—— Smaller, cheaper, safer. That is what multiple projects are promising that plan to build small-scale nuclear reactors in large numbers. Are we headed for a miniature nuclear renaissance?


Since the 1950s, various companies have dreamed of producing miniaturized nuclear reactors in factories. The idea is that these small reactors would be safe, easy to transport and suitable for use in various fields. With the energy transition underway, this concept is once again becoming attractive. Small modular reactors, or SMRs, are supposed to give nuclear power a new boost around the world. According to the International Atomic Energy Agency (IAEA), work is progressing on a total of 80 SMR projects in 18 countries at the moment, although the majority of them are still in their design phase.

The size and operational methods of the individual concepts can vary quite a lot. The target output ranges from 1.5 to 300 megawatts of electricity (MWe); by comparison, conventional nuclear reactors usually have an output of more than 1,000 MWe. Depending on the planned application, some SMRs will be the size of apartment buildings and others no larger than a typical outdoor advertising column. Functionally, most SMR projects are based on a scaled-down version of the water-cooled reactor, which is by far the most common type of conventional nuclear reactor in use today. The main difference of the SMRs in these cases, apart from their size, is their modular design, which is intended to allow the small powerplants to be transported as individual parts and assembled on site. However, there are also innovative concepts such as high-temperature reactors, fast-neutron reactors and molten-salt reactors.

Concept of an SMR modeled after water-cooled reactors.

Many SMR projects also advertise themselves as having a much lower risk factor compared to traditional nuclear reactors. Yet a report by Germany’s Federal Office for the Safety of Nuclear Waste Management (BASE in German) takes a critical view of these claims. With regard to accident safety, the report notes that the existing testing procedures for the safety of water-cooled reactors can only be applied to SMRs to a limited extent and would have to be adapted. Furthermore, the final risk assessment for the more novel reactor concepts is difficult to estimate at this time. The BASE report also points out that, as far as terrorism is concerned, although an attack on a conventional nuclear powerplant represents a much larger individual threat, the deployment of hundreds or even thousands of SMRs, as envisaged by many of the projects, would multiply the number of potential targets, thus failing to reduce the overall risk factor.

The first American SMRs were supposed to be built in the state of Idaho. However, this previous showcase project, which was a public–private partnership, has since been discontinued due to increasingly pessimistic assessments of its economic viability. The technology still requires further development and subsidies before it will be able to compete on the open market – SMRs will only become profitable when they can be produced in large quantities. Until that day comes, their use will be limited to niche applications for the time being. For instance, for supplying electricity to regions with poor connection to the power grid.