Impacts from Change of Dose Equivalent Iodine for Fission Products on Pressurized Water Reactor Design

Fission products are important radiation source in Pressurized Water Reactor that could have significant contribution to exposure of workers and public, hence should be carefully paid attention to during radiation shielding design and plant operation management. The widely applied practice to consider the design basis of fission products in reactor coolant for Pressurized Water Reactor is to calculate the radioactivity concentration of fission products under assumption of 0.25% fuel failures and normalized to Dose Equivalent Iodine of 37GBq/t I-131eq. This practice has been proved overconservative especially with improvement on fuel manufacture (i.e. reliability of fuel cladding and management of surface contamination with uranium of fuel), plant design and operation management in recent decades, leading to large cost on radiation shielding but not enough pressure on promoting the operation management performance. This paper seeks for potential improvement on consideration of the design basis of fission products for Pressurized Water Reactor. The potential impacts from taking a lower Dose Equivalent Iodine, e.g. 16GBq/t I-131eq, which has been proved adequate for the UK HPR1000, instead of 37GBq/t I-131eq as design basis for fission products in reactor coolant have been analyzed. Significance benefits on reduction of shielding cost (lower requirements on shielding walls, shielding doors, bio-shield sealing material for penetrations and valve remote transmission mechanism) and structure and component cost (lower requirements on radiation dose resistance) and accessibility in terms of radiation safety management with actually reasonably pressure on improving plant operation management have been recognized. It is hence fit for purpose to seek for optimizing the design basis of Dose Equivalent Iodine for fission products design basis to an adequate conservative level to reflect the improvement on fuel manufacture, plant design and operation management and enhance the economic viability of nuclear power plant.