Irradiation capsule design for neutron coloration of topaz in a WWR-K reactor

Abstract

This study justifies irradiation capsule design calculations used for efficient coloring of topaz in a WWR-K reactor. Various radiation screens used for removing thermal and epithermal neutrons and their influence on the activation of the main impurities in topaz are considered. Neutron analysis has been performed by means MCNP transport code. It is shown that the use of a sandwich screen composed of boron carbide and tantalum decreases the fraction of thermal neutrons by 24% and increases the fraction of fast neutrons by 15%. These are the optimal neutron conditions for topaz irradiation in a WWR-K reactor. Thermal analysis has been performed by means Comsol code and two approaches were taken: conservative and realistic. A thermo-physical analysis with a conservative approach showed that for boron carbide and tantalum screen the temperatures under forced and natural convection modes were 134°С and 274°С, respectively. The temperature of the case body was 75 °C with forced cooling and 238 °C without cooling. In case of realistic approach, the topaz temperature does not exceed 65°С if regular cooling of the irradiation capsule is ensured. Calculation results showed the importance of the ensure circulation between topaz during irradiation, which makes it possible to reduce the temperature of topaz by almost half.