EXPERT REACTION: Fire at Ukrainian nuclear power plant

The Zaporizhzhia nuclear power plant in Ukraine is under siege from Russian troops, with reports of fire in a building in the sprawling six-reactor complex. Though highly concerning, this is not tracking to be another Chernobyl. The Zaporizhzhia reactors have many levels of protection, and it is not in Russia’s interest to create a nuclear incident on its doorstep. More likely, the Russian military seeks to secure the facility to control electricity supply in Ukraine. US Govt reports indicate the reactors have already been moved into a safe mode. The reactor buildings are designed to withstand a wide range of scenarios, including light-plane impacts. Given that the reactors are a widely-used Russian design, the military are presumably tuning their actions according to the strength of the facility. But this is all supposition from afar, and war is a notorious time for unexpected consequences.

A single fire located somewhere on the same site as a nuclear power plant cannot feasibility trigger a meltdown, however if the blaze cannot be contained then the nuclear power plant at the Zaporizhzhia site will be shut down and cannot generate electricity for the people of the Ukraine. A greater risk to nuclear safety is a direct hit on a reactor building or spent fuel pool by explosive ordnance, which could release radioactive material if the blast is sufficiently powerful to breach containment.

Please try to forego the temptation to contribute to quasi-apocalyptic media coverage of the risks at nuclear power installations. The availability of nuclear power is vital to energy security in multiple European States and particularly in Ukraine. All nuclear-related risks to people in the vicinity, even in very worst case scenarios, pale in comparison to the very direct and lethal hazard of continued fighting on the ground.

The six nuclear power reactors at Zaporizhzhia are not Chernobyl type reactors, they are 950 MW VVER-320 (Pressurised Water Reactors), built 1980/86.

Unlike Chernobyl, they have a containment around the reactor to stop any radioactive release. Unlike Fukushima, these VVER reactors have separate water circuits to cool the reactor and to produce steam.

In addition to the normal cooling systems, these reactors have emergency core cooling systems consisting of 4 hyroaccumulators which will passively inject cooling water into the reactor in the event of a problem. They also have multiple train high pressure and low pressure injection systems to prevent a core melt.

The fire is reported to be in a training building. The reactor is enclosed in a massive concrete containment which protects it from fires.

At present it seems as though it is only ancillary buildings that have been damaged by Russian missiles. The real concern is not a catastrophic explosion as happened at Chernobyl but damage to the cooling system which is required even when the reactor is shut down. It was this type of damage that led to the Fukushima accident.

There are significant concerns at the moment about a meltdown if any part of the core were to be affected. This would be catastrophic.

We also need to understand if the plant has been shut down, and where external power is coming from. If the connection to the grid is broken we're relying on back-up diesel generators which are a massive fire hazard.