To describe the breeding performances of such a system, we can use the conversion ratio C, which is defined by the ratio between the 233 U production rate by Pa decay, and the U feeding flow. If one chooses a reprocessing time of 10 days, which seems to be a minimal value, this type of molten salt reactor leads to a conversion ratio C at equilibrium of 1.05. The 233Pa inventory is around 20 kg in the core.

It appears clear that the deployment ability of the asymptotic Th/U MSR is better than that of fast neutron thorium reactors. The doubling time is around 25 years. This favourable behaviour is essentially due to the reduced fissile inventory. One has then to study the possibility of reaching the asymptotic Th/U cycle, starting Th/Pu reactors with the plutonium coming from the PWR spent fuel.

Different reprocessing methods can be considered, depending on the desired scenarios. Complex and fast reprocessing, where a lot of nuclei are extracted during a short time, will lead to a very good neutron balance and large breeding rates. This makes a fast development of such reactors possible. On the contrary, if fast development is not the priority, the

reprocessing principle can be largely simplified by increasing the reprocessing time or by reprocessing only a few nuclei.

In the same vein, the reprocessing can be simplified by the use of an accelerator driven molten salt reactor. For example, the performance, in term of breeding rates, of a critical reactor using an online 233Pa extraction is similar to that of an accelerator driven system, running at k = 0.98, without protactinium extraction.