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Tritium permeation through Breeding Blanket and Steam Generator heat transfer areas is a crucial aspect for the design of the next generation DEMO fusion power plants. Tritium is generated inside the breeder, dissolves in and permeates through materials, thus leading to a potential hazard for the environment. For this reason it is important to carry out the tritium migration analysis for a specific DEMO blanket configuration in order to predict the released amount of tritium during the plant operation. Unfortunately, tritium assessments are often affected by several uncertainties implying very important modelling and parametric issues. In this study the main permeation issues are identified and possible solutions are discussed to face the modelling issues and the parametric uncertainties affecting the T migration assessments for the two DEMO helium-cooled breeding blankets, i.e.: 1) Helium-Cooled Pebble Beds (HCPB) and 2) Helium-Cooled Lithium-Lead (HCLL). For these two helium-cooled blanket concepts various tritium migration analyses will be carried out by means of the computational tool FUS-TPC in order to define proper and feasible tritium mitigation techniques which are needed to keep the tritium losses lower than the allowable environmental release (i.e. 20 Ci/d). © 2013 IEEE.

The next generation of fusion power plants (DEMO) should rely on a breeding blanket able to efficiently convert into heat the neutrons kinetics energy, to ensure the tritium self-sufficiency and to adequately shield the Toroidal Field Coils from neutrons and gamma rays. The eutectic lithium-lead alloy is a consolidate liquid blanket material which simultaneously includes the breeder (Li) and the neutron multiplier (Pb). The assessment of the tritium inventory inside the blanket and its environmental release requires the knowledge of the hydrogen isotopes interactions with blanket materials, in particular the hydrogen solubility in lithium-lead which is defined by means of the hydrogen Sievert's constant. Several experiments, aiming to determine the hydrogen isotopes solubility in lithium-lead, have been performed in the past giving values of the temperature-dependent Sieverts' constant, KS, distributed in a wide range (covering about two orders of magnitude on the Arrhenius plot). Starting from a literature review of KS values, this work provides a parametric analysis for the most influencing parameters related to tritium migration in Helium-Cooled and Water-Cooled Lead-Lithium DEMO breeding blankets. This analysis has been performed by using the computational code FUS-TPC for several operative scenarios and considering the different KS values. This study demonstrates that the tritium Sieverts' constant in Pb-17Li has a great impact on the assessment of tritium losses, whose value can spread in more than one order of magnitude. Furthermore, the analysis suggests suitable permeation reduction factors to be adopted in the different scenarios as well as the need of addressing new accurate experiments on the solubility constant. © 2013 IEEE.