VERACITY NUCLEAR, LLC — Department of Energy SBIR Phase I: C55-01a

Description

Neutron and gamma radiation are critical factors in the lifetime analysis of nuclear reactor structures that includes 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. An ongoing need with the operating reactor fleet is the performance of radiation fluence analyses to assess the lifetime remaining for 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 lifetimes. Most reactors have already extended their lifetime to 60 years with a number seeking to extend lifetimes to 80 and possibly 100 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. Fluence analyses are also the basis for component inspections and maintenance schedules and applies to in-vessel structures such as control blades, baffle bolts, and upper reactor vessel internals. The periodicity of such inspections is a significant maintenance expense for operating reactors that could be reduced with less uncertainty in calculated fluence values. This proposal seeks to develop a broadly applicable, first-of-a-kind computational capability to identify, quantify and potentially eliminate excess margin in existing 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, higher accuracy of source terms with reduced uncertainties in predicted fluence will be achieved. Incorporation of 3-dimensional digital representations of reactor components and structures 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. Advanced analysis for beltline vessel fluence and excore response has been demonstrated using recently developed state-of-the-art capabilities for the reactor core and radiation transport. The technology has already been demonstrated for beltline vessel fluence and was shown to have an accuracy of < 2% when compared with measured fluence coupon data. In Phase 1 of this proposal, the focus will be to extend this capability to integrate the geometry necessary to accurately represent the upper and lower internals and provide a streamlined methodology to extract the fluence for all regions. This capability will be demonstrated by partnering with a utility that is currently requiring upper internal surveillance during outages. Phase 2 will generalize to incorporate 3-D digital representations of all structures within core as well as ex-core structural materials allowing any region of concern to be modeled with high resolution.