The FUSTIN dedicated computer code has been developed to predict the transient response of pool-type fast reactor components in a core disruptive accident. FUSTIN accurately simulates several complex phenomena, such as large distortions in the fluids, large displacements of the structure, fast transient fluid-structure interaction, etc., involved in determining the transient pressures, vessel displacements, and strains. FUSTIN has been validated by solving a few international benchmark problems. Further, for experimental validation of FUSTIN, dedicated tests were conducted to (a) characterize a low-density explosive that can appropriately simulate the nuclear energy release rate and (b) generate data, particularly deformations in the vessels representing the scaled-down model of the main vessel of a typical pool-type fast reactor. In the tests, the nuclear energy release rate was simulated by a low-density chemical explosive, which has been thoroughly characterized. The validation exercise demonstrates the excellent prediction capability of FUSTIN. The paper presents the mathematical formulations, solution strategy, and validation aspects of FUSTIN.