ML17258A369

Responds to Generic Ltr 81-21 Re Void Formation in Reactor Vessel Head During Natural Circulation Cooldown Event of 800601.If Large Variations in Pressurizer Level Were to Occur,Cooldown Would Be Stopped & RCS Repressurized

ML17258A369
Person / Time
Site:	Ginna
Issue date:	11/13/1981
From:	Maier J ROCHESTER GAS & ELECTRIC CORP.
To:	Crutchfield D Office of Nuclear Reactor Regulation
References
GL-81-21, NUDOCS 8112160185
Download: ML17258A369 (6)

Text

0 REGULATORY, INFORMATION DISTRIBUTION SYSTEM (RIDS)

AOCE'SSION NBR:8112160185 DOC ~ DATE: 81/11/13 NOTARIZED:

NO DOCKET FAOIL:SO"244 Robert Emmet Ginna Nuclear PlantE Unitt 1E 'Rochester G

05000244 AUTH ~ NAME AUTHOR AFFILIATION MAIEREJ,E, "Rochester Gas 8 Electric Carp>

IRBC IP ~ NAME RECIPIENT AFFILIATION GRUTCHFIEI DED, Operating Reactors Branch S

SUBJECT:

Responds

.to Generic Ltr 81 21 re void formation in reactor vessel head during natural circulation cooldown event of 800601,If large variations in pressurizer level were to occur<cooldown would be Nstopped 8

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'g TOIL SlaTC ROCHESTER GAS AND ELECTRIC CORPORATION

~ 89 EAST AVENUE, ROCHESTER, N.Y. 14649 JOHN E. MAIER Vee WraNent TCLCPH'INC naca conc vie 546 2700

, November 13, 1981 Director of Nuclear Reactor Regulation Attention:

Mr. Dennis M. Crutchfield, Chief Operating Reactors Branch No. 5 U.S. Nuclear Regulatory Corm'.ssion Washington, D.C.

20555

Subject:

Generic Letter No. 81-21, Natural Circulation Cooldown R.E. Ginna Nuclear Power Plant Docket No. 50-244

Dear Mr. Crutchfield:

Generic Letter No. 81-21 requested us to review our plant operation in light of the St. Lucie Unit 1 void formation, in the reactor vessel head during natural circulation cooldown event of 6/1/80, and to furnish the NRC an assessment of our facility procedures and training program.

'Ihe assessment was to include:

F 1)

A demonstration (e.g. analysis and/or test) that controlled natural circulation cooldown from operating conditions to cold shutdown conditions, conducted.in accordance with your procedure, should not result in reactor vessel voiding:

Response

The Westinghouse Owners Group undertook a study with Westinghouse to ascertain the potential for void formation in Westinghouse designed NSSS's during natural circulation cooldown/ depressurization transients and to develop appropriate modifications to Westinghouse Owners Group Reference Operat~ Instructions.

A description of the study including ma)or assumptions and results were transmitted to the NRC, Mr. Paul S.

Check on April 20, 1981, through OG-57 by Mr. Robert W. Jurgensen.

Following the issuance af the WCB Reference Abnormal Operating Instructions and Workshops with utility personnel, Ginna g'Y operating procedure 0-2.4 "Plant shutdown fran hot shutdown to cold shutdown during blackout" was revised to incorporate 0

instructions to the operators on how to conduct a controlled natural circulation cooldown from operating conditions to cold shutdown conditions precluding void formation in the upper reactor vessel head region.

8ii2i60i85 81iii3 PDR ADQCK 05000244 F'DR

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Page 2

2)

Verification that supplies of condensate-grade auxiliary feedwater are sufficient to support your cooldown nathod:

Response

The amount af feedwater necessary to remove decay heat during natural circulation cooldown has been evaluated.

The evaluation assumed a 25 F/hour cooldown from 550'F to 350'F (8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br />).

Ches would take the plant from hot shutdown conditions to the point where the residual heat removal system (HHRS) could be activated for decay heat removal.

In addition, it was assumed that the CKN fans were unavailable, thereby requiring an additional-9 hours "soak Cine" prior Co RHRS initiation.

The analysis employed Che decay heat relationship given in Branch Techrd.cal Position ASB 9-2 of NUR1F-0800 for 16,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of full power operation.

The result, is that approximately 72,000 gallons of water are required. If a cooldown. rate of 20'F/hour is assumed, in order Co provide operating nargin, they lass than 79,000 gallons of water is required for the 19 hour2.199074e-4 days <br />0.00528 hours <br />3.141534e-5 weeks <br />7.2295e-6 months <br /> period.

The quantity cf."condensate grade water available on site exceeds the minimum required.

Plant Technical Specifications require at least 22,500 gallons of water in the condensate storage tanks.

Normally each of Wo tanks contains this amount.

The 22,500 gallons is adequate to remove decay heat for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 20 minutes based on ASB 9-2 (or 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> based on the more conservative Technical Specifications relationship for decay heat).

In addition; the hotwells contain at least 50,000 gallons of.water and the AVT condensate storage tank normally contains between 30,000 and 75,000 gallons of water.

Thus this total available condensate grade water is at least 102,500 gallons and nay exceed 170,000 gallons.

Condensate transfer pumps can be used to transfer water from the hotwell or the AVT condensate storage tank to the auxiliary feedwater system condensate tanks for use.

These pumps are normally supp'.ed from a non-safeguards bus; however, M off-site power is lost, the non-safeguards bus could be energized from a safeguards bus by manual transfer.

Sufficient time is available prior to a need for the hotwell or AVT condensate water to ~i lement the bus tie.

In

addition, the deminerialized water treatment system could also be placed in operation by energizing from a safeguard bus by manual transfer, should off-site power be lost.

Page 3

Should any of the previous mentioned methods be unavailable, an unlimited supply of water is available from the city-fed fire hydrant system.

Hoses would be used to transfer water from the hydrants located on site to the condensate storage tanks.

3)

A description of your training program and the provisions af your procedures (e.g. lind.ted cooldown rate, response to rapid change in pressurizer level) that deal with prevention af mitigation of reator vessel voiding.

Response

Training for Ginna licensed personnel on operating procedure 0-2.4 was conducted during October 15, 16 and 17, 1981.

Licensed personnel that could not attend the training classes were issued training naterial'or self study.

Provisions have been included M operating procedure 0-2.4. to: a)

< limit cooldown rate to 25'F/hour, b) maintain necessary

'subcooling requirements during depressurization, c) preclude depressurization of the RCS before the entire RCS (including~'he upper head region and the steam generator U-tubes) is less than 200'F, d) to make personnel aware that a possible steam void formation under the reactor vessel upper head during natural circulation cooldown would be indicated by a rapid variation in pressurizer level, arxi e) if large variations in pressurizer level were to occur, cooldown would be stopped and the RCS would be repressurized to collapse potential voids.

Very truly yours,

'Jo E. Maker