ML18025B174

Requests Commission Assessment of Causes of 800628 Event & Possible Consequences Had Control Rod Failures Occurred During Full Power Operation & Following Design Basis Event

ML18025B174
Person / Time
Site:	Browns Ferry
Issue date:	07/16/1980
From:	Udall M HOUSE OF REP., INTERIOR & INSULAR AFFAIRS
To:	Ahearne J NRC COMMISSION (OCM)
Shared Package
ML18025B173	List: ML18025B171 ML18025B174 ML19339A773
References
NUDOCS 8011050062
Download: ML18025B174 (8)

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NINETYSIXTH CONGRESS ARIZ>> CKAIRMAN DON IL CLAVSEH CALIF MAHVCLLLIJAH,JR>> N, MCX, KCITH O SCSCLIVS, KANS DOH YOUHO, ALASKA SYCVCH D, SYMMS, IDAHO JAMCS P, (JIM) JOHHSOHe COLO ROSCRT J, LAOOMARSINOe CAUI DAH MARRIOTTe UTAH ROH MARLCHCC, MONI'ICKCY EDWARDS, OKLA RICHARD D CHCHEYe WYO CHARLCS PASHAYAH, JR CALIF ROSCRT WHIYTAKCR,KANS DOVOLAS K, SCRCUTCR, NCSI4 MELVINH EVANS, V.l MORRIS K, UDALI>>

PHIUJP SURRHL CAUF.

ROSCRT W KASYCHMCICR, WIS, ASRAHAM KAECH, JR., TCX JONATHANA SIHOHAM, H,Y JOHN F SEISERUHO, OHIO HAROLD RVHHCLS, N MCX, ANTONIO SORJA WOH PAT, OVAM SOO ECKHARDTe TEX JIM SANYIHI,HEV JAMES WCAVER, ORCO DOO CARR, MICH, OEOROC MILLERe CALIF JAMCS J, FLORIO, ILJ DAWSON MAYHISe GI4 PHIUP R. SHARP, IHO.

EDWARD J MARKCYe MASS PETER N KOSTMAYER, PAe DALTASARCORRADA, PJ4 AUSTINJ, MVRPHYe PI4 NICK JOC RAHALLII~ We Vi4 DRUCE F VCNTDe MIIOI JERRY HUCKASYe LA LAMAROVDOER, NA JAMCS J HOWARD, ILJ JERRY M, PATTERSON, CAUF RAY KOOOVSEKe COLD PAT WILLIAMSe MONTe

,*e A.,

e COMMITTEE ON INTERIOR AND INSULAR AFFAIRS U.S. HOUSE OF REPRESENTATIVES WASHIN(PTONI DeCi 20515 July.16, 1980 CKARLES CONKLIN STAFF DIRECTOR STANLEYSCOVILLE ASSOCIATE STAFF OIRECTOR ANO COUNSEL LEE MC ELVAIN GCNERAI COUNSEL GARYG ELLSWORTK MINORITYCOUNSEL The Honorable John Ahearne

Chairman, Nuclear Regulatory Commission Washington, D. C.

20555

Dear Mr. Chairman:

The recent control rod system failure at Browns Ferry III demonstrates the appropriateness of the persistence of NRC staff and the ACRS in pressing the industry to adopt measures to mitigate the consequences of Anticipated Transient Without Scram (ATWS) events.

In order that it be clear that the staff has not been seeking to impose superfluous regulatory requirements, it. is important that the Commission present at an early date its assessment both of the causes of the problem at Browns Ferry III and of the consequences had the control rod failure occurred during full power operation and following a design basis event. such as loss of condensor vacuum or inadvertent closure of main steam isolation valves.

Sincerely, MORR S 'K. UDALL Chairman

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'0 ENCLOSURE The Honorable Morris K. Udall Chairman, Comittee on Interior and Insular Affairs U. S.

House of Representatives Mashington, D. C;'20515

Dear Mr. Chairman:

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r%qoest$ that the hot Cori ssion fh d-p

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Browns Ferry Unit 3 control rod system failure

~77~J qg our assessment>and a brief description of our in response to this event~

ct~n-The Browns Ferry Unit 3>was caused by

~ater that had accumulated in one of the two headers of the scram discharge volume (SDV).

The SDY normally -provides ~~me-for-44e collection of e M the water displaced by scram.

Mith a partia],ly filled SDV theirod motion s4t ~~ ~~ r o~ 'It on scram was restricted~~

The accumulation of water resulted from=-improper de@

'4 drainage of the SDV

~e system Q LIBAQ.c-4M/

{!{p hyd 1{

h h df and the instrumented

volume, (2) inadequate SDY venting, and (3) deficien-cies in installed instrumentation.

T reactor-s imu&Md-tests-byMh~enera,l-E 1 ec tr ie-Company-.(6~he-nuel ear 9~4s~QKN4igs

~

'k~~~nsiderad-the-impl.iwt ions-ofwcram-f ai.lures with rmpeGt to, p

Ild lipd

'imp~!. 0&

~O[03 5 rulemaking to ures o re uce e

>Feei'lf5vd~ATMS,a d nts.

A s taff paper on ATWS, that "recomnends

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ft{ ',

I d ~

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. I~d

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rel i me~~4e-impact-~he-&r owns-Ferry-Uni-t-3-par-tAaM he-es44a4ed-scram-f+i tur~robabi+rty.

Me anti cipate that a regulation which sets forth requirements to.achieve protection from ATMS events will be in effect by early 1981. 'he staff has recommended that licensees be required to implement hardware modifications to reduce the likelihood and mitigate the consequences of ATMS events.

The analyses of postulated ATMS events for BMRs have generally been con-cerned with two requirements:

(1)

The assurance of the integrity of the reactor coolant pressure boundary (RCPB);

and (2) The assurance that the

~ heat generated by the reactor core is removed.

s A"r "To assist~

immediate revjew of the importance of the Browns Ferry gQ Q ~

rv(Ref

~A~ 4

'Unit 3 failure, we-h.~

'd-a GElanalysis of the most limiting of the postulated anticipated transients accompanied by a partial scram failure simi')ar to what occurred at Browns Ferry Unit 3.

The transient )s q, clogure

,vvhLE d, amc f @la &~4.~>

s.em esvr. e yamm

,. "of the main steamline isolation valves>

The analysis assumes full power initial conditions ATMS related automatic recirculation pump trip~~

p lh 1t cab show that[the integrity of the RCPB w'ill be maintained andgthe heat. genera-tion rate in the core vail be within heat system removal capabilities> ~

is newm<~4 hoick& ~ mhMW~ tw &r IQ rwinr~+

'bc'> flu

~4 5r~r @~I g

Me elieve.it is arguable whether an operator would have responded correctly and in sufficient time to prevent major plant damage r procedures~er-

~ in place at BMRs prior to the Browns Ferry event.

Accordingly,-,eh~

wn we required mori fications emergency procedures the operator could activate the alternate shutdown system (standby liquid control system) within 10 minutes.

0 Our asses ment of the analysis is that it is easonable ssmulatlon o~f e most severe postulated trans'ith a scram, failure simil to that which occurred at Brow Merry Unit 3.

However, our mary goal in response to the Bro n Ferry Unit 3 event is not to emonstrate the accepta-

.bility of t consequences, but to eliminate the potential for such control rod ram failures+ The Browns Ferry event has provided additional evidence that it is difficult to predict all scram system failure modes and design failure-free reactors.

In the bounding case, where all controlrods fail to

• ~~P~lS insert, i e..,

a full+ATMS) the RCPB and containment integrety can not be a sured.

'The consequences of such an event are otnrra~y-extremely

severe,

'drrnji&.v'ery drn-favneiW~~

'h,p~

pv and would yes~

e health and safety>M the public.

n.

vsc~)Lcm'e short term actions required by our Office of Inspection and Enforcement Bullet,have focused on increasing the reliability of the SOY operating reactors Th Bulletin requirements provide an accepta

.basis for conti-nued plant operations.

By separate letter to all o

ating BWR licensees, we will outline ou'r require ts for long ter ctions and a schedule.

Our plan of action to require modifica ns ecessary to assure adequate relia-bility of the SDY system includes gnif1 t owner group participation.

We have encouraged the BMR ow s to form a group ch will analyze those prob-lems associated with e scram system and, in coopera n with the staff, develop desig nd performance criteria which will form the is for future plant-s ific modifications.

This group has been formed and we e

ct to di uss their recommendations with them on September 19, 1980.

~ tp 6~ -BTy ]8~2.,

h~ i~'

Hti dpi c ion including the expected action on the staff's proposed ATMS rule,

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