Evaluation of low pressure leak flows in metallic vacuum vessels for detection systems using helium dissolved in an external water cooling jacket

Vacuum containment vessels are often utilized in industrial and research applications to isolate equipment and experiments from the surrounding environment. The development of leaks in these vessels may result in damage to internal components and facility downtime. The inclusion of a vessel integrity monitoring system (VIMS) in such a facility allows detection of leak formation, characterization of leak size, and provides a tool for the evaluation of the risk for significant damage to the facility with continued operation.The proposed vessel integrity monitoring system (VIMS) evaluated herein utilizes helium dissolved in a water jacket surrounding a vacuum vessel for the detection of leaks. The Water jacket and vacuum vessel that are considered in these analyses are part of athermal management and isolation system for a cold neutron moderator in the High FluxIsotope Reactor. However, the results of the theoretical and computational evaluations are of use to a variety of similar low pressure applications. The concentration of helium in the vacuum vessel is monitored using commercially available Residual Gas Analyzer(RGA) technology to detect leaks as they develop. Conservative system simulations indicate that using existing technology a leak as small as 5 x 10"® m can be detected in less than 3 hours when the vacuum vessel volume is 29 liters or less, demonstrating the feasibility of the proposed system.