Activation product transport using TRACT: ORE estimation of a generic cooling loop under SEAFP-99 conditions

Occupational radiation exposure (ORE) from the gradual activation of the primary cooling loops with time in fusion power stations and experimental devices is one of the safety and environmental issues. As part of the European safety and environmental assessment of fusion power study (SEAFP) the time-dependent activation transport and deposition code transport of activation (TRACT) was used to predict the behaviour of soluble ions, crud particles and the resulting activity levels. Coolant and pipe surface atomic and activity concentrations are calculated for a simplified cooling loop using SEAFP-2 related thermal–hydraulic data, for the water-cooled lithium–lead (WCLL) blanket concept using low activation martensitic steel. It is determined that ∼12 ml/kg of dissolved H2 are required for the suppression of radiolysis. During plant operation the doses at contact and 1 m away would both be dominated by the active long-lived nuclides in the coolant. After ∼8 days from shutdown the dose values become 1303 man mSv/year (contact) and 27 man mSv/year (1 m away). The implied collective dose rate, if unmitigated, would be roughly six times higher than the value reported for modern PWR plants. The analysis indicates that the time and temperature dependent corrosion rate must be known, as well as the way the cooling loop will be operated, to minimise activation product effects and ORE.