ML101310199
| ML101310199 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 05/12/2010 |
| From: | Michael Mahoney Plant Licensing Branch III |
| To: | Allen B FirstEnergy Nuclear Generation Corp |
| Mahoney, M NRR/DORL/LPLIII- 2 415-3867 | |
| References | |
| TAC ME3703 | |
| Download: ML101310199 (7) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555*0001 May 12, 2010 Mr. Barry S. Allen Site Vice President FirstEnergy Nuclear Operating Company Davis-Besse Nuclear Power Station Mail Stop A-DB-3080 5501 North State Route 2 Oak Harbor, OH 43449-9760
SUBJECT:
DAVIS-BESSE NUCLEAR POWER STATION. UNIT NO.1 - REQUEST FOR ADDITIONAL INFORMATION RELATED TO THE RELIEF REQUEST FOR 10 CFR 50.55A REQUEST FOR ALTERNATE REPAIR METHODS FOR REACTOR PRESSURE VESSEL HEAD PENTRATION NOZZLES (TAC NO. ME3703)
Dear Mr. Allen:
By letter to the Nuclear Regulatory Commission (NRC) dated April 1,2010 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML100960276), FirstEnergy Nuclear Operating Company submitted a relief request for Davis-Besse Nuclear Power Station. Unit 1 (DBPNS), associated with approval of proposed alternatives to certain requirements associated with reactor pressure vessel head penetration nozzle repairs.
By letter dated April 16, 2010 (ADAMS Accession No. ML101110149), the licensee, in response to an NRC request for additional information (April 9. 2010. ADAMS Accession No. ML100980486).
submitted a flaw evaluation for a postulated weld anomaly at the triple pOint of the repaired nozzles.
By letter dated April 21. 2010 (ADAMS Accession No. ML101160438). the licensee, in response to an NRC request for additional information, submitted a flaw evaluation for the J-groove weld of the repaired nozzles.
The 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. During a discussion with your staff on May 5, 2010, it was agreed that you would provide a response within 14 days from the date of this letter.
- 2 The NRC staff considers that timely responses to requests for additional information 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) 415-3867.
Sin7Ri fi Michael Mahoney, Project~
Plant Licensing Branch 111-2 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-346
Enclosure:
Request for Additional Information cc w/encl: Distribution via Listserv
REQUEST FOR ADDITIONAL INFORMATION DAVIS BESSE NUCLEAR POWER STATION FIRSTENERGY NUCLEAR OPERATING COMPANY DOCKET NUMBER NO. 50-346 By letter dated April 1, 2010 (Agencywide Documents Access and Management System (ADAMS)
Accession No. ML100960276), FirstEnergy Nuclear Operating Company requested Nuclear Regulatory Commission (NRC) review and approval of relief request RR-A34 which pertains to an alternative to the requirements of the American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code in the repair of reactor pressure vessel head penetration nozzles at the Davis-Besse Nuclear Power Station, Unit 1 (DBNPS).
By letter dated April 9, 2010 (ADAMS Accession No. ML100980486), the NRC requested additional information to complete its review of Relief Request RR-A34.
By letter dated April 16, 2010 (ADAMS Accession No. ML101110149), the licensee, in response to an NRC request for additional information, submitted a flaw evaluation for a postulated weld anomaly at the triple point of the repaired nozzles.
By letter dated April 21,2010 (ADAMS Accession No. ML101160438), the licensee, in response to an NRC request for additional information, submitted a flaw evaluation for the J-groove weld of the repaired nozzles.
To complete its review, the staff requests the following additional information of these two flaw evaluations and the relief request.
- 1. Page 3 of Relief Request RR-A34 states that "The 1992 Edition of ASME Code Section III subparagraph NB-5330(b) states: Indications characterized as cracks, lack of fusion, or incomplete penetration are unacceptable regardless of length." The licensee proposed to use ASME Code Case N-638-1 to perform welding for the nozzle repair.
Regulatory Guide 1.147, Revision 15, imposes a condition on Code Case N-638-1 which specifies that "... The acceptance criteria of NB-5330 in the 1998 edition through 2000 addenda of Section III apply to all flaws identified within the repaired volume."
(1) Specify the edition and addenda of the ASME Code that will be used.
(2) Specify the subarticles of the ASME Code that the acceptance criteria will be based on.
(3) Specify the ASME Code information for both the surface and volumetric examinations.
(4) Specify the ASME Code information for both the preservice and inservice inspections.
Enclosure
- 2
- 2. As part of the above question. the NRC staff understands that the acceptance criteria for the surface examination in the 1989 edition of the ASME Code.Section III, will be used to disposition fabrication defects in the repaired nozzles because the design of the half nozzle was based on the 1989 edition of the ASME Code. Discuss why the design of the half nozzle repair did not use the 1995 edition of the ASME Code which is the code of record for the current third inservice inspection (lSI) interval..
- 3. In its response to RAI Question 12(2) regarding the lSI of the repaired nozzles dated April 16. 2010, the licensee stated that the IS I will include 1 or 1.5 inches of the remnant nozzles as shown in Figure 9 of RR-A34, depending on the angle of the nozzles with respect to the vessel head. The licensee stated further that although the examination does not completely encompass the rolled region of the nozzle, it does examine a significant portion of the rolled area. The examination will be performed with penetrant testing (PT). The NRC staff has questions regarding the adequacy of the lSI examination coverage of the repaired nozzles.
(1) Provide the stress profile (the worst case) of a remnant nozzle after it has been rolled, but before abrasive water jet is applied.
(2) Identify the maximum vertical distance of the rolled region and the vertical distance that will be examined with PT in lSI. Justify why it is acceptable not to examine the entire rolled region plus 0.5 inch on either end of the rolled region of the remnant nozzle.
- 4. Discuss the potential for general corrosion in the bore region of the reactor vessel head penetration where the nozzle has been removed as part of the proposed repair
- 5. Triple Point Weld Anomaly Flaw Evaluation, Page 8, Section 1.1. The licensee stated that a maximum 0.1 inch weld anomaly is assumed at the triple pOint of the repaired nozzles. Discuss whether the 0.1 inch flaw size bounds the actual weld anomalies that may be detected by ultrasonic testing in the repair of the control rod drive mechanism (CRDM) nozzles at DBNPS during this refueling outage.
- 6. Triple Point Weld Anomaly Flaw Evaluation, Page 10. For path 2, the licensee assumed a continuous cylindrical surface flaw propagating along the interface between the new Alloy 52M weld and low alloy steel head. Describe the shape or configuration of this flaw (e.g., an axially oriented flaw, a circumferentially oriented flaw. or a semi-circular planar flaw).
- 7. Triple Point Weld Anomaly Flaw Evaluation. Page 15, Section 4.2. Clarify whether the analysis include stresses due to thermal expansion of the nozzle in the vessel head penetration bore, dead weight of the nozzle, seismic loads, and pressure. If not, provide justification.
- 8. Triple Point Weld Anomaly Flaw Evaluation, Page 15, middle of the page. The licensee stated that component stresses for the two crack propagation paths were obtained from Reference 14. Reference 14 appears to be a generic analysis performed by AREVA for
- 3
- 9. the temper bead welding, which was issued in 2004. Explain how and why a generic analysis in Reference 14 is applicable to the plant-specific half-nozzle repair at DBNPS.
- 10. Triple Point Weld Anomaly Flaw Evaluation, Page 26, middle of the page. The licensee used a stress distribution based on a third order polynomial. The stresses represented by a third order polynomial may not be adequate, especially for welding residual stress.
This approximation can underpredict the stresses on the crack face. Discuss the validity of using the third order approximation for the through wall thickness stress.
- 11. Triple Point Weld Anomaly Flaw Evaluation, Page 37. Explain why the same fracture toughness value (Kia) of 200 ksi-vin is used for all postulated flaws along paths 1 and 2 even though the materials (Alloy 52M weld, Alloy 600 remnant nozzle, and low alloy steel reactor vessel) in which the flaws propagate in each of the paths are different and may have different fracture toughness.
- 12. J-Groove Weld Flaw Evaluation, Page 9. Provide references for the safety factors used in the elastic-plastic fracture mechanics analysis.
- 13. J-Groove Weld Flaw Evaluation, Page 11. Item 3 discusses a mapping procedure to transfer stresses from uncracked finite element stress analysis models in Figures 4-3 and 4-4 to the crack face of the crack model. The finite element model in Figures 4-3 and 4-4 include the original nozzle, not the half nozzle configuration after the repair. A more appropriate model would use the half nozzle configuration after the repair, calculate the loads and stresses from the repaired nozzle configuration, and apply the loads and stresses to the crack face. Justify why and how the finite element model in Figures 4-3 and 4-4 provides the appropriate loads and stresses to calculate the growth of a postulated flaw in the J-groove weld into the vessel head.
- 14. J-Groove Weld Flaw Evaluation, Page 11. Item 4.
(1) Describe how the final crack size is calculated with respect to the finite element model and crack growth calculation described in Section 2.1.
(2) Clarify the analytical methodology on page 11 regarding how the final crack model was constructed in Figure 2-2.
- 15. J-Groove Weld Flaw Evaluation, Page 14. Figure 2-2 presents the finite element model for the final crack size which shows that half of the final crack (length) is located in the reactor vessel head shell and the other half is located in the butter. However, based on the postulated initial flaw size of 2.035 inches, and the calculated final flaw size (proprietary information) as shown on page 36, the final flaw size cannot possibly have 50 percent of its length in the butter and 50 percent of its length in the reactor vessel shell.
(1) Explain the discrepancy between the final crack size model in Figure 2-2 and the calculated final flaw size on page 36.
- 4 (2) Discuss the exact length of the final crack size that is located in the reactor vessel head.
(3) Discuss the allowable flaw size of the reactor vessel head.
- 16. J-Groove Weld Flaw Evaluation, in the flaw growth calculation on pages 32, 35, and 36, the initial flaw size was assumed as 2.035 inches.
(1) Discuss whether the initial flaw size of 2.035 inches is the same length as modeled in the finite element crack model as shown on page 12 (i.e., the crack tip is at the interface between the butter and the reactor vessel head).
{2} How is the initial flaw size derived?
- 17. J-Groove Weld Flaw Evaluation, Page 24. Confirm that the fatigue crack growth rate used in the analysis is based on the water environment.
- 18. J-Groove Weld Flaw Evaluation, Discuss whether the crack model includes pressure loading on the crack face. If not, provide justification.
- 19. J-Groove Weld Flaw Evaluation, Page 44, Section 6.0, states that the final flaw size in the reactor vessel head was determined by linear elastic fracture mechanics for 4 years of fatigue crack growth. However, it is shown on page 37 of the report, "DB-1 CRDM Nozzle Weld Anomaly Flaw Evaluation of IDTB Repair", submitted on April 16, 2010, that the flaw evaluation for the weld anomaly at the triple point was calculated for 25 years.
Discuss the discrepancy in the number of years (4 years vs. 25 years) assumed in the two flaw evaluations for the J-groove weld and weld anomaly at the triple point.
- 20. Provide a requirement for the performance of a pressure test after the reactor vessel head penetration nozzles are repaired.
'.. ML101310199 OFFICE LPL3-2/PM LPL3-2/LA LPL3-2/BC NAME MMahoney BTully for THarris SCampbell DATE 2/10 05/12/10 05/12/10