Analysis of Calculation Model for Primary Coolant Fission Products

Abstract

The sources of radioactive contamination of the primary coolant by fission products when the unit is operating at the rated power are as follows: defect fuel elements with gas leakiness and substantial damages, surface contamination of the outer surfaces of fuel claddings, superficial contamination of structural materials of fuel assemblies. Initially in the reactor operation (if there are no manufacturing defects in fuel elements), the contamination of the coolant by fission products is determined by the release into the reactor coolant circuit of fission fragments of Uranium-235 (due to their kinetic energy) that is present on the outer surfaces of fuel elements as contamination in their manufacturing. During normal operation of the reactor, the integrity of cladding may fail due to various processes of corrosion fatigue type. These processes result in, first of all, micro-fissures and then in large defects in the claddings, which is accompanied by an increase in the release of fission products from fuel elements into the primary coolant.