C59-01a: Boiling Water Reactor Lifetime Extensions Enabled through Advanced Computing

Neutron and gamma radiation are critical factors in the lifetime analysis of nuclear reactor structures, including large components such as the reactor pressure vessel and concrete biological shield, as well as many smaller reactor components that must be replaced periodically as part of normal plant maintenance. Irradiation-induced embrittlement and irradiation-assisted stress corrosion cracking can lead to more frequent outage inspections, more frequent component repair or replacement, and premature shutdown of existing reactors. An ongoing task with the operating reactor fleet is the performance of radiation fluence analyses to assess the lifetime remaining for critical reactor components. In addition to being time consuming, fluence analyses are performed with many approximations that require significant conservatism to maintain margin to material exposure limits. This has implications for many reactors where there is high interest to extend reactor lifetime beyond 80 years. The current conservatism of 10-15% in estimated fluence can have a profound effect on large component lifetime. The value of extending a nuclear reactor’s life is estimated at $300 million per year of extended operation. Boiling water reactor fluence analyses are also the basis for component inspections and maintenance schedules and applies to in-vessel structures such as the core shroud, jet pump assembly, core spray spargers, and control blade components. The frequency of such inspections is a significant maintenance expense for operating reactors that could be reduced with better estimated of component fluence. This proposal seeks to develop a broadly applicable, first-of-a-kind computational capability to identify, quantify and potentially eliminate excess margin in existing reactor fluence analyses leveraging advanced computing. The key advantage of the methodology is that it integrates high-resolution, high-fidelity predictions for all reactor core radiation source terms (neutron and gamma) in conjunction with highly accurate 3-dimensional radiation transport simulations. Through modeling of the as-built and as-loaded fuel loading patterns over the operating history of the reactor, including detailed coolant void distribution, higher accuracy of source terms with reduced uncertainties in predicted fluence will be achieved. Incorporation of 3-dimensional digital representations of reactor components with the modeling and simulation capabilities will allow for Just-In-Time calculations of fluence to be performed for any region of materials concern both within and external to the reactor pressure vessel. Analyses of beltline and non-beltline vessel fluence for pressurized water reactors, including upper and lower internals, using this methodology have been demonstrated using recently developed state-of-the-art software capabilities. The technology has been shown to have accuracy within 2% of measured fluence coupon data. In Phase 1 of this proposal, this technology will be extended to boiling water reactors, which comprise nearly 1/3rd of the nuclear fleet, incorporating reactor specific fuel and plant geometry and development of models to accurately represent each of the major components inside of the pressure vessel. This capability will be demonstrated using a publicly available commercial reactor model. In Phase 2, validation and commercial application will be achieved through partnering with a nuclear utility or fuel vendor.