The Japan Atomic Energy Agency and the High-Energy Accelerator Research Organization are collaborating in the construction of the Japan Proton Accelerator Research Complex, a high-intensity proton accelerator complex with MW beam power. The use of various secondary particle beams (neutrons, mesons, antiprotons, etc.) that are produced in proton-nucleus reactions is the prime purpose of the project. Accordingly, four science experimental facilities are being constructed, including a materials and life science experimental facility, a nuclear and particle experimental facility, a neutrino experimental facility, and a nuclear transmutation facility (planned for the future). At the materials and life science experimental facility, where materials or biological structures are analyzed by neutron beam scattering experiments, a spallation neutron source has been constructed to provide experiment users with neutron beams that have the world's highest pulse intensity. Neutrons produced using spallation reaction should possess a high energy of MeV order, but neutrons used for experiments should have energy of a low meV order. Therefore, an effective material that is capable of moderating neutron energy by approximately nine orders is required. That material is supercritical hydrogen; and the spallation neutron source should therefore be equipped with a cryogenic hydrogen system that provides supercritical hydrogen to the neutron energy moderating system. This paper discusses the spallation neutron source and introduces the cryogenic hydrogen system that is used for constructing the neutron source.
The Japan Atomic Energy Agency has been constructing the Japan Proton Accelerator Research Complex (J-PARC), a high intensity proton accelerator complex with MW beam power, in collaboration with the High-Energy Accelerator Research Organization. The materials and life science experimental facility (MLF), where materials and biological structures are analyzed using neutron beam-scattering experiment, has been constructed as one of the experimental science facilities at J-PARC. A spallation neutron source that produces neutrons through nuclear spallation reaction using high-energy proton beam injection and provides neutron beams for experimental users has been installed at the MLF. Hydrogen nuclei are used as a neutron moderating material (moderator) to reduce the neutron energy from MeV to meV order. Therefore, a cryogenic hydrogen system should be installed at the spallation neutron source to provide supercritical hydrogen to moderators. This paper describes the safety design of the cryogenic hydrogen system. Especially, the system is subject to high-pressure gas safety laws, and refrigeration safety regulations are applied to the system for the first time. We also discuss the technical contents that were argued through this application.