ML20141E711

Forwards,For Review,Draft Info Notice Re Generic Implications of Estimated Core Melt Frequency.To Reduce Estimated Frequency for Unit 1,licensee Committed to Having One Unit 2 Svc Water Pump Available

ML20141E711
Person / Time
Site:	Byron
Issue date:	12/24/1985
From:	Noonan V Office of Nuclear Reactor Regulation
To:	Jordan E NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
NUDOCS 8601080287
Download: ML20141E711 (4)

Text

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MC 2 41985 MEMORANDUM FOR: Edward L. Jordan, Director Division of Emergency Preparedness and Engineering, IE FROM: Vincent Noonan, Director PWR Project Directorate #5, NRR

SUBJECT:

ESTIMATED CORE MELT FREQUENCY.

Enclosed is a draft IE Information Notice for your consideration. We believe that the issue has generic implications and should be sent to all nuclear power reactor facilities. As described in the enclosure, the core melt frequency for Byron 1, wi estimated to be about 10-3h its two-pump

/ year. essential To reduce service the this estimate, water system, was licensee committed to have one of the Byron 2 service water pumps available, even though Byron.2 is not an operating reactor.

This matter has been discussed between R. Baer of your staff and L. Olshan cf NRR.

Vincent Noonan, Director PWR Project Directorate #5, NRR

Enclosure:

As stated cc: H. Denton H. Thompson T. Novak

Contact:

L. Olshan, NRR x27070

._ DISTRIBUTION:

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v 8601080287 851224 PDR ADOCK 05000454

WC 2 41985 i MEMORANDUM FOR: Edward L. Jordan, Director Division of Emergency Preparedness and Engineering IE FROM: Vincent Noonan, Director PWR Project Directorate #5, NRR

SUBJECT:

ESTIMATED CORE MELT FREQUENCY Enclosed is a draft IE Information Notice for your consideration. We believe that the issue has generic implications and should be sent to all nuclear power reactor facilities. As described in the enclosure, the core melt frequency for Byron 1, wi h its two-pump essential service water system, was estimatedtobeabout10j/ year. To reduce this estimate, the licensee connitted to have one of the Byron 2 service water pumps available, even though Byron 2 is not an operating reactor.

This matter has been discussed between R. Baer of your staff and L. 01shan of NRR.

Vincent Noonan, Director PWR Project Directorate #5, NRR

Enclosure:

As stated cc: H. Denton H. Thompson T. Novak

Contact:

L. Olshan, NRR x27070 DISTRIBUTION:

Docket Files -

NRC PDR Local PDR

. PD#5 Reading Files L. 01shan M. 01shan 5 M. Rushbrook

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0FC PD#5  : PD#5: If

' NAME . 1shan:vt : VNoon /  :  :  :  :  :

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i Enclosure

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Estimated Core Melt Frequency ADRRESSEES:

All nuclear power reactor facilities holding an operating license (0L) or a constructionpermit(CP)

PURPOSE:

This information notice is being provided as a notification o'f a potentially significant problem discovered while reviewing a Probablistic Risk Assessment (PRA) done for Byron Station, Units 1 and 2. The core melt frequency to Byron 1 was estimated by the NRC to be about 10-3/ year. The main contributor was the Essential Service Water (ESW) System which contains two 100% capacity pumps. The Byron 2 pumps, which can be cross-tied to Byron 1, were not taken credit for in that estimate of core melt frequency since Byron 2 is not yet licensed.

Recipients of this notice are expected to review the information for applicabfiity to their facilities and consider actions, if appropriate, to preclude a similar problem to their facilities. However, suggestions contained in this Information Notice do not constitute NRC requirements; therefore, no specific action or written response is required.

Discription of Circumstances:

In May,1984, Commonwealth Edison submitted a PRA-type study for Byron in order to justify extending the allowable outage times (A0T) in the Technical Specifications for certain equipment. The study was performed to show that the increase in risk would be negligible if the A0Ts for this equipment were changed from 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> to 7 days. NRC, with assistance from Brookhaven l

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National Laboratory (BNL), reviewed the study. During its review, NRC/BNL determined that the study did not assume loss of both ESW pumps to be an accident initiator. In the Byron design, loss of BSW would result in a loss of reactor coolant pump seal cooling, inducing a small loss-of-cooling accident (LOCA). In addition, loss of ESW also results in loss of cooling to the ECCS pumps that would normally be used to mitigate a LOCA.

When the results of the study were re-evaluated, assuming loss of ESW to be an intiating event, NRC/BNL estimated the core melt frequency for Byron 1 to be about 10~3/ year. This result assumes that the' ESW pumps for Byron 2, which can be cross-tied to Byron, are not available since Byron 2 is not an operating plant. To lower the estimated core melt frequency, Commonwealth Edison committed to make at least one of the Byron 2 ESW pumps available to cross-tie to Byron 1 in the event that either of the Byron 1 pumps becomes inoperable.

No specific action or written response is required by this information notice. If you have any questions about this matter, please contact the Regional Administrator or the appropriate Regional Office or this office.

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