3D space-time analysis of ATWS in compact high temperature reactor with integrated thermal-hydraulic model in code ARCH-TH

The Compact High Temperature Reactor (CHTR) is being designed as a technology demonstrator for comprehensive Indian high temperature reactor programme for hydrogen production and similar process heat applications. The 100 kWth CHTR core consists of 233U-Th based TRISO coated fuel particles, BeO moderator and LBE coolant with natural circulation in vertical prismatic fuel assemblies. The CHTR being a new conceptual design, necessitates comprehensive integrated Neutronics/Thermal-Hydraulics (N-TH) analyses and study. For design and safety studies, 3D space-time analyses of anticipated transient without scram (ATWS) in CHTR have been carried out in detail with indigenous code system with various cases of temperature feedbacks. One of the striking features observed in the analysis is that in case of weak Doppler feedback due to high fissile content and high temperature core conditions in CHTR, the BeO moderator plays a crucial role to limit the rise in nuclear power as well as peak fuel and coolant temperatures during such transient. For these studies, 1D-radial heat conduction in multi-channel based TH module has been developed in 3D space-time code ARCH. The viability of neutronics and adiabatic Doppler feedback capability of the code has also been examined with AER benchmark problems (AER-DYN01 & 02) and results are discussed. The analysis shows that the transient peak fuel and coolant temperatures are limiting at values much below the fuel safety criteria of TRISO particle (∼1600 °C) and boiling point of LBE coolant (1670 °C) even with scram failure. The significance of temperature feedback effects of BeO moderator in CHTR is seems to be a first of its kind observation and is not reported in the literature.