Abstract : Accelerator Driven Systems (ADS), based on a proton accelerator and a sub-critical core coupled with a spallation
target, offer advantages in order to reduce the nuclear waste radiotoxicity before repository closure. Many studies carried out on
the ADS should lead to the definition of an experimental plan which would federate the different works
This thesis deals with the neutronic Monte Carlo simulations with the MCNPX code to optimize such a
system in view of a pilot reactor building.
First, we have recalled the main neutronic properties of an hybrid reactor. The concept of gas-cooled eXperimental
Accelerator Driven System (XADS) chosen for our investigations comes from the preliminary studies done by the Framatome company.
In order to transmute minor actinides, we have considered the time evolution of the main fuels which could be
reasonably used for the demonstration phases. The neutronic parameters of the reactor, concerning minor actinide transmutation, are
Also, we have calculated the characteristic times and the transmutation rates in the case of 99Tc and 129I isotopes.
We have identified some neutronic differences between an experimental and a power ADS according to the infinite
multiplication coefficient, the shape factor and the level of flux to extend the demonstrator concept. We have proposed geometric
solutions to keep the radial shape factor of a power ADS acceptable.
In the last part, beyond the experimental XADS scope, we have examined the possible transition towards an
uranium/thorium cycle based on Molten Salt Reactors using a power ADS in order to generate the required 233U proportion.