Storage and concentration of plutonium and uranium solutions in LES 401 hot cell (ATALANTE) - criticality safety considerations

International audienceATALANTE is one of the main Nuclear Facilities of the French Alternative Energies and Atomic Energy Commission, located in Marcoule. The hot cell LES 401 was built in the 1980’s and, since then, had been operated only with low masses of fissile material. As part of the optimizing of the management of the purified Uranium and Plutonium solutions (“Fin U Pu” Project), the new functions provided in LES 401 are now expected to be the following ones: • Receiving Uranium and Plutonium solutions, • Concentration of these solutions, • Storage of the concentrates and distillates. From the criticality safety point of view, the equipment was originally designed in safe geometry for Plutonium Nitrate, considering only a 2.5 cm-thick water reflector. However, the new criticality safety case had to take into account the following points: • Receiving Plutonium solutions, but also highly enriched Uranium solutions, • Considering the flood risk as a possible contingency, • Considering precipitation as a possible contingency. These more conservative assumptions have led to introduce, in addition to the geometry control mode, a mass limit in the cell. For the equipment containing very low concentrations of fissile material in normal operation, it was necessary, using the double contingency principle, to take into account a concentration limit, in the specific situation of water flooding of the cell. At least, given the mass and geometry control mode, it was necessary to perform all the calculations with both fissile media (Plutonium and Uranium), as it was found that the most penalizing media is not always the same, depending on the selected mass, geometry, and reflection conditions