Utilizing even Plutonium Isotopes as burnable absorbers for controlling the reactivity and power distribution in Pressurized Water Reactors

Abstract

In this paper, a new approach is proposed for controlling the reactivity and power distribution in pressurized water reactor cores without the implementation of burnable absorbers. This approach depended on the homogeneous mixing of uranium oxide with even plutonium isotopes; Pu-238, Pu-240, and Pu-242. Three Plutonium fuels; (99% UO2 + 1% Pu-238), (99% UO2 + 1% Pu-240), and (98% UO2 + 0.5% Pu-238 + 1% Pu-240 + 0.5% Pu-242) were simulated using the MCNPX 2.7 code. The three plutonium fuels are compared with the other three erbium fuels; (99.9% UO2 + 0.1% 167Er2O3), (99.74% UO2 + 0.26% 167Er2O3), and (99.61% UO2 + 0.39% 167Er2O3), which are taken as reference fuels. The weight percent of UO2, plutonium isotopes and enriched erbium is adjusted to provide the same initial reactivity. This is important for holding a fair comparison between the two fuel types. The simulation demonstrated that even plutonium isotopes, like enriched erbium, can improve reactor safety parameters. It was found that Pu-240 added fuel can suppress the initial reactivity by 27% and extend the fuel cycle by 6.9% compared to the conventional UO2. The reason for fuel cycle extension is due to the production of Pu-241. Meanwhile, Pu-238 and Pu-even added fuels provide suppressing the initial keff by 13% and 35% and shortening the fuel cycle by 2.7% and 21%, respectively compared to the reference UO2 fuel. Moreover, the fuel temperature coefficient (FTC), moderator temperature coefficient (MTC) and void reactivity coefficient (VRC) of Plutonium fuels are found to more negative than those of erbium fuels at the later stages of burnup because of the spectrum hardening resulting from Pu-239 production.