A review of french studies on thorium cycles for HTR and MSR including nuclear data evaluation

In the first part, we outline the work performed on nuclear data for the two main isotopes involved in the thorium cycle, i.e, Th 232 and U 233. This work includes differential cross section measurements for Th 232, comparison of neutronic calculations with critical experiments and data evaluation for both isotopes. This brief review stresses on the fact that cross sections were subject to significant modifications along this period of work. The second part deals with thorium fuel cycle studies carried out at C.E.A. on H T R. These studies were mainly based on the utilisation of integrated block design, developed by General Atomic Company (G.A.C.). We particularly discuss the results concerning a symbiotic system specifically adapted to no recycle or full conversion. This system combines two types of cores: the first one using U 235/Th fuel is optimised in order to obtain a minimum fuel cycle cost without reprocessing and the second one using U 233/Th fuel is supposed to be built later, when the reprocessing technology is available. In the third part we give some results obtained on M S R. It is shown that cross section uncertainties may have a great influence on the calculation of typical design parameters such as conversion ratio. In this section we also present preliminary studies concerning the complex problem of approach to equilibrium in an M S R. It is concluded that, it is possible to operate such a reactor with U 235/Th fuel at the beginning and then, progressively change into U 233/Th cycle along a period of a few years. (J.P.N.)