Possibility for using a low-enriched target to produce 99Mo in the MAK-2 research channel of the VVR-ts reactor

Thermal-hydraulic calculations have been conducted with respect to the active part of the MAK-2 loop facility of the VVR-ts research reactor for the 99Mo production. The computational studies were undertaken both for the case of using a highly 235U enriched target and for a low-enriched target. The calculation was performed for the actual technical characteristics of the research channel. The power density for the two simulated cases was obtained in the course of a preliminary neutronic calculation and selected for the most heated channel. The problem is solved for the steady-state mode of the channel coolant flow and takes into account the dependence of the thermophysical parameters of materials on temperature. The volumetric temperature distribution in the channel was obtained in the process of the calculation. The calculation results present the maximum temperatures of the target materials for the 99Mo production. An analysis of the obtained results has shown that the maximum temperatures of the aluminum sleeve and the target filling materials do not exceed the critical values. For the analyzed calculation cases, the maximum coolant temperature is localized at a point near the sleeve wall surface and does not reach the boiling temperature for a given pressure. The study has therefore shown that it is possible to reduce the 235U enrichment of the target filling fissile material to 19.7%, provided the average density of the mixture and the amount of 235U in the target remain the same. At the same time, the amount of the medicinally important 99Mo generated will not practically change, which will lead to reduced capital costs for a highly enriched mixture of the target matrix.