Nuclear Data Impact on HTR-10 Pebble Bed Reactor Metrics

This study investigates the impact of nuclear data on selected key core metrics for the HTR-10 pebble-bed reactor, as part of a broader project that aims to facilitate the identification of nuclear data deficiencies and needs in the US Nuclear Data Program databases that impact the safety of advanced reactors. This study’s focus extends from analyzing a fresh fuel core configuration to examining an equilibrium core, in which additional nuclides significantly influence the reactor’s behavior to the fresh fuel configuration. Sensitivities to and uncertainties due to nuclear data were determined compared for the effective multiplication factor (k_eff) and the temperature of fuel and temperature of pebble graphite reactivity responses of two full-core models of the HTR-10: an initial core with fresh fuel and an equilibrium core. The underlying simulations were performed using the SCALE code system with the ENDF/B-VII.1 nuclear data library. With respect to sensitivities, the results indicate that v-, fission, and (n, γ) reactions of ²³⁵U, elastic scattering and (n, γ) of graphite, and (n, α) of ¹⁰B are significant nuclides and reactions for both fresh fuel and equilibrium cores. For the equilibrium core, additional nuclides and reactions come into play, including v-, fission, (n, γ) of ²³⁹Pu and ²⁴¹Pu, as well as (n, γ) reactions of fission products such as ¹⁴³Nd, ¹⁴⁹Sm, and ¹³⁵Xe. With respect to uncertainties, v- of ²³⁵U and elastic scattering and (n, γ) in graphite are among the top contributors to the nuclear data-induced uncertainty of quantities considered for both core configurations. Specific nuclide-reaction pairs for the equilibrium core are (n, γ) of ¹³⁵Xe, elastic scattering of ¹⁴⁴Nd, and fission and (n, γ) of ²³⁹Pu.