SCALE (Standardized Computer Analyses for Licensing Evaluation)  is a widely used computational code system that has been developed and maintained by Oak Ridge National Laboratory. The purpose of SCALE is to provide a comprehensive collection of easy-to-use automated calculational sequences for performing accurate analyses of nuclear facilities and transport/ storage package designs. The primary shielding analysis sequence included in SCALE has been the SAS4 sequence that uses the three-dimensional (3-D) Monte Carlo shielding code, MORSE-SGC, along with automated variance reduction techniques specifically designed for spent fuel cask analyses. The SAS4 sequence uses a one-dimensional adjoint XSDRNPM calculation to generate the biasing parameters for MORSE-SGC. SAS4 automatically passes the biasing parameters to MORSE-SGC to perform axial or radial shielding calculations for cylindrical cask-type geometry models.
The SAS4 sequence was created to reduce long computational times. SAS4 is quite successful for a specific class of cask problems, but more complex problems, such as thick shields with streaming paths, demand general 3-D variance reduction.