The extraction of ⁹⁹Mo medical isotopes from off-gas of molten salt reactors (MSRs) has attracted significant attention. However, previous studies focused only on the estimation of ⁹⁹Mo nuclide production in the reactor core, and limited studies have focused on the expansion of the entire reactor system.

This study aims to estimate ⁹⁹Mo production in the off-gas of a molten salt reactor.

In this study, a ⁹⁹Mo migration model with noble metal deposition and a flow effect in an MSR was established by using scientific computing software “Mathematica”, and a corresponding verification based on the deposition result of a molten salt reactor experiment (MSRE) was implemented. Subsequently, an analysis was conducted on the impact of changes in the yield, specific activity, and operational status of ⁹⁹Mo crude product in MSRE off-gas on the stability of production.

The analysis results of Mo transport in the MSRE show that the production of ⁹⁹Mo in the off-gas can reach 69.30 TBq with a specific activity of 0.39 PBq?g^-1 under normal operating conditions. In addition, an increase in the removal rate is conducive to the effect on the specific activity of ⁹⁹Mo whilst the working conditions of bubble surface ratio bubble ratio and oxidation-reduction potential changes have little effect on the specific activity of the product.

The ⁹⁹Mo in off-gas has high yield and specific activity, and the effects of the conventional operating conditions on the specific activity of ⁹⁹Mo are beneficial, which indicates that this method can be a potential alternative for ⁹⁹Mo production.