ICSI Rm. Valcea is the leading research institute involved in the Romanian heavy water detrititiation program. ICSI has built a Tritium Removal Facility which is an experimental pilot plant for deuterium and tritium separation - its main objectives being to demonstrate detritiation technology followed by implementation at the CANDU nuclear power plant in Cernavoda.

Within isotope separation installations using a cryogenic distillation process, the required gas purity must be high to avoid the risk of impurity condensation. A preferred and recommended purification process is solidifying impurities over a large material area heat exchanger device. Such a system is usually a regenerative type to ensure continuous operation. Gas Purification is achieved either by means of reversible heat exchangers or thermal regenerators.

Reversible exchangers and regenerators have a periodic operation, a warm period and a cold period. During the warm period, the heat exchanger or regenerator mass heat up cooling the purified gas, while in the cold period, the cold waste gas heat up the exchanger or the regenerator.

Essentially, the impurity solidification purification process is the same for both the reversible exchanger and regenerator, but because of their differences the process description will be different and so also the design method. Due to periodic operation of a regenerative system the process is unsteady, its description utilizing highly complex mathematics. For this reason it is of particular interest to have a very well developed mathematical description of non-stationary heat exchange processes, incorporating simultaneous mass and heat exchange processes taking place in the regenerative systems.

This paper presents a conceptual scheme of a purification unit consisting of two stages (the first being a drying system followed by an advanced cryogenic purification). A theoretical analysis of the second stage of the process will be developed. Due to cyclic operation (cooling, retention, cleaning) the process is carried-out in the non-stationary regime, thus the mathematical description is complex but needed to design such a system.

Also presented is a theoretical analysis of the purification of an impurity-laden gas, using the calculation model developed with the proposed regenerative system.