DUAL FLUID | REACTOR TECHNOLOGY


argues Dual Fluid: reactors with fuel rods are well suited to powering submarines, plus they can provide plutonium for nuclear weapons in an uncomplicated way. Other concepts that were known to be more suitable for civilian use were dropped. The fact that we are still using the same LWR technology several decades on is attributable to the immense energy density of the fuel: it provides so much energy that even inefficient nuclear power plants are profitable. Of the early designs that were not developed


commercially, two stand out: one with liquid fuel; one with liquid lead cooling. In the 1960s, the USA successfully operated an experimental reactor with liquid fuel (molten salt reactor) that was able to make better use of the fuel. However, since the fuel salt also transferred the heat, the power density was limited because the two functions are difficult to reconcile. Russia built a reactor with high-performance liquid lead cooling in the 1970s for its submarine fleet. But these reactors used fuel rods, making fuel supply and recycling difficult. The Dual Fluid concept is a fast reactor that aims to


combine the advantages of the molten salt reactor with those of a lead-cooled reactor in a completely new design. The key innovation lies in using two liquids in the reactor


core. There, liquid fuel can develop its full power, at around 1000°C (compared with 320°C for a typical LWR), while liquid lead handles the heat transfer.


High power density The principle is completely new in nuclear technology, says Dual Fluid. The decisive advantage is the high power density, which is due to the compactness of the system and the high operating temperature. The fuel can circulate as slowly as required for an optimum burn-up rate, while the coolant can circulate as fast as required for optimum heat removal. As a result, undiluted liquid fuel – a metallic actinide mixture – can be used, significantly increasing the amount of fissile material in the reactor core. The compactness of the core reduces the amount of structural materials required, which allows the use of expensive, high-temperature and corrosion- resistant materials. Using molten lead as a coolant also dissipates the heat without slowing down the neutrons in the reactor core.


High power density goes hand-in-hand with high efficiency: a small Dual Fluid core rated at 300 MWe is eight to 10 times more efficient than current LWRs. With larger cores, power density and efficiency increase further. Because Dual Fluid, as a fast reactor, operates with a high


neutron excess, the reactor – in combination with the Dual Fluid recycling plant – can fully utilise any fissile material, including thorium, natural uranium, and nuclear waste from current reactors.


Nuclear power redefined The principle of separate cycles for fuel and coolant “completely redefines nuclear power”, Dual Fluid believes. In combination with the Dual Fluid recycling plant, all the fuel loaded is used productively, without the need for a final repository. Application of the Dual Fluid principle is not confined to


SMRs, but the first realisation of the concept is expected to be a small modular reactor, rated at about 300 MWe, the DF300 (Figure 1).


LWR DF300 0.5 - 0.6 TWh LWR


Fuel procurement and refining Waste disposal, construction & dismantling of disposal plants Operation, construction & dismantling of power plant Other


Total


72% 10% 10% 8%


100% DF300


1% 1% 4% 4%


10%


Fuel procurement and refining


Waste disposal, construction & dismantling of disposal plants


Operation, construction & dismantling of power plant Other


80%̴ In the DF300 modular power plant, the fuel is delivered


to the power plant in a sealed cartridge. There it is heated and pumped in liquid form into the reactor core, where it produces heat for around 25 years. The spent fuel is then returned to the cartridge and transported for recycling. Larger cores, such as in the DF1500 power plant, – 1500


MWe/3000 MWth – have a higher fuel throughput and can be combined directly with a Dual Fluid recycling system. This enables permanent fuel processing on site. The Dual Fluid recycling process differs fundamentally


from ‘conventional’ fuel reprocessing based on PUREX wet chemistry. In the Dual Fluid recycling plant, the spent fuel is first converted into liquid salt form and then separated into its components using a distillation process that is already established outside the nuclear industry. All fissionable materials are then mixed with fresh fuel and returned to the reactor core. This recycling method, based on pyrochemical distillation, enables the complete utilisation of any fissionable material, achieving, for the first time, a truly circular economy in the nuclear fuel chain, says Dual Fluid. In addition to electricity generation, the DF1500 power plant, with its 3000 MWth of heat, is particularly suitable for energy-intensive heat applications such as the U


of the energy demand of LWR is related to the fuel cycle


Above, figure 2: Life cycle energy consumption associated with a typical light water reactor, with today’s inefficient fuel cycle Source: Vattenfall EPD Forsmark


Below, figure 3: Life cycle energy consumption for a Dual Fluid 300 MWe modular power plant (DF300) vs LWR (estimates based on Vattenfall and Dual Fluid calculations)


6 TWh


www.neimagazine.com | July 2022 | 37


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