ML17324B148

Submits Description of Condition Involving post-LOCA long- Term Core Cooling Boron Requirements That May Be of Interest to Other Operators of Westinghouse Pwrs.Westinghouse Hc Walls Re Situation Encl

ML17324B148
Person / Time
Site:	Cook
Issue date:	11/17/1986
From:	Alexich M INDIANA MICHIGAN POWER CO. (FORMERLY INDIANA & MICHIG
To:	Harold Denton Office of Nuclear Reactor Regulation
References
AEP:NRC:1008, NUDOCS 8611260273
Download: ML17324B148 (11)

Text

REGULATORY IN l'lATION DISTRIBUTION.SYSTEM i (R IDS)

ACCESSIQN NBR: 8611260273 DOC. DATE: 86/11/17 NOTARIZED:

NO DOCKET I FACIL: 50-315 Donald C.

Cook Nuclear Poeer Plant>

Unit 1>

Ind iana 5

05000315 50-316 Donald C.

Cook Nuclear Power Plant>

Unit 2>

Ind iana 5

05000316 AUTH. NAl'lE AUTHOR AFFILIATION ALEXICH>l'l. P.

Indiana 8c Nichigan Electric Co.

REC IP. NANE RECIPIENT AFFILIATION DENTON> H. R.

Office of Nuclear Reactor Regulation>

Directov (post 851125

SUBJECT:

Submits descv iption of condition involving post-LOCA long-tevm cove cooling bovon requirements that may be of interest to other operatov'5 of Westinghouse PWRs. Westinghouse HC Walls 860821 ltv v e situation encl.

DISTRIBUTION CODE:

A001D COPIES RECEIVED: LTR ENCL SIZE:

TITLE:

OR Submittal:

General Distv ibution NOTES:

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INDIANA8 MICHIGAN ELECTRIC COMPANY P.O. BOX 16631 COLUMBUS, OHlO 43216 November 17, 1986 AEP:NRC:1008 Donald C.

Cook Nuclear Plant Unit Nos.

1 and 2

Docket Nos.

50-315 and 50-316 License Nos.

DPR-58 and DPR-74 POST-LOCA LONG-TERM CORE COOLING BORON REQUIREMENTS Mr. Harold R. Denton, Director Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C.

20555

Dear Mr. Denton:

This letter describes a condition involving post-LOCA long-term core cooling boron requirements which was applicable to the Donald C.

Cook Nuclear Plant Units 1 and 2.

The letter is being submitted because the situation may be of interest to other operators of Westinghouse pressurized water reactors.

By letter dated August 21, 1986 (attached),

Westinghouse Electric Corporation (Westinghouse) recommended that we evaluate the boron concentration which would exist in the containment sump following a LOCA to ensure that it was sufficient to maintain the reactor in a subcritical state.

The Westinghouse letter suggested that the Technical Specification requirements for Refueling Water Storage Tank (RWST) and Accumulator boron concentration were based on typical 12-month cycle core designs, and under some circumstances may not be sufficient because of the recent trend towards longer cycle life, increased fuel'nrichment, and positive moderator temperature coeff cients below 70$ of full power.

Evaluations were performed by the American Electric Power Service Corporation (AEPSC) using a methodology based on the "Recommended Action" section found on pages 2 and 3 of the attached Westinghouse letter.

The evaluations were performed assuming the minimum allowable T/S boron concentrations for the ice bed, RWST, accumulators, and Spray Additive Tank.

These evaluations showed that all of the D.

C.

Cook Unit 1 and 2

cycles (including the present) would have had a sufficient boron concentration in the sump post-LOCA to maintain subcriticality, with the exception of Unit 2 Cycle 3.

However, when actual plant data for ice bed and tank boron concentrations were considered, i.t was determined. that-this cycl'e also would have had sufficient boron to ensure subcriticality post-LOCA.

All of the evaluations performed considered the effects of depletion of Boron-10 which was described in our letter AEP:NRC:1011, dated October 8,

1986.

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Mr. Harold R. Denton AEP:NRC:1008 Because Unit 2 Cycle 3 had the potential for a post-LOCA boron shortfall, Westinghouse was asked to evaluate whether the issue would be reportable under the requirements of 10 CFR 21.

By letter dated September 17,

1986, Westinghouse advised AEPSC that they did not consider the issue reportable per 10 CFR 21, since actual plant data showed that a post-LOCA boron shortfall would not have existed.

Although Westinghouse concluded the issue was not reportable under the requirements of 10 CFR 21, we have chosen to inform you of it since it may be of interest to other licensees.

This issue was discussed previously with your staff and the NRC Region III staff.

This document has been prepared following Corporate procedures which incorporate a reasonable set of controls to insure its accuracy and completeness prior to signature by the undersigned.

Very truly yours I

M.

~ Al xich Vice President P~Q4>

cm Attachment cc:

John E. Dolan W.

G. Smith, Jr.

- Bridgman R.

C. Callen G. Bruchmann G. Charnoff NRC Resident Inspector

- Bridgman

ATTACHMENT TO AEP:NRC:1008 WESTINGHOUSE ELECTRIC CORPORATION LETTER DATED AUGUST 21, 1986

Westinghouse Electric Corporation Power Systems Box 355

,PittSOury t)en()S) lgatua 15230 0355 M'.

W.

G. Smith, Plant Manager D.

C.

Cook Nuclear Plant Indiana and Michigan Electric Company P.

O.

Box 458

Bridgman, Michigan 49106

Dear Mr. Smith:

August 21, 1986 AEP-86-665 American Electric Power Service Corporation D.

C.

Cook Units 1 and 2

POST-LOCA LONG-TERM CORE COOLING BORON REQUIREMENT Back round Information 10CFR50.46 "Acceptance Criteria for Emergency Core Cooling Systems for Light Mater Nuclear Power Reactors" paragraph (b) item (5) sets forth requirements for Long-Term Cooling.

During the development and subsequent NRC review of the Westinghouse ECCS model, credit for thy shutdown provided by the control rods (RCCs) for breaks greater than 3.0 ft (i.ese large breaks) was not taken and this assumption is part of the current licensing basis for Westinghouse PWRs.

As a result, the Westinghouse licensing position is that

"... the ECCS water has enough boron concentration to maintain the core shutdown" (MCAP-8339, Westinghouse Proprietary Class 3,

"Westin house Emer enc Core Coolin S stem Evaluation Model - Summar g.

, June n or er to take cre it or contro ro s

or reaks larger than 3.0 ft specific NRC approval would be needed for any Westinghouse designed PMR regardless of fuel vendor or ECCS evaluation model used to perform the required Appendix K analysis.

The traditional boron concentrations of 2000 ppm for the RMST and 1900-2000 ppm for the cold leg accumulators have provided, with margin, boron concentrations capable of keeping the core subcritical (K f less than 1.0) assuming All Rods Out (ARO) for typical 12 month cycle coF designs.

The recent trend to longer cycle life, increased fuel enrichment necessary to support a longer cycle life, and the introduction of a positive moderator temperature coefficient at 'power levels below 70% has resulted in the need to

August 21, 1986 Page 2

reexamine the boron concentrations necessary to demonstrate that the reactor

'ore remains subcritical, post-LOCA, ARO.

This is required regardless of the fuel design or the fuel vendor.

This LOCA licensing'ommitment applies to all Westinghouse designed PWRs.

Recommended Action The boron concentration (Cn) required to keep the core subcritical (X

less than 1.0), All controT Rods Out (ARO),

no xenon (NOXE), for the (s ft reactive time in core life, with an assumed post-LOCA core/fluid temperature in the range of 68-212'F, should be determined.

Then a detailed calculation to determine the RCS/containment sump post-LOCA boron concentration will be needed2to demonstrate that the core remains subcritical following a LOCA of 3.0 ft or greater.

This calculation must consider the initial pre-LOCA boron concentrations for the RWST, Cold Leg Accumulators, Pre-Trip RCS Hot Full Power (HFP) boron concentration (including appropriate assumptions for xenon) and the concentrations of any other source of water that may

" eventually reside in the containment sump (i.esa Spray Additive Tank, Boron Injection Tank, water residing in piping associated with the suction and injection of the

ECCS, CVCS, containment spray system, and switchover of the ECCS).

Additionally, the assumption for containment spray actuation and operation as it affects the delivery of RWST water subsequent to SI switchover from the injection phase to the cold leg recirculation phase must be considered.

A review of all tanks residing in either the containment, auxiliary building or outside should be conducted to determine if any tank can reasonably be hypothesized to deliver its contents following a LOCA.

Westinghouse plants utilizing ice condensor containments must account for the ice melt and the associated boron concentration of the ice bed.

Once all sources of water and their associated pre-LOCA boron concentrations have been determined, the mass average boron concentration of the mixture must be calculated.

The result of the mass average boron concentration must show a post-LOCA boron concentration greater than the core CB, in order to demonstrate that the condition of K f is less'han 1.0,

ARO, NOXE, most reactive time in life,68-212'F, wi'fVbe met.

If the post-LOCA mass average boron concentration does not'xceed the core C

requirement then to demonstrate that the core will be subcritical he RNST and Cold Leg Accumulator minimum Tech-Spec boron concentrations must be increased or the core must be redesigned to reduce the core C

Increases in the maximum allowable Tech-Spec values of the RWST and Accumulator boron concentrations may require a

new calculation to determine the hot leg recirculation switchover time necessary to preclude boron precipitation following a LOCA.

August 21, 1986 Page 3

This time is provided in Emergency Operating Procedures to ensure operator action.

In the event that Tech-Spec changes for the boron concentrations of the RWST and Accumulators are needed, then the post-LOCA sump pH should be evaluated.

Additional Guidance and Information A preliminary review of currently'perating Westinghouse cores performed by Westinghouse has found that these cores satisfy the long-term post-LOCA core cooling requirement.

Future reload safety evaluations provided by Westinghouse in support of reloads for which Westinghouse performs the safety evaluation will determine if the post-LOCA long-term core cooling requirement is satisfied by the current pla'nt Technical Specifications covering boron concentrations.

Should Technical Specification changes become necessary for cores supplied by Westinghouse, Westinghouse will advise the affected utility of the necessary changes.

Westinghouse plants not currently utilizing Westinghouse fuel or utilities which perform their own reload safety evaluations should consider developing internal procedures for tracking boron requirements to demonstrate that the reactor core remains subcritical following a hypothetical large break LOCA.

Also, a provision for maintaining an appropriate hot leg recirculation switchover time should also be considered.

Sincerely, HT/1886R (j

c H.

C. Walls, Manager Mid-America Region Projects Department cc:

M. P. Alexich W. G. Smith M. J. Parvin J. Feinstein WOG Rep.

V. Vandeburg J.

Waleko W

C. Swist W

'14s tribetion:

WDocket-File

- -~

NRC PDR Local PDR PRC System PWR/I4 Rdg BJYoungblood Rdg DOCKET NO(S) '0-315 OGC/Bethesda Nr. John Dolan,vVice Pr esidoat Indiana and Michigan Electric Company c/o Amer ican ElectrCic1 PBAer Service Corporation 1 Riverside Plaza EJordan

Columbus, Ohio 43216 NThompson MDuncan

SUBJECT:

D. C. Cook Nuclear Plant, UnitsNo.

1 0

The following documents concerning our review of the subject facility are transmitted for your information.

Notice of Receipt of Application, dated Draft/Final Environmental Statement, dated Notice of Availability of Draft/Final Environmental Statement, dated Safety Evaluation Report, or Supplement No.

dated Environmental Assessment and Finding of No Significant Impact, dated Notice of Consideration of Issuance of Facility Operating License or Amendment to Facility Operating License, dated Q Bi-Weekly Notice; Applications and Amendments to Operating Licenses Involving No Ei if'I*d C

id i

.d d~&

all 29 Exemption, dated Construction Permit No.

CPPR-

, Amendment No.

dated Facility Operating License No.

, Amendment No.

dated Order Extending Construction Completion Date, dated Monthly Operating Report for transmitted by letter dated Annual/Semi-Annual Report-transmitted by letter dated

Enclosures:

As stated Office of Nuclear Reactor Regulation cc:

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