Parametric study of enriched gadolinium in burnable neutron poison fuel rods for Angra-2

Abstract

Evaluation of gadolinium enrichment in Gadolinia (Gd2O3) burnable poison fuel rods was performed for a model of PWR Angra-2 reactor fuel assembly. A parametric study of the effect of 155Gd enrichment on neutronic performance was investigated during burn-up for a proposed very low gadolinium design (VLowGad-FA) having 1% of Gadolinia in weight fraction. Low fraction gadolinium designs enable the Angra-2 reactor to use its licensed limit of 235U to its maximum potential, that is 4.25%, with better reactivity behavior for some cases. Thermal transport performance of irradiated fuel was followed through estimation of inter-assembly peak pin power during burn-up. Results showed that Gd enriched design would behave very similar to LowGad assembly in terms of controlling local core power. It was confirmed in the neutronic context that low gadolinium design provides fuel cycle economic benefits while supporting longer cycle operation. It was estimated savings of 18 effective full power days if LowGad (2.0% Gadolinia, 4.25% 235U) is used in place of refGad (7.0% Gadolinia, 2.90% 235U). Respect the proposed design, savings are up to 41 effective full power hours if the burnable poison fuel rod VLowGad (1% Gadolinia, 99% 155Gd) is used in place of the commercial LowGad. The break-even point for Gd-155 enrichment cost for VLow155Gd99 fuel assembly was calculated to be 371 US$/gram-Gd-155 based in year 2018 prices of MWe for Angra-2.