Small and modular is the future of clean power
A new generation of 'walk-away safe' reactors promises to spark a nuclear renaissance
Nuclear reactors produce enormous amounts of power, typically ranging from 1,000MW to 1,500MW, and multi-reactor installations can operate at well over 7,000MW, a capacity only rivalled by the world’s largest hydro plants.
In my last post I discussed how that leads to a big hurdle to deploying more clean energy: expanding the nuclear fleet is extremely capital intensive and mega-industrial projects often face major delays. When combined with poor public perception, the result is that little new nuclear capacity is currently being built.
In this third piece in my series on nuclear power I explore the new generation of small and modular reactors being brought to market.
Small modular reactors (SMRs) are low-capacity reactors that can be manufactured in assembly lines with lower production costs, which should make them cheaper and a lot faster to build. Many of these small reactors use new technologies that are even safer, more efficient, and generate less waste than conventional nuclear plants.
Although is impossible to cover all the 80+ reactors reportedly in development (also: I’m not a nuclear engineer!) a few interesting aspects are worth calling out.
Build it in a factory
The current approach is to pick a reactor model, customize it for the specific location, then navigate years of paperwork before construction can start. The operator then hopes to do a good enough job managing the project so that the new plant starts generating electricity in years rather than decades. SMRs promise a more streamlined approach, with factory-built modules assembled on-site. The smaller generating capacity can be expanded by rapidly adding more modules.
One interesting example is Last Energy with its 20MW SMR that only uses existing technology, essentially a miniature of today’s reactors. The company claims installation can take as little as three months, with orders placed for dozens of reactors to be delivered across the UK and Poland before the end of this decade.
SMRs rely on economies of scale for financial viability, much like traditional nuclear. However, SMRs achieve this through mass production and rapid construction of multiple units, instead of high generating capacity.
Many new reactors rely on so-called high-assay low-enriched uranium (HALEU), enriched between 5% and 20% of currently used fuel, but less than the 20% minimum required to make weapons.
Although more expensive and less common today, HALEU offers several advantages. It can power a reactor for up to 20 years, reducing or completely eliminating the need to refuel, a process that requires handling radioactive used fuel rods. It can also extract more energy from the same amount of fuel, generating less waste.
Molten salt reactors use a liquid mixture of salts as both fuel and coolant, instead of the solid fuel and water or gas coolant used in conventional reactors. They can operate at higher temperatures and low pressure, and allow for better control of the fission process, making it easier to adjust the power output to match fluctuations in electricity demand, which means they are ideal for pairing with renewables.
Thorium is a fuel that has a lot of people excited. It is more efficient than uranium, also requires less refueling, generates less waste, and can take advantage of the molten salt design. Thorium is also three times more abundant in Earth’s crust, alleviating fears of depleting uranium supplies. The United States ran an experimental thorium reactor in the 1960s to prove that it was viable, but today China is leading the pack, testing the world’s only active thorium reactor.
The new designs incorporate passive safety features, allowing the core to cool down by itself in case of power failure or human error. Here is an interview with the Director of Fuel Cycle Innovation at Ultra Safe Nuclear (from minute 19, edited for clarity):
A nuclear reactor is driven by a fission chain reaction. So you have a neutron that splits a uranium-235 atom, and that will release more neutrons, which causes a positive feedback loop. There are three kinds of interaction with a neutron: you can have an absorption event where U-235 absorbs a neutron and becomes U-236; you can have a scattering event where the neutron will bounce off; or you can have a fission event where the atom splits.
Our reactor has a negative temperature reactivity coefficient. What that means is, as the core heats up, the absorption spectrum broadens, so the bulk of the reaction shifts from fission events to absorption events. That shuts down the chain reaction and the reactor itself.
We could have a complete loss of coolant in the reactor, total ejection of all our control rods, and the reactor would come down into a safe state.
Reactors that use liquid fuels like molten salt include a “freeze plug” at the bottom of the reactor that melts in case of overheating, allowing the fuel to drain into a passive cooling system, preventing meltdown. This design also greatly reduces proliferation risk by making it harder to extract fissile material from the mixture.
SMRs that can be installed quickly and more predictably open up a lot of new use cases beyond electricity generation.
District heating: converting fossil fuel heating systems to SMR-powered solutions for residential and commercial buildings.
Industrial heat: high-temperature gas-cooled reactor (HTGR) designs can replace natural gas and coal in many industrial processes.
Clean & reliable energy for all
As public perception continues to shift toward nuclear power, the arrival of SMRs can help dispel a lingering fear of the atom. Their unassuming, warehouse-like exteriors and smaller exclusion zones (hundreds of meters instead of kilometers) make them less intimidating.
Additionally, SMRs present an opportunity for developing countries. The International Atomic Energy Agency considers that SMRs are suitable for an order of magnitude more countries: they require less upfront investment and can be more easily integrated into existing lower-capacity grids in the Global South.
With the end of the coal era visible in the horizon, the next few decades will bring a wholesale decommissioning of coal power plants. The United States is already re-purposing shuttered coal plants for SMRs, taking advantage of the high-voltage power lines already in place.
In partnership with renewables, SMRs could provide reliability to enable coal-dependent countries to phase out fossil fuels and bring clean, reliable energy to the masses.
A dose of skepticism
Despite their potential, SMRs have caused considerable hype in climate circles. The reality is that the majority of new reactor designs are still in concept stage. Even those fastest to market won’t be operational until the late 2020s, with a widespread deployments unlikely until the mid 2030s. Furthermore, regulatory adaptation to smaller designs may prove time-consuming create bottleneck in some countries.
Recent increases in reactor capacity and reduced factory-built components have led to criticisms that SMRs are no longer small nor modular. Some argue that SMRs are being oversold. It is certainly concerning to see mistakes of conventional nuclear mega-projects be repeated with SMRs, even accounting for learning curves in first-of-a-kind projects. For example, NuScale’s much touted first SMR installation in the United States is already significantly over budget years before starting operations.
Nevertheless, I take the view that SMRs remain a promising avenue for revitalizing nuclear power. Given the plethora of new designs proposed, several of them will likely fail to find a path to market. However, each new product should be judged on their own merits, so any one failure need not be an indictment on SMRs as a whole. It is always worth repeating: the world cannot get to net-zero without more nuclear power, therefore finding a way forward for this industry is of crucial importance.
Small Modular Resources
This short promotional video by TerraPower who are building a molten salt reactor on the site of a decommissioned coal plant in Wyoming.
Nuclear is not the only power source betting on small and modular installations. That is also hydro power’s future:
Geek out with this information-dense overview of SMRs
This interview with the CEO of Rolls-Royce SMR has a robust exchange thirty minutes in discussing SMRs vs. offshore wind, cost of electricity, and whether the United Kingdom really needs baseload power.
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