Progress of Cryogenics and Isotopes Separation , ISSN: 1582-2575
2005, Volume 8, Issue 15+16

Operating Optimization of the Cernavoda NPP Heavy Water Upgrading Systems by Using PC Simulation Programs

Abstract

Heavy water used in CANDU nuclear power plants as moderator or primary coolant degrades as a result of thermonuclear reactions and chemical purification process. Concentrations below 99.75% D₂O for the moderator and 97.5% D₂O for the primary coolant may cause a low operating efficiency of the CANDU reactor. For this reason heavy water is upgraded by using the vacuum distillation process, therefore Cernavoda Nuclear power plant is provided with two upgrading systems. Since the distillation columns packing did not met the initial design intent, the two systems were serially connected through a temporary modification in order to increase the upgrading efficiency. Operating mode was changed to upgrade alternatively moderator and coolant D₂O. Simulation programs were developed in order to evaluate and optimize the production capacity of the coupled systems. The paper presents the mathematical model and software developed in order to determine optimal operation conditions for the serially connected heavy water upgrading plants, momentary operating evaluation and solutions to maintain a constantly improved production level. The simulation describes accurately the steady-state distillation process and will be a very useful tool for optimal plant operation when the two systems shall be permanently connected in series.