Resident inspector, Millstone Unit Nos. I and 2

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1 U'.5'. Nuctur R:gulat::ry Commission

--: 1 B12527/A06437/Page 4 May.12,1987 .

STATE OF CONNECTICUT)~

. . ) ss. Berlin _

'.' COUNTY. OF HARTFORD ) '

-- Then personally appeared before me, E. 3.' Mroczka, who being duly; sworn, did state' that he is Senior Vice President of Northeast Nuclear Energy Company, a

.: Licensee herein, .that .he- is authorized to execute and file the foregoing ,

information in -the name and on behalf of the Licensee' herein, and- that the

statements contained in 'said information are true and correct

to the best of his

' knowledge and bellef.'

Ju%wai >?P Notary Pu e My Commiss10h Expires March 31,1988 -

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