clean energy nuclear

Advanced Nuclear Innovation: Thermionics

If you’re thinking about what the next innovation in advanced nuclear power could be, you might want to look at thermionics. One thing that’s been a constant in nuclear power is the steam cycle. It’s one of the largest cost components of a nuclear plant. However, think about the possibilities if you could eliminate that and still produce carbon-free electricity.

Nuclear Power Plants

Before you read any further about my view points on nuclear plants, let me first say that I don’t claim to be an expert in nuclear physics and reactor technologies. However, I’ve had the unique vantage point of seeing the pain points and lessons learned in the industry over many years.

Let’s just say it hasn’t been pretty in recent history. Overall, permitting a nuclear power plant isn’t a nimble process. Not only that, nuclear is very capital intensive and it doesn’t have a great track record with being built on time and on budget.

Nuclear power plants aren’t built that often so it’s hard to find a lot of data points. However, a recent example of one that’s experienced a lot of challenges is Plant Vogtle in Georgia.

Plant Vogtle

Plant Vogtle has been around for a long time. It’s majority owned by Georgia Power and the rest is shared by other utilities. However, in 2006, Southern Nuclear applied for a Early Site Permit to expand Plant Vogtle by two more units, units 3 and 4. Southern Nuclear is a subsidiary of Southern Company, the parent of Georgia Power as well.

Picture of Plant Vogtle, nuclear power station
Plant Vogtle

In 2009, Vogtle received its Early Site Permit. Then soon after Vogtle was a recipient of a $8.33 billion loan guarantee from the Department of Energy. See my post on flywheels about the DOE’s loan guarantee program. At the time, the expected cost to build Units 3 and 4 was $14.3 billion. Both units were expected to be completed in the 2016 and 2017 timeframe.

Long story short, today both Units, after a bunch of setbacks, have not yet started operations yet. The project has been fraught by cost overruns, delays and lawsuits. A decade later, the current cost estimate is now $25 billion to completion. That’s equates to a 75% cost overrun. Also, operations aren’t expected to begin until 2021 and 2022.

Lessons Learned

Don’t get me wrong, nuclear power has a starring role to play in the clean energy future. Having baseload, high energy density, carbon-free power in your portfolio is a big deal. But, there must be a new way for nuclear.

Since the start of the nuclear era, many countries around the world have enjoyed the benefits of nuclear energy. Cheap fuel costs and energy independence have been the big draw.

However, with nuclear, it’s been the alarming events that have left their mark on our psyche. Fukushima, Chernobyl, Three Mile Island … We often, in our nature, dwarf the positive with the few disasters that make all the headlines. Obviously that’s why safety has become the biggest factor in the development of nuclear projects.

Generally, with increased safety, comes increased costs. Costs that add up from enhanced designs, greater due-diligence and lengthy times for permitting. All things to help lessen tail risks.

What Vogtle has taught us is that high-capital and high-risk projects can do major financial harm to utilities and ultimately their customers.

Nuclear Innovation

You might be wondering if there will be any major innovation in nuclear any time soon. In my post, “Small and Modular Nukes (plus H2)” I talk about SMRs as a solution for the future (along with hydrogen). SMRs could help overcome some of the issues faced by traditional nuclear plants.

NuScale’s SMR design recently received approval from the US Nuclear Regulatory Commission. It’s scalability and simplified design results in lower cost overrun risk and lower operational costs.

NuScale's innovative small modular reactor nuclear plant
NuScale SMR Rendering

What if we looked beyond SMRs, a decade or two into the future? What lies ahead for nuclear energy?


Hand Built Thermionics Device

So what is thermionics? For you non-physics geeks, it’s basically a method of converting heat to electricity. It shouldn’t be confused with a thermoelectric generator, another form of thermal to electric energy conversion. From an article from Lawrence Berkeley National Laboratory:

Thermionics is a method for converting heat to electricity that was developed in the 1960s and 1970s, primarily for use in the space-nuclear program. In a thermionic device, electrons evaporate from a hot cathode into a vacuum and are collected by a cooler anode, generating current.

The work function is basically a measure of how tightly a material clings to its electrons. “In thermionics you take two materials that have very different work functions, put plates next to each other, make one plate hotter than the other, and magically, electricity comes out”

Thermionics really found favor in the 70s as part of the space program. Because of its high efficiency and power density, it could be used in powering probes. However, NASA shut down the program in 1973 and since then it has never really been talked about much.

But with efficiencies that can get over 30%, it’s got some pretty unique use cases when you pair it with something that generates a lot of heat.

Just like the space program where they paired thermionics with nuclear material, using the heat from nuclear decay to make a nuclear battery, I believe that there’s a way to harness this on earth.

Glimpse of the Future

One invention that gives us a sense of how thermionics could be deployed with nuclear is shown in the patent application below:

Breeding reactor tandem with thermionic avalance cell

What’s shown here is a cross section of a nuclear reactor system. Without getting into the weeds, if you can remember four numbers from the diagram, you’re doing good. 107 is the Nuclear Thermionic Avalanche Cell or NTAC and a thermoelectric generator in the diagram. 103 is the fuel rod and 102 is the primary neutron source rod. 105 is the cobalt-59 layer.

102 and 103 make up the radioactive element. It releases neutrons to the cobalt-59 layer which then breeds cobalt-60. The NTAC generates electricity from the gamma rays it receives from the fission process and the cobalt-60.

You can read the application to dive into the details, but here’s the key highlight of this invention:

In this manner, the various embodiment nuclear fission reactors combined with a NTAC and thermoelectric generator generate power directly, rather than through the generation of steam to turn a turbine. Accordingly, no steam or condensate lines may be required in the various embodiments and no turbine is required in the various embodiments to generate electricity.

Game Changer?

If there’s one thing that you should take away from this – it’s knowing that there’s still people dreaming up new ideas for nuclear energy. I’m giving you a simplistic view of how lessons from the past can drive drastic change. SMRs are a way to reduce the risk profile of nuclear plants. But, imagine if you could replace a major cost component with something more simple.

Steam turbine efficiency ranges between 35-42%. So if you could generate electricity without mechanical parts and hit over 50% efficiency, is it worth it? I think so. Outages for maintenance, wear and tear and failures all come with moving parts. NTACs also have much higher energy densities compared to traditional nuclear reactors. So the footprint you need to generate the same amount of energy is a lot less.

Nuclear propulsion in space

R&D for space programs have sometimes given us great innovations for earth applications. If you’re looking for innovation in advanced nuclear technology, keep an eye on this.

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