ML061000643
| ML061000643 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 04/07/2006 |
| From: | Travers W D Region 2 Administrator |
| To: | Singer K W Tennessee Valley Authority |
| References | |
| EA-05-169 IR-06-007 | |
| Download: ML061000643 (9) | |
Text
April 7, 2006EA-05-169 Tennessee Valley AuthorityATTN:Mr. K. W. SingerChief Nuclear Officer and Executive Vice President6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801
SUBJECT:
FINAL SIGNIFICANCE DETERMINATION FOR A WHITE FINDING ANDNOTICE OF VIOLATION (Watts Bar Nuclear Power Plant - NRC Inspection Report No. 05000390/2006007)
Dear Mr. Singer:
The purpose of this letter is to provide you with the Nuclear Regulatory Commission's (NRC)final significance determination for a finding involving a challenge to reactor coolant system(RCS) integrity by multiple pressurizer power-operated relief valve (PORV) actuations and a challenge to RCS inventory control by the loss of RCS coolant via the open PORVs which occurred on February 22, 2005, during transition to solid plant operations.The finding was documented in NRC Inspection Report No. 05000390/2005013, datedSeptember 7, 2005, and was assessed under the significance determination (SDP) process asa preliminary "greater than Green" issue (i.e., an issue of at least low to moderate safety significance which may require additional NRC inspection). The cover letter to the inspectionreport informed the Tennessee Valley Authority (TVA) of the NRC's preliminary conclusion,provided TVA with an opportunity to request a regulatory conference on this matter, and forwarded the details of the NRC's preliminary estimate of the change in core damagefrequency (CDF) for this finding. At TVA's request, an open regulatory conference was conducted on October 25, 2005, to discuss TVA's position on this issue. The enclosures to this letter include the list of attendees at the regulatory conference and material presented by TVA.During the conference, TVA presented the results of its estimate of the increase in CDF due tothe performance deficiency, including influential assumptions and its analysis methodology.
TVA concluded that the finding was of very low safety significance (Green). TVA's analysis included the following five key differences between its evaluation and the NRC's preliminaryevaluation: (1) the number of PORV lifts totaled five instead of the seven lifts used in the NRC's event tree, (2) TVA concluded that a more rigorous mathematical treatment of eachsuccessive PORV lift was warranted, (3) the Residual Heat Removal (RHR) suction relief valvereliability to open was greater than that assumed in the NRC's preliminary estimate, (4) TVA'sanalysis included two additional RHR discharge relief valves to relieve increasing RCS pressurewhich were not included in the NRC's evaluation, and (5) TVA contended that secondary plantcooling was available to prevent core damage. TVA agreed with the NRC's characterization of Tennessee Valley Authority2the finding as a violation of plant procedures. At the regulatory conference, the NRC requestedthat TVA provide the basis for its RHR system relief valve reliability, the availability of emergency core cooling system sump during the event, and the basis for its human errorprobabilities used in risk calculations for the event. In addition, TVA agreed to perform asimulator run to assess the likelihood of success by operators in establishing secondary plant cooling with the RHR system isolated and the RCS closed without exceeding the pressure andtemperature limits report (PTLR). TVA also agreed to provide the results of this activity to the NRC. This information was subsequently transmitted to the NRC by TVA's letter datedDecember 27, 2005.The information provided by TVA caused the NRC to change the event tree that described thefinding. TVA's simulator results indicated that when the operators isolated the RHR system tostop the leak from a stuck open RHR relief valve, an over pressurization event will occur. Inaddition, this resulted in a reduction in the importance of the five key differences that TVA presented at the conference as they no longer have a major impact on the dominant risksequence and the NRC's final risk characterization.After considering the information developed during the inspection, the information TVA providedat the conference, and supplemental information as discussed above, the NRC has concl udedthat the final inspection finding is appropriately characterized as White in the barrier integrity cornerstone.As part of the NRC's final risk characterization, the dominant risk sequence included anassumption that plant procedures required isolation of the RHR system in response to an RHRrelief valve that fails to close during the scenario. The NRC's risk characterization alsoconsidered 12 challenges to the PORVs. This value is based on the total demands seen by the PORV circuitry during the scenario. The NRC's evaluation also assumed both PORV blockvalves to be open instead of the actual condition that existed during the event. This assumption is consistent with the NRC's SDP methodology in which the failure probability of mitigatingequipment is determined based on the average condition of the equipment.These assumptions resulted in a dominant risk sequence that involves the over pressurizationof the RCS. The dominant risk sequence would progress with the subsequent unavailability ofthe PORVs to relieve pressure in the low temperature overpressure protection mode, the subsequent challenge of the RHR relief valves, and the failure of the relief valves to reclose. Subsequent to this, the sequence would progress with successful operator action to isolate the RHR system in accordance with plant procedures which would cause a pressure spike thatwould exceed the reactor vessel's material limits as specified in the PTLR. This could induce a consequential reactor vessel failure from brittle fracture resulting in subsequent core damage.
The staff's preliminary risk assessment assumed the failure probability of the reactor vessel,given this scenario, to be 1.0 which resulted in an estimated delta CDF of approximately 7E-5 per year (Yellow). The staff recognized that the reactor vessel failure probability of 1.0 wasbased on a conservative assumption and conducted a reassessment using multiple approaches, both quantitative and qualitative, to assess the importance of the low temperatureoverpressure sequence.The quantitative results were used as inputs to a qualitative risk evaluation. This evaluationalso considered defense-in-depth concepts and the uncertainties of the different numerical Tennessee Valley Authority3methods used in the sensitivity screening analysis. The qualitative analysis was used for thefinal risk determination reassessment.During the reassessment, the NRC used multiple approaches to assess the importance of thelow temperature overpressure sequence. Low temperature overpressure prevention and mitigation is most critical during RCS water-solid conditions which correlates to the plant conditions of the Watts Bar performance deficiency. Quantitative delta CDF results were within the range of 1E-6 to 1E-5 per year. For the quantitative assessment, the staff performed several sensitivity cases. These cases included application of a vessel failure probabilityscreening value supported by engineering expert opinion regarding the vessel's robustness and, separately, use of previous agency regulatory work for resolution of Generic Safety Issue 94, Additional Low Temperature Overpressure Protection Requirements.The NRC's preliminary significance determination for the performance deficiency, astransmitted in our letter of September 7, 2005, did not specifically address the change in large early release frequency (LERF), in part, because of the complexities and rigor that would be necessary to quantify an estimate. However, the staff has subsequently conducted a qualitative assessment of the change in LERF and considers this to be non-trivial due, in part, to the potential for the containment to be open to support outage work and the relevant mode ofoperations. From a defense-in-depth perspective, unlike most other accident initiators that can lead to core damage, a low temperature overpressure event could result in the reactor pressure vessel being unavailable for either subsequent recovery of the reactor core or as an additional barrier for fission product retention. The consequences of such an event can be significant as a result of containment bypass or failure of containment isolation following vessel failure.Overall, given the above considerations taken in the aggregate, the staff concluded that thefinding should be characterized as White in the barrier integrity cornerstone.You have 10 calendar days from the date of this letter to appeal the staff's determination ofsignificance for the identified finding. Such appeals will be considered to have merit only if theymeet the criteria given in NRC Inspection Manual Chapter 0609, Attachment 2.The NRC also determined that a violation of Technical Specification 5.7.1.1 andProcedure GO-6, Unit Shutdown from Hot Standby to Cold Shutdown, occurred in that TVA personnel failed to slowly raise charging flow to fill the pressure at less than 30 gallons perminute as required by procedure. The violation is set forth in the enclosed Notice of Violation.You are not required to respond to this letter unless the description herein does not accuratelyreflect your position or if you choose to provide additional information. For administrative purposes, this letter is issued as a separate NRC Inspection Report (No. 05000390/2006007)and the above violation is identified as VIO 05000390/2006007-01, White Finding - Failure to Implement Shutdown Procedures which Resulted in Pressurizer PORV Actuations.
Accordingly, Apparent Violation (AV)05000390/2005013-01, Failure to Implement and Maintain Shutdown Procedures which Resulted in Pressurizer PORV Actuations, is closed.In accordance with 10 CFR 2.390 of the NRC's "Rules of Practice," a copy of this letter, itsenclosures, and your response (should you choose to provide one) will be made availableelectronically for public inspection in the NRC Public Document Room or from the NRC's document system (ADAMS) which is accessible from the NRC Web site at Tennessee Valley Authority4http://www.nrc.gov/reading-rm/adams.html. To the extent possible, any response should notinclude any personal privacy, proprietary, classified, or safeguards information so that it can be made available to the Public without redaction. The NRC also includes significant enforcementactions on its Web site at www.nrc.gov; select What We Do , Enforcement , then SignificantEnforcement Actions
.Should you have any questions regarding this letter, please contact Mr. Charles A. Casto,Director, Division of Reactor Projects, at (404)562-4500.Sincerely,/RA/William D. Travers Regional AdministratorDocket No.:50-390License No.:NPF-90
Enclosures:
- 2. List of Attendees
- 3. Material presented by TVAcc w/encl: (See next page)
Tennessee Valley Authority5cc w/encls:Ashok S. Bhatnagar Senior Vice President Nuclear Operations Tennessee Valley Authority Electronic Mail DistributionLarry S. Bryant, Vice PresentEngineering and Technical Services Tennessee Valley Authority Electronic Mail DistributionMichael D. SkaggsSite Vice President Watts Bar Nuclear Plant Tennessee Valley Authority Electronic Mail DistributionRobert J. Beecken, Vice PresidentNuclear Support Tennessee Valley Authority Electronic Mail DistributionGeneral CounselTennessee Valley Authority Electronic Mail DistributionJohn C. Fornicola, ManagerNuclear Assurance and Licensing Tennessee Valley Authority Electronic Mail DistributionGlenn W. Morris, ManagerCorporate Nuclear Licensing and Industry Affairs Tennessee Valley Authority Electronic Mail DistributionPaul L. Pace, ManagerLicensing and Industry Affairs Watts Bar Nuclear Plant Tennessee Valley Authority Electronic Mail DistributionJay Laughlin, Plant ManagerWatts Bar Nuclear Plant Tennessee Valley Authority Electronic Mail DistributionCounty ExecutiveRhea County Courthouse 375 Church Street, Suite 215 Dayton, TN 37321-1300County Mayor P. O. Box 156 Decatur, TN 37322Lawrence E. Nanney, DirectorTN Dept. of Environment & Conservation Division of Radiological Health Electronic Mail DistributionAnn Harris341 Swing Loop Rockwood, TN 37854James H. Bassham, DirectorTennessee Emergency Management Agency Electronic Mail Distribution
___letter ML061000643 enclosure ML061000626 Pkg ML061000605______________________OFFICERII:EICSRII:DRPNRROESIGNATURECFECAC
- NAMECEVANSCCASTORPASCARELLICNOLANDATE3/24/063/24/0603/30/0604/04/06 E-MAIL COPY? YESNO YESNO YESNO YESNO YESNO YESNO NOTICE OF VIOLATIONTennessee Valley Authority Docket No. 50-390Watts Bar Nuclear PlantLicense No. NPF-90 Unit 1EA-05-169During an NRC inspection completed on April 6, 2005, a violation of NRC requirements wasidentified. In accordance with the NRC Enforcement Policy, the violation is listed below:Technical Specification 5.7.1.1 requires that written procedures be implemented andmaintained covering the activities in the applicable procedures recommended by Regulatory Guide 1.33, Revision 2, Appendix A, February 1978, of which Part 2.jrequires a procedure for hot standby to cold shutdown. Procedure GO-6, Unit Shutdown from Hot Standby to Cold Shutdown, Section 5.5, Step [1] [e] states, "SlowlyRAISE charging to fill Pressurizer at less than 30 gpm."Contrary to the above, on February 22, 2005, the licensee failed to followprocedure GO-6, Section 5.5, Step [1] [e], in that net charging flow was raised to a rate that exceeded the 30 gpm procedural specification.This violation is associated with a White significance determination process finding forUnit 1 in the barrier integrity cornerstone.The NRC has concluded that information regarding the reason for the violation, the correctiveactions taken and planned to correct the violation and prevent recurrence, and the date whenfull compliance was achieved is already adequately addressed on the docket and in the information provided by TVA at the conference (Enclosure 3). However, you are required to submit a written statement or explanation pursuant to 10 CFR 2.201 if the description thereindoes not accurately reflect your corrective actions or your position. In that case, or if you choose to respond, clearly mark your response as a "Reply to a Notice of Violation -
EA-05-169," and send it to the U.S. Nuclear Regulatory Commission, ATTN: Document ControlDesk, Washington, DC 20555, with a copy to the Regional Administrator, Region II, within 30 days of the date of the letter transmitting this Notice of Violation (Notice).If you contest this enforcement action, you should also provide a copy of your response with thebasis for your denial to the Director, Office of Enforcement, U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001.If you choose to respond, your response will be made available electronically for publicinspection in the NRC Public Document Room or from the NRC's document system (ADAMS).
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. ADAMS is accessible from the NRC Web site at http://www.nrc.gov/reading-rm/adams.html. If personalprivacy 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 beprotected and a redacted copy of your response that deletes such information. If you requestwithholding of such material, you must specifically identify the portions of your response thatyou 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 pers onalprivacy or provide the information required by 10 CFR 2.390(b) to support a request for Notice of Violation2withholding confidential commercial or financial information). If safeguards information isnecessary to provide an acceptable response, please provide the level of protection described in 10 CFR 73.21.In accordance with 10 CFR 19.11, you may be required to post this Notice within 2 workingdays. Dated this 7 th day of April 2006Enclosure 1 LIST OF ATTENDEESNuclear Regulatory Commission
- W. Travers, Region II (RII)
J. Shea, Deputy Director, Division of Reactor Projects (DRP), RII C. Christensen, Deputy Director, Division of Reactor Safety (DRS), RII S. Cahill, Branch Chief, DRP, RII J. Bartley, Senior Resident Inspector, DRP, RII R. Bernhard, Senior Risk Analyst, DRS, RII L. Trocine, Senior Enforcement Specialist, Office of Enforcement C. Evans, Regional Attorney and Enforcement Officer, RII S. Sparks, Senior Enforcement Specialist, RII M. Reinhart, Office of Reactor Regulation (telecon)
M. Pohida, Office of Reactor Regulation (telecon)
F. Bonnett, Office of Reactor Regulation (telecon)Tennessee Valley Authority:M. Skaggs, Site Vice PresidentD. White, Operations Manager F. Koontz, Engineering Specialist P. Pace, Licensing and Industrial Affairs Manager J. Smith, Sequoyah Licensing Manager T. Langley, Browns Ferry Licensing Manager J. Mayo, Watts Bar Shift Manager C. Borrelli, TVA PSA EngineerS. Roa, Director of Risk Management Solutions, ABS ConsultingEnclosure 2