A new computer program, PLENUM-2A, has been developed to predict the conditions in the outlet plenum of a liquid-metal fast breeder reactor after a transient scram. This program divides the transient into three main consecutive discrete states. Two additional stages, one occurring before the transient begins and the other occurring as the transient ends, are also considered. The three main stages are described in detail, and calculations and experimental results are compared. The agreement between the calculations and experimental data is very good.