ML081070060
| ML081070060 | |
| Person / Time | |
|---|---|
| Site: | Oyster Creek |
| Issue date: | 04/09/2008 |
| From: | Rausch T AmerGen Energy Co, Exelon Corp |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NUREG-1801, RA-08-030 | |
| Download: ML081070060 (7) | |
Text
AmerGam AmerGen Energy Company www.exeloncorp.com An Exelon Company Oyster Creek US Route 9 South, P.O. Box 388 Forked River, NJ o8731-0388 10 CFR 54 RA-08-030 April 9, 2008 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Oyster Creek Nuclear Generating Station Facility Operating License No. DPR-16 NRC Docket No. 50-219
Subject:
License Renewal Commitment Concerning Thermal Aging and Neutron Irradiation Embrittlement of Cast Austenitic Stainless Steel (CASS)
As discussed in the "Safety Evaluation Report Related to Oyster Creek Generating Station," NUREG-1875, Volume 1, dated April 2007, License Renewal Commitment No.10 contained in Table A.5 (Thermal Aging and Neutron Irradiation Embrittlement of CASS (Cast Austenitic Stainless Steel)) states the following:
"Program is new. The program will include a component specific evaluation of the loss of fracture toughness in accordance with the criteria specified in NUREG-1801, XI.M13. At least one year prior to the period of extended operation, the following information will be submitted to the NRC:
- 1) the type and composition of CASS reactor internal components within the scope of license renewal; and
- 2) the results of evaluations performed to determine susceptibility to thermal aging and neutron irradiation embrittlement.
For those components where loss of fracture toughness may affect the intended function of the component, a supplemental inspection will be performed. This inspection will ensure the integrity of the CASS components exposed to the high temperature and neutron fluence present in the reactor environment." provides our response to this commitment. Attachment 2 contains a summary of the regulatory commitments made in this letter.
If you have any questions or require additional information, please contact Tom Loomis (610-765-5510).
Respectfully, Tim yS RascJ Nuclear Generating Station
April 9, 2008 Page 2 of 2 Attachments - 1) Response to License Renewal Commitment No. 10 - Thermal Aging and Neutron Irradiation Embrittlement of Cast Austenitic Stainless Steel (CASS)
- 2)
Summary of Regulatory Commitments cc:
S. J. Collins, Administrator, USNRC, Region I (w/attachment)
M. A. Ferdas, USNRC Senior Resident Inspector, OCNGS (w/attachment)
G. E. Miller, Senior Project Manager, USNRC (w/attachment)
Response to License Renewal Commitment No. 10 Thermal Aging and Neutron Irradiation Embrittlement of Cast Austenitic Stainless Steel (CASS)
Page 1 of 3
Background:
During 2007, the BWRVIP conducted a project to evaluate cast austenitic stainless steel (CASS) for license renewal.
Oyster Creek Nuclear Generating Station (OCNGS) has been working with the BWRVIP on an ongoing project to generically evaluate thermal aging and neutron irradiation embrittlement of cast austenitic stainless steel reactor vessel internals for the BWR fleet. This project has not been completed.
Therefore, OCNGS has attempted to locate material details of the CASS components to determine the type and composition of CASS reactor internal components with the following results:
The molybdenum (MO) content of the Core Spray sparger spray nozzle elbows is not available. A review of the original Certified Material Test Reports (CMTRs) for the Core Spray sparger spray nozzle elbows (street ells) identified that the MO content was not evaluated as part of these CMTRs.
Based on the General Electric specification requirements for the OCNGS reactor vessel internals, all these CASS components should meet the minimum material properties specified in ASTM-A-296, Grade CF-8. The type of casting (centrifugal or static) could not be identified.
" Searches for the material details (CMTRs) for the fuel support piece and control rod guide tube were conducted and it was determined that the information was not available onsite.
Because the material details for the OCNGS CASS components have not yet been identified, OCNGS is unable to differentiate between those components that may be susceptible to loss of fracture toughness and those that would not be susceptible. Therefore, OCNGS plans to conservatively implement supplemental inspections as described below, to ensure continued integrity of CASS components exposed to the high temperature and neutron fluence present in the reactor environment.
Supplemental Inspections:
The Aging Management Program (AMP) for CASS components contains a requirement to implement supplemental inspections on CASS components that show a loss of fracture toughness that may affect the intended function of the component. OCNGS proposes to implement supplemental inspections or increased frequency of current inspections to monitor the structural integrity of these CASS components. A review of the BWRVIP and owner inspections currently performed on these CASS components at OCNGS is listed below, followed by the planned supplemental inspections.
FUEL SUPPORT PIECE Current Inspections: In the case of the fuel support pieces, the component is removed for certain maintenance activities during refueling outages. During this activity, as part of OCNGS procedure 205.29 ("Control Rod Blade / Fuel Support Piece Removal and Replacement"), the fuel support piece is required to be inspected using an underwater camera during any routine control rod blade exchange work during refueling outages. This is a BWRVIP-47-A approved alternative inspection.
Planned Supplemental Inspection: Add a VT-i inspection of accessible surfaces of one fuel support piece each refueling outage when removed from the core plate to support Control Rod Blade (CRB) exchange. If no CRB exchange or replacements are performed during a refueling outage, then at least Response to License Renewal Commitment No. 10 Thermal Aging and Neutron Irradiation Embrittlement of Cast Austenitic Stainless Steel (CASS)
Page 2 of 3 one fuel support piece will be inspected every other refueling outage during the period of extended operation. This additional inspection will be implemented starting in the Fall 2010 refueling outage.
Basis: The fuel support piece is normally not accessible for inspection due to its location in the core plate. Any loss of fracture toughness is not expected to impact the intended function of the component.
The loading on the fuel support piece is mostly in compression and as such any loss of fracture toughness is not expected to affect the structural integrity of the component.
CORE SPRAY LINE SPRAY NOZZLE ELBOWS Current Inspections: BWRVIP-1 8-A requires a VT-1 of a rotating sample of at least 50 percent of all sparger to nozzle lock welds (S3) every other refueling outage. If new cracking or unexpected growth of existing cracks is found, a VT-1 inspection of all remaining S3 welds shall be done. An EVT-1 inspection of all welds found to be newly cracked or exhibiting unexpected crack growth shall be performed to characterize the flaws. These inspections are expected to identify any degradation of the spray nozzle elbows that could affect their structural integrity.
Planned Supplemental Inspection: The BWRVIP inspection scope on the spray nozzle elbows will be increased from 50 percent every other refueling outage to 100 percent every other refueling outage.
This inspection will identify any significant cracking or structural failure of the spray nozzle elbows. This scope increase will be implemented starting in the Fall 2010 refueling outage.
Basis: The spray nozzle elbows are constructed of standard stainless steel piping components that were fabricated by cast methods. The OCNGS General Electric Specification required that CASS components meet the minimum material properties specified in ASTM-A-296, Grade CF-8. A review of the original CMTRs for the core spray nozzle elbows found that, the molybdenum (MO) content was not evaluated as part of these CMTRs. These components are inspected routinely as part of the BWRVIP-18-A required VT-1 inspection of the sparger spray nozzles. This inspection would identify any significant cracking or structural failure of the spray nozzle elbows.
CONTROL ROD GUIDE TUBE BASE Current Inspections: BWRVIP-47-A requires inspection of weld CRGT-3; an EVT-1 inspection on both the casting and wrought sides of the weld are performed. Therefore, any cracking in the CASS component in the vicinity of the weld will be detected. At least 10 percent of the Guide Tube population is required to be inspected using EVT-1 (1/2 mil) within a 12-year period with a minimum of 5 percent of the guide tube population inspected within the first six (6) years of the period.
Planned Supplemental Inspection: A VT-1 inspection of one control rod guide tube base will be added each refueling outage during BWRVIP CRGT-3 exam on the lower ID of accessible guide tubes.
If the Control Rod Guide Tube (CRGT) inside diameter is not accessible because no CRB exchange or replacements are performed during a refueling outage, then at least one control rod guide tube base will be inspected every other refueling outage during the period of extended operation. This additional inspection will be implemented starting in the Fall 2010 refueling outage.
Basis: At least 10 of these CRGT-3 EVT-1 exams have been completed at Oyster Creek since 2004 and no indications have been identified in the CASS material. Many CRGT-3 weld inspections have been successfully completed in the BWR fleet with no significant degradation of the adjacent guide tube base identified. In addition, this CRGT base is located just above the reactor bottom head and as such Response to License Renewal Commitment No. 10 Thermal Aging and Neutron Irradiation Embrittlement of Cast Austenitic Stainless Steel (CASS)
Page 3 of 3 is not expected to exceed the fluence threshold of 1017 n/cm 2. Therefore, a significant loss of fracture toughness on this CASS component is not expected.
SCOPE EXPANSION
- 1) Scope expansion for the fuel support piece and control rod guide tube base, similar to that specified in BWRVIP-47-A, is as follows:
a) If one or more flaws are found which are determined to impact on the structural integrity of the component, similar locations in 5 percent of the total population of similar components must be inspected during the same outage. The additional components to be inspected must be previously uninspected.
b) If flaws are found which are determined to impact on the structural integrity of the component during the additional inspection defined in a), then the expansion criteria given in a) is repeated until no new flaws are found.
- 2) Scope expansion for the core spray nozzle elbow inspections is as follows:
If one or more flaws are found which are determined to impact on the structural integrity of the component, then 100 percent of the core spray nozzle elbows will be inspected in the same outage.
==
Conclusion:==
AmerGen believes that performance of the ongoing and proposed supplemental inspections will be adequate to ensure structural integrity of the fuel support pieces, core spray line spray nozzle elbows and the control rod guide tube base during the period of extended operation, and that having this program in place prior to the period of extended operation meets the commitment associated with the CASS program (commitment # 10 of the license renewal SER), since supplemental inspections will be performed based on the conservative assumption that the subject components are susceptible to loss of fracture toughness. Therefore, AmerGen will ensure that the aging management program (AMP) and associated implementing documents reflect these inspection activities prior to entering the period of extended operation. The supplemental inspections themselves will be started in the first refueling outage following the beginning of the period of extended operation. If the BWRVIP CASS project work is successful in determining which components are susceptible to loss of fracture toughness, the OCNGS program may be revised under the appropriate process controls (i.e., commitment management and/or 10 CFR 50.59).
Summary of Regulatory Commitments Page l of 2 The following table identifies commitments made in this document. (Any other actions discussed in the submittal represent intended or planned actions. They are described to the NRC for the NRC's information and are not regulatory commitments.)
COMMITTED COMMITMENT TYPE COMMITMENT DATE OR ONE-TIME ACTION Programmatic "OUTAGE" (Yes/No)
(Yes/No)
Fuel Support Piece:
Fall 2010 No Yes refueling outage Planned Supplemental Inspection: Add a VT-1 inspection of accessible surfaces of one fuel support piece each refueling outage when removed from the core plate to support Control Rod Blade (CRB) exchange. If no CRB exchange or replacements are performed during a refueling outage, then at least one fuel support piece will be inspected every other refueling outage during the period of extended operation. This additional inspection will be implemented starting in the Fall 2010 refueling outage.
Core Spray Line Spray Nozzle Elbows:
Fall 2010 No Yes refueling outage Planned Supplemental Inspection: The BWRVIP inspection scope on the spray nozzle elbows will be increased from 50 percent every other refueling outage to 100 percent every other refueling outage. This inspection will identify any significant cracking or structural failure of the spray nozzle elbows. This scope increase will be implemented starting in the Fall 2010 refueling outage.
Summary of Regulatory Commitments Page 2 of 2 Control Rod Guide Tube Base:
Fall 2010 No Yes refueling outage Planned Supplemental Inspection: A VT-1 inspection of one control rod guide tube base will be added each refueling outage during BWRVIP CRGT-3 exam on the lower ID of accessible guide tubes. If the Control Rod Guide Tube (CRGT) inside diameter is not accessible because no CRB exchange or replacements are performed during a refueling outage, then at least one control rod guide tube base will be inspected every other refueling outage during the period of extended operation.
This additional inspection will be implemented starting in the Fall 2010 refueling outage.
SCOPE EXPANSION:
Fall 2010 No Yes refueling outage
- 1) Scope expansion for the fuel support piece and control rod guide tube base, similar to that specified in BWRVIP-47-A, is as follows:
a) If one or more flaws are found which are determined to impact on the structural integrity of the component, similar locations in 5 percent of the total population of similar components must be inspected during the same outage. The additional components to be inspected must be previously uninspected.
b) If flaws are found which are determined to impact on the structural integrity of the component during the additional inspection defined in a), then the expansion criteria given in a) is repeated until no new flaws are found.
- 2) Scope expansion for the core spray nozzle elbow inspections is as follows:
If one or more flaws are found which are determined to impact on the structural integrity of the component, then 100 percent of the core spray nozzle elbows will be inspected in the same outaqe.