Modelling Incineration of Minor Actinides

A possibility to incinerate the minor actinides (MA) in a subcritical accelerator-driven system (ADS) is a subject of study around the world. The choice of the subcritical core option and cooling technology is among the most important decisions to make. On one side, the fast neutron spectrum is needed for efficient fission of MA, because their fission-to-capture ratio is greater at high neutron energies. On the other side, the high values of the cross-sections in thermal and epithermal energy regions can make effective a two-step transmutation-incineration. Since 1997, the Belgian Nuclear Research Centre SCK•CEN is performing the design studies aiming at the development of a small experimental ADS called MYRRHA which could be a step towards a prototype design of an ADS transmuter. In the current design, a highly enriched MOX is used as a driver fuel in the subcritical core, whereas different sorts of fuels containing minor actinides (MA) will be tested in the experimental channels and fuel elements. Four typical neutron spectra – thermal, resonance, fast and quasi-spallation – can be provided in the experimental channels by using different configurations of the MYRRHA core in order to assure a large range of the experimental possibilities. In the proposed paper, the evolution of composition of three inert matrix fuel (IMF) targets with a high content of plutonium, americium and curium is analysed during its long term irradiation in two regions of the fast spectrum zone of the MYRRHA ADS. The IMF-target compound consists of (Cm0.1Am0.6Pu04)O1.88 fuel powder and in MgO matrix. MCNPX and ORIGEN-2.2 codes, coupled within the home-made ALEPH code system to use burn-up and problem-dependent neutron spectra, is used to perform the irradiation simulation. The studied operational period is three years subdivided into 9 cycles ( each one consisting of 90 effective full power days of irradiation followed by 30- or 90 days of shut-down for maintenance) and two years of the spent fuel storage. The transmutation potential and the limiting factors of MA burning in the different spectral zones are estimated and discussed.