PLA-6449, Request for Additional Information for the Review of License Renewal Application, Section B.2.1 - Questions and Responses
| ML083370201 | |
| Person / Time | |
|---|---|
| Site: | Susquehanna  |
| Issue date: | 11/17/2008 |
| From: | Spence W PPL Corp, Susquehanna |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| PLA-6449 | |
| Download: ML083370201 (7) | |
Text
William H. Spence PPL Corporation Executive Vice President and Two North Ninth Street P~I, Chief Operating Officer/Ciief Nuclear Officer Allentown, PA 18101-1179 Tel. 610.774.3683 Fax 610.774.5019 Tel. 610.774.5151 Whspence@pplweb.com www.pplweb.coin
- TM eov7 J?20mU0 U. S. Nuclear Regulatory Commission Document Control Desk Mail Stop OP1-17 Washington, DC 20555 SUSQUEHANNA STEAM ELECTRIC STATION REQUEST FOR ADDITIONAL INFORMATION FOR THE REVIEW OF THE SUSQUEHANNA STEAM ELECTRIC STATION UNITS 1 AND 2, LICENSE RENEWAL APPLICATION (LRA)
SECTION B.2.1 Docket Nos. 50-387 PLA-6449 and 50-388
References:
"Applicationfor Renewed OperatingLicense Numbers NPF-14and NPF-22,"
dated September 13, 2006.
"Requestfor Additional Infornalionfor the Review of the SusquehannaSteam ElectricStation, Units I and2 License Renewal Application,"
dated October 27, 2008.
In accordance with the requirements of 10 CFR 50, 51, and 54, PPL requested the renewal of the operating licenses for the Susquehanna Steam Electric Station (SSES)
Units 1 and 2 in Reference 1.
Reference 2 is a request for additional information (RAI) related to License Renewal Application (LRA) Section B.2.1. The enclosure to this letter provides the question responses and the additional requested information.
There are no new regulatory commitments contained herein as a result of the attached response.
If you have any questions, please contact Mr. Duane L. Filchner at (610) 774-7819.
I4/90
Document Control Desk PLA-6449 I declare, under penalty of perjury, that the foregoing is true and correct.
Executed on: ____"-____- __
W. H. Spence
Enclosure:
PPL Response to NRC's Request for Additional Information (RAI)
Copy: NRC Region I Ms. E. H. Gettys, NRC Project Manager, License Renewal, Safety Mr. R. Janati, DEP/BRP Mr. F. W. Jaxheimer, NRC Sr. Resident Inspector Mr. A. L. Stuyvenberg, NRC Project Manager, License Renewal, Environmental
Enclosure to PLA-6449 PPL Response to NRC's Request for Additional Information (RAI)
Enclosure to PLA-6449 Page 1 of 4 RAI B.2.1-1R:
In letter dated July 14, 2008, in response to RAI B.2.1-1, Susquehanna Steam Electric Station (SSES) states that Inservice Inspection (ISI) Program is credited to manage loss of fracture toughness due to thermal aging embrittlement of cast austenitic stainless steel (CASS) components. It further states that loss of fracture toughness due to thermal aging embrittlement of CASS is managed via the detection of cracking and the monitoring of crack growth.
In license renewal application Table 3.1.2-3, SSES credits the ISI Program to manage loss of fracture toughness of CASS recirculation pump thermal barriers. The thermal barriers in the pumps (which provide a Class 1 to Class 2 interface) may not actually be accessible for inspection. Ultrasonic testing volumetric techniques to date cannot distinguish between signals that come from the CASS microstructures from those that arise for crack/flaw indications in the CASS material. Given that thermal aging of CASS can lead to a lower fracture toughness and cracking, please describe the aging management of the primary recirculation pump CASS thermal barrier cover. Address specifically the management of cracking that could occur between the pump shaft cavity and the cooling water cavity of the Reactor Building Closed Cooling Water system.
Identify what inspection technique will be used to perform the inspection.
PPL Response:
PPL credits the SSES ISI Program, LRA Section B.2.1, to manage loss of fracture toughness due to thermal aging embrittlement of cast austenitic stainless steel (CASS) recirculation pump components. This is based on the NRC staff's evaluation of thermal aging embrittlement of CASS components for license renewal, as documented in the staff's letter dated May 19, 2000, from C. Grimes (NRC) to D. Walters (NEI). The conclusion of the staff, relative to the management of loss of fracture toughness due to thermal aging of Class 1 pumps and valves, is:
"Valve bodies and pump casings are adequately covered by existing inspection requirements in Section XI of the ASME Code, including the alternative requirements of ASME Code Case N-481 for pump casings.
Screening for susceptibility to thermal aging is not required and the current ASME Code inspection requirements are sufficient."
This conclusion is directly reflected in the guidance provided by NUREG-1801 in Table 1, ID 55, and in Chapter IV, item IV.C1-3, for Class 1 pump casings, and valve bodies and bonnets, in the BWR reactor coolant pressure boundary.
In February 2008, the NRC staff reinforced the acceptance of this conclusion in the "Safety Evaluation Report Related to the License Renewal of James A. FitzPatrick Nuclear Power Plant." In section 3.1.2.1.6 of the SER, the staff accepted the plant's use
Enclosure to PLA-6449 Page 2 of 4 of the ISI program, which corresponds to NUREG-1 801 Chapter XI.Ml, to manage loss of fracture toughness due to thermal aging embrittlement of the recirculation pumps.
And, section 3.0.3.3.3 of the SER details the review of the ISI program, including the staff's acceptance of applying the conclusion of the May. 19, 2000, letter, as stated above, as the explanation for how the ISI program manages loss of fracture toughness.
For the aging management review of the SSES recirculation pump components, as reflected in LRA Table 3.1.2-3, PPL identified the thermal barrier as a separate component of the pump, even though it is part of the pump cover. The SSES recirculation pump is constructed with two separate CASS components: 1) the pump casing, and 2) the pump cover. The pump cover has a series of passages, created by machining and drilling, to allow cooling water, from the Reactor Building Closed Cooling Water (RBCCW) system, to be circulated through the portion of the casting that surrounds the pump shaft. The portion of the pump cover that contains these passages and performs the cooling function is called the thermal barrier.
While the thermal barrier is not a separate component, PPL treated it as such in order to address the aging effects attributed to the RBCCW environment in the internal passages in the pump cover (i.e., the thermal barrier portion). Since the RBCCW system temperature is below the threshold for thermal aging embrittlement, loss of fracture toughness is not identified as an aging effect for the RBCCW side of the thermal barrier.
The reactor coolant side of the thermal barrier, which is also the pump cover, is subject to loss of fracture toughness.
In LRA Table 3.1.2-3, the aging effects, including reduction (loss) of fracture toughness, identified for the thermal barrier with the "Treated Water - RCS" external environment are identical to the aging effects identified for the pump casing and cover with the "Treated Water" internal environment. This is due to the fact that there are no physical, material, or environmental differences between the external surface of the thermal barrier and the internal surface of the pump cover, since they are the same component.
NUREG-1 801 Item IV.C1-3 identifies the aging management program from Chapter XI.M1, "ASME Section XI Inservice Inspection Subsections IWB, IWC, and IWD," as the applicable program to manage loss of fracture toughness for Class 1 pump casings, and valve bodies and bonnets. While NUREG-1 801 Item IV.Cl-3 does not identify pump covers, per se, they are necessary reactor coolant pressure boundary components of the SSES recirculation pumps. A pump design that incorporates a cover to complete the pressure boundary is analogous to a valve body and bonnet. Therefore, the pump covers, like valve bonnets, are considered part of the pressure boundary and, as described in NUREG-1801, the Chapter XI.M1 program is the appropriate AMP to manage loss of fracture toughness.
Enclosure to PLA-6449 Page 3 of 4 Following NUREG-1801 Item IV.C1-3, the SSES ISI Program, which is consistent with NUREG-l 801 Chapter XI.M1, is credited for managing reduction (loss) of fracture toughness of the reactor coolant pressure boundary of the pump cover. Since the thermal barrier is the same cast component as the pump cover, the ISI Program is also credited for managing loss of fracture toughness for the reactor coolant pressure boundary of the thermal barrier, which includes the portion of the pump cover between the pump shaft cavity and the cooling water cavity of the RBCCW system.
PPL concludes that the LRA provides adequate aging management for the aging effect of loss of fracture toughness for the thermal barriers in the reactor recirculation pumps, in accordance with the guidance provided in NUREG-1801, Revision 1.
RAI B.2.1-4R:
In letter dated July 14, 2008, in response to RAI B2.1-4, Part B, SSES states that the recirculation nozzle safe-end weld overlay design was based on the requirements of the American Society of Mechanical Engineers (ASME)Section XI, IWB-3640 and Code Case N-504-2. SSES also states that the ASME Code required no flaw tolerance evaluations to be performed as part of the design basis for these repairs. There were no design basis analyses performed for the weld overlay repairs that constitute a time-limited aging analysis.
However, Paragraph (g) of the code case mandates to perform an evaluation of the flaws that are left in place as part of the alternative repair weld overlay technology that is mandated by ASME. Please explain what SSES did to meet paragraph (g) of the code case and, if a flaw growth assessment was performed that covers the remainder of the current life of the plant.
PPL Response:
The weld overlay repairs for the SSES Unit I NIB and N2J recirculation nozzle-to-safe-end welds were designed to the requirements of ASME Section XI, IWB-3640 and Code Case N-504-2. Additionally, the repairs were "full structural overlays," or Standard Weld Overlays, as defined in Section 4.4 ofNUREG-0313 Revision 2. As such, the overlay repairs were designed with the assumption that the underlying flaw was entirely through-wall and completely around the circumference of the component. No credit was taken for any remaining ligament in the repair location. The design of the overlays provides the necessary wall thickness to satisfy the flaw evaluation procedures of IWB-3640, in accordance with Code Case N-504-2 paragraph (f)(l), and ensures the structural adequacy of the component for all design loading conditions. This design approach is consistent with similar overlay repairs on BWR recirculation nozzles and other IGSCC-susceptible components in the industry since 1985.
Enclosure to PLA-6449 Page 4 of 4 When the overlays were designed in 2004, there was conclusive evidence from past and present volumetric examinations that flaw growth had been arrested by the application of the Mechanical Stress Improvement Process (MSIP) in 1993 (for the N2J) and 1995 (for the NIB). The volumetric examination data was reviewed by PPL, General Electric, and EPRI NDE experts. The consensus conclusion was that the flaws had not grown since the application of MSIP. The lack of flaw growth between the time of MSIP application and 2004 confirmed that the residual compressive stress in the welds from MSIP, combined with the benefits of hydrogen water chemistry implementation in January 1999, had effectively eliminated further IGSCC. It was also recognized that weld overlay repairs would impose additional compressive stress in the welds.
Therefore, it was concluded that there would be no, or negligible, flaw growth due to IGSCC into the future.
Since there was no flaw growth projected to exceed the assumed flaw in the overlay design, a flaw growth assessment and a flaw tolerance evaluation to demonstrate the structural adequacy for a predicted flaw size at the end of a specific operating interval (e.g., 40 years or 60 years) were not necessary. The full structural overlay, as designed with an assumed through-wall crack around the entire circumference in accordance with IWB-3640 and Code Case N-504-2, will remain structurally adequate for the operating life of the plant.
Code Case N-504-2 paragraph (g)(2) requires a weld repair evaluation to demonstrate that the requirements of IWB-3640 are satisfied for the design life of the repair, considering potential flaw growth. As discussed above, the potential flaw growth was determined to be zero, or negligible, such that the flaw assumed in the overlay design remains bounding for the life of the component. Therefore, the calculations performed to determine the required design size and thickness of the overlays serves as the evaluation required by Code Case N-504-2 paragraph (g)(2). Since those calculations are not dependent on any flaw growth assessments, they are not time-limited aging analyses (TLAA).