Modeling of ice formation and condensation on a cryogenic surface

Current designs for next-generation fusion devices feature superconducting magnets for confining and managing the plasma. Often the design also features water as the primary circuit coolant. Thus, a potential accident scenario is steam injection from the primary circuit into the magnets’ cryogenic chamber (cryostat). An important question to be answered for the above scenario is whether the pressure suppression created by the cryogenic surfaces is sufficient to circumvent cryostat damage. Providing an answer to this question is the objective of the Experimental Vacuum Ingress Test Apparatus (EVITA). This paper presents pre-experiment calculations on the ice layer growth and condensation formation within EVITA. The analyses focused on two scenarios: the power of the injected vapor (Ps) equals the removal power of the cryogenic system (Pln) and Pv exceeds Pln. The first scenario produced a pressure increase of 30 mbar for Pv=Pln=10 kW while the second scenario produced pressurization to the 2 bar EVITA limit when Pv=10 and Pln=5 kW. The primary conclusion is that the saturation temperature at 3 mbar and the heat transfer coefficient of the film condensate are important variables since they greatly influence the pressurization.