Core Layout

A previous nuclear engineering project by Jonathan Schattke was a signficant contribution to the Missouri University of Science and Technology Lead Fast Reactor team in 2013.
Jonathan was head of the heat transfer team, one of two MCNP modelers for the core design team, and part of the economics team.
Part of the Design report is included here.

This SMR consists of a reactor pressure vessel and a secondary side for the conversion of
thermal energy to electricity. The pressure vessel is cylindrical with a hemispherical bottom and
flat top. The core sits near the bottom, 1.5 meters above the absolute lowest point. A heat
exchanger consisting of coiled pipes within the pressure vessel has its center 10 meters above
the center of the core. This height difference is because natural convection drives the flow of
primary coolant from the core to the heat exchanger.

A secondary coolant flows within the heat exchanger and is heated by the primary coolant
flowing over the outside surfaces of the heat exchanger pipes. The secondary coolant then
passes through a Brayton cycle to convert the thermal energy into electricity. In this process,
the secondary fluid turns a turbine, then gives off heat through a regenerator and radiator,
then is compressed and gains heat through the regenerator before returning to the heat
exchanger within the pressure vessel, starting the process over again.

The primary coolant is Lead Bismuth Eutectic (LBE) as a primary coolant. It is heated by the core
and natural convection will move it upward toward a heat exchanger. This heat exchanger
consists of 4 pipes that circle within the core 2.5 times. The secondary fluid is supercritical
carbon dioxide (SC-CO2). This process is described in more detail in section V, heat transfer and
fluid flow.

The nuclear fuel which provides the thermal energy is thorium based. Specifically, it is thorium
nitride. The thorium will breed 233U, which is fissile. In addition to the thorium nitride, a driver
fuel consisting of uranium nitride is used to obtain initial criticality. In order to breed, this SMR
operates with a fast neutron spectrum. This topic is further discussed in section VI, criticality.
Table 4.1 includes some basic data about the SMR.

Table 4.1: Main characteristics of this SMR

Power 25 MWe
Thermal efficiency 46.5%
Primary coolant circulation Natural
Fuel Thorium Mononitride (ThN) with a Uranium Mononitride (UN) driver
Primary coolant 44.5 % Lead-Bismuth Eutectic (LBE)
Secondary coolant Supercritical Carbon Dioxide (SC-CO2)
Core height 1.40 m
Fuel pin diameter 16.9 mm
Clad thickness 1.07 mm
Rod pitch  18.3 mm
Number of fuel elements per assembly  54
Number of assemblies  151
Breeding ratio  1.0166
Pressure vessel height  13.5 m
Clad material  T91 with SiC coating
Heat exchanger  Helical pipes suspended in pool
Control rod material  Boron carbide (B4C)