Since the disaster at the Fukushima power plant there haven’t been any other breakdowns at Japan’s nuclear facilities. Caused by a tsunami wave, the disaster had to undermine, at least partially, the society’s trust in nuclear power. However, as time goes by the Japanese are starting to realize it is not easy to replace this source of energy with another one if one wants to maintain a high level of civilizational development – says professor Mariusz Dąbrowski, head of the Division of Nuclear Energy and Environmental Studies at the National Centre for Nuclear Research, in an interview with BiznesAlert.pl.
BiznesAlert.pl: It’s been ten years since the disaster at the Fukushima nuclear power plant (NPP). Is it enough to be able to carefully explain what happened and whether there is someone to blame?
Professor Mariusz Dąbrowski: Yes, it is. The course of the events is known. Hundreds, perhaps even thousands of nuclear experts dove into every detail of the disaster. Numerous simulations of the breakdown were run in order to explain its causes and prevent such events from happening in the future.
The cause of the breakdown is very clear. It was a natural disaster – a tsunami wave 13 meters high, caused by an underwater earthquake. In the open ocean such a wave is almost unnoticeable (it is a dozen or several dozen centimeters high), but is grows as it approaches the shore. The earthquake did not cause the breakdown, on the contrary, the reactors were automatically shut down in line with the existing procedures. However, shutting down a reactor does not ensure full safety, because in the core nuclear reactions are still taking place and the so-called decay heat is still being released. So the reactor needs to be cooled to handle that. Unfortunately, the incoming tsunami wave went through the tool-low seawall and flooded the power plant, and most importantly, the diesel power generators that were placed by the shore, which made it impossible to cool the reactors. The batteries and supplied mobile generators were not started on time either. In result, pressure and temperature went up in the generator, which led to a chemical reaction between the water and zirconium alloys, which produced hydrogen. After the emergency release of the excess hydrogen outside of the reactor by the crew, the gas entered into a reaction with oxygen and exploded causing damage to the external containment unit. This scenario played out in three blocks of the NPP, one after another. When it comes to how the impact of the breakdown was handled later on, it is difficult to clearly determine whether somebody was at fault. Most of all, the disaster was caused by the fact that the construction was too weak to withstand the magnitude of this unusual cataclysm (the seawall was too low, the diesel engines were located incorrectly, there was no hydrogen recombination system, the external containment unit was too weak), only next in line are the possible human errors with regard to delays in supply and making decisions on whether to cool the reactors.
In case of Fukushima the supporters and opponents of nuclear energy are arguing over the number of victims that either died or may have died due to radiation. Are we able to estimate what environmental losses were caused by the disaster?
When it comes to the number of victims, despite the very ambiguous headlines on some front pages, all victims of the earthquake were killed by the tsunami. The breakdown at the plant, or to be more precise the ensuing ionising radiation did not directly cause any deaths. When it comes to the indirect impact, it is difficult to measure, and calculations based on dividing the total radiation dose by the value of a lethal dose make no sense, because the actual absorbed doses were definitely a lot lower, and apart from that the majority of the radiation dispersed in the environment. According to measurements, the level of radiation outside of the plant’s area and its closest protective zone does not exceed the radiation level in which people in various parts of the world live. The health of those residents is not necessarily negatively impacted, or even, as some research shows, they acquire more immunity against ionizing radiation.
When it comes to the surrounding around Fukushima, it needs to be pointed out that the natural environment was damaged, and so was the infrastructure after the tsunami wave. This also resulted in several thousand human casualties. When it comes to radiation, it needs to be said that today the radioactive substances in Chernobyl, where the biggest disaster occurred, have already decayed, which means the level of radiation in the majority of areas surrounding the plant does not differ from natural radiation in Paris, Berlin or London. The same will happen in Fukushima. The area will go back to normal.
Has Fukushima been irreversibly contaminated?
There is no such a term as „irreversibly contaminated”. The radioactive isotopes have their half-lives and some need a few days, whereas others millions of years to go through that process. Of course the local residents are interested in a perspective of a few or a dozen or so years. And here, as I have already mentioned, apart from the direct surrounding of the NPP and a small protective area, the level of radiation does not exceed doses, which would cause clear-cut impact on health. When considered from a year-long perspective, they are comparable to the doses that can be absorbed once, during a CT scan. The residents were evacuated as part of preventative measures, but it had a significant psychological impact on them. A similar situation took place in Chernobyl. Today the radiation level in Pripyat is no different that the on the Marszałkowska Street in Warsaw, so the town could be repopulated.
Besides Chernobyl and Fukushima, were there any other such huge NPP disasters in the world? The supporters of nuclear energy claim that in the first case it was a human error, but in the second nature was at fault.
Fortunately, such breakdowns did not occur. This was possible mostly thanks to the detailed analyses of the events in Chernobyl and Fukushima, as well as to the fact that the right safety measures were implemented in NPPs (the so-called stress tests – tests in extreme conditions, creating first responders groups in case of breakdowns, etc.). Take a look at the aviation sector – previous breakdowns in the industry made it possible to perfect the technology to prevent new ones. Flying is becoming increasingly safer. However, no technology created by men is completely free of at least a minimal risk of a breakdown.
In Chernobyl men were clearly at fault as they conducted an experiment during which some safety systems were switched off. When this was combined with a construction defect of the Soviet RBMK reactor, i.e. the positive void coefficient of reactivity (increase in temperature causes increase in reactor’s capacity, which does not happen in new technologies), the disaster was ready to happen. In Fukushima the human factor also played a role – it’s a hierarchical society, so all decisions are made at the top. A dozen-hour delay in Japan’s prime minister decision on whether to use sea water to cool down the turned off reactor most probably led to the melting of the core. However, there were also technical elements, which did not work, which could have been relatively easily avoided. For instance, the already mentioned diesel generators that provided power to the reactor cooling system could have been placed higher than the maximum water level and behind, not in front of the reactors in relation to the ocean shore. By the way, back in the day professor Zbigniew Jaworski, who advised the government of the People’s Republic of Poland after the Chernobyl debacle, as an expert was free to make decisions about preventative measures. In result, the Polish society received about 11 million doses of the Lugol’s liquid (which turned out unnecessary, but that was difficult to ascertain in the short time after the disaster, because all the information about the breakdown was blocked). Either way, it is necessary to leave enough room for the specialists to work.
What does the safety system of a nuclear power plant look like?
There is an entire system for nuclear reactors called „defence in depth”. It boils down to using the right safety barriers. Those barriers include: ceramic fuel tablets, coating of fuel rods, a steel reactor container, reinforced concrete reactor cover and external safety covering. They work similarly to the insulation layers on power cables. Add to that other numerous (aka passive) safety measures, which do not require human intervention, as they use the laws of physics (e.g. automatic drop of control rods caused by their weight).
The level of radiation outside of the nuclear power plant fence in case of regular exploitation is practically the same as the so called natural background, which is about 2.4 mSv per year, and the „nuclear part” adds to that a small fraction of 0.1 mSv, which over 200 times less. This is possible thanks to the mentioned safety barriers. Therefore, one should not be concerned about radiation outside of the NPP’s fence. However, in the case of a breakdown, the situation may be different. Either way, every power plant must, even before it receives the construction permit, present precise calculations about how much radiation may be released into the environment to determine the so-called emergency zones. Everything is analyzed thoroughly and precise scenarios of preventative measures in case of an emergency are drafted.
Have there been any other breakdowns in Japan since Fukushima? Is Japan changing its mind about nuclear power? How to avoid locating NPPs in areas at risk of an earthquake or a tsunami?
No, there haven’t been any new breakdowns, but the Japanese did experience a „trauma”, so they need to „cope” with it. Of course the breakdown, which was not initiated by a nuclear event, but a natural disaster – a tsunami, had to impact the society and at least partially undermine its trust in nuclear power. However, as time goes by the Japanese are starting to realize it is not easy to replace this source of energy with another one if one wants to maintain a high level of civilizational development (by the way, Germany is also slowly coming to this conclusion, as during the recent cold spell nuclear power plants filled in the gaps where renewables could not keep up). The only thing left to do is choose a safer technology. High temperature reactors could be the answer, because in case of a power cut off the core does not melt, and most of all, the core cools down naturally by slowly releasing the heat. Japan has this technology.
When it comes to locating an NPP in a seismic area, in states such as Japan or the Philipines it is not really possible (the same pertains to, e.g. skyscrapers and other buildings). So the facilities need to be resistant to earthquakes, but there are ways to do this. After all, as I’ve already mentioned, Japanese power plants easily survived the earthquake that occurred on the 11th of March 2011. In Poland the seismic risk is minimal, so we don’t really need to be worried about it. When it comes to the tsunami, the seawall needs to be properly designed, but the magnitude of natural phenomena can be difficult to predict (the events may occur once in a hundred, or even a few thousand, or million years), so taking them into consideration at this scale would render any project unprofitable, if such solutions were implemented at a mass scale.
Either way, in case of Fukushima – and this needs to be stressed again – the disaster was caused by a natural phenomenon, and the deaths were the direct result of the tsunami.
Considering the available sources of energy, nuclear power is the one choice that could support the energy transition. It doesn’t harm the environment and is stable. How does the world perceive this technology?
Increasing numbers of people, institutions, governments and international organizations are starting to understand that nuclear power does not release CO2, dust or any other GHGs, so it is an ally in the war against climate change. It can complement renewable sources very successfully, as it is becoming more flexible in its ability to modify reactors’ capacity, which allows it to generate more power at a time when the weather makes it impossible for wind and solar sources to produce electricity. Apart from that, in the long-term, nuclear fuel efficiency does not have any competition (one kilogram of uranium is enough to power thousands of households for a year, a result that would would take hundreds of carts with coal, oil or liquid gas). All other conventional sources of primary energy (coal, oil, gas) have a limited supply which lasts between 100 and 200 years, whereas nuclear fuel can be acquired even from sea water, which the Earth has plenty of, so it can last for hundreds of thousands of years. Looking even further into the future, the exploration of space (e.g. Mars) does not seem easy without the usage of this most efficient kind of fuel. The existing space probes have systems that run on power from split radioactive elements. This isn’t unusual, because these splits take place around us every day, for instance when we drink milk, or when we are in a bathroom lined with ceramic tiles. Even when we sit comfortably in an armchair, we are bombarded by thousands of particles, but our bodies have adapted to this thanks to evolution.
Interview by Bartłomiej Sawicki