Calculations of radiation levels during reactor operations for safeguard inspections

Abstract

It is necessary to calculate the total level of radioactivity produced by the reactor operation when the reactor cover is opened during periodical safeguard inspections for safety requirements. Also the calculations are performed for different reactor core and spent fuel storage loadings during refuelling after reactor shutdown. When an internal core spent fuel storage is used in the shield tank to accommodate a large number of spent fuel baskets, physical calculations are performed to determine the number of these spent fuel elements which can be accommodated and still maintain the gamma activity outside under the permissible limit. The corresponding reactor power level is determined. The radioactivity calculations are performed for this internal storage at different axial levels to avoid the criticality of the reactor core. Transport theory is used in calculations based on collision probability for multi group cell calculations. Diffusion theory is used in three dimensions in the core calculations. The nuclear fuel history is traced and radioactive decay is calculated, since reactor fission products are very sensitive to power level. The radioactivity is calculated with a developed formula based on fuel basket loading integrity.