Bombings recently intensified at the Russian-controlled Zaporizhzhia nuclear power plant, raising international security concerns. Ukrainian personnel continue to operate the massive plant under tight control and under stressful conditions. The plant, located in the near-frontline town of Enerhodar, is the largest in Europe, and it seems unlikely that either side would want to seriously damage it and cause a release. of radiation.
Could this cause a disaster like Chernobyl?
The Zaporizhzhia power plant is not like Chernobyl, the site of the world’s biggest nuclear disaster. Chernobyl was an older type of reactor, with several questionable design choices. Like Zaporizhzhia, it was cooled by water, but it also contained large amounts of graphite to perform a function known as neutron moderation, necessary for the operation of the reactor.
When the Chernobyl reactor overheated, the water boiled and became less effective for cooling. However, the graphite continued to moderate the neutrons, allowing reactor power, and therefore temperature, to build up uncontrollably. Chernobyl’s shutdown system was also poorly designed and contributed to the accident.
In Zaporizhzhia, as with the majority of reactors in the world, if the reactor overheats, cooling and moderation are reduced, and therefore the power of the reactor also decreases. Nuclear engineers consider this fundamental to the design of safe reactors.
So is the Zaporizhzhia reactor safer than Chernobyl?
A breach in a powered and operating reactor could still be disastrous if attacks damage nuclear materials or safety-critical equipment. This could release large amounts of hazardous nuclear material into the air, potentially contaminating large areas of land and water supplies.
The reactors are surrounded by high strength containment buildings. These are designed both to contain explosions from the inside and to withstand some force from the outside. However, while modern factories are designed to withstand airstrikes, it is debatable whether they could withstand deliberate bombardment. They are made of several meters of concrete, with steel linings, but a concerted effort with appropriate weapons could eventually penetrate them.
Perhaps of more concern are outdoor spent fuel cooling pools, where highly radioactive spent nuclear fuel is stored underwater. A direct attack on one could result in a major release of radioactive material into the atmosphere, as the fuel is relatively unprotected from airstrikes.
Safety-critical equipment, such as pumps and pipes, remain important even after the nuclear plant is shut down. Three of Zaporizhzhia’s six reactors are currently shut down. The fuel inside the reactor, as well as spent fuel, remains very hot for several years after shutdown and removal from the reactor. In factories such as Zaporizhzhia, unless the fuel is constantly cooled, it can overheat, generate explosive gases, melt or catch fire. This would also lead to radiation rejection.
Fuel in Zaporizhzhia requires a constant flow of cooling water to remove excess heat. If this water were to be lost due to damage to pipes, pools or reactors, or if pumps became inoperative, there would be only a limited time to intervene before dangerous consequences were felt. Claimed attacks so far have largely hit power lines, radiation monitoring equipment and non-nuclear buildings such as training facilities.
Attacks on power lines are of particular concern, as reliable access to offsite electrical power is required for pumping cooling water. The plant can generate its own power while in operation and has a range of backup diesel generators in case offsite power access fails, but the loss of any safety systems is a concern.
What risk does a release of radioactive materials pose?
In the event of a release of radioactive material, authorities will need to act quickly to assess the danger and respond appropriately. The risk will depend on factors such as the amount of material released and how it is spread by wind and weather conditions. The level of radiation would be highest near the plant and would decrease as it spreads, with those exposed potentially causing health effects.
For people exposed to very high levels of radiation, there is a risk of acute radiation syndrome, which can be fatal in the worst cases. Lower levels of exposure may increase cancer risks later in life. The best thing to do is to take refuge in buildings, close all doors, windows and air vents and follow the advice of trusted authorities.
What seems to be Russia’s strategy vis-à-vis the plant?
President Vladimir Putin might wish to control the factory for several reasons.
Russia could cut power from the plant to Ukraine, but it was operating in low-power mode at the time of the invasion and so this could have a limited impact. Alternatively, Russia could use it as a political bargaining chip or propaganda tool, to legitimize claims to occupied territory. Various sources also suggest that Russia stationed troops and equipment at the plant. This allows it to be used both as a fortress and a missile launch site, against which Ukraine dares not retaliate.
Military conflicts around nuclear sites were prohibited by the 1977 amendment to the Geneva Conventions. However, attempts by the international community to deal with the Russian occupation of Zaporizhzhia were largely unsuccessful. The International Atomic Energy Agency has repeatedly requested access to review conditions and verify that nuclear material remains in place, but has not yet been granted entry.
The UN recently called for the site to be demilitarized, but Russia says this would put the plant at greater risk due to alleged nuclear terrorism threats. Placing the plant under the guard of a neutral third party for security reasons could be a potential solution. However, there is a risk that even a neutrally owned factory could be attacked by disguised military forces, in order to support the Russian narratives of Ukrainian terrorist groups.
Above all, the violence around the plant must stop and verification access must be granted to the international community. Military action around the plant must cease as soon as possible to protect people, the environment and infrastructure.
(Ross Peel is a nuclear expert at King’s College London.)