Nuclear power innovation |
A thorium molten salt reactor that refuels with fertile rather than fissile fuel
Electricity at $20 per MWh is not just a vision. It’s the likely result in 2035 of the ongoing development by Copenhagen Atomics that will result in probably the most cost efficient and scalable energy source in the world. Key to success is refuelling only with fertile* fuel. Prototype (non-nuclear) reactors are already running in Copenhagen, Denmark, and the next big milestone will be to achieve criticality in a reactor test expected in 2027 in Switzerland. Here’s how the Copenhagen Atomics technology will work and what makes it different from other known reactor designs
Jesper Glahn Copenhagen Atomics
All nuclear reactors built up to now have required refuelling with fissile fuel periodically. And looking to Generation 1 fusion reactors, they will need topping up with both deuterium and tritium. They may have a blanket where tritium is produced but not enough to sustain operation without injecting additional tritium from a 3rd party. Figure 1 shows various reactor technologies grouped by refuelling concept: fissile fuelled with repeated refuelling vs fertile fuelled with just an initial load of ‘kickstarter’ fuel. These are further subdivided according to fuel type. The number of sides of the geometric figures (circle, triangle, etc) denote level of difficulty. Only reactors at the circle and triangle level have ever been built. All fission reactors requiring refuelling with enriched fuel or Pu are in the triangle category. There have been very significant investments in Generation 1 fusion and solid fuel fast reactors hoping to leap across the chasm to the realm of
reactors that only require refuelling with fertile fuel (right hand side of Figure 1).
The fuel cost of fissile fuel is typically several orders of magnitude larger than fertile fuel. The inherent technical challenges to be solved to achieve fertile fuelled reactors are: achievement of excellent neutron economy with minimum leakage of neutrons; minimisation of counterproductive neutron absorption inside the core; and reduction of losses in reprocessing or when moving fissile material from blanket to centre. In this article, we present a new thorium reactor design that is refuelled with fertile fuel (Th232) only. Figure 2 shows the concept, a triple fluid molten salt reactor core operating in the thermal spectrum, having a molten thorium salt as blanket, heavy water as moderator and a molten uranium salt as fuel salt. Ideally, fission only happens in the fuel salt, neutrons are absorbed by the
blanket where Th232 is converted into U233 predominantly. Trace amounts of U232 and U234 are also generated in the blanket. A proprietary system is used to transfer all species of uranium from the blanket to the fuel salt periodically several times per operational hour. Each transfer is a few grams of uranium.
The reactor is designed to output 100 MW of heat and the outer diameter of the Onion Core®
is 2.4 m.
There are two barriers between the hot salt and the unpressurised heavy water and graphite insulation foam is placed in the cavity. The transfer of heat from the hot salts to the water has been measured to be ~35 kW. The majority of the temperature increase in the heavy water originates from neutrons and gammas. 5 - 7% of the total reactor energy is injected into the heavy water and can be used for water desalination or district heating. In order to be able to breed more new fissile fuel than is being consumed, we also need to
Figure 1. Various reactor concepts grouped by fuel type and refuelling requirements. The number of sides of the geometric figures (circle, square, etc) denotes level of difficulty
36 | April 2025|
www.modernpowersystems.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47
