Simulation of thermal compensation of the ESS cryogenic moderator system caused by a transient heat load change when the proton beams are turned on or off

Abstract At ESS, the cryogenic moderator system (CMS) provides subcooled liquid hydrogen with a temperature of 17.5 K to two hydrogen moderators, with plans for expansion to four in the future. The CMS removes nuclear heating, which amounts to 6.7 kW fort two moderators and 17.2 kW for four moderators during 5-MW proton beam operations. A large-scale 20 K helium refrigeration system with a cooling capacity of 30.2 kW at 15 K, called Target Moderator CryoPlant (TMCP). It is designed not only to manage a static heat load but also to effectively handle the transient heat load induced by the beam injection. To maintain the stability of the hydrogen supply temperature at 17 K, the cooling power directed toward the CMS will be adjusted by varying a feed flow rate, while the cooling power of the TMCP cold box remains constant. This study investigates the stability of TMCP thermal compensation operation when the rapid thermal fluctuations are applied. A one-dimensional simulation model of the heat exchanger was developed to simulate propagation of the thermal fluctuations resulting from the proton beam injection or trip event. Operational parameters can be optimized to minimize Vluctuations in the hydrogen supply temperature within ±0.1 K.