Helium / hydrogen refrigeration for the ISIS Second Target Station [ Return towards  References  ]

An appropriate solution for a demanding environment
Air Liquide has built a unit consisting of two helium refrigerators with total cold power of 1,300 W at 20 K, an original liquid hydrogen loop, and two tailor-made cryogenic lines (that can be made in sections remotely) and related components (buffers, compression station, controls). The main problem on the project for the specialist engineers involved has been to meet the demands of customer operating modes, modes that are dictated by the principle of having to operate the facility in highly specialised environments (ATEX radiation and atmosphere).

A comprehensive service provision: from qualifying the moderators to testing the built facilityAir Liquide and ISIS started their collaboration by characterising the hydraulics of the combined Hydrogen/Methane moderator in real conditions on the Sassenage site in July 2005. They then worked together on designing the complete facility. Continuous interaction between teams from Air Liquide and ISIS subsequently ensured that project requirements were satisfied as closely as possible and an overall control device was provided. Air Liquide then manufactured the equipment and assembled it in its test area. The complete system (compression – helium refrigerators – hydrogen loop – moderator – methane distribution system – cryogenic lines) was finally tested and received as meeting customer requirements in April 2007.

There are a number of system operation constraints to be overcome, such as regular pollution by by-products from irradiating the methane by neutrons from the moderators, which has to be eliminated. The system must then be heated very regularly and refrigerated again as quickly as possible to ensure optimum availability of the facility: the hydrogen process has had to be designed as a consequence and equipped with a regulated cold buffer.