ML18025B047

Responds to 800723 Request Re 800628 Failure of Control Rods to Fully Insert During Scram.Agrees W/Proposal That Event Should Be Included as Ao,In Quarterly Rept to Congress. Forwards marked-up Draft AO Rept

ML18025B047
Person / Time
Site:	Browns Ferry
Issue date:	08/06/1980
From:	Harold Denton Office of Nuclear Reactor Regulation
To:	Haller N NRC OFFICE OF MANAGEMENT AND PROGRAM ANALYSIS (MPA)
References
NUDOCS 8008270263
Download: ML18025B047 (7)

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-PPAS RAClark BSnyder TIppolito BGrimes TNovak RYpl1',er DRoss SHanauer DEisenhut RMattson MStine EHughes Director, Office of Management and

'NRUST 6

1980 Docket No. 50-296 MEMORANDUM FOR:

Norman M. Hailer, Program Analysis

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FROM:

SUBJECT:

Harold R. Denton, Director, Office of Nuclear Reactor Regulation PROPOSED ABNORMAL OCCURRENCE - FAILURE OF CONTROL RODS TO FULLY INSERT DURING A SCRAM In response to your etnemorandum of July 23, 1980 on the above subject, we agree that the incident of June 28, 1980 at Browns Ferry Unit No.

3 should be included as an abnormal occurrence in the quarterly Report to Congress.

There are several minor changes which we recommend; these are noted in the enclosed marked-up copy of the draft report.

Enclosure:

Draft Report gnginal Signed Bg E. G. Case Ha ld R. Denton, Director Office of Nuclear Reactor Regulation E

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NUCLEAR REGULATORY COb'>>~iISS ION

""'BNORMAL OCCURRENCE r

FAILURE OF CONTROL RODS TO FULLY INSERT: DURING A SCRAM.

C Section 208 of the Energy Reorganization Act of 19)4,.as

amended, requires

~ '-', the NRC to'isseminate information on abnormal occurrences

{i.'e;, unscheduled

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., incidents or events which the Commission determines.are-significant..from the=.-'=.-:=-,".-:--'

standpoint of public-health and safety).

The'ollowing incident was

,. etermined.ta. be an.-abnormal...occurrence.

using..the..critena..published,.in..the.

I

.Federa1. Register on,.'..Pebr'uary-24,.:1977.(42. FR 10950).:One of the general.....

criteria. of the Policy Statement,-notes that major degradation of essential safety-related equipment can be considered an abnormal occurrence.

The following description of the event also contains the remedial-action::taken;..

Date and PIace - On June 28,

l980, Browns Ferry Unit 3, a Boiling Mater

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Reactor (Bh~R), located in-Limestone 'County, Alabama,- r'eported that 76 control.;=:-" '---

rods failed to fully inse'rt during a routine shutdown following a manual scram actuation at 30% power.

Nature and Probable Conse uences

- Following the manual scram actuation,.76

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n><< /,4~/Ii4 is eSicin'~ay/ g//< griszAzd'.

of 185 control rods failed to fully insert>

The partially inserted rods~

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were all on the east side of the core where reactor power level was indicated to be less than one percent.

The west side of the core was subcritical.

A i'econd manual scram was initiated minutes later and all partially - --

inserted rods were observed to drive inward but 59 remained partially withdrawn.

A third manual scram was initiated one=-minute later and 47 rods

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remained part>ally withdrawn>

Six minutes later. an automatic scram fully rOM~ rW eX~~ ~~~~APo~~

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inserted a11'he rod+ Core coolant flow, teeperatuand pressure

'remained

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. 'ormal for the existing plant conditions.

There'was no'danger to the general public-or plant employees as.a r

result of this event.'--No radioactivity was released tt'. the environment;

-. Ther.e 6

-.was.no.indication of fuel damage.

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-" -:.-----=.-;-This type=of-occurrence dcould.resu1t.in failure of..the control. rods to =-=--

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-'-insert;-in','ha1f...of. the wore. on any.;.scram. signal this was.an unexpected A',

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situation which had not been analyzed..

Such a-failure has the potential to ---"

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cause significant fuel damage.

Cause or* Causes'--The exact cause-of the-event-is.-unknown.at"this-kime.---The--;.

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.-,...... problem appears to,be hydraulic. in nature rather than. electrical..The. control

- rod-drives'(CRD's')=,which insert and withdraw"control:rods-in-a General. Electric".'-=

boiling water reactor (BWR), are essentially water-driven hydraulic pistons.

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4-emmpl-iH a-scram, water pressure is placed-"on one sidy-.of.the;piston=-to..::- ;-:

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drive the rod into the reactor core and a solenoid valve opens to release n

water above the. piston:

Hater discharg'ed-from the 185 individua'1 CR

--is--- -,....

(<on e.~4 s.J~

~F +~ r~L) it idi ~di ddi 6

pip did dd'Pd volum (SDY).

Each SDV is designed to be continually drained during. normal operation and ready to receive the scram discharge water when a scram A

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occurs.

The control rods at 8rowrs Ferry are grouped in such a manner that the east'nd west sides of the reactor core are connected to separate SDV s..."..

The east SDV was apparently partially full of water at the time of.the event..

leaving insufficient room for the discharge water.

Upon scram actuation, the ddf Z~

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on each side.of'.

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and implementation of corrective actions.

General Electric Company issued operating'uidelines

.to all BMR licensees. relating.to.IE.Bull.etin-.tlo 80.-.17.

The 1icensee (Tennessee Valley Authority) performed extensive investiga-

=

tions, tests, and evaluations to attempt to identify the cause of the water accumulation in the SDV.

In addition, the requirements of IE Bulletin No. 80-17 were successfully performed.

Also, thirteen ultrasonic sensors were installed on'he drain and vent headers to detect accumulation. of water.,

An atmospheric vent was provided on the east drain header to preclude the possibility of a blocked vent system.

A similar vent already existed on the west header.

CRAd tt d

1 t'ai the pistons and the ro s stopped inserting.

Following each scram'actuation, the

.allowirig water to drain from the-SDV,"-permitting-the=.:rods to insert,further.web each

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scram attempt;. Sufficient water was.finally drained from the SDV to.allow-'-;-.....

the rods to'fully..insert. on..thefourth scram..signal..

The exact cause

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.';=initiating

.the,SDV.water'accumulation problem. is not known at this.,time. It, 1

AL, C

-is postulated..that either the drain piping was.plugged or the vent was restricted which prevented the water from draining from the SDV following.a.

previous scram.

Actions Taken to Prevent Recurrence Licensee - 'The unit remained'hutdown pendiiig:identification. of.the.cause..

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0 NRC - A Pegion II core-physics specialist was.dispatched immediately:.to the:.:,..

site to assist the two NRC resident inspectors. on site.-- Region II-.issued-a Confirmation of Action. Letter to confirm the licensee s commitments.and

.to require concurrence prior to restart.

An evaluation team consisting of

.-;. -;.the Region II Director,".=,Region: II.specialists-,'=and NRC" Headquarters.-.':"-

- personnel was-dispatched;to the. site-to. evaluate. the significanceaf Ahois event;.-

A Preliminary Notification was.issued to.-promptly inform 'other; NRC;-.-'=".=-': =- =.."

~<,',

offices. :

On '. Buly 3,

. 1 980, IE Bu] 1 eti n No. 80-'

7 was is s ued to al 1 1 icens ees -;. -.

--= = of,.Boi 1 ineater.

Reactors. rj'quiring that..they conduct.prompt and peri odi c

.---inspections. of the..SDY;. perform.two reactor. scrams wifhinQO 4ayq awhile

- monitoring. pertinent,paramet'ers.

to Further.confipn operability; review.

emergency procedures to assure pertinent requireme'nts are included; and

--"-- 'onduct additional training to acquaint operating personnel with this-type of problem.

Additional review within NRC is continuing to better identify the cause of -.this event and to determine the long-term corrective acti,ons...

required.

Based on the licensee's corrective actions described

above, the NRC authorized the licensee to restart Brown's Ferry Unit 3 on July 13, 1980.

.A-Confirmation of Concurrence Letter was issued on. July 14, 1980,.confirming the.

actions taken by the licensee and to confirm that the licensee will perform an expedited review of the General Electric Company recommended

• design-changes;--

For the Nuclear Regulatory Commission Dated at 'rjashington, D.C. this Samuel J. Chilk Secretary of the Commission day of

'j980.