L-MT-16-062, Part 1 Response to Probabilistic Risk Assessment Related Requests for Additional Information: License Amendment Request for a Permanent Extension of the 10 CFR 50 Appendix J Containment Type a Test Interval
| ML16355A183 | |
| Person / Time | |
|---|---|
| Site: | Monticello  (DPR-022) |
| Issue date: | 12/16/2016 |
| From: | Gardner P Northern States Power Company, Minnesota, Xcel Energy |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| CAC MF7359, L-MT-16-062 | |
| Download: ML16355A183 (7) | |
Text
,*-.,,.
2807 West County Road 75 Monticello, MN 55362 fl Xcel Energy*
RESPONSIBLE BY NATURE 800.895.4999 xcelenergy. com December 16, 2016 L-MT-16-062 10 CFR 50.90 ATIN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket No. 50-263 Renewed Facility Operating License No. DPR-22 Part 1 Response to Probabilistic Risk Assessment (PRA) Related Requests for Additional Information: License Amendment Request for a Permanent Extension of the 10 CFR 50 Appendix J Containment Type A Test Interval (CAC No. MF7359)
References:
- 1) NSPM (P. Gardner) to NRG, "License Amendment Request: Revise Technical Specification 5.5.11 to Provide a Permanent Extension of the Integrated Leakage Rate (Type A) Test Frequency from Ten to Fifteen Years," (L-MT-16-001), dated February 10, 2016 (ADAMS Accession No. ML16047A272 and ML16047A273)
- 2) NRG (R. Kuntz) to NSPM (R. Loeffler), "Request for Additional Information RE: Monticello license amendment request for ILRT extension (CAC MF7359)," dated September 9, 2016 (ADAMS Accession No. ML16256A004)
- 3) NSPM (P. Gardner) to NRG, "Response to Request for Additional Information: License Amendment Request for a Permanent Extension of the 10 CFR 50 Appendix J Containment Type A Test Interval (CAC No.
MF7359)," (L-MT-16-044), dated October 10, 2016 (ADAMS Accession No. ML16284A015)
- 4) NRG (R. Kuntz) to NSPM (R. Loeffler), "Monticello ILRT extension amendment request for additional information (CAC No. MF7359)," dated November 18, 2016 (ADAMS Accession No. ML16323A242)
On February 10, 2016, the Northern States Power Company, a Minnesota Corporation (NSPM), doing business as Xcel Energy, submitted a license amendment request proposing a change the Technical Specifications.(TS) for the Monticello Nuclear Generating Plant (MNGP).
The proposed change is to permanently revise the frequency specified in Specification 5.5.11
L-MT-16-062 Page 2of2 "Primary Containment Leakage Rate Testing Program", to increase the containment integrated leakage rate test (ILRT) program Type A test interval from 10 years to 15 years (Reference 1).
On September 9, 2016, the U.S. Nuclear Regulatory Commission (NRC) requested additional information pertaining to the primary containment performance history and a clarification of ILRT test results (Reference 2). The responses to these requests for additional information were provided on October 10, 2016, in Reference 3.
From October 13 through 14, 2016, the NRC conducted a regulatory audit to gain a better understanding of the containment accident pressure risk assessment in the MNGP LAR. On November 18, 2016, the NRC requested additional information (RAI) pertaining to probabilistic risk related considerations (Reference 4). The responses to RAls 2 and 3 are provided in the Enclosure. The responses to the remainder of the RAls will be provided separately.
Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.
I declare under penalty of perjury, that the foregoing is true and correct.
Executed on December__&, 2016.
~~
Peter A. Gardner Site Vice President, Monticello Nuclear Generating Plant Northern States Power Company - Minnesota Enclosure cc:
Administrator, Region Ill, USNRC Project Manager, Monticello, USNRC Resident Inspector, Monticello, USNRC State of Minnesota
ENCLOSURE MONTICELLO NUCLEAR GENERATING PLANT PART 1 RESPONSE TO PROBABILISTIC RISK ASSESSMENT (PRA) RELATED REQUESTS FOR ADDITIONAL INFORMATION LICENSE AMENDMENT REQUEST FOR A PERMANENT EXTENSION OF THE 10 CFR 50 APPENDIX J CONTAINMENT TYPE A TEST INTERVAL (4 pages follow)
L-MT-16-062 Enclosure Page 1 of 4 PART 1 RESPONSE TO PROBABILISTIC RISK ASSESSMENT (PRA) RELATED REQUESTS FOR ADDITIONAL INFORMATION LICENSE AMENDMENT REQUEST FOR A PERMANENT EXTENSION OF THE 10 CFR 50 APPENDIX J CONTAINMENT TYPE A TEST INTERVAL On February 10, 2016, NSPM submitted a license amendment request (LAR) proposing a change to the Technical Specifications for the Monticello Nuclear Generating Plant (MNGP).
The proposed change is to permanently revise the frequency specified in Specification 5.5.11 "Primary Containment Leakage Rate Testing Program", to increase the containment integrated leakage rate test (ILRT) program Type A test interval from 10 years to 15 years. On September 9, 2016, the U.S. Nuclear Regulatory Commission (NRG) requested information pertaining to the primary containment performance and history and a clarification of ILRT test results. The responses to these requests for additional information were provided on October 10, 2016.
From October 13 through 14, 2016, the NRG conducted a regulatory audit to gather information on the probabilistic risk assessment (PRA) related portions of the MNGP LAR to increase the contai!'lment ILRT interval from 10 to 15 years. On November 18, 2016, the NRG requested additional information (RAI) pertaining to certain PRA related considerations. The responses to RAls 2 and 3 are provided below.
RAl2 The LAR provides the results of sensitivity analyses on steel liner corrosion in Tables 5-17, 5-18 and 5-19. According to the LAR, the likelihood of non-detected containment leakage due to corrosion is applied to "those core damage accidents that are not already independently LERF [Large Early Release Frequency] or that could never result in LERF". The steel liner corrosion likelihood is increased by a factor of 1000, 10000, and 100000 for the sensitivity analyses. It is not clear how these steel liner corrosion sensitivity analyses were performed.
As reported in Table 5-17, instead of increasing, the Class 3b frequency appears to drop by two to three orders of magnitude when including the effects of corrosion.
- a.
Explain how the steel liner corrosion sensitivity analyses were performed, and provide example(s).
Response to RAI 2a The steel 1.iner corrosion sensitivity analyses were performed using the values from Section 5.2.6, "Impact of Extension on Detection of Steel Liner Corrosion that Leads to
L-MT-16-062 Enclosure Page 2of4 Leakage,"(1) and increasing the values by factors of 1000, 10000, and 100000 to calculate Class 3b probability, Conditional Containment Failure Probability (CCFP), and dose rate. The Class 3b probability in the Steel Liner Corrosion Sensitivity discussed in Section 5.3.2, "Potential Impact from Steel Liner Corrosion Likelihood," is calculated using the following formula:
Freq3s = (GDF - LERF)* P class3b *(1 +P corrosion *F corrosion) where P corrosion = likelihood of non-detected containment leakage due to corrosion (depends on ILRT interval, see Tables 5-14 and 5-15 for details)
Pc1ass3b = 0.0023 (3-per-10 year ILRT)
= 0.0023
- 10/3 = 0.0077 (1-per-10 year ILRT)
= 0.0023
- 15/3 = 0.0115 (1-per-15 year ILRT)
Fcorrosion = additional corrosion factor ranging from 1 (baseline) to 100,000 During preparation of this RAI response, an error in the spreadsheet formulas used in Table 5-17, "Steel Liner Corrosion Sensitivity Case: 38 Contribution," was identified. This condition has been entered into the Corrective Action Program. These formulas have been corrected, and the table has been updated. The revised table is provided below:
Steel Liner Corrosion Sensitivity Case: 38 Contribution 3b 3b 3b LERF LERF LERF Frequency Frequency Frequency Increase Increase Increase (3-per-10 (1-per-10 (1-per-15 (3-per-10 to (3-per-10 to (1-per-10 to year ILRT) year ILRT) year ILRT) 1-per-10) 1-per-15) 1-per-15)
Internal Event 38 1.63E-08 5.42E-08 8.13E-08 3.80E-08 6.51E-08
. 2.71E-08 Contribution Corrosion Likelihood 1.64E-08 5.76E-08 9.31 E-08 4.12E-08 7.67E-08 3.55E-08 x 1000 Corrosion Likelihood 1.80E-08 8.82E-08 1.99E-07 7.01 E-08 1.81E-07 1.11 E-07 x 10000 Corrosion Likelihood 3.40E-08 3.94E-07 1.26E-06 3.60E-07 1.22E-06 8.65E-07 x 100000 As expected, the Class 3b frequency increases when magnifying the effects of corrosion.
These sensitivity cases show the Class 3b frequency is relatively insensitive to corrosion likelihood, except for the extremely high, bounding factors of 10000 and.100000.
- 1.
Where a section or table is referred to within this response, it is referring to that item in the report entitled "Monticello Nuclear Generating Station: Evaluation of Risk Significance of Permanent ILRT Extension", provided as Enclosure 2 to the LAR (Reference 1 in the cover letter).
L-MT-16-062 Enclosure Page 3 of 4 RAI 2b
- b.
Table 5-17 shows a case, "corrosion likelihoodx100000," with an increase in LERF of 2.81 E-9/yr for the ILRT frequency change from 3-in-10 years to 1-in-15 years. Clarify whether this is considered an "upper bound" case and explain why the LERF result is low if the case represents a significant increase in the likelihood of not detecting a flaw.
Response to RAI 2b The value in Table 5-17, "Steel Liner Corrosion Sensitivity Case: 38 Contribution" for the corrosion sensitivity case, "corrosion likelihoodx100000," with an increase in LERF of 2.81 E-9/yr for the I LRT frequency change from 3-in-10 years to 1-in-15 years, was the result of the spreadsheet error described in the response to part a. The revised value for the case is shown in the table in the response to part a, and the total LERF increase for the ILRT frequency change from 3-in-10 years to 1-in-15 years is 1.22E-06. The revised change in LERF can be considered an extreme "upper bound" case.
RAl3 Table 5-2 of Enclosure 2 to the LAR shows that the total internal events LERF is 9.20E-7/yr.
Table 5-5 shows that LERF (no bypass) is 6.6E-7/yr, and Table 5-7 shows that the containment bypass frequency is 2.88E-9/yr. The sum of frequencies from Tables 5-5 and 5-7 for LERF (no bypass) and bypass is less than the total internal events LERF reported in Table 5-2.
Please clarify this discrepancy and its significance for the application.
Response to RAI 3 The discrepancy noted in the question occurs because the release frequencies shown in Table 5-5, "Release Category Frequencies," were scaled from the original source (Section 7.2.1 of PRA-MT-L2<2)), so that the total release frequency, when summed, matches the total
- core damage frequency, which is the expected result when comparing total core damage frequency to the total frequency of releases that can occur after a core damage accident.
Scaling accounts for the small double counting of core damage events that can progress to more than one release category in the Level 2 model. The frequencies shown in Table 5-5 are presented for information only, and the table is intended to give the reader a sense of the various release frequencies, in terms of release timing and release magnitude, that can occur for MNGP given a core damage accident, and are not used in the calculation of the risk metrics for the ILRT frequency change presented in the report. The LERF value used in the calculation of the risk metrics for this ILRT frequency change analysis presented in the report is shown in Table 5-2, "Internal Events LERF (MNGP PRA Model Revision 3.2)," and is
- 2.
Calculation PRA-MT-L2, Revision 3.2, Monticello Nuclear Generating Plant, "MNGP Level 2 Notebook."
L-MT-16-062 Enclosure Page 4 of 4 9.20E-07. Because the frequencies shown in Table 5-5 are not used in the calculation of the risk metrics for the ILRT frequency change presented in this report, the discrepancy has no impact nor is it significant to the application.