CHRONICLE OF A TRAGEDY | SPECIAL REPORT


Left: Like all nuclear power plants, Zaporizhzhia was never designed to withstand conflict


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 – U


Above: The IAEA Support and Assistance Mission to Zaporizhzhya (ISAMZ) arrives at the plant Photo Credit: IAEA


www.neimagazine.com | November 2022 | 21


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