Quality Assurance Calculations to Support Use of HELIOS Version 1.6 for Plutonium Disposition Studies

In mid-2000, the Reactor Physics Group at Oak Ridge National Laboratory (ORNL) purchased a new version of the HELIOS, assembly-level reactor physics computer program (version 1.6). While the authors of the HELIOS program had performed validation and verification studies and compared results to versions 1.4 and 1.5, geometries and materials similar to those expected for mixed oxide fuel (MOX) in Russian water-water energetic reactors (VVER) had not been investigated. The studies reported in this document are a program-specific supplement to the work performed by the computer program authors and are performed to comply with quality assurance procedures of the Reactor Physics Group of ORNL. There were two goals for these studies. First, quantify the differences in nuclide inventories or other physics parameters, such as multiplication factors, due to the use of version 1.6 instead of 1.4. Second, determine if results from the version 1.6 design library (a 45 energy group library) differed significantly (meaning absolute value of the difference greater than or equal to 1%) from values obtained with the 190 group master library. Changes in nuclide inventories and multiplication factors are dependent on the system studied (whether U.S. or Russian reactors) and the type of fuel (whether low-enriched or mixed oxide). For selected actinides, the differences between the design library for version 1.4 and the master library for version 1.6 can be as high as 15%