Assessing Criteria to Pick Ideal Moderators for Nuclear Fission Reactors

Abstract

The goal of this study is to find the best and most feasible compound(s) to use in a nuclear reactor as a moderator in order to achieve a chain reaction with maximum efficiency. To obtain a chain reaction with the most energy output per volume material used, neutrons need to be able to collide with radioactive material in a manner that will maximize the probability of fission. For this to happen, the cross section for fission must be exceptionally large. This is attainable by slowing down the speed of neutrons by use of a moderator. A number of criteria must be met for a moderator to be considered the most feasible. For one, it must be able to quickly thermalize neutrons from the MeV range down to a few eV. In this paper, we will define thermalization as reducing a neutron's energy from 2 MeV to 0.025 eV [3]. Second, it mustn’t have a high affinity for absorbing neutrons. And lastly, it must be cheap and abundant. If these criteria are met, one has found a good moderator. This study will primarily explore two substances: Zirconium Hydride and Yttrium Hydride, and their abilities to act as moderators for slow water reactors.