Atomic Show #298 – Marcus Seidl – Researching small modular reactors near Hamburg, Germany

I am a traditional utility guy – which means that every reactor which generates noticeably less than 4000MWth is a “small” reactor. Especially in the US there is a distinction between small modular reactors, micro reactors and advanced reactors. From my perspective they are all “small”. In part this adjective is also justified because most of these designs are expected to be mass produced or consist of prefabricated modules and hence cannot be of the same size as a traditional LWR.

The reason why I initiated the ‘special research’ topic: the issue of energy security and climate change are two important factors which currently favor nuclear: it is a compact source of energy (you can easily build up strategic fuel reserves) and it has a small CO2 footprint. So, why are we waiting? Why are there still doubts that nuclear power can help solve these issues? It is not the sole solution, it is not a silver bullet, but it can be part of the solution. From a conservative utility perspective traditional LWRs would be the most reliable bet. For some reasons big, complicated infrastructure projects are out-of-favor today. SMRs have many new design details and confidence must be built that they are safer, more reliable and easier to license.  

Therefore the “research topic” intends to put current research into perspective: we have great experience from many years of traditional LWR operation, we have learned from earlier, advanced reactor concepts and today we have many modern engineering tools. This should be a good basis to fulfill the promises of the next generation of reactors. In my opinion it is important to understand the history of reactor development, to demonstrate that compared to earlier designs and methods we justifiably can be more confident to bring the technology to its next level. And SMRs are not just scaled down versions of bigger plants. They are small in order to make the core damage frequency much smaller than that of their bigger brothers.

As a scientist I am a fan of radical honesty and transparency: reactors are just machines which are an optimized solution for a specific problem. Certainly, there will be failures and setbacks. If a machine encounters conditions for which it was not optimized, it likely will fail. Compared to the risks our fathers took more than 50 years ago, we are now in a much better position. This is why I am optimistic that a new generation of reactors and higher safety standards are possible. Nevertheless, these are complex technological products and they are full of surprises and also “small” reactors will not fully fulfill expectations. No reason to worry, this is the way evolution works: engineering is a sequence of problems, solutions and more problems. Therefore, the research topic invites regulators and sceptics for “perspectives” to explain their concerns.

Small reactors are sometimes criticized for lacking economies of scale and scope. Yes, this may be true from a fuel efficiency point of view.  But these reactors solve another problem: the inability of many organizations to think long-term, being burdened with short-term financial performance. Small reactors are one answer to this environment. But history will not stop here. It may also turn out that small reactors are a necessary, first step to rebuild confidence for projects with larger reactors later.

Nuclear fission is a compact source of energy and therefore also a compact source of spent fuel. I do not like the term “waste” because the question is what you mean with “waste”? The fission products, the actinides, the structural materials? Is it a lack of imagination to not find other solutions than digging holes for them?

To date the question of how to deal with spent fuel has not satisfactorily been answered. Often for political reasons development of new technological solutions has been abandoned. Therefore, it is useless to criticize the current back-end solutions. Better technologies are urgently needed here, too. Nevertheless, the big advantage of nuclear spent fuel is that it is compact and easily controllable. Its volume is small, and it does not spread all over the atmosphere like CO2 emissions.

I do not worry about spent nuclear fuel and long-term storage: it looks like a problem now, but future generations which much better tools and knowledge will “solve” it. No reason to be concerned. Also, we do not use nuclear energy for fun but to solve a problem now: provide energy security and avoid CO2 emission. Climate change is an existential threat, spent nuclear fuel is not.

We are incredibly lucky that nuclear fission works for large scale energy generation – this is not well appreciated, and the technology’s disadvantages are over-emphasized. Many energy-generation processes work in the laboratory, but current tools and know-how are not yet sufficient to employ them for energy generation: fusion works in the laboratory, but for power-plant scale the process has been energy negative for a long time. Storing energy in the form of matter / antimatter pairs also works in the laboratory but is still far too inefficient to use for practical purposes. That nuclear fission has practical utility is due to a fortunate combination of three natural constants: 

1. The size of the neutron fission cross section. If the neutron fission cross section would be as small as the photo-fission cross section, then we probably would not have any reactors, or they would look very differently

2. The number of secondary neutrons per fission event: if there would be less than 1 secondary neutron, no chain reaction would be possible, no neutron amplification would be possible, it would be very expensive to generate enough external fission neutrons. 

3. Fraction of delayed neutrons: if only prompt neutrons existed, then reactor control would be very difficult. 

Luckily all three above mentioned parameters are of the right size to make commercial reactors possible. With fusion or matter/antimatter we might not be so lucky. So, we need to be grateful that energy generation by nuclear fission is working! This is a reason for celebration.

By now you will have noticed that I had my 20 years of professional nuclear career in Germany and it shows how a reliable technology still can fail even though it created no harm. This is hard for me to accept because all the engineering was done right. It is a caveat for those enthusiasts that even the perfect, next generation reactor may not be deployable in some countries or regions. It also shows the skewed risk perception many people have: during Covid-19 about 100000 Germans because of the virus. During 50 years of nuclear power plant operation nobody in the public was harmed. Nevertheless, many Germans are satisfied with “living with the virus” while still being skeptical or afraid of nuclear. This is logic turned upside down.

The German experience also shows the impact of what I call the “dictatorship of a stubborn minority”. Likely, most Germans do not really care about nuclear. They are neutral. But there has been a hardcore group of people who stubbornly refuses to discuss nuclear power rationally. Some of those people are now in government. The same government who urges people to deal “rationally” with the Covid-19 pandemic. These are all contradictions which are hard to swallow for a scientist or engineer.