Multi-physics evaluation of the steady-state operation of an Aqueous Homogeneous Reactor for producing Mo-99 for the Brazilian demand

The studies summarized in this paper aims to predict the steady state operation of a low-enriched uranium fuel ARGUS type aqueous homogeneous reactor for producing 99Mo to meet the domestic demand of Brazil through a coupled multi-physics (Neutronics + Thermal-hydraulics) evaluation. The coupled multi-physics evaluation included aspects related to the neutronic behavior such as fission induced energy deposition profile, medical isotopes production; and the thermal-hydraulic behavior such as temperature, velocities and gas volume fraction profiles. The methodology followed for the multi-physics and multi-scale coupling of the neutronic and thermal-hydraulic codes (MCNP + ANSYS-CFX), discussed in detail in this paper, represent one of the main outcomes of the current study. The methodology was tested for two different operating configurations of the ARGUS reactor, the original high-enriched uranium configuration used since 1981, and the new low-enriched uranium configuration after the conversion process during 2012-2014. The calculations carried out showed that the reactor, in the studied configuration, is able to produce 246.5 six days Curie of 99Mo in operation cycles of five days. Which is equivalent to more than a third of the estimated Brazilian demand for 2025.