Overtemperature protection systems for spallation target in China initiative accelerator driven sub-critical system

Abstract In an accelerator driven sub-critical system (ADS), a spallation target is irradiated by high-power proton beam to drive a sub-critical reactor. To continuously produce very intense neutrons, it is very important to prevent the unsafe operation of the target. This paper reports an over-temperature protection system for the spallation target in China initiative ADS system, where tungsten granules in the target container are used as both coolant and target materials. In order to protect the target from abnormal irradiation by the accelerator's beam when the granules are blocked or when the beam deviates from the target center, 12 sets of thermocouples are mounted inside the target container to monitor the target temperature. To evaluate the protection functions of these thermocouples, the heat transfer model of particles has been employed to investigate the spatio-temporal variations of the target temperatures when tungsten granules stay static in the target. The simulation results indicate that the temperatures of the thermocouples increase with the irradiation time and the granular blockage can be detected by analyzing the temperatures of these thermocouples. On the other hand, when the beam center deviates from the target center, the azimuthal distribution of the target temperature becomes non-uniform, and the temperature of the thermocouple close to the beam center increases faster. Finally, in the monitoring system for the over-temperature protection, 12 thermocouples divided into 3 groups which are fixed within the target in the upper, central and lower parts of the target, and 4 thermocouples in each group are located in four directions of east, south, west, and north. If two or more channels of four directions in one group exceed the set point, the protective function of granular blockage will be initiated; if two or more channels in one direction are greater than the set point, the protective function of beam deviation will be triggered.