The reactors are surrounded by high strength containment buildings. These are designed to both contain explosions from within, and to withstand a certain amount of force from outside. However, while modern plants are designed to withstand aircraft strikes, it is debatable whether they could withstand deliberate bombardment. They are made of many metres of concrete, with steel liners, but a concerted effort with appropriate weapons would eventually be able to penetrate them.
Of perhaps greater concern are the outdoor spent fuel cooling pools, where highly radioactive spent nuclear fuel is stored underwater. A direct attack on any of these could lead to a major release of radioactive material into the atmosphere, as the fuel is relatively unprotected against strikes from the air.
Safety-critical equipment, such as pumps and pipes, remains important even after the nuclear power plant has been shut down. Three of Zaporizhzhia’s six reactor units are currently in a shutdown state. Fuel within the reactor, as well as used fuel, remains very hot for several years after shutdown and removal from the reactor. At plants such as Zaporizhzhia, unless the fuel is constantly cooled, it can overheat, generating explosive gases, melting, or catching fire. This would also lead to a radiation release.
Should there be 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 how much material is released and how it is spread by wind and weather. The level of radiation would be highest close to the plant and reduce as it spreads, with those exposed potentially experiencing health impacts.
For those 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 can increase cancer risks later in life. The best course of action is to take shelter in buildings, close all doors, windows and vents, and follow advice from trusted authorities.
Russia’s president Vladimir Putin might wish to control the plant for several reasons. Russia could cut power supplies from the plant to Ukraine, but it was operating in a low power mode at the time of the invasion and so this may be of limited impact. Alternatively, Russia might use it as a political bargaining chip or propaganda tool, in order to legitimise claims over occupied territory. Various sources also suggest that Russia has stationed troops and equipment at the plant. This allows it to be used as both a fortress and missile launch site, against which Ukraine dare not retaliate.