September-October 2017 NPJ

48 NuclearPlantJournal.com Nuclear Plant Journal, September-October 2017 justification is provided. The uncertainty quantification, an essential part of best- estimate methods, is achieved by a non- parametric order statistical technique. Both Nine Mile Point Unit 1 and Oyster Creek are currently limited in core design and operation by MAPLHGR limits. With TRACG-LOCA, improved MAPLHGR limits, which meet all safety requirements, allow for a more efficient core design and increased operational margin. Safety Enhancing the methods used for Loss of Coolant Accident (LOCA) analyses provides reasonable assurance that nuclear reactors operate safely. Prior to TRACG- LOCA, conservative applications provided a bounding evaluation through use of conservative assumptions, models, and inputs. However, this approach failed to provide a good understanding of the available true margin and/or actual plant response in mitigating events. Realistic applications enable better understanding of the plant response and resulting margin through use of more realistic, more detailed, and representative models for event mitigation as well as bounding licensing results through identification of uncertainties in the model, and hence improving the plant safety. The NRC issued the TRACG-LOCA methodology “NRC Safety Evaluation Report (SER)” in February 2017. Exelon was the first to implement this methodology supporting the Spring 2017 Nine Mile Point Unit 1 and reload. This methodology ensures that the state of the art LOCA analysis approach is used to ensure nuclear safety. Cost-Savings Impact The TRACG-LOCA methodology achieves significant fuel cost savings that will continue through end of plant life for Nine Mile Point Unit 1 and Oyster Creek. TRACG-LOCA produces less restrictive Maximum Average Planar Linear Heat Generation Rate limits which can be leveraged to improve the core design efficiency. The efficiency improvement with this innovation is realized in either a reduced number of fresh fuel bundles and/or enrichment required to meet the fuel cycle energy requirement. Nine Mile Point Unit 1 Cycle 24 realized a reduced enrichment for the reload fuel while Cycle 25 realized a reduction of 4 reload fuel bundles and an enrichment reduction. The Cycle 24 fuel cost savings was $1.5M and the Cycle 25 savings was $3.0M. Continued fuel cost savings are expected for each 2-year fuel cycle to the end of plant life. The overall net present value (NPV) of the fuel cost savings is significant for the remaining plant life of Nine Mile Point Unit 1. Oyster Creek Cycle 27, a short 13-month cycle, will achieve a reload enrichment reduction resulting in fuel cost savings of $2M (based on the market conditions for fuel). Productivity/Efficiency The productivity gain with this innovation is with the efficiency of the core design as a result of the less restrictive MAPLHGR limits produced by TRACG-LOCA. The improved MAPLHGR limits allow for the core design to meet the fuel cycle energy requirement with fewer reload bundles and/or reduced enrichment. The efficiency of the core design results in increased discharge exposures of the fuel. This directly indicates that the fuel is used more efficiently. This improvement was collaborative across the Exelon organization and with the fuel vendor. Nuclear Fuels held meetings with both Nine Mile Point and Oyster Creek stations to coordinate the overall project. A significant amount of input was provided by Exelon to the fuel vendor for the LOCA analysis. Collaboration between Exelon and GNF (Global Nuclear Fuel) existed throughout the project. Exelon prepared a Design Input Request (DIR) which supported the GEH plant-specific model development (basedeck generation), break spectrum calculations and limiting break scenario determination (Figures 2 and 3 on page 49), statistical analyses for the limiting break and exposure- dependent MAPLHGR curve generation. Exelon core design engineers provided live-time feedback to GEH engineers on how the MAPLHGR limits impacted the thermal limit margins. Additionally, both GEH and Exelon participated in meetings with the NRC as they reviewed the TRACG-LOCA methodology Licensing Topical Reports. GEH has addressed 104 RAIs (Requests for Additional Information) from the NRC – keeping Exelon apprised throughout the process. Transferability The TRACG-LOCA methodology is transferable across the industry – applicable to all BWR types, and licensed for application to non-GNF fuel. Exelon TRACG-LOCA... ( Continued from page 46)