Examination and improvement of the SHEM energy group structure for HTR and deep burn HTR design and analysis

The purpose of this study was to study and improve the SHEM energy group structures (281 and 361) and General Atomics-193 energy group structure utilizing the more systematic, consistent, and sophisticated energy group selection method referred to as contribution and point-wise cross-section driven (CPXSD) method. The SHEM-281 and -361 energy group structures were developed for LWR and General Atomics energy group structure was developed for the fast reactors. Pebble bed and Prismatic hexagonal block type fuel are used for cell analysis. DRAGON transport code was used for this task taking advantage of its capability to compute adjoint fluxes for reactor analysis. MCNP5 was used for generation of the reference solution selected due to its accuracy of neutron transport calculations. Comparisons with DRAGON calculations are presented. Pebble fuel element and Prismatic hexagonal block models were created for both codes. In the DRAGON code, analysis are conducted for the starting energy group structure by computing both forward and adjoint fluxes as well as the reaction rates and k-effective. Then forward and adjoint fluxes were used in computing the importance function of the groups, and the groups with high importance function are subdivided accordingly. The whole energy group interval of interest was divided into fast, epithermal and thermal regions. Firstly, the improvement was done for fast region and a new library was created and applied in the fuel cell analysis until the selected target criteria’s were met (10 pcm relative deviation of Δk/k and 1 percent deviation of reaction rate of interest). Then similar procedure was repeated for epithermal and thermal regions. The dominant parameters for each energy region were considered as required such as the fission cross section for fast region, absorption and scattering cross sections for epithermal region and absorption cross section for thermal region and k-effective applied for all energy regions. Pebble fuel element and the Prismatic hexagonal block were analyzed for depletion based on the improved energy group structure SHEM_TPN-531.