Blanket is the strategic component in hydrogen fusion energy system, converting nuclear energy of hydrogen nuclei to thermal energy which could be further transported for the production of electricity. In order to investigate blanket transient behaviors induced by the in-box LOCA (Loss of Coolant Accident), a code named LBBFoam for high pressure compressible multi-phase flow is developed based on OpenFOAM, which is capable of simulating accident-induced pressure wave propagation in the blanket module. Two classic one dimension shock tube cases were simulated to verify the code. With this code, three scenarios with 8 MPa helium injection into PbLi in a blanket-like container were analyzed to capture pressure oscillation and bubble transportation characteristics. It is found that the maximum pressure in the PbLi zone exceeds and even doubles the helium injection pressure due to the reflection and superposition of pressure waves. This suggests that the traditional structural safety design limits of helium cooled PbLi blanket, which is usually set as the operating pressure of helium coolant, would be too low considering pressure wave superposition. This code will provide an assessment tool for the structural safety of blanket. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.