Forty years later, Chernobyl remains relevant. The disaster shapes the way we currently view nuclear power plants and crisis management. In this article, ANVS staff share lessons learned from the worst nuclear disaster in history.
On Saturday, 26 April 1986, the largest nuclear disaster in history began in the Soviet Union. At the Chernobyl nuclear power plant in Ukraine, the hot fuel melted through the steel vessel of reactor 4. Radioactive material from the reactor settled in the surrounding area and drifted across Europe in a massive cloud.
Dozens of emergency workers died from the extreme radiation near the reactor core, and tens of thousands of people were evacuated from the nearby city of Prypiat. In the decades that followed, it is estimated that thousands of people died of cancer caused by radioactive material.
Image: © Laima Kurienė
A reactor control room at the Chernobyl Nuclear Power Plant.
How could things go so wrong?
Nuclear physicist Darcy van Eerten, ANVS policy advisor for nuclear safety:
“Chernobyl is about technology, but it’s just as much about people. A test of the emergency cooling system was planned for reactor 4. Because of delays, the day shift hadn’t gotten around to it, so the night shift had to take over. They were less well-trained and were unable to get the reactor into the required state.”
“When the staff wanted to stop the test, the management insisted; they had to continue. And when the reactor began to malfunction, the team didn’t realise their measuring equipment wasn’t displaying extreme situations correctly. Or, they simply didn’t believe such an accident could happen."
Mark van Bourgondiën, advisor for knowledge development and nuclear accidents at the ANVS:
“Basically, they did not understand the behaviour of their reactor well enough in these kinds of extreme situations. They responded in a way that seemed logical, but actually had the opposite effect of what they intended.”
“The international INSAG committee investigated how the Chernobyl disaster could happen. One of their most important conclusions was that there was something fundamentally wrong with the safety culture. Safety culture means training your people properly in what they need to do in the event of an accident, and above all: listening when employees dare to say that something seems wrong. Nowadays, it is regarded as a fundamental principle across sectors ranging from aviation to industry and offshore drilling platforms. But it actually originated in the world of nuclear energy.”
Image: © USFCRFC
Reactor building 4 of the nuclear power plant Chernobyl on 26 April 1986. Source: IAEA Imagebank
What about the technical side of the disaster?
Mark: “The disaster was caused by all kinds of dangerous weaknesses in the reactor design. Chernobyl used reactors with the RBMK design, which was developed in the Soviet Union and differs from the light-water-cooled reactors commonly used in Western countries. For example, it contains flammable graphite that took almost two weeks to extinguish. And unlike Western reactors, RBMKs do not have a containment building to slow the release of radioactive material. But worst of all, in an RBMK the nuclear reaction accelerates as the temperature rises. This caused the temperature to rise even further. That self-reinforcing effect spiralled out of control, to the point that the hot nuclear fuel melted through the reactor vessel.”
Darcy: “There was also a human factor involved. Prior to Chernobyl, it had already been established at the research centre near Leningrad that higher temperatures could cause a runaway reaction in an RBMK reactor. Not enough action was taken in response. Only after the disaster were the remaining RBMK reactors technically modified so that higher temperatures would instead slow the reaction down.”
“Even so, those modifications were not enough to bring the design up to a European safety level. The problem went beyond this one technical flaw; it was rooted much more deeply in the entire design and operational approach. Lithuania was therefore required to shut down its RBMK reactor when it joined the European Union after the collapse of the Soviet Union.”
Image: © Laima Kurienė
Furniture in an abandoned house in Prypiat.
The West only discovered days after the nuclear disaster that something had happened. How did that unfold?
Darcy: “Actually, it was discovered by accident. At the entrance to the Forsmark nuclear power plant, radiation monitors were installed to detect possible radioactive contamination on footwear. The monitors activated when the morning shift arrived to start work. But Forsmark itself was operating safely, so where was the contamination coming from? The Swedish meteorological service saw that the wind had come from the Soviet Union. After pressure from abroad, Moscow admitted there had been a problem.”
What evidence was there for the disaster?
Darcy: “The staff at Forsmark found two radioactive isotopes of the metal caesium that do not occur naturally in the environment. They can only be produced in a nuclear reactor. The ratio between them showed that the source was an operating reactor, not old spent fuel that had been released.”
“Nowadays, we can determine much more about the release from a nuclear accident. My own PhD is about a method to determine, within a few hours, the ratios between various radioactive substances in such contamination. Those ratios are hard evidence of the source, even of the type of nuclear reactor and how long the fuel has been in there. If something were to go wrong at the Ukrainian nuclear power plant Zaporizhzhia due to acts of war, it would be possible to prove very quickly that any released material really came from there and not from another source.”
Could we still be caught off guard by a nuclear disaster today?
Mark: “Immediately after the Chernobyl disaster, the international community concluded treaties to ensure that countries notify one another in the event of nuclear accidents or radioactive releases. We established extensive radiation monitoring networks. In the Netherlands, approximately 150 monitoring stations are operated by the National Institute for Public Health and the Environment (RIVM).”
“In Europe, we can even directly access each other’s networks. And worldwide, information is shared through the USIE system of the International Atomic Energy Agency in Vienna. That gives much more time to respond. A nuclear disaster remaining secret for half a week would now be impossible. But during the Chernobyl disaster, the cloud of radioactive material was already drifting over Europe by the time we received the first warning signal.”
Image: © Laima Kurienė
Horse standing next to a warning sign for radioactivity in the Zone of Alienation surrounding Chernobyl.
How did we respond in the Netherlands?
Mark: “The Netherlands already had a crisis organisation in place, for example for chemical accidents. But there was no permanent team of radiation experts to assess the source, the spread, and the consequences. Those experts were quickly assembled from organisations such as the KNMI (Royal Netherlands Meteorological Institute) and the RIVM.”
“They calculated that the cloud emitted only a small amount of radiation while passing overhead. As a result, the public faced no immediate health risk. But if rain showers carried radioactive particles to the ground, they could enter drinking water or the food chain, and from there the human body. That is why grazing cows in the Netherlands had to be brought indoors. There was also a temporary ban on harvesting crops such as spinach.”
And how would that work today?
Mark: “The ANVS now maintains the CETsn, the national Crisis Expert Team for radiation and nuclear incidents. It includes all the expertise needed in radiation emergencies, from nuclear reactor operations to public health, crisis management and communication, weather forecasting, food safety, and drinking water. In normal times, we prepare scenarios and train with partners - both emergency response organisations and nuclear facilities. In the event of an accident, the CETsn advises the national government and regional safety authorities. We are also there for municipalities, provinces, embassies, and even the water boards.”
“We also monitor developments worldwide. For example, the Zaporizhzhia nuclear power plant in Ukraine lies on the front line, and there has been shelling near the Bushehr nuclear plant in Iran. No one ever imagined that fighting would take place around nuclear power plants. Fortunately, this has not yet caused any accidents. But nuclear safety is definitely under pressure there.”
How have nuclear power plants changed since this disaster?
Darcy: “After the Chernobyl disaster, and even earlier after the Three Mile Island partial meltdown in 1979, our safety requirements were radically tightened. Modern nuclear power plants operate according to what we in nuclear safety refer to as Defence in Depth. We think in terms of different phases of an accident. Everything is aimed at stabilising the situation and returning to normal operation. Individual failures can no longer lead directly to an incident. For every safety function, there are two or three independent backup systems.”
Mark: “Since the Fukushima disaster, we require nuclear plants to be able to withstand even extremely rare combined natural disasters - for example, a tsunami in addition to an earthquake. And if all other safety systems still fail, there are now all kinds of measures to limit the accident: mobile emergency power generators, for example, or connection points to pump water into the reactor. You consequently have hours, sometimes even days or weeks, to take protective measures in the surrounding area. And during that time, you still also have the opportunity to regain control of the situation.”
Image: © Laima Kurienė
The New Safe Confinement building covers reactor 4 to keep in radioactive material and protect the reactor building against weathering.
And how do we look to the future?
Darcy: “In the Netherlands, there are plans for new nuclear power plants. These must comply with ‘state of the art’ requirements: the best and most reliable technologies and procedures for nuclear safety.”
“In our assessment framework for the safe design and operation of nuclear facilities (the VOBK) we align as closely as possible with the standards of the IAEA and with licensing authorities in Europe. In this way, we strengthen one another and can demonstrate that we all uphold the highest standards. But however international we may be, verifying that a developer in the Netherlands actually meets those standards in both design and organisation is the responsibility of the ANVS. For us, safety comes first.”
Image: © Laima Kurienė
Close-up of a piano keyboard in Prypiat.