Antony Froggatt and Dr Patricia Lewis explain the background of the nuclear facility and assess the possible risks.
Zaporizhzhia, one of the world’s largest nuclear power stations, is situated on the southern bank of the Dnipro River and, as of early August, in a region controlled by Russian military forces. Within days of the start of the war, Russian forces sought to take control of nuclear facilities in the north of Ukraine (Chernobyl) and in the southeast at Zaporizhzhia. The unprecedented attack on Zaporizhzhia was followed by a military takeover of the facility on 4 March. Despite the military confrontation, Ukrainian staff have continued to operate the plant and continue to do so to this day.
Although the shelling of the station did not result in the release of radiation, Olexiy Kovynyevis, an independent expert and former reactor supervisor, reports that shells hit the turbine buildings as well as the external power supply which was ‘almost completely disrupted’. Russian forces also took control of the Chernobyl site on 24 February and held it for five weeks before withdrawing on 31 March.
On 19 April, communication between the plant and the Ukrainian regulator was restored. The International Atomic Energy Agency (IAEA), the UN body charged with overseeing the civil nuclear industry, has subsequently been involved in delivering equipment and restoring the safeguards monitoring system.
The Zaporizhzhia nuclear power plant
In early August, the Zaporizhzhia nuclear power plant once again came under attack, and shelling led to damage in the non-radioactive elements of the facility, including power lines. Zaporizhzhia is host to six Soviet-designed and built VVER light water reactors, which are safer and more proliferation-resistant.
Each of these reactors has an original design output of 950 MW, meaning they produce a significant amount of energy. Nuclear power provided 55 per cent of Ukraine’s electricity in 2021, from 15 reactors at four different power stations.
Prior to the 2022 invasion, plans were already in place to disconnect the Ukrainian grid from Russia to the European Union (EU) and, on 24 February, Ukraine decoupled its grid from Russia and operated in isolation until 16 March when it became synchronized to the EU. Work which was expected to take one year was completed in two weeks.
The Ukrainian authorities want to increase the volume of electricity exported to the EU to raise revenues and are frustrated by the slow and gradual increase that the network for European Grid operators (ENTSOE) are requiring to ensure grid stability.
In early August the president of Ukraine’s nuclear energy agency Energoatom said Russia wanted to connect the Zaporizhzhia power plant to the Crimean grid and there are other power stations in the region including coal-fired and hydroelectric.
What is at stake?
Probably more than any country in the world, Ukraine is aware of the consequences of an explosion and fire at a nuclear power plant. In April 1986, Ukraine suffered the world’s worst nuclear power accident at Chernobyl, which resulted in radioactive material being spread across continental Europe. The monitoring of livestock grazing on land in the UK contaminated by the accident was only lifted in 2012.
The accident also had a significant impact in Ukraine with around 350,000 people evacuated because of the accident and a further 600,000 people registered as emergency and recovery workers. Given the longevity of the consequences and the changing political circumstances with the break-up of the USSR in 1992, assessing the economic consequences is uncertain but will run into hundreds of billions of dollars.
The core of a nuclear power plant holds the radioactive fuel that powers the reactor. The amount of fuel in the core can vary considerably depending on the size of the reactor and the type of fuel that is used, and whether the uranium is enriched or not. Chernobyl reactors used slightly-enriched uranium and consequently the fuel in its core was approximately 200 tonnes, which in Light Water Reactors would be closer to 30 tonnes in weight.
In addition, the RBMK reactors were graphite-moderated which meant that they burned at high temperatures contributing to the enormous amount and height of the radioactive plume from the accident. Although Zaporizhzhia uses enriched uranium, its current VVER reactors are not moderated by graphite, but by water, which means they are safer and will not burn in the way of Chernobyl.
Modern reactors in Ukraine, like Zaporizhzhia, are also surrounded by a secondary containment system – a hard concrete shell designed to withstand explosions and a crashed airplane.
However, it is unclear as to how effective they would be against attacks as the thickness of the containment wall in this design of reactor is traditionally 1.2 metres thick, and a thickness of around two metres is required for new construction projects.
However, radioactive material at Zaporizhzhia is also stored in the spent fuel ponds, where used fuel is kept underwater to cool and to allow radiation levels to fall before being moved to a final store.
If coolant is lost from the ponds, either by a direct hit which breaches containment structures or by a meltdown of the core due to losses of power, the stored fuel will heat up. If the temperature rises above around 900 degrees Celsius, the cladding around the zirconium cladding will ignite, leading to the spreading of radioactive material.
The meltdowns at three reactors at the Fukushima nuclear power plant in Japan in 2011 were caused by a tsunami flooding the site and disabling the back-up emergency generators as well as the external power supply. Consequently, it was impossible to cool the reactors resulting in the eventual melting of the core (between four and 77 hours after the initial tsunami, depending on the unit). More than 100,000 people were initially evacuated from their homes because of the subsequent release of radiation.
Any release of radioactive isotopes could be catastrophic for the surrounding areas, but because of the type of reactors at Zaporizhzhia, the impact would likely be nowhere near as severe as the 1986 Chernobyl disaster and more likely be similar in scale to the 2011 Fukushima nuclear crisis.
It is also important to note neither disaster was on a par with the impact of a single nuclear weapon detonation which, as can be seen from the devastation at Hiroshima and Nagasaki in 1945, would be far more catastrophic than even the worst accidents imaginable at a civil nuclear power facility.
Nonetheless, radioactive debris would likely spread to countries surrounding Ukraine and depending on wind patterns, that could well include Russia, as well as to the rest of Europe, possibly even to the Middle East and North Africa. There would also likely be contamination of the water in the Dnipro river and the Kakhovka Reservoir which would have severe impacts on local agriculture.
According to the head of the Ukrainian nuclear energy agency, as of early August there was only one power line connecting the power station to the grid. This is a safety concern as external power sources are needed to maintain key functions – such as cooling and machine controls – even if the reactor shuts down.
The director general of the IAEA, Rafael Mariano Grossi, has expressed grave concern over the situation and once again called on the Russian authorities to allow his organization access to review nuclear safety, security, and safeguards.