In the wake of the European Commission’s recent proposal to classify nuclear energy as sustainable and include it in the EU taxonomy, we decided to take a closer look at the controversial energy source to see what contribution, if any, it could make to the green transition. In the first of our two-part series, we weighed the pros and cons of the EU’s plan, and now we will discuss some of the technologies that advocates of nuclear energy think deserve to be considered sustainable and, consequently, ought to be employed. We will also give our verdict on whether they have a role to play in a green future. But let’s start with a quick look back into the past.

On December 20, 1951, Experimental Breeder Reactor I in Idaho National Laboratory became the first power plant to generate electricity through atomic fission - successfully powering four 200-watt light bulbs. What was a major breakthrough at the time might only put a smile on many people’s faces 70 years later: the advanced technologies that nuclear plants currently under construction (or planned to be built in the future) rely on seem straight out of a sci-fi movie in comparison. Most of them are still in the development and demonstration phase, but let us explore what the most talked-about ones may have to offer once they are in operation.


Small modular reactors

Small modular reactors (SMRs) have a capacity of up to 300 MWe (megawatts electric) per unit - about one-third of the capacity of a conventional nuclear power reactor - and are much smaller, capable of being manufactured in a factory and then transported and installed on-site. They can also be deployed incrementally to meet increasing energy demand and, unlike traditional reactors, they can run on a variety of fuel types and coolants. Perhaps most importantly, small modular reactors allow for hybrid energy systems, i.e. systems that can combine nuclear with other energy sources, including renewables. 

According to the International Atomic Energy Agency, in 2020 there were 72 SMRs under development or construction in 18 countries. Two reactor units are already in operation in Russia, and last summer, Canada’s first SMR project fulfilled the requirements to move to the licensing phase. Ontario Power Generation is also planning a larger, grid-scale SMR, which could be built by 2028. The United States, the United Kingdom, and China have all been looking into and investing in the technology since the beginning of the decade. Valuates Reports estimates that the global small modular reactor market will reach $18.8 billion by the end of this decade - more than a fivefold increase compared to 2020.

Those in favor of the technology say that it’s financially viable and will lead to significant cost reduction due to modularization and factory construction. The wide applicability of SMRs - also in non-electrical applications, such as industrial heat - can also result in improved efficiency and, in turn, a better return on investment. Speaking of investing, in the US, private companies and the Department of Energy have invested more than $1 billion in the development of SMRs, but now the developers say that more money will be needed.

Not so fast, say the authors of a 2021 study published by the IEEE: small reactors in general tend to cost more per unit of output simply because of economies of scale. They also doubt that the existing demand is sufficient for mass production. Add to that the decreasing costs of other sources of energy, particularly renewables combined with storage technologies, they argue, and the above-mentioned excitement over SMRs will evaporate in time. We’ll have to wait and see who’s right.


Molten salt reactors

The heat transfer medium commonly used by traditional nuclear plants is water, but some technologies rely on other substances, such as molten salt. Molten salt reactors can run safely at higher temperatures and lower pressures because molten salt is a more effective coolant than water, and the reactor components do not need to cope with the considerable pressure present in reactors heated by water. They can meet a dynamic electricity demand thanks to their ability to quickly adjust to output. 

Once again, Canada is at the forefront of developing this technology, with advanced reactor developer Moltex Energy recently saying their reactor design can run on spent nuclear fuel, tackling the issue of nuclear waste. Meanwhile, US-based Elysium Industries is developing a so-called molten chloride salt fast reactor technology, which the company believes will address climate change and the rise in energy demand and consumption. However, the first facility is not expected to be built before the early 2030s.

Elsewhere, the Danish company Seaborg Technologies is developing a compact molten salt reactor and is hoping to bring it to market in 2026. Incidentally, molten salt reactors are nothing new - some operated as early as the 1960s - but with major changes in design philosophy, they are now experiencing something of a renaissance. However, with the literature on MSRs fairly scarce and failing to address economics and finance, as a 2020 study published in the journal Progress in Nuclear Energy found, it is hard to estimate costs, which bodes ill for the technology - no matter how promising, it is unlikely to be embraced by investors until such figures are available.


Traveling wave reactors

Unique among reactors are the so-called traveling wave reactors (TWRs) because they are capable of running “forever” on depleted or natural uranium. While this may sound like the stuff of fiction, the technology allows the uranium to “gradually breed fissionable material through a nuclear reaction without removing it from the reactor’s core,” as explained on the website of TerraPower, a start-up co-founded by Bill Gates. In other words, a traveling wave reactor only needs a certain amount of uranium to run for a very long time and does not require reprocessing plants, meaning it also decreases overall fuel cycle costs.

Sound good? The problem is, pretty much everything about TWRs is hypothetical. No such reactor exists anywhere, let alone potential investors - other than Bill Gates, that is, who has money to burn. The economics are largely unknown, and the predictions of a 2015 article published in Research Nuclear Power - “Over its 60-year life, a 1.15 GW electric TWR refueled with unenriched uranium would cost between 4 billion and 5 billion dollars less to operate than an equivalent LWR (light-water reactor) or traditional SFR (sodium-cooled fast reactor” - should be taken with a grain of salt, given that the authors are associated with TerraPower.


Thorium-based reactors

Much more abundant in nature than uranium, thorium could become fuel for next-generation nuclear reactors and an important technology when uranium reserves start running low. While not fissile, thorium can transmute to a type of uranium and be used in a reactor as a result. China is currently building a thorium-fuelled reactor in Wuwei, and if the project is a success, we can expect the technology to be commercialized. The Swiss startup Transmutex is also developing such a reactor, which is supposed to produce electricity safely - since the plant cannot sustain a chain reaction - and without producing highly radioactive waste.

But despite its potential, experts predict that it may take two decades before such a nuclear power plant can be connected to the grid, not to mention the time needed to realize it on a large industrial scale. As for the costs, Transmutex estimates the pilot reactor would cost around 1.5 billion Swiss francs - with only 8 million raised so far, it could take a while before the company has the entire amount.


A new nuclear age?

In addition to the question of time and money, there is a further, highly contentious issue that has proved to be difficult to tackle: waste disposal. Even if the next generation of nuclear technologies meets stricter safety and security standards, and minimizes the likelihood of major accidents, it will not provide a solution to this basic problem. At the same time, we should note that it’s not only nuclear power plants that present the challenge of hazardous waste disposal. Heringen, a small town in the German federal state of Hesse, is one of the most toxic places in the world, “home” to tons of highly toxic waste from Europe and the United States that contains arsenic, cyanide, mercury, and other chemicals. The toxic waste dump was opened back in 1972, and to this day, many people in Germany do not even know it exists. “Doesn’t that pose a more imminent danger than nuclear waste?” those in favor of keeping nuclear energy in the energy mix may wonder.

Arguably, nuclear energy has a worse reputation than it deserves. But with time running out, the technologies discussed above may not contribute to rapid decarbonization, since they should ideally start operating at once to help us in our fight against climate change. Also, it remains to be seen if they are really as effective as they are supposed to be. In spite of all that uncertainty, however, we wouldn’t give up on nuclear just yet - for now, renewables and other technologies are our best option, but looking further ahead, maybe there is a place for nuclear energy in a green future.