Tag: RBWR

MocDown

Jeffrey Seifried (alumnus)

MocDown (http://jeffseif.github.io/MocDown/) is an efficient tool which loosely couples simulations for neutron transport, isotopic transmutation, thermo-fluids, and the equilibrium core composition search within advanced nuclear reactor cores. The development of MocDown focused on facilitating both fast runtime (by employing concurrent threading and efficient regex parsing when possible) and fast post-processing (with simple and consistent hierarchical storage of result files). MocDown also employs object-oriented programming in Python 3 for flexible modification with external libraries.

To do so, MocDown couples three models for self-consistent simulations: thermo-fluids, neutron transport, and transmutation and recycling. The MocDown accelerated recycling scheme efficiently finds the equilibrium cycle, whose isotopic composition matches that of its successor. Using these techniques, MocDown has been successfully used to simulate the RBWR-Th design, a fuel-self-sustaining nuclear reactor core design which operates with only thorium as its charge.

Thorium-fueled Resource-renewable BWRs (RBWR-Th)

Phillip Gorman, Sandra Bogetic (former), Jeffrey Seifried (alumnus), Christopher Varela (former), Guanheng Zhang (alumnus), Massimiliano Fratoni, Ehud Greenspan

RBWRs are intermediate-spectrum light water reactors (LWRs) that achieve missions normally reserved for sodium fast reactors—fuel sustainability or TRU transmutation with unlimited recycling—while using LWR technology. The spectrum in an RBWR is much harder than in a typical BWR because the fuel is arranged in a tight triangular lattice and the core has a very high exit void fraction. Hitachi developed several designs to achieve these goals using depleted uranium (DU) as the fertile fuel. In order to mitigate the positive void feedback that occurs in high Pu content fuels (such as DU), the Hitachi RBWR designs featured a parfait-style axial design in which the fissile material was loaded into short “seed” sections that were separated by fertile blanket regions. This design led to several safety concerns stemming from the high linear heat rates. At Berkeley, we are investigating using thorium instead of DU as the primary fertile fuel since the number of neutrons emitted per neutron absorbed does not increase with increasing absorbed neutron energy as quickly in U-233 as it does in Pu-239. The change in neutron emissions with energy allows negative void feedback while using a single elongated seed region, which can reduce the linear heat rates.

Results to date have been encouraging. The thorium-fed RBWRs can nearly match the burnup and cycle length of the uranium-fed RBWRs, while featuring much lower linear heat rates and better safety margins. This project is a collaboration between MIT, University of Michigan, and UCB.