Dissolution of spent water reactor fuels at the UP3 plant: criticality safety options

The criticality control mode, retained for the UP3 dissolver, that is, ''fissile material mass limitation in limited geometry'', associated in the major part to the burn-up credit, is exposed. The optimisation of the geometrical dimensions of the apparatus, and of the operating conditions in normal running, relating to this control mode, are shown. The various controls associated with the guarantee of minimum fuel irradiation, which are performed before the shearing of the fuel assemblies, are described. Also the principle of the control of the fissile material mass loaded into the dissolver, versus the burn-up, is explained. (author)