Nuclear Power 3: Dilithium Crystals?
A brief look at the current and coming nuclear technologies and their challenges and capabilities.
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As a kid, I can remember watching and reading science fiction and being fascinated by the ideas of power that could drive space ships and do massive planet-shaping things ... all while being cool. Star Trek somehow used “dilithium” to regulate matter-antimatter reactions that unleashed unimaginable energy, enough to travel faster than light. Star Wars had a bit darker take on this, using “hyper matter” to create massive “Death Star” power. No explanations of how all this worked were offered, but they certainly sounded cool!
I was disappointed, a few years later, to discover there was nothing to any of these technologies. Nuclear fission, as a way to create power, seemed to hold the promise of something different. When I found out that a nuclear reactor was used to boil water to make steam, I was deflated. It turns out nuclear power is just another thermal plant that works like all others: make heat->boil water->spin a turbine->use a generator to make power. The only difference between all thermal power plants is how heat is made.
That said, for those of us fascinated by complicated mechanical devices, a nuclear power plant is the best steam kettle ever! Let’s take a moment to go into the design at a high level. As described in part 1 of our series on nuclear power, at the heart of a nuclear reactor is a nuclear fission reaction wherein plutonium atoms are split by neutrons that are directed at them, resulting in the release of heat and more neutrons. The heat is used to generate steam. The neutrons enable more atoms to be split and the chain reaction to continue.
In order to keep a heat-producing chain reaction going, the speed of the reaction needs to be controlled. Too slow and it will stop; too fast and it can overheat. To control the reaction speed, “moderators” are used. One moderator is the cooling water circulating in the reactor. It is a natural stabilizing force. As water in the reactor gets hotter, it allows neutrons to speed up, which results in fewer fission events and the reactor slowing down. A good natural feedback loop.
Control rods are the other moderator used in reactors (and actively used in operations). They are made of such materials as boron, cadmium, and hafnium that strongly absorb neutrons without causing fission. So inserting a control rod into a reactor results in fewer available neutrons and a slower reaction. Withdrawing the rods causes the opposite. This is a fine- grained control that operators can use to adjust the output of the reactor. 1
There are several different designs of operational nuclear power plants, and many more in experimental or developmental stages. Light-Water Reactors (LWRs) — so called because they use ordinary water as coolant and moderator — make up roughly 90% of the operational reactors in the world today. Other designs rely on alternative cooling strategies: heavy water, gas cooling, molten salt, or liquid metal such as sodium. As described in part 1 of this series, all three major nuclear accidents involved a loss-of-cooling event, underscoring just how critical cooling is to safe operations. 2
Today, nuclear engineers talk about “walk-away-safe” as the ultimate design objective for new nuclear plants. It means: a reactor that will shut itself down and remain safely cooled without any operator action, without external power, and without active mechanical systems (pumps, valves, emergency diesels). In other words, if every human literally walked away and all power was lost, the reactor would still safely shut down ... but not melt down. This is a very high bar and is only met by a couple of reactor designs. It is important to note that walk-away-safe is not a design or engineering standard that can be certified; therefore some companies may claim their products are “walk away safe” when they don’t meet the rigorous definition used here. 3
To be considered walk-away safe, a reactor must:
- Naturally reduce its power as temperature rises
- Remove heat passively without pumps
- Operate at low pressure
- Use fuel that tolerates very high temperatures
- Remain indefinitely stable once shut down
Today the “gold standards” for such reactors are High-Temperature Gas-Cooled Reactors (HTGRs), in which the fuel is TRISO encased and safe up to 1600ºC with helium as the coolant. TRISO fuel is a type of nuclear fuel where each grain is individually encased in multiple ceramic and carbon layers, creating tiny, extremely robust capsules that keep radioactive materials contained even at very high temperatures.4 If cooling stops, the reactor heats up slowly, stabilizes and cools down from natural conduction. The other design that meets these criteria is the Molten Salt Reactor (MSR). In this design, the fuel is liquid, there is no pressure and it incorporates a “freeze” plug that melts if it gets too hot and drains the fuel into subcritical tanks.
Let’s take a little closer look at the current state of reactor designs, starting with the Westinghouse AP1000, which is still in use and being built today and includes many of the innovations for safety that have been learned over the years. The AP1000 is a light water reactor design that has a “name plate” capacity to produce 1.1 Gigawatts (GW) of power. This means that an AP1000 that runs for a year, assuming a capacity factor of 90% (capacity factor is actual output as a percentage of rated power), would generate 8672 GWh per year of energy.5 To put this in practical terms, that is enough electricity for 850,000 homes or 10-15 data centres. It could replace one coal plant.
A brief reminder of terminology: power (Gigawatts) as described here is a measure of near instantaneous output; energy (Gigawatt-hours) describes the amount of power delivered over time.
The AP1000 incorporates design changes that make it much safer than previous designs with a strong emphasis on passive safety, enabling it to maintain safe shutdown and cooling for several days without power, pumps, or operator action, relying on gravity-fed cooling water, natural convection, and stored heat capacity. Not “walk-away safe” ... but getting closer.
A new generation of small modular reactors (SMRs) are being developed to advance the ideas of safety embodied in the AP1000. These designs are smaller — roughly half the size of an AP1000 — and incorporate three ideas: a smaller core with lower total heat, factory fabrication, and more reliance on passive physics. SMRs rely partly on their smaller size to improve safety, making it easier to cool passively. Several companies (NuScale, GE Hitachi, and Rolls-Royce) have small modular reactors in various stages of development, although none are currently operational.6 Russia has two small floating SMRs that are (maybe?) operational, although very little is known about them.
Conclusion
Nuclear power sits in a strange position in our collective imagination. It is simultaneously feared, distrusted, and quietly depended upon. In this series we traced that tension: from the technology’s origins and troubled history, to the misunderstood realities of radiation, to the question that defines its future — what role, if any, should nuclear play in a world racing toward electrification?
On the one hand, nuclear reactors produce enormous amounts of electricity with virtually no greenhouse gas emissions. They operate at high capacity factors that few other energy sources can match, providing the stable base-load that modern grids depend on. Newer designs promise enhanced safety through passive shutdown systems and, potentially, less long-lived waste. In a world grappling with fast-rising electrical demand — from data centres, electrified transport, industrial re-shoring, and climate adaptation — these strengths matter.
On the other hand, nuclear operations bring real constraints and risks. Large reactors take a decade or more to build and cost tens of billions of dollars. They require highly-trained workforces, complex regulatory oversight, and the unsolved long-term waste storage strategies measured in centuries or millennia. Public concern — rooted in both history and perception — remains a limiting factor. And none of these issues align well with the short timelines driving today’s demand growth.
All that brings us to the question about if, and how, nuclear power fits into the future of power generation. This is a matter of opinion ... and around the SweetLightning editors' table, opinions differ. We felt it important to discuss these alternative futures in an open way, so we are adding an opinion article to share these views with our readers.
We welcome you to join the discussion in the final part of this series, which asks the question: Is nuclear power green? Do we follow the yellow-cake road?
Reading
- International Atomic Energy Agency. Nuclear Reactor Physics. Vienna: IAEA, 2014.
- “Nuclear Power Reactors in the World.” Text. IAEA, July 17, 2024. http://www.iaea.org/publications/15748/nuclear-power-reactors-in-the-world.
- “Passive Safety Systems and Natural Circulation in Water Cooled Nuclear Power Plants.” Text. IAEA, November 12, 2009. http://www.iaea.org/publications/8192/passive-safety-systems-and-natural-circulation-in-water-cooled-nuclear-power-plants.
- Demkowicz, Paul A. TRISO Fuel Development and Qualification. n.d.
- “AP1000 Nuclear Power Plant Design | Westinghouse Nuclear.” Accessed January 15, 2026. https://westinghousenuclear.com/new-plants/ap1000-pwr/overview/.
- “Small Modular Reactors: Advances in SMR Developments 2024.” Text. IAEA, August 27, 2024. https://doi.org/10.61092/iaea.3o4h-svum.