Utility Professionals Network Community

Welcome! This community is the default community for every Energy Central registered member. We discuss and share a variety of topics related to the global power industry. We welcome intelligent, insightful contributions and conversations.

200,159 Subscribers

Article Post

Should we be afraid of nuclear energy?

Even more nuclear energy?

There will be a quite significant increase in  the electricity demand worldwide, because there are countries developing very fast, for example, China and India. At the same time, much less energy per person is consumed in India and China than for instance in Europe or in the United States. Naturally, they will want to reach the same standard of living, which means that there will be a very fast increase in electricity demand. Like in a couple of hundred years, there will definitely be not only renewables, but also other types of energy.

Even if not all increased demand in energy will be covered by nuclear, not using the atom will put a lot of burden on the environment due to the use of fossil fuels. For instance, in Sweden half of the electricity comes from hydroelectric plants and there cannot be more because of the environmental risks they bring.

Another important point that people unfortunately don’t associate directly with nuclear energy is that it has a lot of benefits like nuclear medicine. I would also like to stress that nuclear energy has a lot of indirect benefits. As for the inevitable increase of the electricity consumption, I do believe that it is a very good decision to use nuclear for the production of a large amount of energy..

Being afraid

In the nuclear industry business security can mean the safety of the people working with the construction — the safety against an accident in the working place. First of all, those reactors that suffered the accident at Fukushima were of an older generation. I’m not sure that it is known, but the Fukushima Daiichi reactor №1 would have reached 40 years of operation at the end of March 2011, so that power plant was already to be closed down permanently.

The modern construction of power plants is much safer, not only because of the Fukushima accident. We can definitely say that after the accident a lot of attention was given to the resistance of nuclear power plants, for instance, against natural catastrophes such as earthquakes. For example, the fifth reactor that is being built in Finland at Olkiluoto and which is actually very similar to the VVER-1200 reactor which will be built in my home country — Hungary. They have double or multiple safety systems even the reactor core will be confined inside the reactor containment, meaning that no radioactivity would come out. They can even resist an impact of a jumbo jet.

Getting into details

There are active and passive security systems that are implemented in the construction of NPPs. An active system that requires an action from the personnel (they have to press the button; find out what is wrong and etc.), and a passive system can handle the event without an intervention or human activity. The main condition is that a reactor must be designed in a way to be stable for any disturbance or disaster.

Hypothetically, if for some reason there is more energy generated by the reactor, then it will become hotter and if this continues, then in the end there will be a meltdown of the fuel. But there are also physical processes that are based on laws of nature. In a VVER reactor if there is a change to a normal mode operation and it becomes somewhat dangerous, then naturally the physical processes will revert this action. In technical terms this is called a “negative feedback”.

For example, the VVER reactor is cooled by water, but the water also serves to slow down the fission neutrons. Namely, slow neutrons are much more effective to induce fission than the fast neutrons which come from fission. There is a contradiction, as some believe that neutrons are much more effective at higher speed, so they induce nuclear reactions easier, but nuclear physics is a little bit different. A slow neutron is a lot more effective, and to slow it down we need to have a low atom number, heavy water and even graphite.

The passive system consists of the following. If a VVER reactor becomes very hot, then instead of just liquid water, the process of boiling will start, which will create bubbles, which means that some of the water will be missing, thus slowing down of the neutrons will be less effective than before and then the reactor will not become critical any longer — that is practically the passive safety system — when you start a process bringing the reactor to a more unstable/hotter behavior, then because of this boiling it cannot do anything. This is only the simplest example; there are also other, more subtle nuclear processes which have a similar effect with negative feedback.

Chernobyl versus Fukushima

The problem at Chernobyl was that the neutrons were slowed down with the graphite but the heat was taken away by the water. Now in a VVER reactor the water is a moderator (this is the term for slowing down) and the medium which takes away the heat. But in an RBMK reactor, like in Chernobyl, the neutrons are slowed down by graphite which is better that water, because water not only slows down the neutrons but also absorbs them. Now in such a reactor if it becomes hotter than it should be, and there will be a boiling in those channels, as it is a channel-type reactor (there are holes in the graphite), and when it becomes supercritical, neutrons will be slowed down anyway by the graphite, but won’t be absorbed by the water, hence the reactor becomes even more supercritical. That is why those reactors are not built any longer.

VVER-1200 and EPR have such systems that work not only when the water starts boiling but also when it becomes hot, it will become lighter, as it expands. That means that if you have an increase of the temperature in the reactor, then the water around it will be hotter and will create a natural circulation that can cool the reactor for a long time even after the accident. If, contrary to the expectations, there was some damage done to the core, then it would be confined.

The real problem with Fukushima is completely different from Chernobyl (there it was unfortunate construction and the safety culture). In Japan they had water moderated reactors that are more stable but when you shut down a reactor putting those control roads which absorb a lot of neutrons, the chain reaction will stop, but one still must cool the reactor core. Even if there is no chain reaction, there are already so many radioactive elements. At the moment you shut down the reactor, the part for the heat production will not be zero but about 10% of the amount comparing to when it is operated at the full capacity. That’s why there was a core meltdown at Fukushima. To cool the reactor one needs electricity, but because of the earthquake the external gridlines were damaged, the diesel engines were also damaged, and the batteries were out in two hours. Now, such a thing cannot happen to a VVER-1200 or an EPR reactor as they are more protected and save.

Discussions

No discussions yet. Start a discussion below.