MSR Review

MSR Review - Appendix A
MSR 4 – Seaborg Technologies – Seaborg Waste Burner (SWaB)
The SWaB prototype proposal is a 50MWth single fluid reactor that operates in the thermalepithermal
spectrum. It is graphite moderated and fuelled by a combination of spent nuclear fuel
and thorium. The design team based in Denmark, is a combination of physicists and chemists
from the Niels Bohr Institute and the Technical University of Denmark.
The fuel salt is a lithium-7 fluoride with dissolved thorium and fissile actinides from spent nuclear
fuel. This is pumped through the graphite core and heat exchanger into a hold tank which is an
important safety device. In most accident scenarios the fuel flows from this hold tank into a drain
tank where it is rendered subcritical. A ‘freeze valve’ ▲ also exists as a secondary safety feature.
The core itself consists of hexagonal graphite columns through which the fuel salt flows in the
centre. An operating temperature of 700˚C is maintained by a secondary flow of coolant salt.
The reactor relies on a novel, patent pending, on-board chemical fluorination flame reactor,
based on the Fluorex process which can continually extract fission products from the salt during
operation. This reprocessing system can process spent fuel pellets from conventional reactors
whilst removing the uranium for other uses. The system is also used to adjust the fuel levels in the
salt, avoiding the need for control rods. Shut down rods do exist in the core but primary reactivity
control is via the coolant salt pump which changes the temperature of the fuel salt in the core
thus altering reactivity due to its strong negative reactivity coefficient. This is a common feature
to all MSR configurations.
The inner vessel is formed of Hastelloy-N. A second barrier exists around the core and heat
exchanger made of boron carbide clad in Hastelloy-N. This acts as a neutron and heat shield
and as primary containment in the event of an extreme accident scenario where the inner vessel
fails. The core, hold tank and off-gassing system are contained within a Ni-alloy vessel (3rd
barrier). Finally, the core, reprocessing system, and dump tank are contained within a steel dome
under large blocks of concrete underground.
Figure A8
Schematic of reactor
▲ see Glossary
Figure A9
Illustration of SWaB reactor in sealed container style unit
under several concrete slabs
Energy Process Developments Ltd. 50