Assessment of Concept Feasibility of Combined Electrolysis and Catalytic Exchange in Decontamination of Low Deuterium – Tritiated Heavy Water

Abstract

A CANDU type fission reactor maintains large amounts of heavy water inventory with desired isotopic purity for use in the moderator and coolant circulation loops. But substantial amounts of water escape out of reactor system pressure boundaries and fills into the containment building volume due to normal, off-normal, maintenance and emergency activities in the power station. The heavy water escape poses a radiological hazard owing to the tritium activity and thus needs to be processed in heavy water inventory management units and the nuclear power station effluent treatment facility. These escapes are collected using vapour/liquid recovery systems of power station and processed either in vacuum distillation based upgrading columns or treated directly in liquid effluent treatment units and discharged into environment. Whenever the escapes recovered are small in quantities and low in deuterium isotopic purity, chemical exchange based Combined Electrolysis and Catalytic Exchange process is a more viable option for decontamination over conventional distillation. This paper assesses the concept feasibility of using CECE process as an effective volume reduction method for decontamination of low deuterium-tritiated heavy water. The study proposes a scheme for decontamination considering a base case analysis in a typical CANDU station. It is theoretically proved that in comparison to the dilution methods followed in liquid effluent treatment units of power station, CECE process not only results in the recovery of valuable heavy water, but also in the reduction of diluent requirements by several orders of magnitude. Moreover, similar low radioactivity water effluents are expected during the operation of upcoming fusion reactors like ITER, DEMO facilities, etc. CECE based decontamination system shall be considered as an efficient effluent processing technology for nuclear material accounting and recovery of fuel isotopes in ITER, DEMO facilities also.