The Leak Testing of the Helium Purification Pilot Plant. Dragon Project Report

The primary object of the helium purification pilot plant is to study the process of removal of gaseous impurities from helium adopted for the Dragon Reactor Experiment. Purified helium containing residual concentrations varying between 5 vpm and 1 x 10^-4 vpm is circulated through the clean sections of the plant at the pressure and mass flow rate specified for the Dragon purge flow whilst impurities are added at known rates at certain points in the plant. For the success of the experimental programme investigating the performance of the plant accurate accounting of admitted and residual gases is required, consequently a reasonably leak-tight system is essential. To meet this pre-requisite a total leak rate of 30 l per h was considered acceptable [1] at the time of building the plant, i.e., approximately 2.4% per day of the total mass of helium in the pilot plant provided that individual specified leak rates in certain sections of the plant were not exceeded, By comparison the proposed maximum permissible loss of helium from the Dragon Reactor primary circuit which will contain radioactive materials is 0.1% [2] per day or approximately 40 l per h. A leakage of only 0.14 l per h is considered acceptable from the Dragon clean-up plant, i.e. 0.014% per day for a volume of 1,000 l.