What Is a Nuclear Reactor? Ukraine Accuses Russia of Firing at Kharkiv Nuclear Facility

Russian forces have fired upon another Ukrainian nuclear facility, according to reports.

The invading army "shot the Kharkiv Institute of Physics and Technology," which is said to house nuclear material and an experimental reactor, government-affiliated news outlet Ukraine NOW reported via Telegram on Sunday, citing Ukraine's security service, SBU.

Emine Dzheppar, Ukraine's first deputy minister of foreign affairs, criticized the attack on Twitter and said, in translation, that the attackers had used "multiple rocket launchers."

The extent of the damage to the facility or to the alleged nuclear material inside is unclear. Ukraine NOW reported that damage to the stored nuclear material "could lead to a large-scale environmental disaster."

Russia's defense ministry is claiming that it is in fact Ukrainian forces that are planning to damage the reactor and then accuse Russian forces of doing so, Russia's TASS news agency reported on Monday.

Russia carried out a high-profile attack on Ukraine's Zaporizhzhia nuclear power plant last week. It is now under the control of Russian forces.

The attack led to international alarm as it caused a fire at the plant that was later extinguished. Damage to nuclear power plants or to their safety systems poses an environmental risk due to radiation leakage and it could potentially lead to a meltdown situation in which hot nuclear fuel escapes its containment.

Staff have remained at the nuclear plant to carry out safety and security duties, though communications between the plant and the Ukrainian nuclear regulator have been affected.

Rafael Mariano Grossi, director of the International Atomic Energy Agency (IAEA), voiced concern about the situation and said in a statement posted to the agency's website: "Reliable communications between the regulator and the operator are a critical part of overall nuclear safety and security."

How Nuclear Reactors Work

Nuclear reactors are what nuclear power plants use to create energy. They are, essentially, large kettles that use heat from nuclear reactions to boil water that turns into steam that can be used to turn a turbine.

In order to generate this heat, reactors contain a radioactive nuclear fuel like uranium. Atoms of uranium can be split apart in a process called fission, which happens when a particle called a neutron collides with a uranium atom.

This collision releases heat and also causes the uranium atom to fire off neutrons of its own, which go on to split apart other uranium atoms in a chain reaction.

Reactors have systems that control this process and are capable of slowing it down or speeding it up. Crucially, reactors must be controlled so that the chain reaction doesn't occur too quickly, otherwise the nuclear fuel will overheat and melt—a meltdown.

A meltdown can be a catastrophic situation if the melted nuclear fuel escapes the reactor, since this would expose the environment to massive amounts of radiation.

Reactors therefore have systems that can control the speed of the nuclear chain reactions and also circulate coolant around the fuel—usually water.

Nuclear power plant
Cooling towers release steam at a nuclear power plant near Grafenrheinfeld, Germany, in June, 2015. Nuclear reactors have various safety systems to control the reactions that take place. Sean Gallup/Getty