Feasibility Study Of Nuclear Material Accounting In A Molten Salt Fast Reactor To Develop A Safeguards Approach

Molten Salt Fast Reactor (MSFR) is a fast neutron spectrum reactor being developed in France. The MSFR can be operated in the thorium fuel cycle with 233 U as the initial fissile load. The R&D efforts in France have shown that the MSFR can provide a long-term alternative to solid-fueled fast neutron systems because of its merits. However, there are limited studies on the development of nuclear safeguards approaches for the MSFR. Because of the non-use of solid-fuel in MSFR, there are several nuclear material safeguards challenges because of the bulk form (instead of the item form) of the material handled. The study presented here focus on these challenges for the case of MSFR. A MSFR neutronics model is made to perform the reactor core and radial blanket fuel burnup simulations in multi-time-steps including the recycling/purification of both (core and blanket) molten salt loops. Simulations are carried out using the Monte Carlo radiation transport code, MCNP6.2. The output from the simulations provided a time-dependent buildup of actinide concentrations of uranium, plutonium, neptunium, americium and curium isotopes. The paper presents the utilization of these predicted actinide isotope concentrations to develop nuclear material accounting (NMA) procedures in order to support safeguards approach development for the MSFR. One of the measurement methodologies studied for carrying out NMA is Hybrid K-edge Densitometry (HKED). The paper also presents the proliferation resistance characteristics of the MSFR salt due to the production of some of the actinide isotopes in the core that emit high energy radiation (neutron and photons) and decay heat. The NMA procedure adopted using HKED will provide an estimate of Material Unaccounted For (MUF) that may be encountered in the MSFR considering core as an Material Balance Area (MBA) and the circulating molten salt loop outside the core as another MBA. Discussion of HKED MUF measurement accuracy (σ_MUF) is made to illustrate whether the three nuclear safeguards governing conditions; (a) MUF less than 3σ_MUF, (b) MUF less than one Significant Quantity (SQ), and (c) 3σ_MUF less than one SQ, are met.