Heat-treatment and storage technology for spent ion-exchange resins for new-generation nuclear power plants

Abstract

A technology for thermovacuum drying of spent radioactively contaminated ion-exchange resins was developed. It was shown experimentally that thermovacuum drying yields a product suitable for long-term storage and subsequent disposal. Recommendations were made for using NZK and KMZ concrete and metal casks for holding dry, spent, low-and medium-activity ion-exchange resins without additional solidification. Because the volume of the product obtained is greatly reduced, thermovacuum drying will decrease by at least 15-fold (from 100 to 7) the number of casks required for long-term storage and subsequent disposal of spent ion-exchange resins produced in one year of operation of a single VVER-1200 power-generating unit.The development and implementation of new-generation nuclear power plant designs (AES-2006 and promising new nuclear power plants) require optimization of the approach to reprocessing and storage of liquid and solid radwastes. The main problem is to decrease the volume of solid wastes subject to intermediate storage and final disposal, including the liquid wastes obtained from reprocessing and conditioning.One form of liquid wastes produced during the operation of nuclear power plants are spent ion-exchange resins, which are not reprocessed and are stored in the form of pulps in metal casks. These wastes must be reprocessed and conditioned. The main technology under consideration for conditioning ion-exchange resins is inclusions of the resins in a solid matrix, for example, cement [1, 2]. A facility for cementing the filtering materials which have accumulated over more than 30 years of operation of power-generating units is under construction at the Leningradskaya nuclear power plant. Cementing of spent ion-exchange resins is also included in the AES-2006 designs. Spent resins as well as the bottoms of an evaporation facility are supposed to be immediately solidified. The AES-2006 design provides a facility for cementing spent ion-changers in non-retrievable NZK-150-1,5P protective casks.For all the advantages of cementing as a method of conditioning spent ion-exchangers, there are drawbacks, one of which is the several-fold larger volume of the conditioned product. In reality, 10-15% ion-exchanger is incorporated into cement [1] and the maximum attainable inclusion does not exceed 25% [2]. The casks with the cement compound must be stored for a long time on site in a solid-wastes repository at the nuclear power plant followed by disposal at regional points, which increases considerably the cost of these stages in the handling of ion-exchange resins. According to design data from the St. Petersburg State Research and Design Institute ATOMENERGOPROEKT (SPbAEP), the yearly volume of mediumlevel ion-exchange resins from one unit of the Leningradskaya NPP-2 will be 15 m 3 , the volume of low-level resins will be 10 m 3 , and the specific activity of both will be 100 and <0.37 GBq/m 3 , respectively. The radionuclide composition of the medium-level ion-exchange resins is as follows, %: 60