Assessment of radiation dose due to the accidental release of radionuclides from a DCLL reactor

Abstract

A conceptual design for a DEMO fusion reactor based on a dual coolant He/Pb15.7Li breeding blanket (DCLL) is being developed within the Spanish Breeding Blanket Technology Programme: TECNO_FUS. The production of tritium and activation products of LiPb might be a concern from the radiological safety point of view. Thus, in this contribution, an accidental release in atmosphere of radionuclides from LiPb breeder has been studied.Activation calculations have been performed with ACAB code assuming an irradiation scenario of 5 FPY for the maximum neutron fluence rate in the equatorial breeding zone. The results in terms of specific activity, surface gamma dose rate and committed effective dose (CED) due to inhalation at different times have been used to chose the potentially more hazardous radionuclides.Dispersion of the selected radionuclides has been modeled with HOTSPOT code using the Gaussian plume model and two different atmospheric conditions. Offsite dose (for external irradiation and inhalation) due to an accidental release of 1kg of activated LiPb has been calculated after 5 FPY of irradiation (shutdown) using HOTSPOT atmospheric dispersion in class D weather conditions. According to the results, fulfilling the dose requirement for no evacuation would permit to release up to 40kg of activated LiPb, without taking into account the possible isotopic purification and detritiation systems. This value can be compared with the actually released amount in a given accidental scenario for designing the reactor confinement barriers and safety systems.