My relationship with nuclear energy is best described by the infamous Facebook relationship status “it’s complicated”. Like so many people of my generation, the nuclear catastrophe in Chernobyl and its impact on Europe was one of the formative experiences of my youth.
As I grew older, I studied physics and specialised in particle and nuclear physics as well as astrophysics. I wrote my Master’s thesis working inside the nuclear reactor at the Paul Scherrer Institute in Switzerland, where I learned to appreciate the many security measures that are in place to safeguard a nuclear reactor.
Because my biggest concern for the future of the planet is the reduction of greenhouse gas emissions to avoid or at least limit climate change, I have always been a fan of nuclear energy as a complementary form of energy production to solar, wind and other renewables. The reason is simply that solar and wind are energy sources that vary during the day as well as over the course of a year. In the absence of large-scale energy storage systems, it is unlikely that we will be able to provide a baseload supply of energy with solar and wind alone. Furthermore, a nuclear catastrophe like Chernobyl seemed highly unlikely to happen in developed countries with better technology and better oversight of the safety of a reactor.
This view changed with the Fukushima nuclear catastrophe in 2011. If a nuclear catastrophe like that can happen in one of the most technologically advanced countries in the world, it can happen anywhere.
The problem is that we still need a stable source of electricity that has low carbon emissions, is safe, cost-effective and can cover the baseload needs for electricity around the world. Expanding the global capacity of energy storage systems is one way to get there, but the maths shows it is not going to be enough – at least not in the next couple of decades.
And this is where the Fukushima catastrophe may have been a blessing in disguise because it created renewed research into nuclear reactors that are much safer than existing designs. The main drawback of current nuclear reactors is that they work with rods of enriched uranium, held in a pool of water or heavy water (if you don’t know what heavy water is, click here ). Because of this design, it is possible for the reactor to overheat and create a nuclear meltdown that can create an explosion and distribute the radioactive material across large areas. Graphite rods and other moderators are commonly used as fail-safes to stop the reactor from overheating, but as accidents like the ones in Chernobyl and Fukushima have shown that these fail-safes sometimes fail as well.
The new research efforts are investigating completely new designs for nuclear reactors and they found a template in the very first efforts to build a nuclear reactor in the 1950s and 1960s. The idea is to heat the uranium to such high temperatures (> 650 ⁰C) that it melts and as a result a “meltdown” is physically impossible. The most promising designs in this area are molten salt reactors. The advantage of such a molten salt reactor is that the temperatures inside the reactor are much higher than for a conventional reactor and as a result, one needs much less uranium to generate electricity than in a conventional reactor. Furthermore, the system provides its own “fail-safe” mechanism. If the temperature in the reactor rises beyond a certain limit, it will melt a frozen “plug” to a tank below the ground and the molten uranium salt will flow out of the reactor into the underground storage tank, where it can cool off slowly.
Another advantage of the system is that the uranium used in the reactor does not have to be enriched and the amount of uranium used in the reactor is so small that it is physically impossible to use the material to build a bomb. Hence, such reactors can be installed in emerging markets with minimal risks of nuclear proliferation.
Finally, these molten salt reactors create almost no nuclear waste and can, in fact, burn existing nuclear waste from traditional reactors and provide a way out of the unsolved problem of long-term storage of nuclear waste.
But, you may ask, why did the industry not built reactors with this design in the 1960s? The reasons are manifold, but essentially, it was a matter of cost. Traditional nuclear reactors are cheaper to build and run than molten salt reactors.
Of course, there is still research needed to overcome technological hurdles. For example, molten uranium salt is highly corrosive, and the reactor needs to be able to withstand the corrosive effects of the salt. Also, the technology in the beginning might be relatively expensive to build and costs will come down only as time progresses. Finally, the fail-safes of this reactor must be better than those of traditional reactors. We must be sure that the frozen valve really thaws if the reactor gets too hot, because otherwise we get another reactor catastrophe that, albeit smaller than a traditional reactor meltdown, will still devastate the nearby environment.
However, environmentalists, in my view, should keep an open mind about this technology (just because it is nuclear energy does not mean it is bad per se) and investors might want to think about the long-term opportunities in this technology. After all, Bill Gates has been supporting research in this area since 2008 with substantial amounts of money.
How a molten salt reactor works
Source: Knowable Magazine.