Activation characteristics of the fusion pwer plant coolants He, water, Pb-Li and aspects of Tritium extraction techniques

This paper presents the activation characteristics of the helium, water and Pb-Li coolants when employed in the HCPB, DCLL and WCLL DEMO power plants. Related activation analyses were performed on the basis of coupled MCNP transport and FISPACT inventory calculations using 3D DEMO models developed within the PPPT programme. The He coolant shows a very low activity level with no emission of gamma radiation. The water coolant shows a very high activity and gamma radiation level during plant operation and shortly after shut-down due to the radionuclide ¹⁶N generated from ¹⁶O. This results in a permanent γ-radiation source in the entire water loop during plant operation. The Pb-Li coolant acts also as breeder material and thus shows a high activity level due to the tritium generated. Without considering tritium, the activation level is significantly lower and is dominated by Pb activation products. The generation (and potential release) of ²¹⁰Po is of serious concern requiring possibly the continuous extraction of the Bi produced from the irradiated Pb-Li. Furthermore, some aspects of the tritium extraction from the considered coolants are presented. Tritium will be produced in large amounts in the Pb-Li coolant which serves also as tritium breeding material. Small quantities may be present in the helium or the water coolant due to permeation processes. A preliminary evaluation as far as tritium permeation in the WCLL, HCLL, HCPB and DCLL is concerned is introduced. A critical review of the technologies that have the potential for the industrialization at DEMO conditions and the features of the implementation in the coolant systems is presented as well. (author)