The ITER ventilation system adds air at the top and exhausts it from the bottom of the room to avoid rapid spreading of tritium into the ventilation system. The ITER strategy of double confinement and inertization keeps the probability of hydrogen explosion below design base values; however, for hypothetical hydrogen releases, the rising of hydrogen to the ceiling and spreading in a layer along the ceiling is modeled, to estimate the amount of flammable and detonable hydrogen. In the case of high energetic releases, jet dilution and entrainment of hydrogen from the layer by the air jets of the ventilation system as well as by the turbulence of the room atmosphere, limit the build up of flammable hydrogen to <200 mol. For slow releases e.g. continued pumping after line break, plume dilution and air turbulence are small and the amount of hydrogen build up is up to 750 mol D/sub 2/, but for a flow rate more than one order of magnitude higher than the typical ITER flow rate <0.25 mol/sec. Higher flows would lead to a concentration above the detonation limit. Deflagration of the 750 mol leads to an overpressure <0.3 bar, tolerated by the building. The amount of detonable hydrogen stays below 2 mol for the cases considered.

Reference accidents are selected to envelope possible accident sequences to confirm the adequacy of ITER's safety design. Analyses of ITER reference accidents were carried out starting from postulated initiating events (PIE) to all consequential failures including environmental releases, if any. In case of plasma control malfunctioning, up to 3.3GW of fusion power can be reached transiently, however, no radiological consequence is expected from those transients. Assuming multiple first wall pipe failures, the pressure suppression system limits the maximum pressure within the vacuum vessel to below 0.5MPa. Long-term decay heat removal is assured by the vacuum vessel cooling system operating in natural circulation. In case of ex-vessel coolant loss with continued plasma burn, the plasma facing components can potentially reach large temperatures. This is avoided by the fusion power shutdown system that terminates plasma burn. A small in-vessel coolant leak with failure of one vacuum vessel penetration line and several confinement options are investigated to show compliance with release limits. Failures in the magnet system are analyzed and their impact on other systems such as damage to neighboring confinement barriers are investigated by postulating air, water and helium ingress into the cryostat. Failures in the tritium plant are analyzed to demonstrate the adequacy of confinement. Radioactive releases for all reference accidents are shown to be well below conservatively defined design guidelines.

This paper describes the design status of the ITER tritium plant. The key processing requirements and basis for process selection are summarized. Status of the remaining R&D efforts and selection of the process for impurity detritiation are also given.Evaluation studies for preliminary tritium plant processes;were completed during the ITER Conceptual Design Activities (CDA) phase with an emphasis towards use of existing technology and proven industrial applications, where available [1]. Design of systems has continued during the Engineering Design Activities (EDA) phase. Layout designs are now available of most subsystems.

The Tritium Plant design for the ITER Engineering Design Activity (EDA) phase is based on the results of almost 20 years of development effort in support of tritium processing and handling as part of the fusion energy program. During this period there have been many evaluations, investigations, and proposals for tritium processing. This paper presents an overview of the planned design for Torus Exhaust Processing and Hydrogen Storage Systems, including plant layout, and equipment arrangements. Process selection and system design are based on using proven technologies, where available, with emphasis on safety, practical application, reliability, and minimization of tritium inventory. The basis for selection of permeation, instead of the Conceptual Design [1] cryogenic sorption, for initial separation of hydrogen from impurities is highlighted. The importance of continuing and future development activities, including demonstration of the integrated exhaust processing system is also presented.

The design of the ITER tritium systems must ensure that the public is protected from operational and accidental tritium release and that worker exposures are minimized. The ITER public exposure limits are consistent with international recommendations and the As Low As Reasonably achievable (ALARA) concept is being implemented. We describe design approaches that will allow us to achieve these objectives.Although the design is still in its early stages, we have estimated the tritium flows and inventories and have started the safety analysis. Operational and accidental releases from ITER have not yet been determined, but we have used experience from other facilities to estimate ITER releases.

The reaction of hydrogen isotopes with the storage bed hydride material is exothermic during absorption and endothermic during desorption. Therefore, storage bed operation requires a cooling system to remove heat during absorption, and a heating system to add the heat needed for desorption. Three storage bed designs and their associated methods of heating and cooling and accountability are presented within. The first design is the current RTF (Replacement Tritium Facility) nitrogen heating and cooling system. The second design uses natural convection cooling with ambient glove box nitrogen and electrical resistance for heating. This design is referred to as the Naturally Cooled/Electrically Heated (NCEH) design. The third design uses forced convection cooling with ambient glove box nitrogen and electrical resistance for heating. The design is referred to as the Forced Convection Cooled/Electrically Heated (FCCEH) design. In this report the operation, storage bed design, and equipment required for heating, cooling, and accountability of each design are described. The advantages and disadvantages of each design are listed and discussed. Based on the information presented within, it is recommended that the NCEH design be selected for further development.