Tritium permeation from the primary helium cooling loop for the ESS target

The tritium permeation from the target cooling primary helium loop to the intermediate water loop through heat exchangers is studied, for the 5 MW operation of the target station at European Spallation Source (ESS). Both bi-metallic and mono-metallic heat exchanger concepts are studied, for the co-current and counter flow cases. The quasi two-dimensional temperature profiles in the helium, in the water and in the metallic barrier separating the two flow regions are calculated. The surface temperature of the metallic barrier facing to the helium side determines the tritium concentration dissolved in this region. The diffusion flux of the surface tritium through the wall thickness is calculated. The permeation rates via these different heat exchanger configurations are compared and a recommendation is made. It is shown that the tritium contamination level in the intermediate cooling loop allows controlled discharge of water to the city sewage system. The methodology presented in this paper can be applied to general engineering analyses of the tritium permeation problems in spallation facilities.