ML11129A187
| ML11129A187 | |
| Person / Time | |
|---|---|
| Site: | Browns Ferry  |
| Issue date: | 05/04/2011 |
| From: | Krich R Tennessee Valley Authority |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC ME3720 | |
| Download: ML11129A187 (7) | |
Text
Tennessee Valley Authority 1101 Market Street, LP 3R Chattanooga, Tennessee 37402-2801 R. M. Krich Vice President Nuclear Licensing May 4, 2011 10 CFR 50.4 10 CFR 50.55a ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, D.C. 20555-0001 Browns Ferry Nuclear Plant, Unit 2 Facility Operation License No. DPR-52 NRC Docket No. 50-260
Subject:
Response to NRC Request for Additional Information Regarding Relief Request 2-ISI-1, Updated Risk Informed Inservice Inspection Program
References:
- 1. NRC Letter to TVA, "Browns Ferry Nuclear Plant, Unit 2 - Request for Additional Information Regarding Relief Request 2-1S1-1, Updated Risk Informed Inservice Inspection Program (TAC No. ME3720)," dated March 28, 2011
- 2. TVA Letter to NRC, "American Society of Mechanical Engineers Boiler and Pressure Vessel Code, Section Xl, Inservice Inspection Program for the Fourth Ten-Year Inspection Interval," dated March 31, 2010 On March 31, 2010, the Tennessee Valley Authority (TVA) submitted the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section Xl Inservice Inspection Program for the Fourth Ten-Year Inspection Interval for Browns Ferry Nuclear Plant, Unit 2, which included Request for Relief 2-11-1 (Reference 2, Attachment 10 of 2-SI-4.6.G). By letter dated March 28, 2011, the NRC transmitted a Request for Additional Information regarding Relief Request 2-1S1-1, Updated Risk Informed Inservice Inspection Program (Reference 1).
The enclosure to this letter provides the TVA response to the Reference 1 request.
Acwr7 printed on recycled paper '4-AO
U.S. Nuclear Regulatory Commission Page 2 May 4, 2011 The due date for this response was specified in Reference 1 as May 6, 2011.
There are no new regulatory commitments contained in this letter. Please direct any questions concerning this matter to Tom Matthews at (423) 751-2687.
Respectfully, r R.M. Klch
Enclosure:
TVA Responses to NRC Request for Additional Information Questions cc (Enclosure):
NRC Regional Administrator - Region II NRC Senior Resident Inspector - Browns Ferry Nuclear Plant
ENCLOSURE Tennessee Valley Authority Browns Ferry Nuclear Plant, Unit 2 Request for Relief 2-ISI-1, Updated Risk Informed Inservice Inspection Program TVA Responses to NRC Request for Additional Information Questions NRC Question 1 The March 31, 2010, submittal (Agencywide Documents Access and Management System Accession No. ML100920542) states that the revised risk-informed inservice inspection (RI-ISI) program represents a reduction in risk with regard to core damage frequency (CDF)and large early release fraction (LERF). There are other risk criteriain Section 4.4.2 of WCAP-14572, Revision 1-NP-A, "Westinghouse Owners Group Application of Risk-Informed Methods to Piping Inservice Inspection Topical Report," February 1999 (WCAP), that must also be met. Please provide the results of your evaluation that will allow you to state that the risk/safety evaluation criteriain 4.4.2 of the WCAP are met.
TVA Response There are four criteria listed in 4.4.2:
- 1. The total change in piping risk should be risk neutral or a risk reduction in moving from the Current Section XI to RI-ISI. This criterion is satisfied.
- 2. Dominant system contributors (>10% total risk) should be examined to identify where no improvement has been proposed. The dominant system contributors are Reactor Recirculation (Recirc) CDF and LERF, Reactor Water Clean Up (RWCU) LERF, and Residual Heat Removal (RHR) CDF and LERF. In each of these cases, an improvement was proposed. This criterion is satisfied.
- 3. The results should be reviewed to identify any system in which there is a risk increase. No such systems were identified. This criterion is satisfied.
- 4. If additional examinations are identified, the change in risk calculations should be revised. No additional examinations were identified. This criterion is satisfied.
See Attachment 1, Evaluation against criteriain Section 4.4.2 of WCAP-14572, Revision 1-NP-A, at the end of this document.
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NRC Question 2 0, page 6, of the submittal clearly lists 51 previous RI-ISI examinations for RI. 16.
The value(s) provided for the revised programare unclear. Please clarify how many examinationsare listed as RI. 16 for the revised RI-ISI program.
TVA Response See Attachment 2 for the revised table. In the revised RI-ISI program, column R1.16 has a total of 48 RI. 16 examinations summarized below:
System Revised R1.16 No.
Recirc 1 Cat A, 17 Cat C, and 6 Cat E 24 RWCU 5 Cat A, 1 Cat D, and 3 Cat E 9 RHR 4 Cat C, 1 Cat D, and 2 Cat G 7 CS 8 Cat C 8 Total = 48 NRC Question 3.A 0, page 3, of the submittal states:
"A new Delta Risk Evaluation was performed, and the revised RI-ISI program continues to representa risk reduction when compared to the last deterministic ASME Section X1 inspectionprogram. The revised RI-/Sl program representsa reduction of 1.869E-05 in regardsto CDF and 1.596E-07 in regardsto LERF."
A) Perletter dated October 16, 2000, the Tennessee Valley Authority reported an increase in CDFand LERF for the previous RI-ISI program when compared to the last deterministicAmerican Society of MechanicalEngineers (ASME), Section X1 inspection program. The estimated change in risk was in the third and fourth significant digits for the estimated LERF and CDF; therefore, the R/-/Sl programwas consideredrisk neutral.
Please clarify the above statement to properly reflect the change in risk of the previous RI-ISI program.
TVA Response Please see the response to question 3.B below. For clarification, the quoted paragraph from Request for Relief, 2-1S1-1 (2-SI-4.6.G, Attachment 10), page 3 of 6 (Reference 2) is revised to read:
"A new Delta Risk Evaluation was performed, and the revised RI-ISI program continues to represent a risk reduction when compared to the last deterministic ASME Section XI inspection program and a risk neutral position when compared to a combination of the last deterministic ASME Section XI inspection program and the augmented programs. See the attached table."
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Program Piping CDF Piping LERF Base Case (without IS[) 1.926E-05 1.7919E-07 Section X1 1.923E-05 1.788E-07 Augmented 5.253E-07 1.913E-08 Risk-Informed 5.260E-07 1.918E-08 NRC Question 3.B B) Please provide additionalinformation and clarificationfor how a decrease in volumetric examinations associatedwith thermal fatigue and intergranularstress corrosioncracking, when compared to the last RI-/SI program, can produce a very significantrisk decrease when compared to the last deterministic ASME,Section XI inspection program. In addition, please provide a table comparing CDF and LERF for "without/SI", "SectionXI",
and "Risk-Informed"programs.
TVA Response The TVA letter to NRC on October 16, 2000, states "Each of these systems represents reduction in risk compared to current Section XI and risk neutrality compared to the combination of current Section Xl and augmented programs." The specific details are provided in the following table (from Table 3.10-2 in the June 1, 2000 submittal):
2000 Program Piping CDF Piping LERF Base Case (without ISI) 2.155E-05 7.329E-06 Section Xl 2.154E-05 7.328E-06 Augmented 1.325E-05 4.508E-06 Risk-Informed 1.325E-05 4.508E-06 The current submittal exhibits similar characteristics. See the table below:
2009 Program Piping CDF Piping LERF Base Case (without ISI) 1.926E-05 1.7919E-07 Section X1 1.923E-05 1.788E-07 Augmented 5.253E-07 1.913E-08 Risk-Informed 5.260E-07 1.918E-08 There have been multiple significant changes to the plant and the program between the two submittals, including implementation of hydrogen water chemistry greatly reducing the failure probability with resultant reduction in CDF and LERF for welds subject to intergranular stress corrosion cracking, and a completely new Probabilistic Risk Assessment (PRA), including a change in PRA technique. These have greatly affected the welds examined under both Augmented and RI-ISI programs, while having minimal impact on the previous deterministic Section Xl.
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ATTACHMENT 1 Evaluationagainstcriteria in Section 4.4.2 of WCAP-14572, Revision 1-NP-A, "Westinghouse Owners Group Application of Risk-Informed Methods to Piping Inservice Inspection Topical Report" SYSTEM No ISI X/ Aug RI Comparison of RI to Xl DominantSystem?
- NAME CDF LERF %CDF %LERF CDF LERF CDF LERF CDF LERF CDF LERF CDF LERF 001 MS 3.47E-09 1.48E-09 0.02% 0.83% 3.47E-09 1.48E-09 3.47E-09 1.48E-09 3.47E-09 1.48E-09 neutral neutral No No 003 FW 1.35E-08 7.06E-09 0.07% 3.94% 1.35E-08 7.06E-09 1.35E-08 7.06E-09 1.35E-08 7.06E-09 neutral neutral No No 063 SLC 3.09E-09 4.97E-11 0.02% 0.03% 3.09E-09 4.9 7E-11 3.09E-09 4.9 7E-11 3.09E-09 4.9 7E-11 neutral neutral No No 068 RECIRC 1.04E-05 8.35E-08 53.99% 46.63% 1.04E-05 8.35E-08 4.83E-08 3.88E-10 4.83E-08 3.88E-10 decrease decrease Yes Yes 069 RWCU 4.95E-07 1.90E-08 2.57% 10.63% 4.95E-07 1.90E-08 2.57E-08 6.16E-09 2.56E-08 6.16E-09 decrease decrease No Yes 070 RBCCW 1.51E-14 1.88E-14 0.00% 0.00% 1.51E-14 1.88E-14 1.51E-14 1.88E-14 1.51E-14 1.88E-14 neutral neutral No No 071 RCIC 4.13E-10 5.72E-11 0.00% 0.03% 4.13E-10 5.72E-11 3.71E-10 4.98E-11 4.13E-10 5.72E-11 neutral neutral No No 073 HPCI 6.33E-09 1.43E-10 0.03% 0.08% 6.33E-09 1.43E-10 6.21E-09 8.62E-11 6.33E-09 1.43E-10 neutral neutral No No 074 RHR 8.34E-06 6.74E-08 43.29% 37.65% 8.29E-06 6.71E-08 4.23E-07 3.53E-09 4.24E-07 3.53E-09 decrease decrease Yes Yes 075 CS 1.80E-09 3.20E-10 0.01% 0.18% 1.80E-09 3.20E-10 1.79E-09 3.17E-10 1.79E-09 3.17E-10 decrease decrease No No 085 CRD 2.48E-12 3. IOE-12 0.00% 0.00% 2.48E-12 3.1OE-12 2.48E-12 3. IOE-12 2.48E-12 3.1OE-12 neutral neutral No No GRAND TOTALS 1.93E-05 1. 79E-07 1.92E-05 1.79E-07 5.25E-07 1.91E-08 5.26E-07 1.92E-08 decrease decrease E-4 of 5
ATTACHMENT 2 STRUCTURAL ELEMENT SELECTION RESULTS AND COMPARISON TO ORIGINAL PROGRAM AND PREVIOUS R1I-SI PROGRAM OriginalProgram (1989 ASME & GL88-01) Previous RI-ISI Program (a) (b) (c) Revised RI-/SI Program (a) (b) (c)
A X dSME Elements Augmented Elements RI-/SI Examinations RI-ISI Examinations B- B- ~)ual Credit FAC R1. 1 #g R1.
R System Segs B-F -F-I -F-2 A C D E G uaX/ redi FA) RI R1.16 R1.18 A C D E G Seg R1. 16 R1. 18 A C D E G 001 MS 56 32 10 295 2 C12 4 30 2 C1 2 4 003 FW 46 18 321 2 Cl 1 10 32 2 C1 1 12 063 SLC 5 5 068 RECIRC 16 21 10 58 10 35 CI 1 17 C 58 10 16 1 A I 65 10 17 C 9 E 6 E 069 RWCU 19 6 1 8 2 3 5 CI 1 1 CI I 5 C 8 2 3 4 5 A 5 4 4 3 1 D 2 D 3 E 070 RBCCW 17 2 071 RCIC 13 2 6 1 C12 11 1 C12 073 HPCI 11 5 5 14 4 CI 1 10 4 C1 1 2 CI2 2 C12 074 RHR 31 I 9 2 37 29 I 2 2 10 CI 1 9 C 29 1 2 2 28 4 C12 4 C 29 3 2 2 2 C12 1 D I D 2 E 2 G 075 CS 15 8 5 6 12 14 1 16 Cl 1 6 C 14 1 15 8 C 14 1 085 CRD 31 6 3 1 CI 1 3 14 4 67 CI1 7C01 51 14 109 6 16 2 6CI1 Total Examinations 9 98 13 85 11 109 6 16 2 21 48 16 6 112 16 2 TotalEl e me nts 92 CI 2 9 C12 9 C12 Total Elements 9 392 173 940 Notes (a) System pressuretest requirementsand VT-2 visual examinations shall continue to be performed in allASME Code Class 1, 2, and 3 systems.
(b) Augmented programsincluding FAC and ReactorNozzle Thermal Fatigue Cracking (NUREG-0619) continue (c) Augmented program for lGSCC CategoriesC through G (VIP-075, GL88-01, NUREG-0313) continues.
(d) The currentASME Section X1 ISI Programexamines a minimum of 25% of the Class I and a minimum of 7.5% of the Class 2 elements (e) The FAC Augmented Programexamines approximately 10% of the identified locations each refueling outage.
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