The proposed reactor design consists of vertical fuel tubes in heavy-water moderator surrounded on the sides, bottom, and top with a heavy-water reflector. The fuel tubes taper in the top and bottom reflector zones to a smaller sized transport tube to convey the molten uranium fuel/coolant between the reactor core and the primary heat exchanger. Most of the core moderator is contained in control cavities, one surrounding each fuel tube. The moderator control cavities are in the form of a very tall ring surrounding each fuel tube. The cavity is closed at the top and opens at the bottom into the bottom reflector zone which in turn opens into the bottom of the side reflector which opens into the top reflector.
The moderator in the cavity is heated by slowing the fast neutrons and is cooled by the flow of cool moderator from the moderator cooling pump. Negative feedback forces the heating rate to match the cooling rate. If the heating rate is higher than the cooling rate there is net boiling and the steam bubble size increases, decreasing keff (the fission multiplication rate) and the fission rate. Conversely, if the cooling rate is greater than the heating rate there is net condensation and the steam bubble size decreases, increasing keff and the fission rate. The steam bubble size is controlled by negative feedback to the size which makes keff equal to one, and the total reactor power follows the moderator cooling rate. If the moderator cooling pump fails or the pump power fails the cooling stops and the reactor quickly shuts down. The reactor control method works by under-moderating excess thermal neutrons which causes them to be absorbed by U-238 in resonance capture, increasing the conversion ratio.
The advantages of this patented control method include improved safety and simplicity of operation, low neutron loss, a flat radial power distribution, and a very wide control range of around 20,000 pcm which allows use of fuel with a wide range of fissile content and fission products. Load following is simple and effective and does not cause any changes in the temperature profile and therefore no thermal shock because the moderator cooling pump, the magnetohydrodynamic (MHD) fuel circulation pump, and the MHD secondary coolant circulation pump change their power in tandem so the fuel temperature range is always 1200 to 1400 degrees C.
page last modified 06/20/2021