Monte Carlo simulation of Mo-99 isotope production with increased specific activity in WWR-K reactor

The activation method used for the production of molybdenum-99 in the WWR-K reactor currently allows the maximum production of the specific activity of molybdenum-99 equal to (85 ± 11) GBq/g Mo as a result of seven-day neutron irradiation of natural molybdenum (VI) oxide. It is known that the reaction 98Mo(n,γ)99Mo is induced in the thermal region, and there are also large resonances in the energy region of about 12 eV and in the range of 0.4–10 keV, and these resonances do not compete with the radiative absorption reactions of other molybdenum isotopes in this area. Thus, an increase in the proportion of epithermal and thermal neutrons will lead to an increase in the production of molybdenum-99. The purpose of this work is to develop the design of an irradiation capsule that creates specified irradiation conditions. For this purpose, various designs of irradiation capsules with different materials that moderate neutrons were considered by calculation. Based on the results of Monte Carlo simulation, the optimal design of the irradiation capsule was selected, which makes it possible to increase the production of specific activity of molybdenum-99. Irradiating trioxide molybdenum with natural composition allows to increase the specific activity by 26%, while using trioxide molybdenum with a 98.7% enrichment molybdenum-98 – by 25%. The paper provides a description of the capsule designs considered and the results of computational modeling with MCNP code for molybdenum of different enrichments.