People around the world watched live through a security camera as Russian forces attacked and seized Ukraine’s Zaporizhzhya nuclear power plant – Europe’s largest – on Friday morning local time. Against the background of shelling and shooting at the training complex in the complex there was a fire, which was later extinguished, according to news. The incident has alarmed world leaders and nuclear experts about the possibility of targeted or accidental damage to the reactor, which could cause radiation leakage or, at worst, melting of the reactor core.
Rafael Grossi, director general of the International Atomic Energy Agency (IAEA), told the UN Security Council that the station was operating normally after the attack, and said there were no radioactive materials. But he and other nuclear experts have warned that there is a danger of accidents there and at other nuclear power plants in Ukraine as the conflict continues.
Scientific American spoke with Edwin Lyman, director of nuclear safety at the Union of Interested Scientists, to explain concerns about such facilities in wartime and to discuss some of the security measures in place.
[An edited transcript of the interview follows.]
What type of reactors in the Zaporozhye complex and how can they differ from the reactors at the Chernobyl or American nuclear power plants?
Six reactors in Zaporozhye are called VVER-1000, and they are cooled and moderated by light. [ordinary] water. So in this respect they are similar to American pressurized water reactors. These are slightly more advanced models than previous versions [this type of reactor], so they have some features that are more in line with modern security philosophy, but not completely. And they are different from Chernobyl-type reactors called RBMK, which used a different retarder material – graphite – and had many technical shortcomings that contributed to the emergence and severity [Chernobyl] accident in 1986. Thus, the type of Chernobyl accident that is essentially a power outage is highly unlikely in a light water reactor.
In any nuclear reactor, the goal is to support the fission chain reaction in a fuel that generates heat, as well as the extra neutrons used to propagate the chain reaction. When uranium atoms fission, they emit heat, so the fuel heats up. Water in this type of reactor is pumped through the core and heated and then transferred to another circuit that is under high pressure. And then it is transferred to another system of steam generators, where the water turns into steam, and that turns the turbine.
These [Zaporizhzhia reactors] were developed in the Soviet Union and they date back to the early 1980s. Thus, they expired, but the Ukrainians extended their licenses.
Does the age of the reactors here affect safety issues?
Well, this should always be considered because they got a license extension. They have been repaired to some extent, but there are always systems that cannot be replaced. For example, the capacity of the reactor fuel, which becomes brittle over time, is dangerous in some types of accidents, so you need to consider this.
What types of safety systems will this type of emergency reactor have?
The great danger of any nuclear reactor is that the cooling of the fuel is somehow disrupted, because without sufficient cooling the fuel heats up to such an extent that it can destroy itself. This is what happened, to a lesser extent, on Three Mile Island [in Pennsylvania in 1979] and, to a greater extent, on Fukushima [in Japan] in 2011. In addition, these stations store spent nuclear fuel on site, and some of this fuel is stored in cooling water, which also needs to be replenished with pumps.
Modern reactors of this type have emergency core cooling systems, so that if there is a break in the cooling pipe, they have systems that can directly inject emergency coolant. And these [VVER-1000s] there are such systems, unlike some earlier versions of these Soviet reactors.
In addition to the break in the pipeline, there may be a loss of electricity, which affected Fukushima. These stations typically draw electricity from the grid to operate their systems, and if this is interrupted, they must rely on backup power from emergency diesel generators. Each reactor has three, and then a couple more, so the plant has a lot of spare diesels. But there is always the possibility that something will happen that could disable several units at once – for example, in Fukushima, where the site was flooded, and despite the fact that they had a lot of backup diesels, they stopped working. After Fukushima, as in many other countries, Ukraine has developed additional measures to cope with such an accident, similar to Fukushima, where there is a prolonged loss of electricity. And this included the purchase of additional mobile pumps that do not require electricity and run on diesel fuel.
What are the main problems associated with the fighting at or near these nuclear facilities?
Clearly, there is potential for different types of damage: either direct, destructive damage to station systems, security systems, infrastructure, or indirect damage to ancillary systems such as off-site electricity. And [there is] the potential of a fire that can spread and disable an instrument control system. Very few of them are considered what you would need if you are going to worry that there is a real possibility of locating this plant in the middle of a war zone.
I guess the moral is that if you want to potentially seriously damage a plant, you don’t need to go after building a sealant, which is the hardest part. There are other systems that are not as well protected. But even these deterrent buildings are not necessarily capable of withstanding certain types of military attacks. Even if they are not broken, they can crack and concrete can fall on the reactor vessel. Or just strong vibrations can also cause damage.
Prior to this attack, was there growing concern in the nuclear community that something like this could and could potentially cause an accident?
It’s like unspoken fear. There have been some individuals who have been raising this for a long time, but these fears have largely been dismissed. You may have many concerns about nuclear power, and some of them seem very unbelievable – and until they happen, people tend to abandon them. And this is one example.
The cost of hardening commercial nuclear power plants so they can survive military pressure is probably too high. At the beginning of the nuclear era, people like Edward Teller [a theoretical physicist and member of the Manhattan Project] thought that nuclear power plants should be underground.
If there was damage to the Zaporozhye plant, what explosion or radiation leak?
It depends on the progression of the accident, how serious it is and whether these emergency measures can be applied. In the worst case, if you have a permanent loss of cooling capability, the nuclear fuel can overheat, melt and burn out the steel body of the reactor that holds it, and fall to the floor of the container. And in this case, defensive protection is the only barrier between the radioactive material in the reactor and the environment. It is designed to withstand certain types of events but not others.
On Three Mile Island, the core partially melted, but operators were able to stop in time – before it reached the point where it melted through the reactor vessel. But even then, the damaged fuel formed a lot of radioactive gases that needed to be removed, although they had relatively low radiotoxicity. If the tightness is not broken, they leak – no building can be perfectly sealed. But this leak is designed and tested as relatively low. [In] In the United States, there is a regulatory limit on how serious an accident can be in terms of public exposure, and safety and containment systems have been developed for this purpose. But, again, this implies certain things about the nature of the accident that may turn out to be false or exceed, for example, at Fukushima.
I think a particular type of Chernobyl emission – which was quite large and was pumped high into the atmosphere and was widespread – is probably less likely with such a reactor. If you look at Fukushima, the emissions were smaller and they didn’t spread over such a wide area. This is, of course, a regional problem. But if several reactors are affected at the same time, if the spent fuel is damaged, if the sealing protection is broken mechanically, then all rates are canceled.
Reports indicate that after Russia seized the Chernobyl site in Ukraine, its staff is still working and unable to cross. What are the worries there and in Zaporozhye, if the changes can not unload each other?
Well, well-rested operators are very important because the tasks they have to perform are complex and they have to be alert. You need to make sure that fatigue is controlled. If there are factory workers and they don’t get any help and they can’t go home and they work under duress, it’s a dangerous combination. There must be measures for this.
What should combatants and the IAEA do?
The IAEA doesn’t have much power in this area, and I see Director General Grossi struggling with that. He made this offer to go to Chernobyl and agree on some deal. But it is not clear exactly what, and it will depend on the goodwill of the parties. This means resolving this in the context of a military conflict.
Ukraine and Russia have agreed on a temporary ceasefire in certain areas for the safe passage of the population, and they could simulate this until some agreement is reached on how the nuclear power plant will operate.
This raises these complex questions about how far Ukraine will go to prevent a military seizure of a nuclear power plant, and the possibility of harm.
Risks of Russian attacks near Ukrainian nuclear power plants
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