This report summarizes the efforts of NIA, and more than 100 other participants, to establish a collective understanding of the gaps that exist between the real and anticipated costs and capabilities of advanced nuclear energy technologies and the characterization of those costs and capabilities in prominent energy system modeling efforts; and to outline collectively a set of actions that could be taken by the energy modeling community and the federal government to help close those gaps. The recommendations in the report call for the establishment of an advanced nuclear energy cost and performance database that will be developed, housed, and overseen by a Department of Energy office or national laboratory with expertise in advanced nuclear energy technologies. Moreover, the recommendations call for energy system modelers to update their default system model assumptions to reflect ranges based on advanced nuclear reactor developer survey results and the cost and performance parameters published in recent studies.