Patent Number: 062185926
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to a method and an apparatus for the treatment of radioactive evaporator concentrates from the evaporation system of nuclear plants, which allow efficient separation, as a non-radioactive product, of the sodium sulfate contained therein and, thus, a cost-effective reduction in volume of the concentrates to be decontaminated and disposed. 2. Description of the Related Art In nuclear power plants comprising a boiling water reactor, the main condensate is freed from solid ionic and radiochemical contaminations by means of ion exchange resins. During regeneration of said ion exchange resins with caustic and sulfuric acid, solutions are produced which, after having been neutralized, are conveyed into an evaporating plant, where they are concentrated together with other radioactively loaded effluents to a solids content of about 20%. Thus, depending on the size of the plant, about 20 to 100 m.sup.3 of evaporator concentrates per year are obtained as liquid radioactive waste. The evaporator concentrates contain about 1 to 30% by volume of separable solids (ion exchange resin residues, flocculated detergent residues, heavy metal oxides, fibers etc.). Dissolved components are mainly sodium sulfate, the proportion of which may be about 10 to 25% by weight, and other components, such as incrustation inhibitors (e.g. EDTA), surfactants, organic and inorganic salts of decontaminating agents (e.g. citrates, oxalates, phosphates), activation products and others. In the past, these evaporator concentrates had been further evaporated in a subsequent process step for conditioning and solidified to form a monolithic sodium sulfate block which then proceeded to ultimate waste disposal or interim storage. This, however, has the disadvantage that vast volumes of waste are produced and no decontamination effect is achieved, since radioactive components are encapsulated in the crystals when the sodium sulfate crystallizes. Although 80% or more of the mass to be ultimately disposed of consists of non-radioactive sodium sulfate, according to current practice the latter has to be disposed of in a rather expensive way together with the radioactive components. The suggestions made so far for improving the treatment of evaporator concentrates and similar effluents from nuclear plants were directed to binding the effluent's radioactivity by suitable precipitation or flocculation reactions in such a way that the radioactive products can be removed. The remaining decontaminated solution should then be disposed of as weakly radioactive effluent. The disadvantages thereof were the bad precipitation efficiency, so that said process could not be used in modern nuclear plants due to the associated increase in radioactive release. BRIEF SUMMARY OF THE INVENTION An object of the invention, thus, is to provide a method and an apparatus for the treatment of radioactive evaporator concentrates from nuclear plants, which allow efficient separation of radioactive and non-radioactive components and, thus, a cost-effective reduction in the volume of waste to be disposed. These and other objects are achieved in accordance with the invention by a method for the treatment of radioactive evaporator concentrates from the evaporation system of nuclear plants, wherein (a) the evaporator concentrate is freed from undissolved components, PA1 (b) the sodium sulfate contained in the evaporator concentrate is crystallized as Glauber's salt (Na.sub.2 SO.sub.4.10H.sub.2 O) on an immersion cooler, PA1 (c) the Glauber's salt deposited on the immersion cooler is recrystallized, PA1 (d) optionally, the recrystallization step (c) is repeated once or several times, PA1 (e) essentially inactive sodium sulfate is separated from the process, and PA1 (f) the depleted evaporator concentrate of step (a) is recycled to the evaporation system. The present invention also provides an apparatus for carrying out said method, said apparatus comprising a container for the evaporator concentrate, an immersion cooler having inlet(s) and outlet(s) for a cooling or heating medium, and a cooling or heating aggregate for providing said cooling or heating medium.