The Future of SMRs Is All About the “R”

small modular reactor innovation is found in the Reactor design, not its small size or it modular characteristics

By Simon Irish

A lot of people are speculating about the potential role of small modular reactors, known in the nuclear industry by the acronym “SMRs.” These new reactor designs promise to deliver a clean and reliable alternative to fossil fuels – but the discussion typically focuses on the “S” and the “M,” as if those features represent the true innovation. They do not. The real game-changer is in the “R,” or rather, in the reactor itself.

SMRs are smaller nuclear power plants. This clearly implies they are less costly to build than the massive facilities we built last century. But that cuts both ways. The nuclear industry designed and built big – very big – Conventional Nuclear power plants because with size came critically important economies of scale for electricity generation.

Today, however, they are too big and unaffordable – even for governments, much less the private sector. They have become too capital-intensive, a problem compounded by their 10-year-plus construction period.

Even with today’s interest rates at multi-century lows, a new Conventional Nuclear power plant is an unrealistic investment, yet the financial conditions have never been so good: That Conventional Nuclear plant is simply too large and too capital-intensive and its resulting power still too costly. Capital intensity, and, by extension, the cost of a kilowatt-hour (KWh) of electricity, are the problems to solve, and to do this, the industry must innovate.

For decades the nuclear industry kept making plants larger and larger to capture the economies of scale that ensure a minimum financial performance in generating electricity. The industry’s view now is that new nuclear plants need to be smaller – the “S” in SMR.

However, downsizing will unwind those huge economies of scale, and it will have a large negative economic impact on the cost of a KWh of electric power. All other factors being equal, smaller plants cost less to build, but the electricity they produce will be more expensive.

Then there’s the “M” in SMR for “modular.” Some argue that using modern modular design, manufacturing, and construction techniques to build increasing numbers of smaller plants will reduce the capital cost of each SMR power plant. This is a solid reason, but these techniques apply to all SMR technologies. This benefit is not, however, a criterion to select one SMR design.

This proposition poses an interesting question, which is seldom asked. Will the positive impacts of modularity offset the negative impacts of smallness if we keep using Light Water and Heavy Water Reactors – the Conventional Nuclear technologies we have employed for over half a century?  No. Smallness and Modularity alone will not change the economic fortunes of nuclear power.

The economic benefit of modularity is not strong enough to offset the economic drag of smallness. It also misses the fundamental root cause of the entire economic problem. Any nuclear power plant, big or small, modular or stick-built on site with Conventional Nuclear technology, remains a fundamentally inefficient machine for converting nuclear heat to electricity for sale and economic gain. To solve nuclear power’s existential economic problem, we must focus on the “R” in SMR, the reactor itself, for that is where the real problem lays.

The thermal efficiency of any machine in the modern world defines its economics, whether a car engine, a jet engine, or any type of power plant. We spend a lot of R&D dollars making our many machines ever more efficient.

A Conventional Nuclear plant operates at 32 percent thermal efficiency, a coal plant at 45 percent and a gas plant at more than 50 percent. That has nothing to do with small design or modular construction. It is all to do with temperature of operation and “heat quality.” This is an issue rarely if ever discussed in the great SMR debate, perhaps because the Conventional Nuclear community has nothing new to offer.

The 32 percent thermal efficiency of a Conventional Nuclear plant is a fundamental and immutable limitation of the technology: It operates at low temperatures, generating low-quality heat, leading to low thermal efficiency and power economics – this is a result of using water as a coolant. A Conventional Nuclear plant is an inefficient machine.

From the 1950s until recently, 32 percent thermal efficiency was “good enough” for nuclear to just about compete and perhaps that was helped by a past age with a lighter regulatory touch. But not today, and this economic problem has been compounded further as other energy technologies became ever more competitive through successful innovations of their own.

Commercial nuclear power plants have remained fundamentally unchanged for over half a century. They all use Conventional Nuclear technology – solid fuel rods cooled and moderated by water.

There have been variations on this same technology theme: Canada’s CANDU uses heavy water (deuterium) rather than light water. General Electric developed a boiling water reactor, and Westinghouse a pressurized water reactor.

But all these technologies have the same limitation: low-quality heat and low thermal efficiency. The choice of water as a coolant and moderator limits the temperature at which the reactor can operate, and by extension, its low-quality heat and thermal efficiency. These technologies lock Conventional Nuclear power generation into a low-efficiency economic box with low-quality heat from which the laws of physics offer no escape.

SMRs are really all about the “R”

However, we need not remain limited to Conventional Nuclear technology with water cooling.  We have other fission technologies from which to choose – the generation technologies known as Generation IV – and we have a choice whether to deploy them. They solve the low-efficiency problem and today they are on the verge of commercialization.

Generation IV technologies represent a broad range of fission technologies, but they share one feature in common: They all operate at high temperatures. With that “high-quality” heat, they are capable of step-change improvements in thermal efficiency and economics – something plain enough to see in high school physics. Without that step-change, nuclear power generation will remain in slow decline unless governments can be persuaded to buy new plants.

Terrestrial Energy’s Integral Molten Salt Reactor (IMSR), a Generation IV SMR, operates at 700 degrees C, 375 degrees C hotter than Conventional Nuclear technologies. The IMSR delivers high quality heat that drives net thermal efficiency to 44 percent. This is a level of efficiency nearly 50 percent higher than Conventional Nuclear power plants.

By any economic standard, a 50 percent improvement is a game-changer, especially in an industry that has measured progress in small single-digit increments. By achieving such high thermal efficiency, Terrestrial Energy’s IMSR lowers the cost of every kilowatt-hour generated by a third; waste is also reduced by more than a third.

In addition, the quality of the IMSR’s heat produces steam at high temperature and high pressure, allowing for the use of a standard industrial steam turbine, which is much less expensive than the large systems used in Conventional Nuclear plants. There are many other advantages, but to be part of the solution, SMRs must start with the heat quality of a Generation IV technology.

Clearly, the game-changing factor for an SMR is the “R” and its thermal efficiency.  By deploying Generation IV technologies with innovative designs, we can demonstrate to the world that nuclear power is not only reliable and clean but also a cost-competitive alternative to fossil fuels and can finally stand on its own two feet.

So let’s start talking about the “R” – that is where we find the innovation that really matters.