ML083570574
| ML083570574 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 12/11/2008 |
| From: | Brandon M Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC MD9596, TVA-WBN-TS-08-04 | |
| Download: ML083570574 (6) | |
Text
December 11, 2008 TVA-WBN-TS-08-04 10 CFR 50.55a U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D.C. 20555-0001 Gentlemen:
In the Matter of ) Docket No. 50-390 Tennessee Valley Authority (TVA) )
WATTS BAR NUCLEAR PLANT (WBN) UNIT 1 - SECOND CORRECTED RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING THE RELIEF REQUEST FOR THE RISK-INFORMED INSERVICE INSPECTION PROGRAM (TAC NO. MD9596)
The purpose of this letter is to respond to NRCs request for additional information (RAI) dated October 28, 2008. This corrected response supersedes TVAs December 3 and 10, 2008 letters on this subject.
On December 4, 2007, TVA submitted proposed alternatives to 10 CFR 50.55a(g),
Inservice Inspection Requirements, based on alternative methodology described in Electric Power Research Institute (EPRI) Technical Report TR-112657 Revision B-A, Revised Risk-Informed Inservice Inspection Evaluation Procedure. NRCs October 28, 2008 request for additional information requested clarification of elements of the original submittal. On December 3 and 10, 2008, TVA responded to the RAI. However, the response to question 1 was incomplete. TVAs second corrected response to this RAI is provided in the enclosure. There are no regulatory commitments in this submittal.
If you have any questions concerning this matter, please call me at (423) 365-1824.
Sincerely, original signed by M. K. Brandon Manager, Site Licensing and Industry Affairs U.S. Nuclear Regulatory Commission
Page 2 December 11, 2008 Enclosure cc: NRC Resident Inspector Watts Bar Nuclear Plant 1260 Nuclear Plant Road Spring City, Tennessee 37381 Mr. John G. Lamb, Senior Project Manager U.S. Nuclear Regulatory Commission Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation MS 0-8H1A Washington, DC 20555-0001 U.S. Nuclear Regulatory Commission Region II Sam Nunn Atlanta Federal Center 61 Forsyth St., SW, Suite 23T85 Atlanta, Georgia 30303
ENCLOSURE WATTS BAR NUCLEAR PLANT (WBN) UNIT 1 SECOND CORRECTED RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING THE RELIEF REQUEST FOR THE RISK-INFORMED INSERVICE INSPECTION PROGRAM By letter dated December 4, 2007, TVA submitted proposed alternatives to 10 CFR 50.55a(g),
Inservice Inspection Requirements, based on alternative methodology described in Electric Power Research Institute (EPRI) Technical Report TR-112657 Revision B-A, Revised Risk-Informed Inservice Inspection Evaluation Procedure. On October 28, 2008 NRC issued a request for additional information seeking clarification of three elements of the original submittal.
NRCs questions and TVAs responses are provided below:
Question 1 Section 3.1 of the submittal states that, segments were defined as continuous runs of piping whose failure would result in the same consequence. Section 3.4 further defines risk groups as welds susceptible to the same degradation mechanism and whose failure would result in the same consequence. Table 3.1 identifies segments and Table 3.4 identifies risk groups, and the entries in the two tables are not easily comparable.
Please clarify what the same consequence in Section 3.1 means (e.g., is it the consequential failure of exactly the same functions and equipment, or simply the same consequence category?) Based on this clarification, please explain how the number of segments in a system in Table 3.1 is related to the number of risk groups in the same system in Table 3.4.
Response 1 The term same consequence as used in Section 3.1 refers to consequential failure of exactly the same functions and equipment. However, as used in Section 3.4, the term same consequence refers to the same consequence category.
Risk Group refers to a grouping of inspection elements within a single system that all have the same Risk Category, and are all potentially subject to the same degradation mechanism.
As such, each Risk Group is analogous to an individual line in Table 3.6. There is no fixed relationship between the number of Segments in a system in Table 3.1 and the number of Risk Groups in the same system in Table 3.4.
Question 2 Section 3.5.1, Additional Examinations (page E1-9 of the submittal), presents the criteria for engineering evaluation and additional examinations. The submittal states that "Additional examinations will be performed on those elements with the same root cause conditions or degradation mechanisms. The additional examinations will include high-risk significant elements and medium risk significant elements, if needed, up to a number equivalent to the number of elements required to be inspected on the segment or segments during the current outage. If unacceptable flaws or relevant conditions are again found E-1 of 4
similar to the initial problem, the remaining elements identified as susceptible will be examined." Please clarify when these remaining elements will be examined.
Response 2 The additional examination sample would be examined during the current outage. If unacceptable flaws or relevant conditions are identified in the first additional examination sample, the remaining elements identified as susceptible would also be examined during the current outage.
Question 3 Table 3.5 shows that, in Category 4, there are 21 elements selected for inspection in the Reactor Coolant System (RCS). However, Table 3.6 shows only 20 Category 4 inspection locations in the RCS system. Please clarify this apparent inconsistency.
Response 3 The inconsistency was due to an error in transposition. The 21 elements selected for inspection in the RCS system in Category 4 consist of 20 B-J welds and one B-F weld. In the transposition to Table 3.6, the B-F weld was inadvertently omitted. The B-F weld omitted was 1-068D-B001-02. Table 3.6 should show 21 RI-ISI Inspection Locations for RCS Category 4. As a result, the delta in table 3.6 will change to -20, CDF impact will decrease to 1.18 E-09 and LERF impact will decrease to 1.37E-11. A revised Table 3.6 is provided below. A few other minor errors were identified in total rows, and these have also been corrected in the table below.
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Table 3.6 WBN Unit 1 - Risk Impact Analysis Results (3) (3)
(1) Consequence Failure Potential Inspection Locations CDF Impact LERF Impact System Category Rank (2)
DMs Rank Section XI RI-ISI Delta w/ POD w/o POD w/ POD w/o POD RCS 2 High TT, PWSCC Medium 1 1 0 0.00E+00 0.00E+00 0.00E+00 0.00E+00 RCS 2 High PWSCC Medium 13 8 -5 5.90E-09 5.90E-09 6.83E-11 6.83E-11 RCS 2 High TASCS Medium 0 2 2 -4.24E-09 -2.36E-09 -4.91E-11 -2.73E-11 RCS 2 High TASCS, TT Medium 1 1 0 -1.41E-09 0.00E+00 -1.64E-11 0.00E+00 RCS 2 High TT Medium 1 0 -1 7.07E-10 1.18E-09 8.19E-12 1.37E-11 RCS 4 High None Low 41 21 -20 1.18E-09 1.18E-09 1.37E-11 1.37E-11 RCS 7a Low None Low 0 0 0 negligible negligible negligible negligible RCS Total 2.12E-09 5.90E-09 -2.46E-11 6.83E-11 CVCS 2 High TASCS Medium 0 1 1 -2.12E-09 -1.18E-09 -2.46E-11 -1.37E-11 CVCS 2 High TASCS, TT Medium 0 1 1 -2.12E-09 -1.18E-09 -2.46E-11 -1.37E-11 CVCS 2 High TT Medium 0 2 2 -4.24E-09 -2.36E-09 -4.91E-11 -2.73E-11 CVCS 4 High None Low 0 12 12 -7.07E-10 -7.07E-10 -8.19E-12 -8.19E-12 CVCS 6a Medium None Low 32 0 -32 negligible negligible negligible negligible CVCS 6b Low TT Medium 0 0 0 negligible negligible negligible negligible CVCS 7a Low None Low 0 0 0 negligible negligible negligible negligible CVCS Total -9.20E-09 -5.42E-09 -1.06E-10 -6.28E-11 RHR 2 High IGSCC Medium 1 3 2 -2.36E-09 -2.36E-09 -2.73E-11 -2.73E-11 RHR 2 High TASCS Medium 0 2 2 -4.24E-09 -2.36E-09 -4.91E-11 -2.73E-11 RHR 4 High None Low 17 13 -4 2.36E-10 2.36E-10 2.73E-12 2.73E-12 RHR 6a Medium None Low 23 0 -23 negligible negligible negligible negligible RHR Total -6.37E-09 -4.48E-09 -7.37E-11 -5.19E-11 SIS 2 High IGSCC Medium 1 7 6 -6.00E-11 -6.00E-11 -6.00E-12 -6.00E-12 SIS 4 High None Low 22 68 46 -2.71E-09 -2.71E-09 -3.14E-11 -3.14E-11 SIS 5a Medium IGSCC Medium 5 2 -3 3.00E-11 3.00E-11 3.00E-12 3.00E-12 SIS 6a Medium None Low 33 0 -33 negligible negligible negligible negligible SIS 7a Low None Low 6 0 -6 negligible negligible negligible negligible SIS Total -2.74E-09 -2.74E-09 -3.44E-11 -3.44E-11 E-3 of 4
Table 3.6 (cont.)
WBN Unit 1 - Risk Impact Analysis Results (3) (3)
(1) Consequence Failure Potential Inspection Locations CDF Impact LERF Impact System Category Rank (2)
DMs Rank Section XI RI-ISI Delta w/ POD w/o POD w/ POD w/o POD CI 6a Medium None Low 0 0 0 negligible negligible negligible negligible CI 7a Low None Low 0 0 0 negligible negligible negligible negligible CI Total 0.00E+00 0.00E+00 0.00E+00 0.00E+00 CSS 6a Medium None Low 3 0 -3 negligible negligible negligible negligible CSS 7a Low None Low 13 0 -13 negligible negligible negligible negligible CSS Total 0.00E+00 0.00E+00 0.00E+00 0.00E+00 AFW* 5a (3) Medium (High) TASCS (FAC) Medium 1 1 0 -1.20E-11 0.00E+00 -1.20E-12 0.00E+00 AFW* 6a Low None (FAC) Low 8 0 -8 negligible negligible negligible negligible AFW 6a (3) Low (High) None (FAC) Low 1 0 -1 negligible negligible negligible negligible AFW 6b (5b) Low (Medium) TASCS, TT (FAC) Medium 1 0 -1 negligible negligible negligible negligible AFW* 7a Low None (FAC) Low 4 0 -4 negligible negligible negligible negligible AFW 7a (5b) Low (Medium) None (FAC) Low 1 0 -1 negligible negligible negligible negligible AFW Total -1.20E-11 0.00E+00 -1.20E-12 0.00E+00 FWS 6a (3) Low (High) None (FAC) Low 14 0 -14 negligible negligible negligible negligible FWS 6b (5b) Low (Medium) TASCS, TT (FAC) Medium 2 0 -2 negligible negligible negligible negligible FWS 7a (5b) Low Medium) None (FAC) Low 3 0 -3 negligible negligible negligible negligible FWS Total 0.00E+00 0.00E+00 0.00E+00 0.00E+00 MSS 4 High None (High) 23 3 -20 1.18E-09 1.18E-09 1.37E-11 1.37E-11 MSS 6a Low None (High) 120 0 -120 negligible negligible negligible negligible MSS Total 1.18E-09 1.18E-09 1.37E-11 1.37E-11 Grand Total -1.50E-08 -5.57E-09 -1.78E-10 -6.72E-11
- AFW <4NPS added in Interval 2.Section XI locations estimated at 7.5% of population Table 3.6 shows values as two significant digits; however, totals are based on four significant digits (following the decimal).
Notes
- 1. Systems are described in Table 3.1-1.
- 2. Only those ASME Section XI Code inspection locations that received a volumetric examination in addition to a surface examination are included in the count. Inspection locations previously subjected to a surface examination only were not considered in accordance with Section 3.7.1 of EPRI TR-112657.
Per Section 3.7.1 of EPRI TR-112657, the contribution of low risk categories 6 and 7 need not be considered in assessing the change in risk. Hence, the word negligible is given in these cases in lieu of values for CDF and LERF Impact. For those cases in high, medium or low risk region piping where the change in risk calculation produces a value of zero for CDF or LERF Impact, "no change" is listed.
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