The enrichment section consist of a three stage cascade with a variation that the first stage is superimposed with two stripping columns, one cold and the other hot. This variation is incorporated to increase the recovery of deuterium. Each stage consists of a pair of cold and hot column. The deuterium concentration is maximum in liquid ammonia at the bottom of the cold column and in the synthesis gas at the top of the hot column. Part of these streams are passed to the subsequent stage for further enrichment. The maximum concentration of deuterium in this cascade is in liquid ammonia at the bottom of the third stage column. A part of this stream with D₂O content of 17.5% is withdrawn as product of enrichment section and sent to the final concentration section to produce nuclear grade heavy water.

The enriched liquid ammonia from the enrichment section is first distilled to separate the catalyst potassium amide. The catalyst free liquid ammonia thus obtained is then contacted with demineralised water in an ammonia water exchange column which operates at 2 kg./cm². Part of the deuterium in ammonia lets transferred to water. The lean ammonia, after transferring deuterium to water is recovered and after mixing with the separated catalyst is recycled to the enrichment section. Water enriched in deuterium, after separation from ammonia is distilled to produce nuclear grade heavy water.

The power supply to the plant is provided by Orissa State Electricity from their 132 KV grid. Steam, Nitrogen & Make-up water required for the operation of the plant is supplied by FCI.

Some of the special features of the plant include the following:

i) HWP (Talcher) is the only plant in the world based on NH₃-H₂ exchange (Bithermal) process. Apart from problems relating to process design engineering there were several mechanical engineering problems to be solved. The isotopic exchange section of the plant operates at a pressure of 320 kg/cm² and at two temperature levels of -30 deg. C. & +65 deg.C. The purification and the transfer section of the plant operates at the operating pressure of the ammonia plant and is designed for 250 kg/cm², at a temperature of -30 deg.C. The operation at high pressure involves thick wall, multi-layer vessel construction and since these towers are operated at low temperatures, this involves use of special materials capable of withstanding such low temperature. The diameter of the exchanger towers (total 11 in no.) are of the order of 2 to 2.5 m and of approx. 40 m in height. The maximum weight of a single tower is approx. 350 tonnes.

ii) All exchange towers are equipped with special sieve trays, which are of conventional design and fabricated indigenously. According to the special features of the system with regard to the low kinetics of the reaction and the hydro-dynamic characterisation of the fluids, the design of the sieve trays differs from the design normally used for distillation.

Testing and precommissioning of the plant which started in beginning of 1980 has been held up due to non-availability of power to the plant as well as to the fertilizer plant and non-availability of synthesis gas from Ammonia Plant.

As and when synthesis gas and other inputs were available, several trial runs of the plant were performed. Production of heavy water commenced for the first time on 24th October 1984. However, sustained production from this plant could not be achieved so far due to various external and internal constraints.

Several modifications and changes in operating procedures have been incorporated during this period for improving the performance of the plant. However, the efficacy of all these modifications can be fully evaluated only when the plant is run continuously without any external constraints, viz. interruption of feed gas, steam and power supply.