ML14168A216
| ML14168A216 | |
| Person / Time | |
|---|---|
| Site: | Pilgrim |
| Issue date: | 06/10/2014 |
| From: | Jeffery Lynch Entergy Nuclear Operations |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 2.14.044, TAC K81136 | |
| Download: ML14168A216 (4) | |
Text
"'Entergy-Entergy Nuclear Operations, Inc.
Pilgrim Nuclear Power Station 600 Rocky Hill Road Plymouth, MA 02360 June 10, 2014 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, D.C. 20555
SUBJECT:
Entergy Nuclear Operations, Inc.
Pilgrim Nuclear Power Station Docket No.: 50-293 License No.: DPR-35 Entergy Comments on Pilgrim Nuclear Power Plant-Preliminary Accident Sequence Precursor Analysis (TAC No. K81136)
REFERENCE:
NRC Letter, "Pilgrim Nuclear Power Plant-Preliminary Accident Sequence Precursor Analysis for Licensee review (TAC No.
K81136), dated April 11, 2014 LETTER NUMBER: 2.14.044
Dear Sir or Madam:
The Attachment to this letter provides Entergy's comments on the referenced letter on the Pilgrim Nuclear Power Plant Preliminary Accident Sequence Precursor Analysis that was forwarded to Entergy for review.
This letter contains no commitments.
Should you have questions or require additional information, I can be contacted at (508) 830-8403.
Sincerely, Joseph R. Lynch Manager, Regulatory Assurance
Attachment:
Entergy Comments on Pilgrim Nuclear Power Plant-Preliminary Accident Sequence Precursor Analysis (TAC. No. K81136) cc:
U.S. Nuclear Regulatory Commission Region 1 2100 Renaissance Blvd, Suite 100 King of Prussia, PA 19406-2713 USNRC Senior Resident Inspector Pilgrim Nuclear Power Station Ms. Nadiyah Morgan, Project Manager Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Mail Stop O-8C2A 11555 Rockville Pike Rockville, MD. 20852 4
0 "
Attachment Letter Number 2.14.044 Entergy Comments on Pilgrim Nuclear Power Plant-Preliminary Accident Sequence Precursor Analysis (TAC. No. K81136)
(2 Panes)
Entergy Comments on Pilgrim Nuclear Power Plant-Preliminary Accident Sequence Precursor Analysis (TAC. No. K81136)
Reference:
NRC Letter, "Pilgrim Nuclear Power Plant-Preliminary Accident Sequence Precursor Analysis for Licensee review (TAC NO. K81136), dated April 11, 2014
SUMMARY
Entergy staff has reviewed the NRC letter on Pilgrim Nuclear Power Plant Preliminary Accident Sequence Precursor (ASP) Analysis of Operational Event that occurred on February 8, 2013 (Winter Storm Nemo).
The point estimate conditional core damage probability (CCDP) for this event is 1.2E-4 and is considered significant in regards to the Industry Trends Program (ITP). Comments were provided to the NRC as discussed below.
BACKGROUND It should be noted that there is no direct regulatory impact to Pilgrim from the ASP standpoint.
The ASP evaluates the event regardless of licensee performance (no licensee performance deficiency is required for an ASP analysis). In addition, the ASP analyses have different modeling rules than the Significance Determination Process (SDP). For example, if there was an Emergency Diesel Generator (EDG) out for maintenance at the time event, that would be rolled up into the analysis (whereas SDP assessments use nominal test and maintenance probabilities). The role of ASP is to inform internal and external stakeholders (including the public) of the best estimate risk significance of an event and any insights from the analysis, regardless of licensee performance. In addition, overall ASP results are a part of the ITP.
Events with a CCDP/delta-CDP of > 1 E-5 are considered significant events in the ITP (Note: this is different than a significant precursor that has a CCDP/delta-CDP - 1 E-3 that are reportable to Congress).
COMMENTS The ASP assessment is dominated by a non-recoverable loss of offsite power and subsequent station blackout (SBO) due to postulated failures of all EDGs (including the SBO diesel generator) and the failure to restore offsite power to a safety bus prior to battery depletion.
The following comments have been forwarded to Chris Hunter and others of the NRC-RES staff during the last few weeks. Procedures 2.4.16, 5.3.26, 5.4.6, and 5.3.36 Attachment 9 were subsequently provided, as well as evidence of 23kV line availability during the event.
- 1. No credit for 345 kV recovery due to damaged condition prior to Startup Transformer (SUT) restoration (-21 hours) which is not challenged due to the damage. However, no credit was given for recovery of the 23kV line. There were indications from Nstar that this line was available for 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> after the event and then again some 16 hours1.851852e-4 days <br />0.00444 hours <br />2.645503e-5 weeks <br />6.088e-6 months <br /> later. Had the EDGs not run, this line would have been pursued for AC power recovery.
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- 2. The Pilgrim PRA report contains a Station Blackout (SBO) Modular Accident Analysis Program (MAAP) run which shows that with Reactor Core Isolation Cooling (RCIC), High Pressure Coolant Injection (HPCI), and Fire Water Systems available from the beginning, and successful DC load shedding, there are up to 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> to recover AC power prior to core damage. Therefore, the 345kV source would have been available in time to avoid core damage.
- 3.
No credit was given for breaker alignment after battery depletion, but breakers can be manipulated without DC power in accordance with (lAW) Procedure 2.4.16. This will allow for some offsite power recovery which is currently not credited in the ASP assessment.
- 4. The ASP assessment assumes 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> 125VDC battery service life with DC load shedding, whereas PRA assumes 14 hour1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> with successful DC power load shedding lAW Procedure 5.3.31.
- 5. No credit for EDG recovery within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> due to battery depletion (no DC power) yet EDGs can be started and loaded without DC lAW Procedure 2.4.16.
- 6. No credit was given for containment venting due to loss of DC power. Additionally, no credit was given for local direct torus vent operation in accordance with Procedure 5.3.36 Attachment 9.
CONCLUSION The ASP assessment of the NEMO Loss of Offsite Power (LOOP) event is too conservative. It should be reperformed to include the recovery actions and modeling differences detailed in the comments above. While the resultant CCDP will most likely still indicate it was a significant event for ITP, it most likely will be below 1 E-4.
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