1.7: Carbon free grid and Nuclear

I won’t talk much about clean energy generation here, instead pointing readers to David MacKay’s amazing book and this review paper.This section is going to primarily look at some specific technologies and the costs we might face to get these technologies to the scale we need.

Firstly let’s quickly try to ballpark the cost of switching over to a fully carbon free grid.

Construction costs for different generator types
Let’s use the figure of needing to decarbonize 16 TeraWatts (TW) or so, without introducing negative emissions technologies. A typical coal plant is, say, 600 MW or so. 16 TW / (600 MW) / (30 years *365 days per year) = equivalent of replacing 2.5 coal plants per day with non-fossil energy.

Now let’s consider the cost of constructing new energy infrastructure. We’ll assume that constructing renewables or nuclear can be made cost-competitive with constructing fossil fuel plants. A new fossil fuel based plant costs say on the order of $1000/kW, so we’re talking $1000/kW * 16 TW / (30 years) = $500 billion per year. That’s half a percent of world GDP every year as a kind of lower-end estimate of up-front capital costs, barring much better/cheaper technology.


¹ Including probably fusion, long term, which we’ll discuss belowThe details are continually vigorously debated, but aggressive development and deployment of improved nuclear power systems seems¹ like an important component, at least in some countries. It is worth reading David MacKay’s blunt comments on the subject, as it applies to the UK specifically, just before his untimely death.

Steven Chu has stated on a podcast that one decent possibility would be a factory to repeatedly and certifiably crank out lots of small modular reactors in the way Boeing cranks out airplanes.Some would propose to keep existing nuclear plants operating, but wait for the cost, speed of deployability, safety and performance of next-generation nuclear systems — like “small modular reactors” — to improve before deploying new nuclear. But the idea that existing nuclear is fundamentally too expensive in the current regulatory environment is perhaps at least debatable.

Nuclear is the largest single source of energy in France with 58 reactors — although the just-linked post points out that the French nuclear industry is in financial trouble. In this blog post Chris Uhlik calculates what it would take to scale up nuclear technologies at current cost levels, and concludes the following:He also mentions some alternative assumptions that could drives this down by over 50%“In this future, we need 7.7 kW per person, provided by $3/watt capitalized sources with 8% cost of capital and 35% surcharge for O&M. The cost of this infrastructure: $2,550/person/year or 5% of GDP.”

So that’s about 5-10x as much as our 0.5% world GDP per year lower-end estimate above, based on the approximate cost of fossil plants, a cost level which new renewables appear to be rapidly approaching. Uhlik still calls it “cheap”, and that doesn’t seem unreasonable given the benefits.

Is Uhlik missing anything? Well, one key issue is the fuel. There are two issues within that:

  • availability
  • safe disposal

You might thus not be surprised that Uhlik is involved in thorium reactor projects — indeed I think his post should be understood in the context of scaling up thorium reactors, not existing uranium light water reactors.As far as availability, this review paper suggests that getting enough for traditional U235 reactors to completely power the planet for decades may be a stretch. They suggest either using breeder reactors, such as thorium reactors, or getting fusion to work, to get around this.

Beyond thorium per se, though, there are many other apparently promising types of molten salt reactors.Thorium is still at an early stage of development, although some companies are trying to scale up the existing experiments. For two contrary perspectives on thorium, see here and here.

Here’s something cool a company making a nuclear reactor that runs on existing stockpiles of spent nuclear fuel and that is expressly designed to provide tunable output to be used to buffer variability in renewables and thus speed the integration of renewables into the grid.The waste disposal problem seems complex and depends on the reactor technology. Moreover, some novel reactors could be fueled on the waste of others, or even consume their own waste over time. There are also a lot of questions about how waste streams from existing nuclear technologies could be better dealt with.

What about safety? My impression is that nuclear can actually be very safe, Chernobyl notwithstanding. Moreover, advancing technologies intersect in all sorts of ways that could make nuclear more feasible in more places, e.g., improved Earthquake prediction might help.

The basic idea of: make a surplus of cheap, safe, robust nuclear energy → electrify many other sectors to reduce their GHG emissions → also power negative emissions industrial direct air capture… seems like something we should be seriously considering.

But in practice, the high up front construction cost — currently perhaps $4000-$5000/kW, roughly 5x the construction cost of the other types of power plant shown above — could be a concern, as could be the need to move beyond traditional Uranium light water reactors to get to full grid scale. Analyzing this is complex, as prices are changing and will change further with the advent of small modular reactors, and there will naturally be an ever-changing mixture of energy sources used and needed as renewables scale up to a significant fraction of the power grid.

A particularly interesting entity here is TerraPower. In the 1990s a group including Lowell Wood proposed a reactor concept involving “use of a propagating mode of nuclear fuel burn which is notably efficient”, in a paper titled “PROBLEM-FREE NUCLEAR POWER AND GLOBAL CHANGE”. I think this evolved into the traveling wave reactor concept that they developed for a while.

This was based on a pretty deep bottleneck analysis of the field. They proposed: “This integration obviates all fuel supply issues, including the entire set of isotopic enrichment ones, while rendering comparably useful as nuclear fuels all of the actinide elements and isotopes. It entirely avoids transport and reprocessing and the full set of ad hoc waste disposal issues, and completely precludes all those involving proliferation/diversion of fissile isotopes into weapons’ programs. It offers high-grade heat in pressurized helium gas for thermodynamically efficient, economically appealing, environmentally attractive combined-cycle conversion to electricity while robustly avoiding prospects of internal overheating of any portion of the reactor’s core or fuel. It provides highly redundant means of any desired statistical reliability for prevention of core meltdown in LOCA circumstances. It provides zero biospheric hazard in event of either natural or man-made catastrophe. It requires – indeed, admits of – no operator control actions, other than initial start-up and final shutdown commands, so that operator errors are entirely precluded; during the half-century of potentially full-power operational life in between these two commands, it thermostatically regulates in an entirely automatic manner its own nuclear power generation to match the heat removed from its core in a time-varying fashion. The thorium-burning variant of this new class of reactors involves no long-lived actinide isotopes, thereby obviating a present-day keystone issue of long-term reactor waste storage and disposal.”

As of late 2020, according to Wikipedia, and in reference to a later reactor design from them: “In October 2020, the company was chosen by the United States Department of Energy as a recipient of a matching grant totaling between $400 million and $4 billion over the next 5 to 7 years for the cost of building a demonstration reactor of their “Natrium” design, which uses liquid sodium as a core coolant (this reduces the cost by having a non-pressurized primary loop).” They had also had a plan to build a prototype in China, but it was canceled due to Trump trade restrictions — not sure if this will eventually be reversed.


The review paper mentioned earlier talked about the possibility of using nuclear fusion as a way to get around the scaling issue traditional nuclear power would likely have if we tried to get to full grid scale. So one obvious question is how is nuclear fusion coming along?

Fusion has no fundamental obstacle, and many advantages over fission-based nuclear. Paraphrasing from the ITER website:

  • Can have roughly 4x energy per fuel mass over fission
  • Abundant fuel, e.g., hydrogen isotopes deuterium and tritium. Deuterium can be distilled from water, then tritium generated (“bred”) during operation, when neutrons hit lithium in the walls of the reactor: “While a 1000 MW coal-fired power plant requires 2.7 million tonnes of coal per year, a fusion plant of the kind envisioned for the second half of this century will only require 250 kilos of fuel per year, half of it deuterium, half of it tritium.”
  • Less of a radioactive waste problem. Basically makes helium from isotopes of hydrogen. Particles hitting materials in the reactor do activate the materials in the reactor, but not creating large amounts of long-lived waste like in fission.
  • Safety: “Only a few grams of fuel are present in the plasma at any given moment. This makes a fusion reactor incredibly economical in its fuel consumption and also confers important safety benefits to the installation.” Also, “A Fukushima-type nuclear accident is not possible in a tokamak fusion device. It is difficult enough to reach and maintain the precise conditions necessary for fusion—if any disturbance occurs, the plasma cools within seconds and the reaction stops. The quantity of fuel present in the vessel at any one time is enough for a few seconds only and there is no risk of a chain reaction.”

Around mid-century, it will probably be working and becoming widespread. The key question is whether this can happen sooner, say in the next 15 years as currently no demonstration reactor has yet generated net energy gain.


Tokamaks are one class of magnetic confinement system, in which the plasma, which we want to heat to >100 million degrees Celsius, follows a helical magnetic field path inside a toroidal shaped vacuum chamberITER is a Tokamak and is a big, long, complex international project that is deliberately distributing effort across many international organizations. It extends well past 2040 for its major scientific milestones, not to mention future power plant scale followups and commercialization.

It will take at minimum years, if not a decade or more, perhaps much longer, just to get to a compact fusion pilot plant, which may not even be strongly net-positive in energy gain, let alone full scale useful power plants with economies of scale and proven industrial rollout: “The initial pilot plant operation would demonstrate net-electric equivalent performance in a compact fusion system, focusing on integrated core/edge performance, assessing plasma material interactions, demonstrating tritium pumping, limited breeding, safe handling, and extraction. This initial phase would not include long-pulse fusion power production and would not demonstrate self-sufficient tritium production. The second phase of the pilot plant would seek near continuous operation, allow for materials/component testing with neutron fluences approaching power-plant levels, and provide integrated blanket testing. Upon success of this second phase, the compact fusion pilot plant studies would have reduced both the economic and technical risks for fusion energy-based electricity production and will motivate further involvement from industries and utilities…”

Other attempts

There are a number of companies pursuing things that are along these lines of some kind of next-gen compact magnetic confinement, including Commonwealth Fusion, Tokamak Energy, and Lockheed Martin’s Skunkworks.

There is also a need to move beyond the framework ITER is using to include other novel ways of confining the plasma. A distinct hybrid approach is being pursued by TAE.

There was an ARPA-E program called ALPHA to pursue initial academic-scale research on hybrid approaches that move beyond classical magnetic confinement type approaches, including so-called magneto-inertial fusion, of which an example is the "z-pinch". Here is from the ALPHA website: “Most mainstream fusion research currently focuses on one of two approaches to confining plasmas: magnetic confinement, which uses magnetic fields and lower-than-air ion densities, and inertial confinement, which uses heating and compression and involves greater-than-solid densities. The ALPHA program aims to create additional options for fusion research by developing the tools for new, lower-cost pathways to fusion, and with a focus on intermediate densities in between these two approaches. These new intermediate density options may offer reduced size, energy, and power-density requirements for fusion reactors and enable low-cost, transformative routes to economical fusion power.”

The company General Fusion appears to be pursuing something along those lines, and the company Helion was in the ALPHA portfolio according to the just-linked retrospective.

Update 2021: The National Ignition Facility (NIF) is getting very close to Q>1, although this inertial fusion method doesn’t lend itself to building practical reactors.That is, there are magnetic confinement fusion methods, and inertial confinement fusion methods. The magnetic confinement methods are making progress with compact versions but still have huge engineering challenges to make the overall systems low-cost, even once you get Q>1, i.e., more energy released than consumed. The inertial methods are even more stricken to large and complex experimental setups rather than economical reactors.

Todd Rider, circa 1990s, has lots of broader ideas and critiques of the fusion field, which may have pointed to a need for more novel designs.The claim behind ALPHA, and magneto-inertial methods, is that you have a bit of scientific risk to solve upfront as far as how to stabilize the plasma, but when you solve that then you have a path to lower-cost systems with less engineering risk. Z-pinches in particular were studied as far back as the 1950s, and there are a couple of startups pursuing this now such as Zap Energy, but it needs a renewed government effort. This emphasis on low-cost setups is important if fusion is going to matter soon, not just many decades from now.

It seems like US fusion funding stalled in the 1990s and onward, and is only starting to be rebooted. I have no idea of whether it will indeed be possible to demonstrate a full net-positive energy gain pilot plant, let alone really commercialize, in the next 10-15 years, but it may happen if pushed very aggressively and with some luck.