Zaporizhzhia: Chronicle of a tragedy

8 December 2022

At the Zaporizhzhia nuclear power plant in Ukraine armed conflict still brings the threat of a disaster that could sweep the continent. Can the nuclear industry learn lessons from the situation?

Zaporizhzhia nuclear plant consists of six 1000 MWe VVER units. Before the war, it supplied about half of Ukraine’s nuclear power and a quarter of the country’s total electricity. It was operated by Energoatom, the national nuclear utility which ran all four Ukrainian operating nuclear plants.

At the time of the invasion, all nuclear units at the station and in the country were in operation. Soon, however, due to the war activity and damaging industrial infrastructure, electricity consumption in Ukraine dropped sharply, and some of the nuclear units were disconnected from the grid and put in reserve. Turning off power lines with the unloading of power units has become a regular event.

On March 4, 2020, the station and its dry storage facility for spent fuel was captured by Russian troops, with shelling the site. A new stage of the station life began. Russian military completely controlled the plant territory and forced the plant management to adjust with them all the important issues of operation. Rosatom specialists consulted on site their military on all technical issues.

The city has serious problems with food, goods and cash. People gradually left the city, trying first of all to move out children. The Russians committed individual acts of violence to keep everyone in fear. The staff started resigning. The conditions were unpleasant but not critical. The war was going somewhere far away, although the peals of artillery shelling in the city were sometimes heard. Several months of occupation passed.

Shelling of the Zaporizhzhia power station and the city of Energodar

The city and the station are still occupied – the spring hopes that the occupation would be only temporary have not been justified. There are still large numbers of Russian military equipment and personnel on the site. In early August three unloaded units were in operation at ZNPP. The remaining units were in reserve.

On 5 August, Russian troops shelled the territory of the ZNPP site. One of the operating reactors was scrammed. Equipment and some buildings were damaged. According to the Ukrainian staff, the Rosatom employees which were present at the site left the station in advance of the shelling. Military personnel also took cover. The Ukrainian army was blamed for the shelling. The Ukrainians, apparently for humanitarian reasons, warned the Russians about the shelling and forgot to warn the station staff. On this day, everyone parted with the last illusions that a nuclear facility is sacred and inviolable, and the March shelling during the capture of the station could be dismissed as an excess of an individual in the conflict.

After that day, shelling the plant and the territory adjacent to the plant and the city became a regular event. During the later shelling, damage occurred near the spent fuel storage facilities and windows were broken in various buildings at the station. Deaths and injuries of civilians were reported. At the UN Security Council, the Russian representative said that the station and its satellite town Energodar were being shelled by the Ukrainian military and a nuclear catastrophe had not occurred only thanks to the Russian army.

Complete disconnection of the station from the network

For a long time, only two units were in operation. At the end of August, after a trip of the only power line in operation, both units were disconnected from the grid. One reactor was scrammed, and the second unit unloaded and switched to supplying its own electrical needs – this is just a few per cent of the nominal capacity. However, this mode of operation is designed as a temporary measure only, due to the instability associated with both keeping the electrical load stable and transients in the reactor physics. Thus, there was a blackout at five units, which necessitated starting the emergency diesel generators.

In an attempt to energise the de-energised units, the last turbogenerator in operation tripped with a scram of the reactor. At that moment, the entire station was de-energised – the first time this had occurred in its almost 40 years of operation. The huge nuclear facility was in darkness, except for the extremely important battery-powered systems. Operators had only ever seen this mode of operation in nightmares. Designers supposed that this can only happen during a collapse of a power system. The Russian army managed to realise this but nonetheless blamed the Ukrainian army as responsible for this event.

Whoever was ultimately to blame, the nuclear station was left without an important safety element – the power system. This is a very unpleasant situation. In this mode, safety systems and safety-related systems are powered by emergency diesel generators, which must quickly start up and operate until external power is supplied, for at least three days. It was assumed that during this time all problems would be solved.

We must pay tribute to the reliability of the systems – all emergency diesel generators, which, one might say, have been waiting for this moment for forty years. They started up within 15 seconds and powered all the unit safety systems. The cooling of reactors and the spent fuel pools has indeed got a last line of defence. However, the countdown had begun, determined by the stock of diesel fuel at the station.

Start-up of two units and inclusion of the station in the network

A day later, on 26 August, by using a backup 330 kV line connecting Zaporizhzhia thermal power plant and factories on the right bank of Dnieper River, the nuclear workers managed to supply power to the station and begin starting up the units. One of the serious problems in this situation is the lack of steam in the station steam header. Typically, steam is always available because there were always units in operation. During the commissioning of the station, steam was supplied from the thermal plant through a pipeline which was disused for many years. A day later, also due to the high residual heat of the reactors, it was possible to bring the reactors to the minimum level, increase the power, start the turbines and connect the station to the grid. This is a significant technical achievement by the Zaporizhzhia nuclear specialists, which has no analogues. This is a good, if serious, reason for professional pride, but uncertain prospects remain – there are no guarantees that this would not happen again tomorrow.

Indeed, two days later, Russia shelled residential areas of Energodar. The city was shocked by the damage, burned- out cars and flats without windows. Another misconception – that those who captured the city would not shell it – evaporated. In a mixture of real and hybrid war, anything is possible but Ukrainian military units were blamed for the shelling, as before.

After long negotiations and even accusations from the Ukrainian side, the IAEA, headed by Director General Grossi, announced a mission to the plant. The preparations were carried out in the face of a fierce diplomatic struggle – each of the “hosts” demanded the mission travel only through the territory under its control. Nonetheless, at the end of August, the mission arrived in Kyiv, then at the regional centre of Zaporizhzhia, and on 1 September moved towards the station.

From the Russia perspective a desirable outcome of the mission would be to confirm that the station was doing just fine under the “new conditions”. Some attempts were made to disrupt the mission – on that day, shelling began on the line of movement of the mission. The station was shelled – one unit was scrammed, one unit remained in operation, and the 330 kV line was damaged. Early in the morning, terrible shelling of the city began again – in the same district that had been hit three days previously.

By noon, when it became clear that Grossi’s team would persist and not give up the goal of getting to the station, the shelling stopped. This required a ceasefire guarantee from the Russian military at the highest level. The mission stayed at the station for about three hours. The Russians showed the territory and even the turbine halls with their military vehicles, supposedly intended for chemical protection. Grossi issued a statement saying “we managed to collect a lot of important information.” Later, the IAEA issued a report in which it demanded the creation of a security zone around the territory of Zaporizhzhia NPP. Grossi has started negotiations to reach this goal but it is clear that such negotiations can take years.

Reactor operators are under incredible strain, while artillery shells fall on the reactor site and the operating unit has been scrammed, the city is also being shelled. Where the operator’s home and family sleep bombs explode and windows fly out. There are many such stories and many citizens have not survived this horror. Following this pounding a new wave of a mass exodus from the city began. After all, what happened twice will definitely happen the third time. And if today a shell hit a neighbouring house then tomorrow it could hit yours. For the citizens of Energodar, this IAEA mission will always be associated with the terrible shelling of the city.

Disconnection of the station and complete blackout

The stress associated with the mission subsided but the life of the nuclear staff has not become much calmer. Periodic shelling of the station has continued. During one occasion, the unit transformer, the auxiliary transformers, and the line of connection with the switchgear were all damaged. This resulted in a power outage at the unit and another start cycle for the diesel generators. Units were disconnected more than once due to cut power lines. To keep the last operating unit at minimum power, the personnel were even forced to start up the station mechanisms, such as, for example, the pumps of the cooling pond were switched to their maximum output.

Taking into account the basics of nuclear safety and the necessary conservative approach, the station had to be shut down as the threat of further military action loomed.

But what seems rational for one reactor is not so clear for a large nuclear power plant that provides a quarter of the electricity of a large country. Zaporizhzhia is also perceived by many as an important symbol of military resistance.

In early September, Ukrainian President Zelenskiy said he would not consider a controlled shutdown of Zaporizhzhia nuclear power plant, given that as winter approaches, it provides energy to two regions of Ukraine. But gradually came the understanding that the huge efforts to connect units to the grid are not justified – a disconnection can occur at any moment. Repair of lines involves significant risk to personnel and is not warranted. Considerations of real safety and technology have become more important than considerations of completely unreliable power generation. Military and political considerations also receded into the background – after all, the occupied nuclear plant, which operated for Ukraine for six months, was a symbol of Ukrainian resistance.

On 11 September, the last operating unit of Zaporizhzhia nuclear plant was disconnected from the grid and transferred to a cold state. The plant was shut down and turned from a powerful electricity producer into a consumer. Another page of its sad, at this stage, history turned.

Of course, a cold shutdown is a much safer state than operating a plant at full power. Nuclear professionals worldwide are no doubt breathing a sign of relief, but it’s still a very depressing story. Only the world-famous stories from 1979, 1986 and 2011 were worse.

Technically, the station is still alive. The cold state is, in the current conditions, like an artificial coma but there is a huge amount of nuclear fuel in all six reactors and at the near-reactor spent fuel pools. All this fuel continues to generate heat and needs continuous cooling. If we add the dry spent fuel storage, then, in terms of the number of cassettes, this is the equivalent of about 40 full reactors. All of them are at significant risk due to hostilities. For the units, this is not the risk of a direct hit by a projectile but the risk of a failure of heat removal systems and subsequent melting of the fuel. For the dry storage, it is precisely the risk of disintegrity as a result of a direct hit.

The situation with station safety is deteriorating. Despite the state of shutdown, the units need maintenance and repair. All modernisation programmes have been postponed for an indefinite period. Repairs have been reduced to a minimum. Water circuits need treatment, and the treatment systems need steam which is not available. Indeed, due to the military occupation, the station keeps suffering from a shortage of everything necessary for safe operation. In mid- September, Energoatom managed to deliver a convoy of 25 trucks with spare parts, materials, chemicals and diesel fuel. This is an important achievement by the operating organisation.

Rocket attacks systematically target the Ukrainian energy system

Rocket attacks on Ukrainian energy infrastructure in October led to serious imbalances in the power system and energy outages throughout the country. This, of course, did not add to the safety case at Zaporizhzhia nuclear plant and the rest Ukrainian nuclear plants.

The liberation of this territory by the Ukrainian army doesn’t seem too likely in the short term and the station is preparing for the severest winter in the entire history of its operation. Even in this southern region of Ukraine, in winter temperatures can plunge to -20 degrees Celsius. If an operating unit needs the removal of 2000 MW of heat the current situation is the opposite – a frost can create significant problems at shut down and almost cold units.

The city with 50,000 residents, during all the years of its existence, was heated by the operating station. Now the residents who remained in the city – there is less than half the usual population – are waiting with horror for the approaching winter. With no electricity, due to blackouts, many will fight for survival.

With the city all but deserted, electricity blackouts, water shortages and Internet failures have become commonplace. Ukrainian mobile operators haven’t operated for a long time. Instead, there is a strange operator with a numerical title and Russian telephone codes, apparently using the captured Ukrainian equipment. The situation with access to the territory under Ukrainian control is constantly deteriorating and sometimes it seems impossible to flee the occupied region.

After the pseudo-referendum, Russia announced the annexation of the occupied territories. The station ended up not only in the occupied but in annexed territory. The logic of illegitimate actions led to the declaration of the station as property of Russia. Rosatom immediately created Zaporizhzhia nuclear plant enterprise and appointed a director – the former chief engineer of the Russian Balakovo plant. Immediately after that, the real plant director, Igor Murashov, was kidnapped and later brought out of the occupied territory. Later, three more people from the plant management were kidnapped. Out of 11,000 personnel, only about 6,700 remained at the station by the end of October.

The “new” head of the station is using threats and incentives to force the personnel to sign contracts with Rosatom. Energoatom tries to convince the staff not to do this, as it destroys the station control system and legitimises the annexation. In addition, such actions are a criminal offence under Ukrainian law on collaboration. The psychological state of the personnel, one of the most important elements of nuclear safety, is terrible. The contribution of this factor to the deterioration of safety is significant. Adding this on top of the technological problems caused by shelling and occupation creates a situation in which there is practically no reason for optimism.

Such is the current sad situation at the station. Zaporizhzhia is becoming a new hybrid Chornobyl. It is no longer just the title of a nuclear plant, it is a term for the terrible state in which this nuclear plant has found itself. True, it is not yet in a state of an accident that has happened but it is in a continuous emergency condition. There are no releases of radiation but there are constant violations of safe operation. Nuclear materials have not lost their integrity but the number of barriers has decreased and they are getting thinner. The conditions under which the station is being operated are on a knife edge.

Lessons can be learned from an event that is in the past. Right now, it is impossible to do this: the emergency state of Zaporizhzhia plant continues and anything can happen.

Author: Olexiy Kovynyev, Independent expert, former reactor operator and shift supervisor, Ukraine

The IAEA mission inspects shell damage at ZNPP (Photo Credit: Fredrik Dahl/IAEA)
Like all nuclear power plants, Zaporizhzhia was never designed to withstand conflict
The IAEA Support and Assistance Mission to Zaporizhzhya (ISAMZ) arrives at the plant (Photo Credit: IAEA)
War has come to a nuclear site (Photo credit: Energoatom)
Damage at an overpass between unit 6 and the maintenance-chemical building reveals how close the war has come to nuclear disaster (Photo Credit: Fredrik Dahl/IAEA)

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