Reprocessing of Liquid Radioactive Wastes, from Nuclear Power Generation, in Autonomous Mobile Purification Facilities

Abstract

The necessity for and ways to improve the technology for reprocessing liquid radioactive wastes from nuclear power generation are substantiated taking account of the chemical contaminants (petroleum products and products of corrosion). As a general solution, it is proposed that autonomous modular purification facilities, operating on the principle of combining baromembrane and sorption methods, be developed. The basic scheme of the proposed technology and the construction of the purification facilities are described. The results of industrial tests performed on a tanker for collecting liquid wastes from the Pacific Ocean fleet are presented. It is shown that purification to the level of allowed discharges into the sea is possible and that the radioactive concentrates formed can be solidified by cementation.The general concept of centralized collection and reprocessing of liquid radioactive wastes at the sites of the bases of the nuclear-powered submarine and ice-breaker fleet has proved to be untenable, first and foremost, because it is impossible to follow tractably the overall trend of increasingly stringent radiation-safety requirements. Special vessels (Amur and Pinega) have been developed to collect and reprocess liquid wastes. Their technological operating scheme provided for separate receiving and reprocessing of wastes (purification, concentration of radionuclides, and conditioning of wastes) depending on the form and degree of salinity [1].Water with salt concentration above 1000 mg/liter must be reprocessed using a coagulation-precipitation scheme. Suspensions are removed from water with concentration less than 100 mg/liter using filters and additional purification on ion-exchange filters. The coagulation pulps formed and the spent ion-exchange resins must be incorporated in bitumen compounds for subsequent disposal. Reprocessing using this scheme lowered the concentration of radionuclides in the waters purified to 3.7·10 5 Bq/liter, which met the standards for discharge into the sea in the 1980s, when such facilities were developed. The leaching of radionuclides should be less than 1·10 -4 g/(cm 2 ·day), which at that time was considered to be adequate for disposal at the bottom of the sea.The more stringent requirements for the quality of discharge water, the need for purification to admissable norms for discharge into the sea according to the requirements of first NRB-76/87 and then NRB-99 (to 1.1·10 2 Bq/liter with respect to 137 Cs, to 50 Bq/liter with respect to 90 Sr, and to 4.1·10 2 Bq/liter with respect to 60 Co [2]), and the expansion of the list of wastes which need to be reprocessed required the development of new and more efficient technological schemes. In addition, the technology had to be re-examined from the standpoint of the final stage of solidification of the wastes, since bituminization had to be rejected because of the fire-and explosion hazard of the process and the flammability of the solidified products, which according to modern requirements must be buried on dry land. Conseque...