STORAGE AND CONCENTRATION OF PLUTONIUM AND URANIUM SOLUTIONS IN LES 401 HOT CELL (ATALANTE) - CRITICALITY SAFETY CONSIDERATIONS

摘要

ATALANTE, located in Marcoule, is one of the main nuclear facilities of the French CEA (Atomic Energy and Alternative Energies Commission). The LES 401 hot cell was built in the 1980s and, since then, has been operating only with low masses of fissile material. As part of the management optimization for purified Uranium and Plutonium solutions ("Fin U Pu" Project), the new functions provided in LES 401 are now expected to be the following: ? Reception of 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: ? Reception of not only Plutonium solutions, but also highly enriched Uranium solutions, ? Considering flood risk as a possible contingency, ? Considering precipitation as a possible contingency. These more conservative assumptions have meant introducing a mass limit for the cell, in addition to the geometry control mode. For the equipment containing very low concentrations of fissile material in normal operation, it was necessary, using the double contingency principle, to take a concentration limit into account in the specific situation of water flooding the cell. Finally, 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 depending on the selected mass, geometry, and reflection conditions, the most penalizing media is not always the same.