Effects of thermal-hydraulic feedback on burnup modeling of the deep burn modular high temperature reactor (DB-MHR)

The Deep-Burn concept, developed at General Atomics, investigates the use of commercial high temperature gas-cooled reactors such as modular helium reactors (DB-MHR) to transmute spent fuel from light water reactors (LWRs). An essential feature of this technology is the fabrication of spent fuel into TRISO particles with full transuranic composition to achieve very extensive destruction levels (deep-burn) in a one-pass fuel cycle. In earlier studies, the neutronics behavior of DB-MHR has been analyzed in great detail. However, these studies were performed without considering thermal-hydraulic feedback. Due to the strong temperature influence on the cross sections of transuranics, the coupling between temperature and neutronics is very important to be able to simulate realistic operations of the deep burn reactor. In this study, detailed simulations of the DB-MHR operation are performed with a Monte Carlo code system (MCNP5 + ORIGEN2.2 + MONTEBURNS2 - for neutronics calculations), POKE code (General Atomics, for thermal-hydraulics calculations) and NJOY99 code (for processing nuclear data libraries). Resulting power densities of fuel blocks (from neutronics calculations) are provided as input to the POKE code, which in turn, calculates new temperature distributions. The temperature distributions obtained from POKE are used to update the MCNP input, and NJOY is called to process new nuclear cross sections based on appropriate temperatures. These steps are repeated to calculate the entire burnup performance of the system.