Conceptual issues of cold filter-traps development for sodium coolant purification in fast reactors
Results of investigation of specific features of heat and mass transfer in cold traps for sodium purification from impurities in fast reactor loops performed both in special experimental sections modeling various zones of the trap -isothermal and non- isothermal sedimentation tanks and filters and the final cooling zone, and on prototype trap models are presented. As the result, a scientific justification was formulated for the development of innovative trap design for different reactors. Impurity trapping capacity of such traps is higher than that for the best foreign analogues by 3 – 5 times. Tests of traps demonstrated highly efficient sodium purification from oxygen and hydrogen and significantly lower capacity with respect to corrosion products and carbon. Taking into account that leaks of radioactive sodium during operation of the traps in the primary cooling loop of BN-600 reactor, the decision was made to install the coolant purification system inside the reactor vessel for enhancing the reactor safety. The issue of eliminating accumulation of hydrogen in traps of the primary cooing loop when the reactor is operated in nominal operation mode was resolved. Two designs of a cold trap were suggested - with argon cooling and with sodium cooling. It was demonstrated that 20 replacements of traps are required during the reactor lifespan when the reactor coolant purification system with argon cooling is utilized, with 7 replacements needed if hydrogen accumulation in the cold traps of the primary cooling loop is prevented. The option of sodium-cooled trap built into the reactor vessel has the same overall dimensions as the argon-cooled trap. Cooling sodium is circulated through two cooling paths: up to 30% of the flow rate in the jacket on the outside of the working cavity and up to 70% of the flow along the coil installed inside the working cavity. Based on the calculations using the developed codes for simulating heat and mass transfer processes in the traps the improving technical solutions were proposed.
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