CFD simulation of pressure wave propagation in the helium coolant tube break accident of DFLL-TBM

•Pressure wave propagation in the DFLL-TBM due to the In-box LOCA were studied.•The maximum pressure during the accident is even higher than the operating pressure of helium and its value is related to the location of the break.•The longer distance between the break and the farthest inlet/outlet, the higher the peak pressure.•Compared to the small size break accident, the pressure variation in TBM is more intense in large break accident.