Why Small Modular Reactors?
What is causing current interest in SMR nuclear reactors and what are their main benefits?
Today there are about 50 small modular reactor (SMR) projects going around the world today. There is an enormous variation in the technologies pursued. In the next story I will pick some of the more promising ones and explain their benefits, but here I want to focus what is driving the interest in SMRs, and how the current nuclear industry failed.
What has caused interest in SMRs?
What spurred this investigation was the Olkiluoto Nuclear Power Plant being built in Finland. This is a third generation nuclear reactor design which was supposed to be the future of Europe. Yet it has instead exposed what a failure the current trend in Nuclear reactor design is.
Olkiluoto is 12 years behind schedule, it was supposed to be operational in 2009, but is instead expected to come online in 2021. Current cost estimates are 8.5 billion euros. The reactor was contracted to be built for a fixed price of €3 billion, meaning the builder in principle had to cover cost overruns. Yet today total costs are estimated at €11 billion.
A similar third generation reactor type Hinkley Point C, got the green light in Britain back in 2016. Its estimated cost was £18 billion. But new estimates are 21.5bn and £22.5bn. Hence one risks yet another expensive failure.
And these expensive overruns are not isolated incidents which leads one to ask what is the underlying problem?
The problem with Large Scale Reactors
Current nuclear reactors are typically based on using water inside the reactor. That creates a lot of problems. The water has to be under high pressure because very hot water will turn into gas. Thus light water reactors (LWR) which is what we commonly use today are basically highly unstable systems. We make them safe through tons of sophisticated engineering.
However this gets really complicated:
- You need a strong pressure vessel to contain the reactor core because it is under such high pressure.
- Should the cooling fail the water will get so hot that it splits into hydrogen and oxygen gas which is explosive.
- Radioactive elements are turned into gasses inside the fuel rods.
Due these reactor basically being high pressure systems, with nuclear waste products as gasses, we run the risk that if the reactor blows open, large clouds of radioactive material will be released.
In Fukushima e.g. the tops of the buildings did not blow up due to some kind of nuclear explosion but because backup power systems had failed, which caused cooling to fail, which caused water to be heated enough for hydrogen to form. The accident was really a large hydrogen explosion.
These problems have led to ever more safety systems being built around the reactors: backup power, extra pumps, hydrogen catchers, containment structure etc.
This adds fixed costs, increasing cost per kWh produced by the power plant. The way the nuclear industry has deal with this is by scaling up. By making reactors ever bigger, the fixed cost of all the safety systems is spread over more kWh generated.
However this has turned into a vicious circle. Larger reactors start needing more safety because size creates new problems. And the enormous size means building a reactor becomes an enormous financial risk. They take very long time to build and investors will have to wait a long time before getting a return on investment (ROI).
SMRs — Back to the Drawing Board
The premise of SMRs is that instead of engaging in this carousel of ever larger and more complex reactors, we go back to the drawing board and design reactors which are simple and inherently safe. That typically means designing them around the idea of passive safety.
What we mean by that is that keeping the reactor safe should not rely on something like actively pumping water. Or some operator hitting an important button when something goes bad. Instead it should be safe for reasons of physics, such as gravity, or how the nuclear physics work.
The second idea is to rethink how we get cheap reactors. Economies of scale makes large units cheaper per unit power produced.
But there are other ways of achieving economies of scale. The idea of SMRs is that one achieves economies of scale in production. Basically that the reactors themselves become cheap because they are mass produced in a factory.
To do mass production in a factory, reactors cannot be too large. By making them smaller, you create less financial risk. Delay of one reactor isn’t the same same financial risk as say Olkiluoto. It is easier to raise capital to build a reactor.