NRC-92-0051, Discusses Revised Schedule for Submitting Individual Plant Exam Rept for Facility,Per Generic Ltr 88-20.Extension of Submittal of Rept Until 920901 Will Enable Util to Assure That Proper Credit Given for Current Plant Design Features
| ML20095K101 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 04/30/1992 |
| From: | Orser W DETROIT EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| CON-NRC-92-0051, CON-NRC-92-51 GL-88-20, NUDOCS 9205050007 | |
| Download: ML20095K101 (4) | |
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Newport Whigan 48*66 Nuclear (34)S864201 Operattorse April 30,1992 NRC-92-OuS1 U. S. Nuclear Regulatory Commission Attn: Document Control Desh Washington, D.C. 20555 Refe rences:
- 1) Fermi 2
- NRC Docket No. 50-341 NRC License No. PPF-43
- 2) NRC Generic Letter 88-20, dIndividual Plant Examinations for Severe Accident Vulnerabilities,"
dated November 23, 1988, and Supplement 1, dated August 29, 1989.
- 3) Detroit Edison Letter to NRC, " Fermi 2 Individual Plant Examination Program for Severe Accident Vulnerabilities " NRC-89-0213, da:ed October 25, 1989.
- 4) NRC Letter to Detroit Edison, " Review cf 60-Day Response to Generic Letter 88-20 Individual Plant Examinations (IPE) (TAC No. 74410)," dated Janua ry 18, 1990.
- 5) Detroit Ediron lettc r' to NRC, " Summary Progress' Report cf First IPF Milestone," NRC-91-0013, dated Janua ry 29. 1991.
6)-Detroit Edison letter to NRC, " Summary Progress Report of Lecond iPE Milestone," NRC-91-0083, dated July 9, 1991
- 7) Detroit Edicen letter to NetC, " Summary Progress Report of Third IPE Milestone" NRC-91-0153, dated November 27, 1991 Subj ec t :
Updated Schedule for Submittal of the IPE Report The purpoi.e of this letter.is to provide the NRC staff with a revised schedule for submitting the Fermi 2 IPE Report. By Re--stence 3, Detroit Edison provided its response to NRC Generic Letter 88-20 (Reference 2). This response was found acceptable by the.NRC in Reference 4.
The NRO concluded that the Fermi 2 "IPE approach,
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-methodology, and schedule are acceptable." Also, in the Reference 4
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letter, the NRC Project Manager request ed of Det roit Edison that "if ycut schedule should change, please notify the NRC of the proposed change and the reason for the change." This letter identifies a change in schedule only for submit tel of the final IPE report and the teasons for this change. The change will still result in a schedule concistent with that originally proposed by GL 88-20.
As described belou, insights regarding the t reatment of plant specific features in the IPE models, as well as other f actors, have impactec our schedule j
f or submit t al.
The revised schedule for submit tal of the Fe rmi 2 IPE Report is September 1, 1992. As described below, this will allow suf ficient time to make important adjustments to the IPE and evaluate insights to assure proper credit -is given for current plant design features and operator actions.
The. preliminary result s - f rom our IPE asses sment, and the potential need to extend our schedule for submittal of the report, were discussed in some detail with the NRC/NRR Project Manager, Mr. Timothy Colburn, and other members of your staf f on April 5,1992 via a teleconference. This discussion apprised your staf f of our current understanding of the IPE insights and characterized the significance of our present findings. This was consistent with our previous c ommitment in the Reference 4 let ter 'o provide periodic brief summary progress reports of IPE milestones, as were submit ted in References 5 through 7.
-The numerical results f rom the IPE were discussed with your staf f and should be considered preliminary in nature.
However, it is important to note that the currently estimated total Core Danage Frequency for Fermi 2 is consistent with the results f or similar vintage Boiling Water Reactors (BWhs) of-the Fermi 2 design; i.e., a BWP. 4. Mark I containment. Also, the initial results show that the functional accident class contrioutors to Core Damage Frequency are not unusual or atypical of other similarly designed nuclear fccilities, e.g., loss of decay heac removal and loss of high pressure injection aedident sequences leading to core damage are prima ry contributors. The relative contribution f rom the Station BAackout event sequence is very small for Fermi 2.
As the Level 1 model was being finalized and reviewed in some detail, it became apparent that events involving the loss of a single division of cffsite powet needed explicit evalustion. Historically, most PRAs have treated the loss of offsite pcwer event as a single initiating event (i.e., a total loss of of fsite peser) in the calculation of its contribution to the total Care Damage Frequency (CDF). Howeve r, it seemed appropriate, considering the Fermi 2 design, also to consider the loss of Division 1 and the loss of Division 2 as separate initiating events. With this change the IPE results more accurately
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USNRC April.30s 1992-NRC-92-0051 Page.3' f
account for the 120 kv and 345 kv of fsite power feeds whien supply separate switchyards for Division 1 and Division 2, respectively.
The preliminary impact on the estimated total CDF value of the above change in treatment of loss of of fsite power events was not large.
However, the results also indicated that.the less of one division of offsite power appeared to dominate the overall loss of of fsite power.
contribution to the estimated CDF. Potential procedural enhancements and recovery actions to reduce - this contribution to overall risk thus emerged as a significant insight gained from the IPE process.
The Fermi 2 electrical distribution system already includes significant flexibility in the design which would be useful in responding to a loss of a single division of AC power. Although operations personnel are well aware of these design capabilities, the initial evaluation was conservative in approach and took no credit for such recovery potential.
However, it was-determined through the IPE
_ process, that -additional. procedural guidance and specific training on these ' events-could significantly increase the probability that recovery actions would be successful in responding to such an emergency.
It was therefore decided to proceed with.an evaluation of these -improvements in narallel with the development of a more
- realistic 'model and completion of the final report.
In addition to:the IPE changes b 7olving partial loss of of fsite power, preliminary insights ira r t ~.ng the significance of current maintenance practices are also being examined in greater detail. The
_ present _IPE.model uses unavailability data collected early in the IPE/PRA ef fort, 'just prior to significant improvements in the Fermi 2 i
- prevratative maintenance program. An examination of the IPE results indicate that some calculated system unavailabilities may be skewed in an overly conservat1ve manner due to the usec of _ this older data.
The
> proposed data update will make the PRA model more current and will more accurately reflect the enhanced programs and results being-obtained at Fermi 2.
~ In summary. Detroit Edison has concluded that the changes discussed
'above, along with some other ~1ess significant refinements, should be made before the IPE report is finalized and submit ted.
We believe-that making' these changes now will result in a higher quality report:
which will be more useful for training and one. that more accurately; reflects the Fermi 2 design and accident response capabilities.
Our-schedule' request is in concert with the intent ~ of Generic Letter 88-20 and the_ current indust ry approach to the IPE-program..The Generic Letter expected that IPE recults be submitted within 3 years (i.e., byL September '1,1992) from the date of the associated Federal Regiscer Notice (published on September 1,1989). Again, our updated schedule for submittal'to the NRC of the Fermi 2 IPE Report is 1
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-USNRC April 30,1992 j
Page 4 Septembe r 1' 1992. As in the past, we will keep you fully apprised of developments in this important evalua t ion.
If you have any questions, please contact Mr. Terry L. Riley.
Supervisor Nuclear Licensing, et (313) 586-1684.. Detroit Edison would be happy to discuss these matters in more detail at your
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convenience if-desired.
Sincerely, bW cc:
T. G. Colburn A. - B. Davis M. P. Phillips S. Stasek l.
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