ML20008D853

Requests Recalculation of Boron Dilution Event Under Plant Conditions Not Addressed in Fsar.Licensee Should Provide Commitment to Revise Procedures to Insure Maint of Correct Shutdown Margin

ML20008D853
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	09/30/1980
From:	Clark R Office of Nuclear Reactor Regulation
To:	Goodwin C PORTLAND GENERAL ELECTRIC CO.
References
NUDOCS 8010230314
Download: ML20008D853 (3)

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September 30, 1980 Docket No. 50-344 Mr. Charles Goodwin, Jr.

Assistant Vice President Portland General Electric Company 121 S.W. Salmon Street Portland, Oregon 97204

Dear Mr. Goodwin:

During a recent review of the safety analysis for postulated uncontrolled boron dilution events for Millstone Unit 2, the licensee found that some non-conservative assumptions had been made for shutdown modes. An extract of the Licensee Event Report is attached for your information (Attachment 1).

Our review of this matter indicates that there are two plant conditions which may not have been conservatively considered with respect to inadvertent boron dilution:

1.

Mode 5 (cold shutdown) with the reactor coolant system drained to the "hal f-pipe" level (reduced volume).

2.

Mode 4 (hot shutdown) with no reactor coolant pumps running (an effective reduced RCS volume).

A review of your FSAR (Section 15.2.4) indicates that a boron dilution event under these specific plant conditions is not addressed.

Based on the foregoing, you are requested to:

l 1.

Recalculate the boron dilution event for these plant conditions, l

using the reduced RCS volume and 15-minute criteria contained in the Standard Review Plan Section 15.4.6 ( Attachment 2).

(Note that unless a reactor coolant pump is continuously operating, the conservative volume to be used is tha drained down ("l/2-pipe") volume of the RCS plus that of the residual heat removal system and connecting piping.)

2.

Provide a commitment to revise appropriate plant procedures as necessary to insure that the correct shutdown margin is maintained.

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1 Mr. Charles Goodwin, Jr. '

Portland General Electric Company 1 3.

Propose revised Technical Specification changes as necessary.

The reanalyses and commitment to revise plant procedures as necessary should be completed within 60 days.

Proposed Technical Specification changes should be submitted to us within 180 days.

Please contact us if you have any questions regarding this matter.

Sincerely, Robert A. Clark, Chief Operating Reactors Branch #3 Division of Licensing Attachments :

1.

Fillstone LER 80-05 2.

SRP 15.4.6 cc: w/ attachments See next page l

e.

6 Mr. Charles Goodwin, Jr.

Portland General Electric Company cc:

Mr. J. W. Durham, Esquire Donald W. Godard, Supervisor Vice President and Corporate Counsel Siting and Regulation Portland General Electric Cocpany Oregon Department of Erergy 121 S.W. Salmon Street Labor and Industries Building Portland, Oregon 97204 Room 111 Salem, Oregon 97310 Columbia County Courthouse Law Library, Circuit Court Room

'St. Helens, Oregon 97501 Michael Malmros, Resident Inspector U. S. Nuclear Regulatory Conmission Trojan Nuclear Plant P. O. Box 0 Rainier, Oregon 97045 Robert M. Hunt, Chairman Board of County Conmissioners Columbia County St. Helens, Oregon 97051 Director, Technical Assessrent Division Office of Radiation Programs (AW-459)

U. S. Environmental Protection Agency Crystal Mall #2 Arlington, Virginia 20460 U. S. Environmental Protection Agency Region X Office ATTN:

EIS COORDINATOR 1200 6th Avenue Seattle, Washington 98101 1

ATTACHiiENT 1

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. N tru _a LER 30-05/1T-0 Millstone Unit 2 Docket No. 50 336 Event Description During a review cf the safety analysis it'was discovered that an -

incorrect assumption had been made in the analysis of the boren dilution event.

The analysis of this event while in Mode 5 (cold shutdown) had assumed a full reacter cociant system and a 1% shutdown cargin.

Tnis resulted in a time to beceme critical of 20 minutes which satisfied the requirement for the 15 minute maximum time assumed for the operators to recognize the situatien and take action.' However, the analysis had not considered the fact that cperation is possible with the reactor coolant system drained to the centerline of the hot leg.

Including this reduced volume of reacter coolant to be diluted in the analysis resuits in a time to reach criticality of less than 15 minutes.

Cause Descriction and Corrective Actions

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At the reduced system volume th time to reach criticality during the Mode 5 dilution even: would have been less than the 15 minutes allowed for the operator to terminate the event.

By increasing :he required shutdown margin in Mode 5 to 2%, a time to criticality of greater than 15 minutes is reestablished.

Untii the necessary Technical Specification changes can be approved, the unit will administratively maintain a shu-down margin in excess of 2% in Mode 5.

In the pas it has been standard practice to caintain the Mode 4 shutdown boron concentration recuirement while in Mode 5, vehich provides reasonable assurance that a greater than 25 shutdown margin has been maintained during previous Mcde 5 operation.

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U.bCrated htter can be added to the rea: =r coolant system, via the chemical volu:ne and tj

nt.ol syste: (CYCS),t increase c:re reactivity. This c.ty hap;en inadvertently, because E

cf c:4rator error or CVCS calfun: tion, and cause an unmented increase in reactivity and a de: tase in shutdown margin. The c;erater must s.c; this unplanned dilution before the th:::d.m =2. ;in is eliminated..Since the setuen:es of events that may c::ur depend on f

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conditiens at the tire of the unplanned c:: erat:r dilutien, tne revien-in:1udes c:n:ditions at the time of *he unplanned dilution, su:S as refueling, star u;, :ower i'

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c:e: atica (autc..atic control and canuti medes), t. - stan:by, and cele shuteewn.

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7t.e rtries of postulated c.ederat:r ciiution events censiders causes, initiatin; events, tr.s sa gente Of tvents, tha analytical model, the values cf ; ara:eters used in the ana-i

I lytical e,cdel, and predicted consequen:es of the event.

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't.e se:uence of events described in the a;;1icant's safety analysis re: rt (SAR) is evie--d by both the RS5 and EI5*SS. The RSS revie-er con:entrates en the need for the

-*a...:. ;-: ectica system and the c;trat:r a:tica rt:uired :: secure and caintain the. ea:ter in a safe c:ndition. The EICSS reviente c:ncent ates on the instru.entatien and contr:1s t.:;-e: s of the se:;uence des:riber in the SAR to evaluate wnether'the rea:t:r and plant

te:tica and safeguards c:ntrols and instrumentation syste=s will fun:-icn as assumed in stfety analysis with re;2rd to actsmatic actuatien, ree:te sensing. indication, centrol, it.t and intar1::ks with auxiliary or shared systems. EIC33 aise evaluates ::tential bypass

de.s and the ' :ibility cf e.anual centrol by tr.e :;trat:.

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