The Efficiency of Nuclear Ion Exchange Resins Applied in the Primary Circuit Demineralizers of NPP Krško

Abstract

Chemistry can influence dose rates by two aspects: chemistry conditions applied in the primary circuit and removal of (in)soluble particles. Since the primary coolant activity can have a significant impact on area dose rates and personnel doses, the main objective of purifying the primary coolant is to act on the radioactive source and keep it as low as reasonably achievable. Reduction of occupational exposure maintains confidence among workers and the public. Other factors, such as fuel duty, cycle operation, length and history, materials, steam generator (SG) surface area and particulate redeposition, also have significant contribution to the doses. Ion exchange (IEX) is one of the most common and effective liquid effluents treatment methods in nuclear fuel cycle operations. IEX technology encompasses the sciences of thermodynamics, kinetics, ion chemistry, fluid mechanics, and economics. In the industrial water treatment, cation exchangers are used in combination with downstream anion exchangers or as a mixed bed demineralizer (combination of both cation and anion) for full demineralization. IEX is also an effective treatment method for liquid radioactive waste. In spite of its advanced stage of development, various aspects of ion exchange technology are being studied to improve its efficiency and economy in its application to radioactive waste management and coolant cleaning processes. Over the years desire to improve the efficiency of fine colloidal particles removal and corrosion particulate removal in the primary systems has increased. There is a need for more and more efficient purification in order to decrease worker’s dose during maintenance but also to decrease volumes of radioactive resin waste. Homogenization of products and usage on primary coolant treatment take into account the compromise between source term reductions, liquid and solid waste, and buying and disposal cost. As the disposal costs are much greater than the buying costs, optimization of the lifetime of the purification media, along with an increasing efficiency of pollutant removal is a major goal. One of the effective purification methods for particulate removal is layering of macroporous (MP) resin in clean-up beds, spent fuel pit (SFP) and radwaste beds. Lately, MP resins were also implemented in the primary circuit demineralizers of NPP Krško. The paper evaluates resin purification efficiency of different primary media, and assesses performance of gel and macroporous resin types.