One of the reactors in Europe's largest nuclear power plant, Zaporizhzhya, was shut down on Friday due to damage after Russian artillery fire, according to Ukraine's state nuclear company Energoatom.

The plant consists of six reactors, but only three were operating before Friday's attack.

Russia has claimed that Ukraine is behind the shelling.

Could be a quick stop

According to Tomas Jelinek, inspector at the Radiation Safety Authority, it may be that the reactor went through a quick shutdown, which can be interpreted as a normal safety measure for a nuclear power plant. 

- The safety systems caused the control rods to fall down and the reactor simply shut down production.

This is something that happens on average once a year for a nuclear power plant, he says. 

- It is simply stopped because something is not right. 

Worst case scenario comparable to Fukushima 2011

Tomas Jelinek points out that the most likely thing is that as a result of the war in Ukraine, the nuclear power plant will eventually become unusable, but without that necessarily leading to a nuclear accident or a major breakdown.

In that case, parts of Ukraine's energy system could be knocked out.

- The worst that can happen is a severe accident and then we have analyzed what can happen, which can be compared to Fukushima in 2011. If an incident occurs and all safety systems are out of order, you can have a meltdown, but the consequences occur within a couple miles in the immediate area.

- It is unlikely, but not impossible, he adds.

The nuclear power plant in Fukushima had the same structure as Zaporizhzhya with six light water reactors of the same type, according to Tomas Jelinek.

The security systems must be robust

However, the situation on the ground is difficult to assess, underlines Tomas Jelinek.

According to a statement from the UN atomic energy agency IAEA on Saturday, there is a "very tangible risk of a nuclear disaster", but there is no information about damage to the reactors or the release of radioactive substances.

However, the IAEA has not been allowed to go there to independently assess the nuclear power plant's status, Tomas Jelinek believes.

- Nuclear power plants are built to withstand extreme events and even explosions.

They are robust but there are explosions large enough that parts of the facility can break.