Ozone hazard in the ITER cryostat

The occurrence of an ozone explosion in the ITER cryostat area is evaluated. Attention is focused on the possible oxygen sources, since ozone is formed from oxygen by the effect of energy deposited by radiation at low temperatures. Oxygen can accumulate by condensation on the surfaces of the cryogenic superconducting coils, as a consequence of air ingress into the cryostat, and as impurity in the liquid nitrogen contained in the thermal shielding jacket surrounding the vacuum vessel (if liquid nitrogen is used as refrigerant). The risk of an ozone explosion in the LN2 shield seems unlikely because the amount of ozone produced is low and generated over a very large volume. In the design configuration of the ITER cryostat the amount of ozone produced by solid air condensed on the cryosurface has been found to be negligible and distributed over a large area The associated decomposition energy does not seem capable of causing structural damage to the containment. However, even a small release of energy can damage the superconducting coils and the other equipment enclosed in the cryostat which can have serious consequences in terms of outage time and exposure for maintenance.