Minimisation of the Hydrogenic Inventory of the ITER Neutral Beamline and Torus Cryo-Sorption Pumps

The tritium inventory of all the ITER torus cryopumps open to the vacuum vessel has an administrative limit of 120 g, including tritium bound to hydrocarbon compounds formed by combination of fuel gas with carbon plasma-facing components. The total hydrogenic inventory of each of the torus cryopumps has to be less than that resulting in a deflagration pressure of 0.2 MPa (the design pressure of the ITER vacuum vessel of which the torus and neutral beam cryopump pressure boundaries are a part) following a hydrogen-air ignition. Since the neutral beamline fuelling is with protium and deuterium only, these pumps do not significantly contribute to the 120 g tritium limit. The hydrogenic inventories of both the torus and neutral beam cryopumps add to the total for the vacuum vessel following an in-vessel ingress of coolant from a failed water-cooled component, wherein hydrogen is produced from steam reacting with hot metallic dust. There is therefore a large incentive to keep the peak inventories of both the torus and neutral beamline cryopumps as low as practicable. The paper describes the regeneration patterns of the torus and neutral beamline cryopumps that are used to attain this goal while achieving the required vacuum conditions commensurate with the reference ITER pulse scenarios