ML20099C876

Informs That Due to Unforeseeable Factors,Util Finds It Necessary to Delay Submittal of Individual Plant Exam for Severe Accident Vulnerabilities,Per GL 88-20 from Original 920901 Date Until 930226

ML20099C876
Person / Time
Site:	Davis Besse
Issue date:	07/28/1992
From:	Shelton D CENTERIOR ENERGY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
2077, GL-88-20, NUDOCS 9208040344
Download: ML20099C876 (2)

Text

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.g DoneW C. Shelton 300 Madison Avenue Vu Presideo Nuclear Toledo OH 436524001 Dads Besse (419)249 2300 Docket Number 50-346 License Number NPF-3 Serial Number 2077 >

July-28, 1992 .

1 United States Nuclent Regulatory Commission Document control Desk

-Vashington, D.C. 20555

Subject:

Schedule for Completion of the Davis-Besse Nuclear Power Station, Unit 1, Individual Plaat Examination (IPE) for Severe Accident Vulnerabilities l

Centlemen:

On-November 23, 1988, the NRC issued Generic Letter 88-20 requesting thatEcach utility perform'an I,dividual Plant Examination (IPE) to identify any severe accident vulnerabilities. By letter dated October 27, 1989 (Serial Number 1723), Toledo Edison responded by .

stating thct a Levelil Probabilistic Risk Assessment (PRA) and a  !

l= _ containment performance enalysis vould be performed for the Davis-Besse-Nuclear Pover. Station (DBNPS). Toledo Edison further proposed completing _this analysis by the NRQ requested date of September 1, 1992.- Since that time, Toledo Edison' personnel have been ectively performing the IPE. However,= due to several unforeseeable factors,-

Toledo Edison finds it necessaryLto delay the submittc1 of the IPE from the original September 1,-1992 date. Toledo r.dison now anticipates-submittal of. the IPE to the NRC by February' 26, 1993. As explained.

holov, this.six' month delay results from additional time being required to evaluate an unexpectedly large number of cutsets for some compicx ,

event sequences, and the un.. ailability until May, 1992, of an upgraded version of the EPRI Modular Accident'Aralysis Program (HAAP) better suited for. application'to Babcock & Ullcox (B&V) designed plants.

While the quantification of the core damage-sequences is essentially

-complete, this process took much longer than expected due to the e'volutionlof an atypical set of cutsets for some sequences. -In one sequence, more than 14,000 cutsets vere generated which enceeded the

nominal truncation limits and required'further evaluation. The number of cutsetsifor this sequence is on the_ order of a magnitude larger than vould be typically found'for the most complex l sequences in other PRAs.

Although no single component or system seems to contribute disproportionately'to this sequence, the large number oi combinations

,of_cutsets has takenLeonsiderably longer to evaluate.

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Docket Number 50-346 License Numh. NPF-3

. Serial Numbe*; 2.77 Page 2 Another key factor was the extended delay in the release of Revision 18.0 of the HAAP Code. Revision 18.0. During the development by Toledo Edison personnel of a totally plant-specific frput deck (including detailed models of the Reactor Coolant S) .em, Containment and Emergency Core Cooling Systems), a deficiency in the capabilities of HAAP to accurately analyze events where reactor vessel in+ernal vent valves were important (particulerly small break loss of coolant accident sequences) vas identifled by EPRI. React)r vessel internal vent valves are unique to B&V plants. In December, 1990, Toledo Edison requested EPRI to upgrade HAAP thermal-hydraulic models for B&V plants.

Toledo Edit,on provided significant engineering support to EPRI for the MAAP Revision 18.0 upgrade. Revision 18.0 to HAAP vas finally released in May, 1992, at least six months after its release was originally anticipated. This delayed the analysis for some sequences where teactor vensel internal vent valves are importnnt. Further, with Revision 18.0 now serving as the base version for the IPE, other previoualy analyzed sequence have had to be reanalyzed.

In addition,-to further ensure a technically complete IPE submittal to the NRC, Toledo Edison management has decided to obtain an independent external reviev of the IPE process and results prior to submittal to the NRC. The additional time required for an ladependent external reviev was not considered in the original schedule.

It should be noted that, to date, with the majority of the sequences quantified, no inherent vulnerabilities have been identified.

Furthermore, scveral sequences have been evaluated for containment response and no unusual containment failure mode or unacceptable containment response has been identified.

Toledo Edison believes that this six month delay vill ensure that the DBNPS IPE submittal vill bet ter fulfill the Commission's objectives for the IPE, and vill fully reflect the significant level of resources devoted to PRA/IPE efforts at the DBNPS and the overall quality of this largely in-house effort- .

If you have any questions regarding this letter, please call Mr. R. V. Schrauder, Manager - Nuclear Licensing at-(419) 249-2366.

Very Aruly yours,

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PVS/d c-cci A. D. Davis, Regional Administrator, NRC Region III

-J. B. Ilopkins, NRC/NRR DB-1 Senior Project Manager V. Levis, NRC Reglen III, DB-1 Senior Residant Ins;;ctor i' Utility Radiological Saiety Board

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