Thermal analysis of irradiated secondary neutron source assembly with wet transportation

The irradiated secondary neutron source assembly can be used to start-up reactors. After irradiated, secondary neutron source assembly will produce neutron and γ. So, when used to start-up reactors, it is necessary to transport the irradiated secondary neutron source assembly to the target nuclear power unit safely. The irradiated secondary neutron source assembly can be transferred between reactor units by using spent fuel assembly cask. Thermal analysis of wet and dry transportation of irradiated secondary neutron source assembly with a spent fuel transport cask was carried out under normal and accident conditions. The calculation model was validated by the results of safety analysis report of the cask. Under both normal and accident conditions, most of the result errors of this paper are within the range of ±5 %. The calculation result of 4 secondary neutron source assemblies located in the 4 central fuel tube cells of the spent fuel transport cask show that, under normal conditions of wet transportation, the peak temperature of the secondary neutron source assembly rod is about 180 °C, which is about 100 °C lower than that of the dry transportation. Due to the high specific heat of water, temperatures of different parts under wet transport conditions fluctuate at more narrow range than those under dry transport conditions. The peak temperature of the rods is 314.4 °C reached at about 12.7 h after accident under dry transport conditions, while the peak temperature of the rods is 210.7 °C reached at about 38.6 h after accident under wet transport conditions. Compared with dry transportation, wet transportation can not only simplify the process of draining and drying, but also significantly shorten the operation time. Base on the engineering practice experiences, the wet transportation will save about 24 h and 10 bottles of helium during the draining and drying process.