Criticality Characteristics of Mixtures of Plutonium, Silicon Dioxide, Nevada Tuff, and Water

The parameters that determine when critical mixtures of ²³⁹Pu, SiO₂, and water and mixtures of ²³⁹Pu, Nevada tuff, and water are capable of sustaining an increasing neutron chain reaction as may be caused by a positive void coefficient at constant temperature are established. A single canister is considered that is loaded with up to 75 kg of ²³⁹Pu. A survey of critical spherical mixtures of plutonium, SiO₂, tuff, and water at constant temperature is created and these results are examined to determine the mixtures that might be autocatalytic. Regions of criticality instability are identified that have the possibility of autocatalytic power behavior. A positive void coefficient is possible for a very limited range of wet systems.