ML14322B018
| ML14322B018 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 11/18/2014 |
| From: | Andrew Hon Plant Licensing Branch II |
| To: | Arent G, James Shea, Spink T Tennessee Valley Authority |
| Andy Hon | |
| References | |
| TAC ME9130 | |
| Download: ML14322B018 (5) | |
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Mr. Joseph W. Shea Hon, Andrew Tuesday, November 18, 2014 5:02 PM Shea, Joseph W Owshea@tva.gov); Spink, Thomas E (tespink@tva.gov); Arent, Gordon (garent@tva.gov)
Poole, Justin; Cheng, Yuan; Hoang, Dan; Lupoid, Timothy; Quichocho, Jessie WATTS BAR NUCLEAR STATION, UNIT 1-REQUEST FOR ADDITIONAL INFORMATION RELATED TO UCENSE AMENDMENT REQUEST TO UPDATED FINAL SAFETY ANALYSIS REPORT CHANGES ASSOCIATED WITH HYDROLOGIC ANALYSIS (TAC NO. ME9130)
RAI -last11172014.pdf ML14322B018 Vice President, Nuclear Licensing Tennessee Valley Authority 6A Lookout Place 1101 Market Street Chattanooga, TN 37402-2801
SUBJECT:
WATTS BAR NUCLEAR STATION, UNIT 1-REQUEST FOR ADDITIONAL INFORMATION RELATED TO LICENSE AMENDMENT REQUEST TO UPDATED FINAL SAFETY ANALYSIS REPORT CHANGES ASSOCIATED WITH HYDROLOGIC ANALYSIS (TAG NO. ME9130)
Dear Mr. Shea:
By letter dated July 19, 2012, you submitted an application for license amendment to revise the Updated Final Safety Analysis Report (UFSAR) to adopt a revised hydrologic analysis for Watts Bar Nuclear Plant (WBN)
Unit 1. (ADAMS Accession Number ML12237A167). These changes to the WBN Unit 1 UFSAR incorporated updates previously submitted in support of the initial licensing of WBN Unit 2 as well as more recently discovered input information. TVA supplemented the request in a letter dated September 30, 2014 (ADAMS Accession Number ML14289A106),
The U.S. Nuclear Regulatory Commission (NRC) staff is reviewing your submittal and has determined that additional information is required to complete the review. The specific information requested is addressed in the enclosure to this letter. The proposed questions were discussed by telephone with your staff on November 18, 2014. Your staff confirmed that these questions did not include proprietary or security-related information and agreed to provide a response by December 3, 2014.
1
The NRC staff considers that timely responses to RAis help ensure sufficient time is available for staff review and contribute toward the NRC's goal of efficient and effective use of staff resources. If circumstances result in the need to revise the requested response date, please contact me at (301) 415-8480 or via e-mail Andrew. Hon@nrc.gov.
Docket No. 50-390 ADAMS Accession# ML143228018
Enclosure:
Sincerely, RIA Andrew Han, Project Manager Plant Licensing Branch 11-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Request for Additional Information ADAMS #ML143228016 2
REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION RELATED TO LICENSE AMENDMENT REQUEST TO FACILITY OPERATING LICENSE NO. NPF-90 TENNESSEE VALLEY AUTHORITY WATTS BAR NUCLEAR POWER PLANT. UNIT 1 DOCKET NO. 50-390 1.0 Watershed Hydrology 1.1 Magnitude of Probable Maximum Precipitation (PMP) of same storm The NRC staff has found differences between the PMPs as shown on Table 2.4-11 of the September 301h submittal and other PMPs as shown on Table 2.4-5 of previous final safety analysis reports (FSARs). The NRC staff noted different values are now being used to determine the PMP, which is used as an input to the PMF. Please explain the reasons for the changes of PMPs in the current submittal while using the same 7,980 square-mile storm at the same storm center as shown in the previous FSARs.
To illustrate this, a part of the differing data is presented on Table 1.
Table 1: Example of comparing computed PMPs in the 2010 FSAR vs. 2014 submittal Antecedent Storm Rainfall Depth Main Storm Rainfall Depth (inch)
(inch)
Sub-watershed (Quoted from (Quoted from (Quoted from (Quoted from name Table 2.4-5, Table 2.4-11, Table 2.4-5, Table 2.4-11, precedent September 30, precedent September 30, FSAR, 2010) 2014 submittal FSAR, 2010) 2014 submittal Asheville 6.44 6.0 17.40 10.98 Newport, French 6.44 6.0 18.5 16.56 Broad
- Newport, 6.44 6.0 19.30 15.48 Pigeon Little Tennessee 6.44 6.0 24.00 15.30 Local - Fontana to Chilhowee Dam Little Tennessee 6.44 6.0 21.00 15.84 Local-Chilhowee to Tellico Dam Watts Bar Local 6.44 6.0 15.8 15.84 Above Clinch River ENCLOSURE 1.2 Antecedent Precipitation Index (API) method The FSAR Section 2.4.3.1 of the September 30, 2014, submittal shows the PMP depth is 16.17 inches and the antecedent depth is 6.0 inches. Whereas FSAR Section 2.4.3.1 also states that the antecedent depth is 40 percent of the total PMP depth (6.47 inches). Please clarify and explain the apparent discrepancy between the antecedent depth 6.0 inches and 6.4 7 inches, which is equal to 40 percent of the PMP depth.
NRC also requests that TVA clarify the antecedent depth actually used.
In Section 2.4.3.2 of September 301h 2014 submittal, TVA states that the API numerical value was determined using the observed data from 1997 to 2007. Please provide supporting documents to illustrate use of the API method and its computed numerical values, including computational examples illustrating how the excess rainfall depth showed in Table 2.4-11 were determined.
1.3 Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model for PMF event In Section 2.4.3 on page E1-5 of 38, Probable Maximum Flood on Streams and Rivers, TVA indicated that the HEC-HMS model was applied in the modeling of Probable Maximum Flood. But at the October 8, 2014 meeting, TVA stated that the HEC-HMS model was not used in the PMF simulation. Please clarify Section 2.4.3 on page E1-5 of 38 if the HEC-HMS was not used in the PMF event. If HEC-HMS is not used in the PMF, please elaborate on the other methods that are adopted to convert the precipitation to surface runoff for the PMF event.
1.4 Unit Hydrograph As stated in the markup version of the FSAR Section 2.4.3, page 2.4-29, there is unpublished work by TVA that supports the assumption of linearity of unit hydrographs for large, out-of-bank floods produced by major, basin-wide storms.
Please explain why this statement is being removed from the current FSAR (see Pages 2.4-29 through 2.4-30).
1. 5 Selected flood event In FSAR Section 2.4.2.1, there is a table of historic floods. Examination of this table shows the maximum flood in May 8, 1984 had a Water Surface Elevation of 698.23 feet at the tail-water of the Watts Bar Dam. Please explain why this storm was not included in calibration data set.
2.0 River Hydraulics 2.1 Hydrologic Engineering Center-River Analysis System (HEC-RAS) model calibration for segment between Watts Bar Dam and Fort Loudoun Dam As presented in Section 2.4.3.3.5.1 and Figures 2.4-12 through 2.4-20, TVA selected 1973 and 2003 flood events to calibrate HEC-RAS model for the Tennessee River system.
For calibration purposes, the river system was divided into many river segments.
Each segment contains dams at upstream and downstream boundaries. For example, the Watts Bar segment was assigned for calibrating the river hydraulic condition between Fort Loudoun Dam and Watts Bar Dam. Since TVA set the observed flood elevations at the headwater of the Watts Bar Dam, the HEC-RAS model cannot compute the flood elevation at the dam.
Therefore, the calibration results cannot show the difference between the computed and observed flood elevations at the Watts Bar Dam (Figure 2.4-17, Sheet 1 of 2).
Please provide validation for the computed flood elevation at the headwater of Watts Bar Dam using the observed flow rates of 1973 and 2003 flood events as the downstream boundary condition. The validation should be able to assure the computed flood elevations at the Watts Bar Dam are conservative within 1 foot to meet the calibration rule as indicated in Section 2.4.3.3.5.1.
2.2 Fluctuation of computed flow rates shown in the calibration results Please explain a deviation as shown on Figure 2.4-14 (Sheet 4 of 5), which appears to indicate a bias between the observed data and the HEC-RAS simulation results.
Also, explain why the sharp variation of the flow rates at Watts Bar Dam results in smooth variation of the flood elevations as shown on Figure 2.4-17 (Sheet 1 of 2 and Sheet 2 of 2).
2.4 Calibrated geometry In 007 CDQ000002014000018 HEC-RAS Tributary Model Calibration of Enclosure 11, there are references to calibrated geometry. Please explain and clarify what this means.
3.0 Dam Stability 3.1 Safety Factor 1.52 for Slope Failure at the Embankment of Watts Bar Dam In Section 2.4.4.1 of the 2012 license amendment request submittal, TVA revised the safety factor from 1.52 to 1.0 for the embankment of Watts Bar Dam under an operating basis earthquake (OBE) combined with% PMF. In the September 301h submittal in 2014, TVA changed the safety factor of greater than 1.0 back to 1.52 as the same safety factor from 1977's condition. This 1.52 safety factor remains as one of the unresolved issues without updated loadings and embankment configurations.
Please update the computations according to the OBE concurrent with % PMF condition, including the updated slope failure analysis for Watts Bar dam embankment for NRC Staff review. The updated safety factor needs to be addressed in Section 2.4.4.1.
3.2 Usage of SOCH model On Page E1-6 and 7 of 38, TVA stated that SOCH is still used and provided SOCH documentation in Appendix 2.4A. The SOCH model is used for potential flood levels due to seismically induced dam failures, loss of downstream dams, and warning times.
Please confirm that the HEC-RAS is only used for computing PMF elevation, and that the SOCH is only used for computing % PMF and 25-year flood elevation concurrences with seismic events.