New model developments for fuel supply strategies in molten salt reactors: Application to the REM depletion code

In recent years, a particular family of molten salt reactors (MSRs) – those designed to burn plutonium and minor actinides – has attracted considerable interest from research institutions and companies, including CNRS and Orano. NRS/LPSC Grenoble has been studying and optimising MSRs since the early 2000s, within which framework the in-house precision-driven material evolution REM code was developed. Depletion simulation of burner MSRs has led to the development of new methods for supply management and the addition of additional constraint parameters to the REM code. These developments make it possible to introduce physico-chemical constraints into the analysis of this kind of reactor, enabling more precise studies. Examples include controlling the alkali or alkaline-earth fraction, or regulating the salt volume either by adjusting the supply or by adding a dynamic expansion tank. This paper presents new perspectives that led to work on the numerical stabilization of the system, which helped smooth out reactor characteristics such as reactivity and fuel supply. This, in turn, opened the way to new supply strategies, e.g., by considering separate supplies for each chemical species or for individual elements. Finally, results are presented showing that, in the case of an extraction scheme with actinide reinjection, element-based supplies better satisfy mass balance requirements than species-based supplies. Conversely, in schemes without reinjection, the opposite trend is observed. Considering these strategies, while taking into account chemical constraints such as element valency and salt electroneutrality, could lead to the development of a new model for material extraction.