This work presents a methodology of the equal forced time step for generating accident scenarios in a time-dependent dynamic sequence. The aim is to model DPSA and system reliability of a simple hold-up tank which is a good representative of a steam generator — a component in the secondary loop of a nuclear power plant. This was achieved based on some predicted theoretical calculations on node generating conditions and the cumulative probability of partial failure mode. The computer language Python 3.0 was employed to establish a dynamic event tree of 20 equal time steps (h), the total number of 7367 nodes, 4882 failed nodes for various types of potential accidents. Also, various types of failures and the cumulative probabilities of 0.13 were generated. The program modeled cumulative probabilities and associated errors. However, there is a need to improve and refine the methodology to consider physical parameters such as temperature, pressure, etc. as these are factors that can lead to calculation termination. This will boost the program efficiency and utilize the information extracted from the dynamic event tree in the analysis of the dynamic characteristics. Although extra efforts and improvement still be needed to refine produced accident scenario results, the presented methodology has satisfactorily handled the example.