An economic analysis of a water distillation system for the control of tritium emissions from a nuclear fuel reprocessing plant

An economic analysis was made of a water distillation system which is proposed as a method for controlling tritium emissions from a pilot scale (0.5 MTHM/day) nuclear fuel reprocessing plant. The system examined used high efficiency column packing (Sulzer type BX) and a vapor recompression scheme to reduce the energy requirements of the system. An optimization procedure was developed that calculates the values of two optimization parameters, column vapor rate and operating pressure, which result in a minimum value for the system annualized cost. The optimum conditions are calculated for a base case for which a specific set of system constraints is assumed. The optimization procedure is also used to perform a sensitivity analysis that examines how changes in key system parameters and constraints affect the system annualized cost.

There were no problems identified in the analysis that would pre-vent the use of the water distillation process for the above application. The analysis showed that the system operates most economically under a vacuum as reported in the literature. The optimum operating pressure calculated for the various cases ranged from 55 mmHg to 65 mmHg. The analysis also showed that vapor recompression does significantly reduce the energy requirements of this system. The power required by the vapor compressor represented slightly less than 10 percent of the reboiler heat load.

Results of the base case calculation indicate that the most significant costs, in order of significance, are building cost, column cost, and column packing cost. The sensitivity analysis showed that changes in the building and packing unit volume costs caused significant changes in the system annualized cost. Of the three system constraints examined that effect the material balance, changes in the plant excess water caused the most significant changes in the system annualized cost.