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EA-04-221 - Palo Verde (Arizona Public Service Company)

April 8, 2005

EA-04-221

Gregg R. Overbeck, Senior Vice
President, Nuclear
Arizona Public Service Company
P.O. Box 52034
Phoenix, AZ 85072-2034

Dear Mr. Overbeck:

The NRC’s January 5, 2005, inspection report described the results of a special inspection that followed up on your discovery in July 2004 that a significant section of containment sump safety injection piping at all three Palo Verde Nuclear Generating Station (PVNGS) units was void of water. The report discussed two findings that were being evaluated for further NRC action under the NRC’s Significance Determination Process or NRC Enforcement Policy. This letter provides you the results of our evaluation of one of the findings, the preliminary “Greater than Green” finding involving a failure to maintain portions of the PVNGS emergency core cooling system (ECCS) filled with water in accordance with design control requirements. This finding was processed under the NRC’s significance determination process. In separate correspondence, we are providing you the results of our enforcement deliberations on the second finding, an apparent violation of 10 CFR 50.59 that was processed under the NRC’s Enforcement Policy.

NRC’s evaluation of the design control finding considered the fact that Arizona Public Service Company (APS) discovered this condition at PVNGS in July 2004, following notification from another facility where a similar problem had been identified. On July 31, 2004, APS reported this condition to NRC under the provisions of 10 CFR 50.72(b)(3)(v), noting that the voided section of piping had the potential to prevent the fulfillment of the safety function to remove residual heat and mitigate the consequences of a loss-of-coolant accident. In early August, Palo Verde took corrective action to fill the voided piping in all three units, completing those actions by August 4, 2004.

At your request, a Regulatory and Predecisional Enforcement Conference was held on February 17, 2005, to discuss APS’s perspectives on the risk significance of the design control issue. During the meeting the APS staff described their assessment of the significance of the finding, including the results of detailed pump testing APS sponsored to assess the performance of the high pressure safety injection (HPSI) and containment spray (CS) pumps with portions of the ECCS suction piping voided. The APS staff also described corrective actions, including the root cause evaluations for the failure to maintain the design of ECCS suction piping. The APS staff indicated that maintaining voided ECCS suction piping was contrary to the original design intent and was an unanalyzed condition. Your investigation identified possible causes as including: (1) the design requirement was specified, but the end user did not consider the design requirement and incorporate the requirement into procedures; (2) the design requirement was recognized, but there was a breakdown in communicating the design requirement to the end user; and (3) the design requirement was not recognized by the responsible design organization.

The APS staff indicated that the pump testing demonstrated that high pressure safety injection pumps would function for all loss of coolant accidents associated with a pipe break greater than 2.0 inches in diameter. Additionally, the APS staff indicated that, as a conservative measure during the significance determination, no change was made to your probabilistic safety assessment model to account for small-break loss of coolant accidents between 2.0 and 2.3 inches. The APS staff indicated that the significance of the finding should be characterized as having low to moderate safety significance (White) because the change in core damage frequency from the subject performance deficiency was 7.0 x 10^-6.

After considering the information developed during the inspection, the information APS provided at the conference, and the information APS provided in letters dated December 27, 2004, February 10, 2005, February 15, 2005, February 24, 2005, and February 28, 2005, the NRC has concluded that the inspection finding is most appropriately characterized as a Yellow finding, i.e., an issue with substantial importance to safety that will result in additional NRC inspection and potentially other NRC action. While we agreed with many of the assumptions that formed the basis for your risk determination, we identified many uncertainties associated with the conduct of the pump tests. A discussion of these uncertainties, their effect on our significance determination, and the primary basis for the NRC’s conclusion, follows.

The NRC’s review determined that the pump testing provided useful insights into post-accident high pressure safety injection pump performance. Nevertheless, there were several uncertainties associated with the testing and analysis methodologies that could have an impact on the overall conclusions regarding the availability of ECCS pumps following a loss-of-coolant accident. The significant test method uncertainties were in the areas of: (1) the use of the Froude Correlation and scaling, and (2) the impact of temperature on required net positive suction head. There were also several uncertainties associated with differences between the test configuration and the actual plant configuration. The significant configuration uncertainties were in the areas of: (1) the use of ambient temperature water during testing in lieu of post-accident temperature water, (2) the use of a method of air injection during the full scale testing that did not represent the actual void discovered in the plant, (3) the failure to model the transition between suction sources and the associated impact on check valve and system response, and (4) the failure during testing to account for post-accident conditions affecting the pump discharge.

We evaluated the above test method and test configuration concerns and concluded that they introduced large qualitative uncertainties associated with the selection of the loss-of-coolant accident break spectrum utilized by the APS staff in completing the safety analysis. After accounting for the uncertainties, we concluded that at least some portion of the medium loss-of-coolant accident break spectrum should be included in the significance determination of the failure to maintain the ECCS suction piping filled with water.

Taking into account these uncertainties, we determined that the most appropriate value for the change in core damage frequency lies between 5.7 x 10^-6, the result assuming that the performance deficiency only affects system response to small breaks, and 4.6 x 10^-5, the result assuming that high pressure safety injection pumps would fail on recirculation during a medium-break LOCA. Given that 89 percent of the range of core damage frequency lies in the Yellow region, as defined by the significance determination process, we have concluded that the most appropriate characterization of the significance of this finding is Yellow. Additional details of our evaluation and basis for arriving at a Yellow significance determination are contained in Enclosure 2.

We will use the NRC Action Matrix to determine the most appropriate NRC response for this issue. We will notify you by separate correspondence of that determination.

You have 30 calendar days from the date of this letter to appeal the staff’s determination of significance for this Yellow finding. Such appeals will be considered to have merit only if they meet the criteria in NRC Inspection Manual Chapter 0609, Attachment 2.

The NRC also has determined that the failure to maintain portions of the Palo Verde ECCS in accordance with design specifications is a violation of 10 CFR Part 50, Appendix B, Criterion III, Design Control. This violation is cited in the enclosed Notice of Violation (Notice), Enclosure 1. The circumstances surrounding this violation were described in detail in the subject inspection report. In accordance with the NRC Enforcement Policy, the Notice of Violation is considered escalated enforcement action because it is associated with a Yellow finding. You are required to respond to the violation and should follow the instructions specified in the enclosed Notice in preparing your response.

In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter, its enclosures, and your response will be made available electronically for public inspection in the NRC Public Document Room or from the NRC’s document system (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. The NRC also includes significant enforcement actions on its Web site at www.nrc.gov; select What We Do, Enforcement, then Significant Enforcement Actions.

Docket Nos. 50-528; 50-529; 50-530
License Nos. NPF-41; NPF-51; NPF-74

Enclosures
1. Notice of Violation
2. Final Significance Determination

Enclosure 1

NOTICE OF VIOLATION

During an NRC inspection completed December 8, 2004, a violation of NRC requirements was identified. In accordance with the "General Statement of Policy and Procedure for NRC Enforcement Actions," NUREG-1600, the violation is listed below:

10 CFR Part 50, Appendix B, Criterion III, Design Control states, in part, that measures shall be established to assure that the design basis is correctly translated into specifications, procedures, and instructions.

The design basis for the Palo Verde Nuclear Generating Station (PVNGS) is specified, in part, in the plant Updated Final Safety Analysis Report (UFSAR). Section 6.3 of the UFSAR, "Emergency Core Cooling System," states, in part, that the safety injection piping will be maintained filled with water, and that during recirculation mode, the available net positive suction head for the containment spray and high pressure safety injection pumps is 25.8 feet and 28.8 feet, respectively (values that assume the pump suction piping is filled with water.)

Contrary to the above, from initial plant licensing until July 2004, the design control measures established by the licensee were not adequate to assure that the design basis for the PVNGS emergency core cooling system (ECCS) was appropriately translated into specifications, procedures, and instructions. The licensee had no specifications, procedures or instructions in place to assure that the design basis for the ECCS system was maintained. Specifically, except for limited periods of time following ECCS leak testing prior to 1992, the licensee failed to maintain portions of the containment sump safety injection recirculation piping filled with water in accordance with the UFSAR, a nonconformance that affected the available net positive suction head for the containment spray and high pressure safety injection pumps as described in the UFSAR. This condition existed at Units 1, 2 and 3 of the PVNGS facility from initial plant operation (1985, 1986 and 1987, respectively) until August 2004, at which time corrective actions were taken to fill the affected piping.

This violation is associated with a Yellow SDP finding.

Pursuant to the provisions of 10 CFR 2.201, Arizona Public Service Company is hereby required to submit a written statement or explanation to the U.S. Nuclear Regulatory Commission, ATTN: Document Control Desk, Washington, DC 20555 with a copy to the Regional Administrator, Region IV, 611 Ryan Plaza Drive, Suite 400, Arlington, TX, 76011, and a copy to the NRC Resident Inspector at the Palo Verde facility, within 30 days of the date of the letter transmitting this Notice of Violation (Notice). This reply should be clearly marked as a "Reply to a Notice of Violation; EA-04-221" and should include for each violation: (1) the reason for the violation, or, if contested, the basis for disputing the violation or severity level, (2) the corrective steps that have been taken and the results achieved, (3) the corrective steps that will be taken to avoid further violations, and (4) the date when full compliance will be achieved. Your response may reference or include previous docketed correspondence, if the correspondence adequately addresses the required response. If an adequate reply is not received within the time specified in this Notice, an order or a Demand for Information may be issued as to why the license should not be modified, suspended, or revoked, or why such other action as may be proper should not be taken. Where good cause is shown, consideration will be given to extending the response time.

If you contest this enforcement action, you should also provide a copy of your response, with the basis for your denial, to the Director, Office of Enforcement, U.S. Nuclear Regulatory Commission, One White Flint North, 11555 Rockville Pike, Rockville, MD 20852-2738. Because your response will be made available electronically for public inspection in the NRC Public Document Room or from the NRC's document system (ADAMS), accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html, to the extent possible, it should not include any personal privacy, proprietary, or safeguards information so that it can be made available to the public without redaction. If personal privacy or proprietary information is necessary to provide an acceptable response, then please provide a bracketed copy of your response that identifies the information that should be protected and a redacted copy of your response that deletes such information. If you request withholding of such material, you must specifically identify the portions of your response that you seek to have withheld and provide in detail the bases for your claim of withholding (e.g., explain why the disclosure of information will create an unwarranted invasion of personal privacy or provide the information required by 10 CFR 2.390(b) to support a request for withholding confidential commercial or financial information). If safeguards information is necessary to provide an acceptable response, please provide the level of protection described in 10 CFR 73.21.

Dated this 8th day of April 2005

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