ML16363A429

Diablo Canyon Power Plant - Final Significance Determination of a White Finding, Notice of Violation, and Follow-Up Assessment Letter; NRC Inspection Report 05000275/2016010 and 05000323/2016010

ML16363A429
Person / Time
Site:	Diablo Canyon
Issue date:	12/28/2016
From:	Kennedy K M Region 4 Administrator
To:	Halpin E D Pacific Gas & Electric Co
Jeremy Groom
References
EA-16-168 IR 2016010
Download: ML16363A429 (15)

See also: IR 05000275/2016010

Text

December 28, 2016

EA-16-168 Mr. Edward Senior Vice President and Chief Nuclear Officer Pacific Gas and Electric Company Diablo Canyon Power Plant P.O. Box 56, Mail Code 104/6 Avila Beach, CA 93424

SUBJECT: DIABLO CANYON POWER PLANT - FINAL SIGNIFICANCE DETERMINATION OF A WHITE FINDING, NOTICE OF VIOLATION, AND FOLLOW-UP ASSESSMENT LETTER; NRC INSPECTION REPORT 05000275/2016010 AND 05000323/2016010

Dear Mr. Halpin:

This letter provides you the final significance determination of the preliminary White finding identified in the Diablo Canyon Power Plant NRC Inspection Report 05000275/2016010 and 05000323/2016010; Preliminary White Finding (Agencywide Documents Access and Management System (ADAMS) Accession No. ML16277A340), dated October 3, 2016. The finding is associated with the May 16, 2016, failure of the Unit 2 residual heat removal pump 2-2 suction valve (SI-2-8982B) from the containment recirculation sump to open from the main control room. The NRC has determined the finding is of low-to-moderate safety significance (White). At your request, the NRC held a regulatory conference on November 15, 2016, to further discuss your views on this finding. The meeting summary of this regulatory conference is available at ADAMS Accession No. ML16336A765 and a copy of your presentation is available at ADAMS Accession No. ML16335A439. In your presentation, you described several changes to the probabilistic risk modeling of the failure of valve SI-2-8982B, including changes to the common cause alpha factors and several assumptions related to medium break loss-of-coolant accidents. Your staff also provided their perspectives on a variety of recovery methods available to open valve SI-2-8982B, thereby, restoring the flow path from the containment sump to the reactor core through residual heat removal pump 2-2. evaluation of these factors and the probability of success of these recovery actions, your staff concluded that the change in core damage frequency was less than the Green/White threshold of 1E-6 per year. As a result, you concluded that the inspection finding should be characterized as very low safety significance (Green). We have concluded that our preliminary significance determination change in core damage frequency result of 7.6E-6 per year represents the upper range of the increase in core damage frequency associated with the performance deficiency. Based on the information provided by your staff at the regulatory conference, the NRC adjusted a number of assumptions used in the preliminary significance determination. Specifically, the NRC lowered the common cause alpha factors and adjusted several assumptions related to medium break loss-of-coolant accidents. The NRC also performed a variety of human error probability calculations to determine the likelihood of recovering the functionality of valve SI-2-8982B. The results of these calculations, which removed much of the conservativism from the assumptions used in the preliminary risk assessment, predicted a high likelihood of success (96.4 percent success) for recovering valve SI-2-8982B. Using these assumptions, the NRC concluded the lower range of increase in core damage frequency associated with the performance deficiency to be 1.3E-6 per year. Because the the increase in core damage frequency of the performance deficiency were both greater than 1.0E-6 per year but less than 1.0E-5 per year, the NRC determined the finding was of low-to-moderate safety significance (White). Our evaluation of the risk significance of the finding is provided in the attachment to this letter. significance for the identified White finding. Such appeals will be considered to have merit only if they meet the criteria given in NRC Inspection Manual Chapter 0609, Attachment 2. An appeal must be sent in writing to the Regional Administrator, Region IV, 1600 E. Lamar Blvd., Arlington, TX 76011. The NRC has also determined that the failure to develop adequate instructions for the installation of external limit switches on motor-operated valves is a violation of Technical enclosed Notice of Violation (NOV). In accordance with the NRC's Enforcement Policy, the NOV is considered an escalated enforcement action because it is associated with a White finding for Unit 2. You are required to respond to this letter and should follow the instructions specified in the enclosed NOV when preparing your response. If you have additional information that you believe the NRC should consider, you may provide it in your response to the NOV. The NRC's review of your response to the NOV will also determine whether further enforcement actions are necessary to ensure compliance with regulatory requirements. finding, we have assessed the performance of Diablo Canyon Power Plant, Unit 2, to be in the rd quarter of 2016. Therefore, we plan to conduct a supplemental inspection using Inspection Procedure 95001, notified us of your readiness for this inspection. This inspection procedure is conducted to provide assurance that the root cause and contributing causes of risk significant performance issues are understood, the extent of condition and the extent of cause are identified, and the corrective actions are sufficient to prevent recurrence. In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter and its enclosure will be made available electronically for public inspection in the NRC Public Document Room and in ADAMS, accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html. To the extent possible, your response should not include any personal privacy, proprietary, or safeguards information so that it can be made available to the Public without redaction.

Sincerely,/RA/ Kriss M. Kennedy Regional Administrator Docket Nos. 50-275 and 50-323 License Nos. DPR-80 and DPR-82

Enclosure:

Notice of Violation

w/Attachment:

Final Significance Determination cc: Electronic Distribution via Listserv for Diablo Canyon Power Plant, Units 1 and 2