The MSFR (Molten Salt Fast Reactor) consists in a concept of high power molten salt reactor. In molten salt reactors, the fissile and fertile nuclei are dissolved in a circulating salt that acts as fuel and coolant. The physical state of the fuel permits to consider draining as a way to mitigate hypothetical accidents. Contrary to solid fuel FNR (Fast Neutron Reactor) concepts, in the MSFR, the fuel is nearly in its most compact geometry. That is why a large-scale compaction cannot occur in these cores. These concepts can operate and are studied in the Th/U cycle with a fluoride salt or in the U/Pu cycle with a chloride salt. In the fluoride reference concept, the global temperature reactivity feedback is around -8pcm/K. This strong negative feedback, that guarenties an excellent intrinsic stability of the core, takes into account two effects: Doppler Effect and salt density effect. Each one being approximately half of the total value.
The goal of this work is to study the MSFR behaviour in case of a postulated reactivity insertion. In order to evaluate the consequences of extremes reactivity insertions, the first study concentrates on slow reactivity insertions to verify the efficiency of the draining of the core. Because of the presence of the expansion tank, the beginning of the draining has no impact on the reactivity in the core. Then, we also want to verify that there are wide safety margins between the consequences of plausible reactivity insertion and the consequences of extreme postulated reactivity insertions.
In the case of extreme reactivity insertions, during the early stages of the transient, the salt cannot expand freely and goes out of the core. The pressure increases and the bubbles inside the salt collapse.
To make these studies, we are developing two independent modelling. The first one is being developed in order to study slow reactivity insertion. The second code aims at calculating fast explosion of the vapour formed in the salt in case of fast reactivity insertions.
When the temperature of the salt rises, some vapour could be formed in the salt due to some fission products or because of the vaporization of the salt itself. The vaporisation of the salt could then lead to a quick expansion of the vaporized fluid. Our ultimate goal is the chaining of our codes to calculate any kind of accidental scenarios that could lead to successive recriticalities.
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|Affiliation/Organization||CEA - CNRS|