ML20002C543

Responds to Request in WASH-1270 for Analysis of ATWS Susceptibility.Ge Study Encl.Concludes That ATWS Is Incredible Event & Could Be Terminated Prior to Jeopardizing Containment

ML20002C543
Person / Time
Site:	Big Rock Point File:Consumers Energy icon.png
Issue date:	11/21/1975
From:	Sewell R CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.)
To:	Office of Nuclear Reactor Regulation
Shared Package
ML20002C544	List: ML20002C543 ML20002C546
References
RTR-WASH-1270 NUDOCS 8101100443
Download: ML20002C543 (3)

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c.ene,ai omces: 212 West Michigan Avenue.. Jackson, Michigan 49201 e Area Code 517788 0550 November 21, 1975 sn 4

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Director of Nuclear Reactor Regulation fj j' US Nuclear Regulatory Commission D

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LICENSE DPR-6, DOCKET 50-155 0

i BIG ROCK POINT

$::h In September 1973, the US Atomic Energy Consission (now US Nuclear Regulatory Commission) issued a Technical Report on Anticipated Transients Without Scram for Water-Cooled Reactors (WASH-1270). This report requested that plants in the "C" category, which includes Big Rock Point, be analyzed for both the susceptibility to and conseqttences of a failure to scram under transient conditions.

An analysis to determine the susceptibility of the Big Rock Point reactor shutdown syste= to failure to scram was submitted on October 21, 197h. This analysis showed that the Big Rock Point's system was designed with suffief ent redundancy and functional diversity to make a failure to scram an incredible event.

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On September 30, 1975, Consumers Power Company described the results of the consequence analysis which had been performed but at that time was not in the final report stage. This letter stated that the consequences, assuming no reactor recirculating pump trip and that poison injection is delayed for as i

much as five minutes following the event, were a predicted containment peak j

pressure of approximately 57:7 psig and a peak temperature of approximately l

286 F.

The peak pressure may be compared to a design pressure of 27 psig and j

a membrane yield limit of approximately 54 psig. The analysis also showed that both the fuel and primary system transients vould be quite mild (fuel l

enthalpy less than 165 calories per gram and reactor vessel pressure less than i

the design pressure) because of the a=ple safety valve capacity included in the initial Big Rock Point Plant design.

The attached analysis shows that with a reactor recirculating pump trip con-tainment peak pressure is limited to values significantly less than the case of no reactor recirculating pump trip.

If the reactor recirculating pumps are tripped at 60 seconds, the containment peak pressure is limited to 27.5 psig. If the pumps are tripped within 300 seconds of the event, the contain-ment peak pressure is limited to 43 9 psig. The tripping of one reactor recir-culating pump is presently an immediate action requirement for ppnt control 8102i00 %

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k operators in certain_ transient'aituations and in the past has been accomplished.

successfully in very short periods of time in these situations.

We have concluded that the tripping.of both reactor' recirculating pumps can be accomplished by operator action in a very short period of time following the -

initiation of an event similar to the event postulated in the report and are modifying our operating procedures such tht this.is an immediate action re-Lquirement for plant operators.

Existing plant procedures presently require

' liquid-poison system initiation on failure to scram; even-so, they do not 1

specifically. address an event similar.to.the one postulated-in this report.

Both a trip ^ of the reactor recirculating pumps and initiation of the liquid j -

poison system will be required as.immediate action in a procedure that addresses an event similar to that postulated in the attached analysis. The procedure modifications will-be completed by December 31, 1975 Based on the analysis' described above, we have concluded that the ATWS event is an incredible event'.

Even assuming a transient similar to that described in

'the attached. report were to occur and a failure to scram occurred, we have concluded that,this accident could be terminated prior to', jeopardizing contain-ment integrity.

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wa Ralph B. Sewell

. Nuclear Licensing Administrator CC: 'JGKeppler, USNRC-File I

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.l NRC DISTRIBUTION FOR PART 50 DOCKET MATERIAL

• (TEMPORARY-FORM) e FILE:

FROM: Consumers Pwr Company

' DATE OF DOC DATE REC'D LTR TWX RPT CTHER Jackson, Mich 11-21-75 11-28-75 XXX TO:

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ORIG CC OTHER SENT NRC PDR__

X" XX DL one signed SENT LOCAL PDR-CLASS UNCLASS PROPINFO INPUT NO CYS REC *D DOCKET NO:

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1 50-155 DESCRIPTION:

ENCLCSURES:

Ltr trans the following:

Analysis of ATWR at Big Rock Point Plant

........(40 cys enc 1 rec'd)

PLANT NAME: Big Rock Point

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FOR ACTIO_N/INFC RI.1ATION 11-28-75 enf BUTLER (L)

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