ML071590038
| ML071590038 | |
| Person / Time | |
|---|---|
| Site: | McGuire  |
| Issue date: | 06/07/2007 |
| From: | Harrall T Duke Energy Carolinas, Duke Energy Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| Stang J, NRR/DORL, 415-1345 | |
| References | |
| Download: ML071590038 (30) | |
Text
Attachment 1 Page 6 The current PRA model (Rev. 3a) was used to perform the risk evaluation. The McGuire PRA is full scope PRA including both internal and external events. The base case non-seismic CDF and LERF are 2.9E-5/yr and 2.4E-6/yr, respectively. (The seismic results typically are not sensitive to unavailabilities of individual components and the seismic impact for this application is judged to be insignificant relative to the non-seismic impacts.)
The results indicate that the incremental conditional large early release probability (ICLERP) is more limiting with respect to the Regulatory Guide acceptance criterion. The LERF and CDF results are both dominated by tornado and loss of offsite power initiated sequences resulting in a station blackout on failure of the redundant diesel generator. Subsequent failure of secondary side heat removal results in core damage. The LERF is sensitive to station blackouts because of the loss of the hydrogen mitigation system. Uncontrolled hydrogen accumulation increases the challenge to containment integrity.
With a one-time 10-day outage on EDG 1A, the non-seismic delta CDF and delta LERF are 1.1E-6/yr and 1.3E-7/yr, respectively and the incremental conditional core damage probability (ICCDP) and ICLERP are 1.1E-6 and 1.3E-7, respectively.
For permanent changes, RG 1.177 and RG 1.174 outline acceptance guidance criteria of 5.0E-7 for ICCDP and 5.0E-8 for ICLERP, respectively, based on the baseline CDF being smaller than 1.0E-4/reactor-year.
Consistent with the D. C. Cook Safety Evaluation Report of December 10, 2003, the temporary change acceptance guidance criteria are increased by an order of magnitude. Thus, the ICCDP (1.1E-6) and ICLERP (1.3E-7) are within the acceptable values for temporary increases. Using the temporary change criteria, the Technical Specification. allowed outage time could be increased for up to 34 days. In addition, exercising the proposed 7-day extension would avoid additional risk associated with the plant shutdown and transitional risk.
Probabilistic Risk Assessment (PRA) Quality Duke periodically evaluates changes to the plant with respect to the assumptions and modeling in the McGuire PRA. The original McGuire PRA was initiated in March 1982 by Duke Power Company staff with Technology for Energy Corporation as a contractor.
Law Engineering Testing Company and Structural Mechanics Associates provided specific input to the seismic analysis. It