Analysis of long duration subassembly accidents

The evaluation of the safety aspects of the subassembly configuration of liquid metal fast breeder reactors (LMFBR), requires that effective numerical procedures be available for both short and long duration loadings. Some of the postulated accidents are characterized by rapid load variations followed by very steady loads, whereas other accidents are characterized by loads of a quasi-static nature. The existing STRAW (Structural Transient Response of Assembly Wrappers) code includes only explicit integration in time. Hence, the time step is limited to a percentage (50% to 80%) of the highest frequency of the mesh. An implicit integration option has been added to STRAW. The implicit integration option was added to STRAW, rather than being developed as a separate code, for the following reasons. (1) it permits the same analysis to be performed partially with an explicit temporal integration and partially with an implicit temporal integration in the same computer run, and (2) it permits part of the mesh to be handled with the explicit-part with implicit integration. (Auth.)