SASSI is the System for Analysis of Soil-Structure Interaction, a computer code for performing finite element analyses of soil-structure interaction during seismic ground motions.  It was first developed at the University of California-Berkeley in 1981.  SASSI is widely used within DOE and the commercial nuclear industry to analyze the effect of seismic ground motions on structures.  Its outputs can play a key role in the seismic design of facilities.  Since SASSI was first developed, several organizations and individuals have developed modified, proprietary versions.  In 2010, SASSI was found to sometimes produce spurious results, especially when executed using what is known as the subtraction method.  While investigating this issue, CNS staff noted that the quality assurance pedigree of the code and its verification and validation history was not fully traceable.  The DNFSB became equally concerned about the use of SASSI within DOE, as expressed in their letter to DOE dated April 8, 2011.  CNS subsequently commissioned several SASSI experts to examine the issues with the subtraction method and develop a suite of test problems that can be used to validate that SASSI meets its expectations.  These test problems and solutions can provide users with greater assurance that their SASSI results are reliable for a given site. The test problems and solutions are included in the engineering calculations, associated digital files, and supporting documents accessible through the DOE SASSI V&V Project web site hosted on the external server.

On August 20, 2015, the CNS issued a guidance memorandum to all EM field offices.  The memo summarizes the SASSI V&V project and discusses software quality assurance requirements applicable to SASSI.