[en] The Seismic Safety Margins Research Program (SSMRP) is a NRC-funded, multi-year program conducted by Lawrence Livermore National Laboratory (LLNL). One of the goals of the program is to develop a complete, fully coupled analysis procedure (including methods and computer codes) for estimating the risk of an earthquake-caused radioactive release from commercial nuclear power plant. The analysis procedure is based upon a state-of-the-art evaluation of the current seismic analysis design process and explicitly includes the uncertainties inherent in such a process. The results will be used to improve seismic licensing requirements for nuclear power plants. In Phase I, a probabilistic computational procedure was developed for the seismic safety assessment. In Phase II, sensitivity studies were performed, codes and models were improved, and analysis of the Zion plant was completed