Design Result of the Cryogenic Hydrogen Circulation System for 1 MW Pulse Spallation Neutron Source (JSNS) in J-PARC

A cryogenic hydrogen circulation system to cool cryogenic hydrogen moderators for the spallation neutron source in J-PARC has been designed. This system consists of a helium refrigerator system and a hydrogen circulation system. The refrigeration capacity required for the cryogenic system is specified to be around 6 kW at 17 K. The hydrogen circulation system is composed of a hydrogen-helium heat exchanger, two circulation pumps, multiple transfer lines, three moderator vessels, an Ortho-Para hydrogen converter, an accumulator, a heater and others. The system adopts a centrifugal-type hydrogen pump that can circulate the cryogenic hydrogen (20 K, 0.5 to 1.5 MPa) with the mass flow up to 162 g/s through the three moderators. This forced-flow circulation can remove the nuclear heating from the moderators and can keep the temperature difference through the moderators within 3 K. The Ortho-Para hydrogen converter will be installed to maintain the Para-hydrogen concentration of more than 99% at the inlet of the moderators. For the pressure changes due to the proton beam being turned on and off, we will prepare an accumulator and a heater, which is called a hybrid pressure control. The cryogenic system has been designed with safety concepts that protect the public.