ML12115A165
| ML12115A165 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 04/24/2012 |
| From: | Lyon C, Milano P Watts Bar Special Projects Branch |
| To: | Leeds E Office of Nuclear Reactor Regulation |
| Lyon, Fred | |
| References | |
| TAC MD7169 | |
| Download: ML12115A165 (6) | |
Text
April 24, 2012 MEMORANDUM TO: Eric J. Leeds, Director Office of Nuclear Reactor Regulation FROM: Carl F. Lyon, Project Manager /RA/
Watts Bar Special Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Patrick D. Milano, Senior Project Manager /RA/
Watts Bar Special Projects Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation
SUBJECT:
WATTS BAR NUCLEAR PLANT, UNIT 1 - FOLLOW-UP TO SAFETY CONCERN REGARDING HYDROLOGY/FLOODING (TAC NO. MD7169)
This is a follow-up to the meeting on April 10, 2012, in O-8E2 between Michele Evans (DORL/D) and Patrick Milano and Fred Lyon (DORL/LPWB). See ADAMS Accession No. ML12110A313 (package). The meeting was in regard to a potential safety concern raised by LPWB about TVAs compliance at Watts Bar Nuclear Plant (WBN) Unit 1 with the licensing/design basis flooding event and the staffs proposed 50.54(f) letter to TVA requesting information to verify the licensees compliance with the current licensing basis of WBN Unit 1. LPWB described the safety significance of its concern and recommended that the issue be resolved promptly. Ms.
Evans indicated that she understood the issue and would get alignment with NRR and RII senior management on how to address it, and she acknowledged that she had the responsibility to address this issue. LPWB has not received further management direction on this issue.
LPWB is concerned that there has been no further action on this issue; therefore, this memorandum is to reiterate and document the staffs safety concern.
At WBN Unit 1, the information currently available to the staff indicates that the potential flooding event is not bounded by the current licensing and design bases. Therefore, the staffs original determination of reasonable assurance of adequate safety is no longer supported.
Without additional information, as requested by the proposed WBN Unit 1 50.54(f) letter, the staff no longer has reasonable assurance of safe operation of WBN Unit 1. The long response time and general information requested by the Fukushima 50.54(f) letter does not address the existing safety concern at WBN Unit 1.
On March 28, 2012, in the Watts Bar Unit 2 Reactivation Assessment Group (WRAG) meeting and in the follow-up meeting with Ms. Evans on April 10, 2012, LPWB described the basis for the safety concern and the proposed 50.54(f) letter for WBN Unit 1. LPWB indicated that, based on currently available information, WBN Unit 1 may be operating outside its licensing and design basis for a flooding event. LPWB stated that the staff requires additional information from TVA to confirm that the staff continues to have reasonable assurance of safe operation of WBN Unit 1.
E. Leeds TVA has modified its licensing basis for flooding and hydrology several times since 1995 when the basis was reviewed and approved by the staff in the safety evaluation report for operation of WBN Unit 1. In addition to modifications to some input assumptions and methodologies, TVA made physical changes to dams and embankments, and also modified several of the flood-causing scenarios from those described at the time of Unit 1s licensing. None of these changes were reviewed by the NRC staff prior to implementation by TVA. Thus, the staff does not have a clear understanding of what TVA has as its current licensing basis. In recent discussions, TVA has acknowledged that flood level evaluations, conducted after correction of quality assurance problems with its calculation code and certain input assumptions, have resulted in a new estimated probable maximum flood (PMF) level that has less than 1 inch of margin to a flood mitigation component and limited margins of less than 1 foot to other flood mitigation components. Further, TVA has implemented additional compensatory measures (e.g., sand baskets), for which it took credit in determining the new PMF level. During a recent public pre-submittal meeting on March 29, 2012, to discuss TVAs proposed revision of its licensing basis for WBN Unit 1, TVA indicated that (1) an additional issue surfaced regarding a Watts Bar Dam bypass that could raise the PMF by an additional 0.2 feet, and (2) additional calculations are being done in other areas that could adversely impact the final PMF value.
Thus, the NRC staff does not know the actual current licensing basis PMF level at WBN Unit 1.
Based on the estimates from the ongoing calculations, the staff is not sure that there is margin remaining for the protection of the safety-related equipment required to be operable during the PMF event. In particular, TVA mentioned that it is having difficulty defining the uncertainties within the calculation process and with the accident analysis assumptions, such that the overall uncertainty in the final PMF level is not yet known.
The staff has not evaluated the structural stability of the compensatory measures (i.e., sand baskets) now credited during a flood event. In its January 25, 2012, letter to TVA, the staff stated that these measures may not be adequate. TVA has not yet conducted an evaluation to show that the sand baskets can remain operable when subjected to debris impacts during a flood. Likewise, the staff questioned TVAs approach in the licensees ongoing structural evaluations of upstream dams and their ability to withstand seismically-induced forces and ground motion. These are key evaluations for acceptance of the UFSAR assumptions regarding the ability of the dams to withstand a seismic event without failure.
LPWB drafted a 50.54(f) demand-for-information letter to obtain the required information.
Ms. Evans did not agree with the need for a separate 50.54(f) letter to TVA regarding WBN Unit 1, and stated that the 50.54(f) letter relating to Fukushima event should be sufficient to address this issue at WBN Unit 1. Ms. Evans directed that the proposed 50.54(f) letter not be given to OGC for review until she allowed it.
The Fukushima 50.54(f) letter does not bound the current situation at WBN Unit 1, and it does not address the issue in a prompt manner. LPWB is concerned with the lack of prompt NRC action to address this potential significant safety issue, as discussed below.
A. The Fukushima 50.54(f) letter, Enclosure 2, Page 8, Integrated Assessment Report, requires that, For the plants where the current design basis floods do not bound the reevaluated hazard for all flood causing mechanisms, provide the following:
E. Leeds c. Description of any additional protection and/or mitigation features that were installed or are planned, including those installed during course of reevaluating the hazard. The description should include the specific features and their functions.
- d. identify other actions that have been taken or are planned to address plant-specific vulnerabilities.
These actions may not be completed until 5 years from the information request. At WBN Unit 1, where information shows that the current licensing and design bases may not be adequate, the staff does not currently have enough information to determine that there is a reasonable assurance of safety.
B. The Fukushima 50.54(f) letter, Enclosure 2, Page 9, Required Response, states that:
Within approximately 60 days of the date of this information request, NRC staff will determine the priority for each reactor site to complete the hazard reevaluation report. The site priority will determine the submittal date for addressees to provide written responses to Requested Information item 1 (Hazard Reevaluation Report).
In accordance with Sections 161.c, 103.b, and 182.a of the Atomic Energy Act of 1954, as amended, and 10 CFR 50.54(f), an addressee must respond as described below.
- 1. Within 60 days of the date of the NRCs issuance of guidance
[scheduled to be developed by November 30, 2012] on implementation details of the Integrated Assessment Report, including criteria for identifying vulnerabilities, submit an approach for developing an Integrated Assessment Report including criteria for identifying vulnerabilities.
- 2. In accordance with the NRCs prioritization plan, within 1 to 3 years from the date of this information request, submit the Hazard Reevaluation Report. Include the interim action plan requested in item 1.d, if appropriate.
- 3. Within 2 years following submittal of the Hazard Reevaluation Report to the NRC, any addressee who is requested to complete an Integrated Assessment should submit written responses to Requested Information item 2.
Therefore, the submittal and NRC review of the addressees reports may not be completed for up to 5 years. Based on the information currently available to the NRC staff for WBN Unit 1, the staff does not currently have enough information to determine that there is a reasonable assurance of safety.
E. Leeds C. At WBN Unit 1, there are inconsistencies between the WBN Unit 1 UFSAR and WBN Unit 2 FSAR, TVA has changed the assumptions used in its original flooding accident analysis without NRC staff review or approval, there are unknown uncertainties in TVAs current flooding accident analysis, TVA has not yet completed its analysis, and there is a lack of substantial margin (i.e., less than 1 inch to the thermal barrier booster pump motor) until safety-related equipment required to be operable during a PMF event is flooded. As a result, the staff does not have reasonable assurance that TVA is in compliance at the present time with its licensing basis or with GDC 2 at WBN Unit 1.
Other limiting components with less than 1 foot of margin to flooding discussed by TVA in the public meeting on March 29, 2012, include:
- Essential Raw Cooling Water Flow Control Valves: 0.7 foot margin to flood
- Spent Fuel Cooling Pumps: 0.9 foot margin to flood
- Intake Pumping Station: 0.5 foot margin to flood D. WBN Unit 1 is relying on certain interim compensatory actions (e.g., sand baskets on local dams, temporary barriers) for flood control that have not been evaluated and approved by the NRC staff. In fact, the NRC stated in its January 25, 2012, letter to TVA that, Based on our review...the NRC staff finds that the sand baskets are not capable of resisting debris impact, and that the staff is unable to conclude that these sand baskets were designed to withstand impacts from large debris during a flood. Accordingly, the NRC recognizes that the compensatory measures may not be adequate to control the flooding event. The NRC staff has not reviewed or documented its safety basis for operation of the facility using the interim compensatory measures.
E. TVA acknowledged in a public meeting on March 29, 2012, that it intends to submit a licensing basis change for Unit 1 that raises the PMF level, even though it has not completed its analysis calculations, and that further certain ongoing calculations may result in a new, higher, PMF that, without new plant modifications, will flood safety-related equipment that is required to be operable during the PMF event. Thus, the current safety margin of less than 1 inch may be exceeded without compensatory measures, and the limited margins to other required equipment may be reduced. This is a significant safety issue.
The Davis-Besse Lessons-Learned emphasize that the staff should document its underlying analysis of the available information and the basis for a decision to allow continued operation of a facility in sufficient detail to determine what evaluation or verification was conducted by the staff. The NRC staff has no such documentation for the situation currently existing at WBN Unit 1.
Based on the above, there is a significant safety concern relating to the current operation of WBN Unit 1 that has not been addressed by the NRC staff. LPWB is concerned that the lack of prompt attention to this concern is not consistent with the NRCs safety goal, with an OCWE, and with the Davis-Besse Lessons-Learned.
LPWB recommends the following to confirm that the staff continues to have reasonable assurance of safe operation of WBN Unit 1:
E. Leeds 1. DORL should issue a separate 50.54(f) letter to TVA demanding information necessary to verify compliance with the current licensing basis for WBN Unit 1.
- 2. RII, with NRR support as necessary, should conduct an inspection at WBN Unit 1 to verify that the changes made to the licensing basis for hydrology/flooding at WBN since 1995 comply with 10 CFR 50.59.
- 3. RII, with NRR support as necessary, should conduct an inspection at WBN Unit 1 of the corrective action program to verify compliance with 10 CFR Part 50, Appendix B, with regard to modifications to the flooding barriers at WBN, and to verify compliance with 10 CFR 50.71(e) with regard to changes to the site environs (e.g., changes to dams and river operations that impact WBN).
- 4. The NRC staff should evaluate the information provided by the licensee and the NRC inspection results and document the NRC staffs basis for continued operation of WBN Unit 1.
At WBN Unit 1, the information currently available to the staff indicates that the potential flooding event is not bounded by the current licensing and design bases. Therefore, the staffs original determination of reasonable assurance of adequate safety is no longer supported. Without additional information, as requested by the proposed WBN Unit 1 50.54(f) letter, the staff no longer has reasonable assurance of safe operation of WBN Unit 1. The long response time and general information requested by the Fukushima 50.54(f) letter does not address the existing safety concern at WBN Unit 1.
Docket No. 50-390
ML12115A165 *email to FLyon OFFICE DORL/LPWB/PM DORL/LPWB/LPM DORL/LPWB/LA DORL/LPWB/BC DORL/LPWB/PM NAME FLyon / PMilano LRaghavan* BClayton SCampbell FLyon DATE 4/24/12 4/18/12 4/24/12 Declined 4/24/12