SAFETY ASPECTS OF TRITIUM STORAGE IN METAL HYDRIDE FORM

Air or nitrogen ingress accident scenarios into JET tritium storage co ntainers, filled with uranium or intermetallic compound (IMC) hydrides , are discussed based on the experimentally determined kinetics of the reaction of these hydrides with air, O-2 and N-2. Reaction of uranium with air can occur at room temperature. For the initiation of the rea ctions of uranium with N-2 or of some intermetallic compounds with air , elevated temperatures are required. Temperature rises of the metal h ydrides due to air ingress are estimated for various cases. Modern tri tium storage containers are protected against air ingress by intermedi ate and secondary containments which can be either evacuated or filled with inert gas. Therefore, air ingress can only occur due to double f ailure: failure of secondary containment and process containment at th e same time. At JET, the secondary containments are filled with N-2 Ho wever, even for N-2, temperature increases are expected during the ing ress into uranium beds (U-beds) for particular scenarios. It is shown that the JET design would not fail in this event. The calculation also shows that the smallest temperature rises during air, O-2 or N-2 ingr ess are expected for a getter bed design with free space above the met al getter layer for the gas to flow from inlet to outlet tube, because the reaction with the metal powder is limited by the diffusion rate o f the gas through the powder. Estimates with ZrCo as getter are also m ade.