Weighing the risks of a Zaporizhzhia nuclear meltdown

The United Nations nuclear watchdog has called Russia and Ukraine set up a “protection and safety zone” around the besieged Zaporizhzhia nuclear power plant in the Ukrainian city of Enerhodar.

The appeal, issued on September 6, 2022 by the International Atomic Energy Agency (IAEA), comes amid growing concerns that the facility – Europe’s largest nuclear power plant – is vulnerable nearby fighting, and that damage to the site could cause a catastrophic disaster. accident.

The bombardment has already damaged power and communication lines to the factoryinciting factory safety fears and evoking painful memories in a country still marked by the worst nuclear accident in the world, in Chernobyl in 1986.

In addition, the Russian authorities have made plans to disconnect the factory of the Ukrainian power grid – in the event of damage to the plant, according to the Russians, as a prelude to the switchover of the plant to the network in Russian-occupied territory, according to the Ukrainians. Disconnecting the central from the network is a risky operation.

Najmedin Meshkatiteacher and nuclear safety expert at the University of Southern California, explains the risks of war unfolding in and around nuclear power plants.

How safe was the Zaporizhzhia power plant before the Russian invasion?

The Zaporizhzhia facility is the largest nuclear power plant in Europe and one of the largest in the world. He has six pressurized water reactorswhich use water to sustain the fission reaction and cool the reactor.

These differ from RBMK Chernobyl reactors, which used graphite instead of water to sustain the fission reaction. RBMK reactors are not considered very safe, and there are only eight remaining in service in the world, all in Russia.

Zaporizhzhia’s reactors are of moderately good design and the plant has a decent safety record, with a good operating history.

Ukrainian authorities have tried to move the war away from the site by asking Russia to observe a 30-kilometre (nearly 19-mile) security buffer zone. But Russian troops surrounded the facility and grabbed it in march.

What are the risks for a nuclear power plant in a conflict zone?

Nuclear power plants are built for peacetime operations, not wars.

The worst thing that can happen is for a site to be deliberately or accidentally bombed. If a shell hits the plant spent fuel pool – which contains the still radioactive spent fuel – or if the fire spreads to the spent fuel pool, it could release radiation. This spent fuel pool is not within the containment and is therefore more vulnerable.

The containment buildings, which house nuclear reactors, are also not protected against deliberate bombing. They are built to withstand a minor internal explosion from a pressurized water pipe, for example. But they are not designed to withstand a huge explosion.

As for the reactors in the containment, it depends on the weapons used. The worst case scenario is for a bunker buster to pierce the containment dome – a thick reinforced concrete shell above the reactor – and explode.

This would severely damage the nuclear reactor and release radiation into the atmosphere, making it difficult to dispatch first responders to contain any resulting fires. It could be another Chernobyl.

Ukrainian Emergencies Ministry personnel conducted a drill in the city of Zaporizhzhia on August 17, 2022, to prepare for a possible radioactive leak from the nuclear power plant near the city. Photo: Dimitar Dilkoff / AFP via Getty Images / The conversation

What are the upcoming concerns?

The security issues I see are two-fold:

1) Human error

Settlement workers work under incredible stress, allegedly held at gunpoint. Stress increases the risk of error and poor performance.

There is a human element to managing a nuclear power plant – the operators are the first and last layers of defense for the facility and the public. They are the first to detect any anomaly and stop any incident. Or if there is an accident, they will be the first to heroically try to contain it.

This concern was highlighted in the report by the International Atomic Energy Agency, which noted that Ukrainian staff at the plant were working under “constantly high stress and pressure” – which could have safety consequences. nuclear.

2) Power failure

The second problem is that the nuclear power plant needs constant electricity, which is more difficult to maintain in times of war.

Even if you shut down the reactors, the plant will need offsite power to run the huge cooling system to remove the waste heat in the reactor and bring it to what is called a cold shutdown. Water circulation is always necessary to ensure that the spent fuel does not overheat.

Fuming pools also need constant water circulation to keep them cool, and they must be cooled for several years before they can be put into dry barrels. One of the problems of 2011 Fukushima disaster in Japan, backup generators to replace lost offsite power were flooded with water and failed. In such situations, you get “station power cut” – and that’s one of the worst things that can happen. This means that there is no electricity to run the cooling system.

The spent nuclear fuel rods are stored at the bottom of this pool, which requires constant circulation. Photo: Guillaume Souvant/AFP via Getty Images

In this case, the spent fuel overheats and its zirconium sheath can create hydrogen bubbles. If you cannot evacuate these bubbles, they will explode, spreading the radiation.

If there is a loss of outside power, operators will have to rely on backup generators. But emergency generators are huge machines – finicky, unreliable guzzlers of gas. And you still need cooling water for the generators themselves.

My biggest concern is that Ukraine is suffering from a prolonged power grid outage. The likelihood of this happening during conflict as power line pylons may fall under bombardment or gas-fired power stations may be damaged and cease to operate.

And although the Ukrainian intelligence services claim that the Russians intend to stockpile diesel fuel to run these emergency generators, Russian troops are unlikely to have a surplus of fuel since they must power their own vehicles.

How else does a war affect the safety of nuclear power plants?

One of the main concerns about the effects of war on nuclear power plants is that war degrades safety culturewhich is crucial in the operation of a plant.

I believe the culture of safety is analogous to the human body’s immune system, which protects against pathogens and disease. Safety culture is pervasive and has a wide impact. “It can affect all elements of a system for better or worse,” according psychologist James Reason.

The tragic situation at the Zaporizhzhia nuclear power plant violates all the universally accepted principles of healthy nuclear safety culturein particular maintaining an environment where staff can raise security concerns.

War negatively affects security culture in several ways. Operators are stressed and tired and may be afraid to speak up if something is wrong. Then there is the maintenance of a plant, which can be compromised by the lack of personnel or the unavailability of spare parts.

Governance, regulation and oversight – all crucial to the safe operation of a nuclear industry – are also disrupted, as are local infrastructure, such as the capacity of local firefighters. In war, everything is more difficult.

So what can be done to better protect Ukrainian nuclear power plants?

The only solution is to declare a demilitarized zone around nuclear power plants, similar to the protection zone advocated by the International Atomic Energy Agency. However, Russia previously rejected UN Secretary-General António Guterres’ decision. plea to declare a demilitarized zone around the factory.

I think an optimal, but not ideal, solution is to cold shut down the two operating reactors before any further loss of offsite power and risk of plant failure, to store more fuel for the diesel generators of backups at various locations on the plant site, and keeping only skeletal maintenance staff to tend to the spent fuel pools.

Of course, this is only a palliative measure. Along with the effort of the International Atomic Energy Agency under the leadership of its Director General Rafael Mariano Grossi, the UN Security Council should immediately authorize a special commission to mediate between the warring parties.

It could be modeled on the United Nations Monitoring, Verification and Inspection Commission in 2000, and appoint a prominent international statesman as its head.

I believe the person should be of the caliber and mold of the legendary former director general of the International Atomic Energy Agency, Hans Blix from Sweden. Blix led the agency at the time of the Chernobyl accident in 1986 and commands respect in today’s Russia and Ukraine.

War, in my opinion, is the worst enemy of nuclear safety. This is an unprecedented and volatile situation. Only through active and pragmatic actions nuclear engineering and diplomacy can we find an acceptable and lasting solution to this thorny problem.

Najmedin Meshkati is a professor of engineering and international relations, University of Southern California

This article is republished from The conversation under Creative Commons license. Read it original article.