ENS 50245
ENS Event | |
|---|---|
02:46 Jul 1, 2014 | |
| Title | Unanalyzed Condition That Could Have Resulted in an Increased Maximum Flood Level |
| Event Description | On June 27, 2014, TVA identified in a reanalyzed hydrologic analysis for Watts Bar Nuclear Plant (WBN) a deviation from the current hydrologic analysis. The flooding analysis in Section 2.4.3 of the WBN UFSAR assumes that the Watts Bar West Saddle Dike fails completely and instantaneously at approximately 1.5 feet of overtopping during a Peak Maximum Flood [PMF]. This assumption exists in the original design basis analysis and the revised analysis which supports WBN-UFSAR-12-01 (Application to Revise Watts Bar Nuclear Plant Unit 1 Updated Final Safety Analysis Report Regarding Changes to Hydrologic Analysis).
The results of recent studies of the West Saddle Dike, conducted as part of the Fukushima Order 2.1 flooding review, indicate that the complete and instantaneous failure of the Watts Bar West Saddle Dike may not be a valid assumption. If the dike does not fail, analyses performed using the codes and methods consistent with those used in original plant design show that the east floodwall of the Watts Bar Dam would overtop. As a result of this overtopping, the east floodwall is assumed to fail. Based on this assumption and analysis, failure of the east floodwall of the Watts Bar Dam would result in an increase in the flood level at the WBN Plant Site. The current licensing basis PMF level for WBN is 734.9 feet as stated in Section 2.4.3.5 of the WBN UFSAR. In addition, it should be noted that by letter dated July 19, 2012, TVA proposed a revised PMF level of 739.2 feet. Introducing non failure of the Watts Bar West Saddle Dike indicated a potential increase of approximately 1.7 feet over the revised PMF level. TVA performed additional analysis using current industry standard for flooding analysis. Specifically, TVA modeled the condition using the United States Army Corps of Engineers Hydrologic Engineering Center River Analysis System (HEC-RAS) tool. TVA's analysis of the condition using HEC-RAS determined that all required safety equipment for WBN would not be impacted and are considered operable based on a Prompt Determination of Operability completed on June 30, 2014. This report addresses a condition as described in 10 CFR 50.72 (b)(3)(ii)(B). TVA is making this report consistent with the guidance of NUREG-1022 regarding the application of engineering judgment to the evaluation of reportability of an unanalyzed condition. The NRC Resident Inspector has been notified of this condition.
On June 30, 2014, TVA reported (Event 50245) that during a re-analysis conducted as part of the Fukushima Order 2.1 flooding review, a probable maximum flood (PMF) design assumption that the Watts Bar Dam west saddle dike fails completely and instantaneously at approximately 1.5 feet of overtopping, was determined to be a non-conservative flood model assumption (i.e., invalid). As a result, TVA postulated that Watts Bar Dam's east floodwall would fail, increasing the site flood level at Watts Bar Nuclear Plant (WBN) by 1.7 feet; a condition that was beyond the current licensing basis. Through subsequent analysis, TVA has demonstrated that although the west saddle dike may not completely and instantaneously fail during a PMF (as previously assumed), the consequential increase in reservoir levels does not result in a failure of the Watts Bar Dam east floodwall and would not result in an increase in the flood level at WBN. Therefore, the previously reported 10 CFR 50.72(b)(3)(ii)(B) event is being retracted. The NRC resident Inspector has been informed of this event retraction. Notified the R2DO (Hickey). |
| Where | |
|---|---|
Watts Bar  Tennessee (NRC Region 2) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+-3.37 h-0.14 days <br />-0.0201 weeks <br />-0.00462 months <br />) | |
| Opened: | Damon Fegley 23:24 Jun 30, 2014 |
| NRC Officer: | Howie Crouch |
| Last Updated: | Aug 21, 2014 |
| 50245 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |
WEEKMONTHYEARENS 569102023-12-28T16:29:00028 December 2023 16:29:00
[Table view]10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition ENS 565412023-05-25T17:45:00025 May 2023 17:45:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition of Emergency Diesel Generator ENS 538012018-12-20T05:00:00020 December 2018 05:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Containment Air Return Fan System Inoperable ENS 533492018-04-19T23:44:00019 April 2018 23:44:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Related to Emergency Core Cooling Gas Accumulation Acceptance Criteria ENS 528502017-07-12T16:38:00012 July 2017 16:38:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Related to Gdc-5 (General Design Criterion-5) for Dual Unit Operation ENS 519952016-06-08T19:26:0008 June 2016 19:26:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition That Could Potentially Degrade Plant Safety ENS 509602015-04-06T21:00:0006 April 2015 21:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Volume Control Tank Isolation Time Analysis Error ENS 508872015-03-13T15:00:00013 March 2015 15:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition ENS 505962014-11-05T18:10:0005 November 2014 18:10:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Regarding Appendix R Procedures ENS 505402014-10-15T21:00:00015 October 2014 21:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Appendix R Unanalyzed Condition Affecting the Turbine Driven Aux Feedwater Pump ENS 502452014-07-01T02:46:0001 July 2014 02:46:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition That Could Have Resulted in an Increased Maximum Flood Level ENS 498182014-02-11T23:00:00011 February 2014 23:00:00 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Nonconservative Operator Manual Actions Identified in Appendix R Analysis ENS 495412013-11-14T21:00:00014 November 2013 21:00:00 10 CFR 50.72(b)(3)(v)(A), Loss of Safety Function - Shutdown the Reactor, 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident, 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition, 10 CFR 50.72(b)(3)(v)(C), Loss of Safety Function - Release of Radioactive Material Postulated Fire Induced Failure of Centrifugal Charging Pumps ENS 493892013-09-27T16:45:00027 September 2013 16:45:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Calculation Error Resulted in Unanalyzed Condition for Appendix R Event ENS 480562012-06-29T14:28:00029 June 2012 14:28:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition Due to Increase in Probable Maximum Flood Level ENS 487232009-07-28T05:00:00028 July 2009 05:00:00 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition Unanalyzed Condition That Could Have Resulted in an Increased Maximum Flood Level 2023-05-25T17:45:00 | |