Decontamination of Sodium in the Primary Circuit of Fast Sodium-Cooled Reactors

Invaluable experience of the designing, construction, and operation of sodium-cooled fast reactors, of prolongation of their lifetime, and of their decommissioning has been accumulated in Russia. The BN-600 reactor facility is being prepared for repeated prolongation of the lifetime up to the year 2040. The problem of preparing BN-600 for the decommissioning becomes topical, because this final step of the life cycle of the power unit is time-, material-, and labor-consuming and requires expensive measures for reducing dose loads, the more so as this reactor type is unique. To reduce these expenditures, it is necessary to choose the most effective technologies. Problems of sodium pretreatment to remove radioactive impurities and thus to minimize the staff dose loads when draining the BN-600 sodium coolant and decommissioning the reactor facility are being discussed today. The paper presents data on the radioactive contamination of hot and cold parts of sodium circuits and on the ways of sodium treatment to remove impurities. The processes of sodium decontamination from cesium with MAVR small adsorbers and cesium-accumulating traps are considered in detail for the BN-350 reactor facility as example. The paper objectives are to inform specialists on the experience on treatment of sodium from the primary circuit and to recommend the positively assessed technologies. The study is aimed at justifying the need for removing cesium isotopes from sodium as a preliminary step to reduce the staff dose loads prior to the decommissioning of fast sodium-cooled reactors.