The medical isotope production aqueous reactor (MIPR) has advantages of small size, low power, and high inherent safety, hence is one of better candidate reactor types for the production of ⁹⁹Mo and other medical isotopes.

This study aims at the effects of extraction methods and reprocessing capacity on the production efficiency of ⁹⁹Mo based on low-enriched uranium MIPR designed with neutronic optimization.

First, the calculation method was verified according to existing experimental data, and the neutronic optimization of the MIPR was performed for core design by using SCALE6.1 code and ENDF/B-VII database with 238 groups. Then, the ⁹⁹Mo production efficiency under different extraction methods as well as processing capacities was investigated based on the optimized core structure. The range of achievable critical uranium concentration and enrichment was determined.

There is a minimum critical mass under different enrichment, and with the increase of ²³⁵U enrichment, the uranium concentration at the minimum critical uranium mass decreases. The effective multiplication factor decreases linearly with an increase in nitric acid concentration, and the corresponding nitric acid reactivity coefficient is approximately -1.400×10^-2 L·mol^-1. With an increase in uranium concentration, the void and temperature reactivity coefficients decrease, and the corresponding reactivity coefficients are approximately (-100~-250)×10^-3 ℃^-1 and (-18~-30)×10^-5 ℃^-1.

The production efficiency of the MIPR production of the ⁹⁹Mo online extraction method is slightly greater than that of the offline batch processing method with an increment of about 16% under a five-day production cycle. The reprocessing capability has a greater impact on the production efficiency of the online extraction method. If the reprocessing rate is increased five times, the increment of production efficiency is about 113% under a five-day production cycle.