Parametric Studies and Scale-Up of a Cold Trap in the Tritium Extraction Loop of a HCPB Breeder Test Blanket for ITER

The Helium Cooled Pebble Bed (HCPB) Breeder Test Blanket concept of ITER will comprise 3 He circuits for the heat extraction, the coolant purification and the tritium removal generated by nuclear reactions in the lithium orthosilicate. Tritium production in the orthosilicate will inevitably also produce some tritiated water which should be removed from the helium purge gas stream before the extraction of tritium (mainly HT) by passing it through a liquid nitrogen cooled molecular sieve bed. To minimise the amount of adsorbed water in the molecular sieve beds a cryogenic cold trap (CT) will be included in the tritium extraction system (TES). The expected water concentration in this gas stream is of the order of 10 ppm by volume.A cold trap in a technical scale (1/6 of the ITER operating conditions) with design features meeting the requirements for water vapour trapping, i.e. variable cool-down rates and low velocity of the working gas, was used to investigate the water removal efficiency. In this paper we describe the first results obtained with small He throughputs as well as recent results obtained for medium and high He flow rates containing water vapour ranging from 10 to 16 ppm_v.