13th blackout at ZNPP - expert explained the threat and named the main risks to the plant's safety

On April 14, the Zaporizhzhia Nuclear Power Plant (ZNPP), occupied by Russian troops, experienced its 13th blackout. The NPP lost all external power supply in the morning after the last external power transmission line was disconnected.

Emergency generators immediately started working. And the outage itself lasted only 1.5 hours. But the incident once again drew the attention of the public and specialists to the state of nuclear safety at the occupied facility.

What does the power outage at ZNPP mean and what threatens the plant, UNN asked Oleg Dudar, former head of the ZNPP operational unit and an expert in nuclear energy.

The specialist explains: after another power outage, the plant is not on the verge of a nuclear catastrophe. After all, all six power units of the plant are currently in a state of cold shutdown, which is considered the safest possible for a nuclear facility.

The suspended chain fission reaction in the active zones and the parameters of the first and second circuits correspond to temperatures somewhere less than 70 degrees. The pressure in the first circuit is currently less than 35 kgf/cm2, but it is close to atmospheric. This is considered the safest state, if, of course, these were conditions of reliable operation by Ukrainian officers, and not by the "personnel" who are currently managing the plant

However, even in this mode, the facility constantly requires electricity to cool the active zones and maintain safe operating parameters.

Why the plant needs electricity even in cold shutdown mode

After the shutdown of the power units, residual heat generation remains in the reactors, so the fuel must be continuously cooled. For this, mechanisms that ensure circulation and heat removal must work.

According to the expert, electricity is needed not for generating current, but for maintaining the safest state of the power units. That is why even a short-term loss of external power is considered a serious incident.

Cooling must be continuous. That's exactly what this electricity is needed for

Zaporizhzhia NPP: what happens at the plant during a blackout

The UNN interlocutor says: after the occupation, the plant received power from the territory controlled by Ukraine. For this, two power transmission lines were used: Dniprovska at 750 kV and Ferrosplavna at 330 kV. They provided the internal consumption of ZNPP, necessary to maintain the operation of safety systems.

The expert emphasized that in case of loss of external power, the plant switches to diesel generators. This is a foreseen, but emergency mode.

What can I say about the power going out and the diesels working? It's not normal, it's an emergency

According to him, each power unit has three diesel generators, and even one working diesel is capable of supplying electricity to the systems that cool the active zones. This creates a margin of reliability, but does not cancel the fact of an emergency situation itself.

Why a short outage duration does not mean no risk

Oleg Dudar noted that the thirteenth blackout at ZNPP lasted about an hour and a half, after which power was restored via the 330 kV line. At the same time, according to him, the supply via the 750 kV line has not been restored since the end of March. This means that the plant is actually operating with fewer external power sources than required for a normal safety configuration.

It is the loss of redundancy, and not just the fact of the outage itself, that is one of the main consequences of such events. The fewer available power transmission lines, the higher the dependence on emergency sources and the more vulnerable the plant is to repeated power supply disruptions. Figuratively speaking, the system is still holding on, but the margin of stability is decreasing.

Is a catastrophic scenario possible at ZNPP: expert opinion

According to Dudar, even in case of problems with diesel fuel, it will not be about an immediate loss of control. He explained that due to the low level of residual heat generation after a long shutdown of the plant, there is a certain time reserve for restoring power without transitioning to critical parameters.

Nothing fatal will happen, even if the fuel runs out. Due to the state of these residual heat releases in the active zones, there will be about three weeks to restore power without exceeding parameters that can be considered a threat

At the same time, the expert emphasized that this does not negate the danger of the situation itself, as it is an emergency mode of operation of a nuclear facility.

What are the consequences of constant power outages for the further operation of the plant

Separately, Oleg Dudar drew attention to the fact that the consequences of blackouts go beyond a short-term switch to diesels.

According to him, Russia is trying to create conditions for reconnecting ZNPP to its energy system. He believes that repeated cases of external power loss may be related to attempts to carry out switching actions and prepare the plant for a change in the power supply scheme.

In his opinion, maintaining the supply of electricity from the Ukrainian side has not only technical but also practical significance for controlling the facility. If the plant is reconnected to the Russian energy system, it will create new conditions for further technical and political decisions regarding ZNPP.

Why are we still supplying electricity to the Zaporizhzhia plant, which is occupied? This is a very important political and psychological moment. If they (the Russians, - ed.) can transfer the power supply (of the plant, - ed.) from Russia, it will give them the opportunity to say that they fully control the Zaporizhzhia plant

Can the Russians resume ZNPP operation and what is needed for this

The former head of the ZNPP operational unit believes that even regardless of the specific incident with power loss, the plant currently does not have the conditions for a safe return to operation as an industrial energy facility.

He named the loss of the Kakhovka reservoir after the destruction of the dam by the Russian Armed Forces in 2023 as the first problem. According to him, the reservoir was important for cooling turbine condensers through a cooling pond, which requires constant water replenishment. Currently, the water level in it has decreased, and this is not enough to start the corresponding hydraulic units.

Near the plant there is a so-called cooling pond, from which powerful pumping units pumped water to cool the turbine condensers. There is constant evaporation of water in the pond, so it is necessary to ensure its replenishment. When there was a sea (Kakhovka, - ed.), it was easy to do. Hydraulic structures were built in such a way that they almost automatically replenished the lack of water. Now there is no sea, there is nowhere to replenish, and the level of this cooling pond has dropped significantly. It is not enough to turn on powerful hydraulic units that cooled the turbine condensers

The water level in the pond could be replenished from the old mouth of the Dnieper – the Konka River. But no one will provide such a technical opportunity to the Russian occupiers.

The second problem, according to the expert, is the lack of a full-fledged power transmission scheme for the plant's operation in generation mode. The two remaining lines are not enough for this. In addition, they are not suitable for the Russian occupiers, because in the future they want to produce energy at ZNPP for the needs of annexed Crimea. Therefore, there is a need to build new power transmission lines. This also runs into technical limitations.

But Dudar warns that there is a loophole that Russia can use: if the occupiers are not prevented from fully reconnecting ZNPP to the Russian power system, they will be able to lay any lines. Therefore, it is so important for Ukraine to maintain at least residual control over the plant.

The third problem that will prevent ZNPP from being put back into operation is the shortage of qualified personnel.

They (the Russians, - ed.) will not be able to ensure safe operation in accordance with the requirements of current norms of both Ukrainian and international legislation, because the number of specialists who must manage a nuclear facility is limited

In addition, as the specialist explains, during four years of occupation, the plant has not fully carried out scheduled repairs, technical inspections, and other mandatory regulatory measures necessary for safe operation.

They do not carry out scheduled repairs, mandatory technical inspections, technical measures to maintain safety at the plant. If they do something, it does not comply with any safety standards. No matter how they (the occupiers, - ed.) say that ZNPP is a Russian plant, they treat it as property that fell into their hands from the sky. They are not going to use it for its intended purpose. The plant is only needed as an element of nuclear blackmail of the world and society

That is why, even if external power is restored after another blackout, the facility itself remains in conditions of increased technical vulnerability.

According to the expert, the current state of ZNPP cannot be considered normal even despite the fact that the power units remain in cold shutdown.

Recall

Head of the State Nuclear Regulatory Inspectorate Oleg Korikov stated that the situation at the Zaporizhzhia NPP is deteriorating and called it the biggest problem for nuclear safety.