Measure 1: prevent a blackout
‘The power supply is currently under pressure at Zaporizhzhya’, says Mark van Bourgondiën of the Authority for Nuclear Safety and Radiation Protection. On October 8, 12 and 16, the main connection to the power grid was cut; of the four cables of that connection, only one is still in use.
The connections to a secondary power plant were also damaged by shelling in the area. However, the plant also has twenty diesel generators on site. Each reactor can handle one such aggregate, and has three. In addition, two movable aggregates are available. In total, the diesel generators currently have fuel in stock for ten days.
If one of the nuclear reactors is on, these diesel generators are not necessary; the power station can then supply itself with power. Currently, however, all six reactors are shut down due to the fighting in the area.
Measure 2: prevent meltdown
When all power supplies fail at the same time, there is a risk of a so-called meltdown. Even when the reactors are turned off, fuel rods remain radioactive and hot for a long time. They must therefore be cooled with water. If this does not happen, one or more fuel rods can melt. Around the rods, which together form the core of the reactor, is a steel pressure vessel with steel walls that are centimeters thick. If the radioactive material also melts through it, it may be able to escape into the environment.
The fuel rods lie in water in modern pressurized water reactors. ‘During normal operation of the nuclear power plant, the fuel heats that water, producing the steam that then drives a generator,’ says Joost van den Broek of NRG, which manages, among other things, the Dutch nuclear reactor at Petten. When the reactor is switched off, the same water still serves a second purpose: to cool the fuel rods present in order to remove the residual heat.
‘How long the available water can do this depends on how long the nuclear reactor has been switched off,’ says Van Bourgondiën. Reactors that have already cooled themselves can be without power for at least a hundred hours before the core runs dry. If a reactor that was still running suddenly becomes without power, the water present provides a buffer of a few hours to half a day. Engineers can use that time to restore the power supply or add fresh cooling water.
Measure 3: prevent a break in the casing
If meltdown nevertheless occurs, there is a risk of radioactive material escaping. However, the nuclear reactors at Zaporizhzhya are protected against this. First of all, they have a rudimentary ‘tub’ under the reactor, as radiation expert Lars Roobol of the RIVM describes it. ‘It should prevent the melting material from leaking into the soil.’
Just as important is an extra airtight envelope around the reactor, which should keep the material inside even after it has escaped from the pressure vessel around the core. ‘There was no such cover at Chernobyl and Fukushima,’ says Roobol.
If the pressure is too high due to the released material, it can escape through a valve with a filter that captures the most harmful particles – iodine, cesium. ‘What then remains are radioactive noble gases,’ says Van Bourgondiën. Unlike iodine and cesium, which can adhere to, among other things, soot and dust particles, these noble gases remain in the air. “They don’t rain down, for example.” Residents may have to take shelter in the first kilometers around a nuclear power plant to avoid contact with the radiation cloud, but the further radiological consequences are therefore limited.
‘These domes are also designed to deal with everything from earthquakes to planes crashing into them,’ says Van den Broek. ‘They can certainly take a beating, but of course acts of war around such a power station are never wise.’ The effect of high explosives on the domes is also unknown.
If, despite all the defense lines, it ever comes to the point that there is a meltdown and a damaged dome, the consequences for the immediate environment will be the greatest. It may then be necessary to evacuate people who live within the first tens of kilometers of the power station. And up to a distance of about 100 kilometers, exposure to the radioactive particles can increase the risk of developing cancer for the rest of life.
The Netherlands will not notice much of the direct radiation consequences, says Roobol: ‘When the Chernobyl disaster took place, the extra radiation here was comparable to what you normally have to process in a few weeks in natural radiation.’
Press the employees
The International Atomic Energy Agency also warns emphatically against the non-technological risks of a nuclear disaster. For example, the workload on the employees of the nuclear power plant has increased enormously since the beginning of the war. ‘Due to human errors, you may be faced with one of the emergency scenarios sooner, even if it is not technologically necessary at all,’ says Mark van Bourgondiën. ‘They must be able to make timely adjustments when unexpected situations arise.’
Drying cooling baths
In addition to fuel rods in the nuclear reactor, Zaporizhzhya also has old rods in cooling baths. After a few years they have cooled down to such an extent that they can go to ‘dry storage’ – encased in metal and concrete – but until then they can boil dry and melt when the cooling stops. Those baths are indeed located in a sturdy building, ‘but there is no such protective dome around it’, says Lars Roobol of the RIVM. Even so, the worst-case scenario will take at least a few days to boil dry. That should in principle be enough time to correct any technical issues.