Nuclear fuel vendors around the world are pursuing approaches to sustain the existing nuclear reactor fleet con- sisting primarily of pressurized-water reactors (PWRs) and boiling-water reactors (BWRs). To support the industry’s efforts, advanced modeling and simulation tools need to be capable of analyzing both legacy reactor concepts. BWR fuel rods are significantly different than those used in PWRs, which can affect fuel performance analysis. BWR fuel rods include: (1) an extensive use of gadolinia dopant as a burnable absorber, (2) an axial variation in fuel enrichment and gadolinia content, (3) the inclusion of a liner on the inner cladding surface to mitigate the impact of pellet-clad mechanical interaction (which impacts hydrogen and hydride distribution), (4) a lower initial fill gas pressure, (5) bottom-entry control rods, and (6) a lower coolant pressure that results in the two-phase flow boiling phenomenon. Although the primary focus of BISON has been in the area of PWR and advanced reactor fuel analyses, this paper presents the developments in BISON to support BWR fuel performance analysis. An overview of the models that include gadolinia in the fuel performance analysis is highlighted. Novel internal mesh generation functionality for including a liner on the interior cladding surface is presented. Normal operating and transient (reactivity insertion ac- cident) demonstration problems are presented to illustrate the impact of including the burnable absorber, the hydrogen and hydride evolution due to the presence of the liner, and BISON’s ability to simulate axially varying enrichments and dopant concentration. Bottom-entry control effects are captured by the axial power peaking factors present in the demonstration cases. Comparisons to integral experiments from the Halden IFA-681 test series are discussed for initial validation. Reasonable comparisons are obtained for fuel centerline temperature and rod internal pressure as a function of time for the IFA-681 cases. Simulations of additional experiments containing Gd2O3-bearing fuel are necessary to completely validate the code for BWR applications.
