CALCULATIONS OF RADIATION-LEVELS DURING REACTOR OPERATIONS FOR SAFEGUARD INSPECTIONS

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