remove the majority of fission products outside the lanthanides group.
Figure 3 shows how the Onion Core® is connected
to pipes, pumps, heat exchanger and tanks. The use of a heat exchanger creates three barriers between the radioactive salt and the salt which is sent outside the cocoon to the customer, eg, for electricity generation. The Cocoon wall and the Insulation wall are several meters thick to provide shielding from radiation. When power to the pumps is cut they stop and all liquids (salt & water) drain into their respective dump tanks in 10-300 seconds depending on the volume of each circuit. Cutting the power to the pumps is the primary safety feature. Not all pumps are shown in Figure 3. There is one pump for each of the four channels in the Onion Core®
.
This molten salt reactor is configured such that it can only load follow. This means that the reactor core can only produce the same amount of energy as is removed from the salt circuit leaving the left side of Figure 3. Control rods are not needed and the volume of heavy water in the inner water region can be adjusted to criticality. This type of reactor cannot have a loss of coolant accident with subsequent core meltdown and it cannot have a rapid steam explosion of the type that can be envisaged for PWRs. It also does not have a spent nuclear fuel pool. Figure 4 shows a 25 year burnup simulation of the reactor starting on a 5% enriched uranium fuel salt. It can be seen that the reactor consumes the majority U235 within the first 5 years, while it builds up U233 and plutonium in the fuel salt. It can be seen that ~70% of the power originates from uranium and ~30% originates from plutonium after 5 years. Gradually shifting towards ~85/15 % at 25 years. Every 5 years we siphon off fissile inventory (200 - 500 kg), which can be used to start other reactors. The simulation assumes lithium 7 (Li7) enriched to 99.999% purity and 99.9% deuterium content in the water. Neutron leakage from the reactor core is ~2%.
Figure 2. Cross section view of the Copenhagen Atomics Onion Core® different layers and their temperature
Planned tests
Thermal expansion, thermal cycling and thermal heat transfer have been tested in a full scale prototype non-nuclear rig in Copenhagen. The first nuclear test of the reactor is planned at Paul Scherrer Institute (PSI), Switzerland, in 2027. This first demonstration of criticality seeks to avoid delays by minimising complexity. Therefore, it does not have transfer of uranium from blanket to fuel salt. It does not have the SiC/SiC core envisaged for the commercial offering, and only some of the fission products are removed. For subsequent tests additional features will be added. However, with the first test at PSI, we will be able to validate the accuracy of the
showing the
simulations to a point where uncertainties related to the postponed features become negligible. Already the simulations carry substantial certainty that the Copenhagen Atomics reactor can cross the chasm to fertile fuelled reactors. But the test in 2027 will be the single event where most uncertainty is removed, between now and the point in time at which the first reactor attains 25 y of operation. The uncertainties around the Copenhagen Atomics reactor concept mainly revolve around the use of SiC/SiC materials for core components, Li7 enrichment, online fission product removal and transfer of uranium from blanket to fuel salt. All these concepts are at a low TRL at time
Figure 3. Cross section view of the Copenhagen Atomics fertile fuelled molten salt reactor. Hot section, left of the insulation wall, is typically 600°C and the cold region, to the right, is typically 30°C
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