SPECIAL REPORT - Zaporizhia: Two years of captivity

Above: The Zaporizhia nuclear power station was captured by Russian troops on 4 March, 2022

Despite the abnormal situation the power system of Ukraine is balanced and is currently able to meet demand. Domestic generation is generally sufficient to cover the needs of consumers, although electricity is being imported from time to time. Despite the absence of the six-unit Zaporizhia nuclear power plant from the Ukrainian grid, broadly, there are no shortages of electricity. As a result, power outage schedules do not currently apply in contrast to the previous winter. However, the Ministry of Energy has called for the economical use of electricity during peak hours.

Nonetheless, the war continues, so disconnection of power lines due to shelling, followed by prompt restoration and subsequent energisation have become the norm for Ukraine.

There are 15 nuclear power units at four nuclear power plants in the country – operated by the state nuclear utility Energoatom. The Zaporizhia nuclear plant (6 x 1000 MWe) is currently shut down. There are a further nine nuclear units in operation at the South Ukraine plant (3 x 1000 MWe), Khmelnytski plant (2 x 1000 MWe) and Rivne plant (2 x 1000 MWe and 2 x 440 MWe) with a total nominal capacity of 7880 MWe.

In 2023, Ukrainian nuclear power plants generated 52 TWh of electricity. This is about 50% of the total electricity production in Ukraine. For comparison, the same ratio – though not the same amount – was achieved before the war with the addition of the operating Zaporizhia nuclear plant. All the operating units have undergone outages and refuelling cycles over the recent months.

In addition to Russian nuclear fuel, Ukraine had been using Westinghouse fuel for many years at its VVER-1000 units. Due to specific design characteristics, the fuel for two VVER-440 units at the Rivne plant was supplied only by the Russian TVEL company. After the beginning of the war, Energoatom announced a complete refusal of any further fuel supplies from Russia and recently the company announced that Westinghouse fuel was being loaded into the VVER-440 Unit 2 reactor of Rivne. It is also planned for this fuel to be loaded into the second VVER-440 unit at the plant. This strategy opens up a new opportunity for VVER-440 reactors in the Czech Republic, Slovakia, Finland and possibly in Hungary too.

Earlier in 2023 Energoatom began to transport its spent fuel from the three operating plants to the centralised dry spent fuel storage build not far from the Chornobyl plant. While the Zaporizhia plant has had its own storage facility since the early 2000s, the three other plants had previously transported spent fuel to Russia with an obligation to eventually receive the radioactive waste back after reprocessing. This project to store the spent fuel at the Chornobyl (along with the VVER-440 fuel) cut off the last Russian-Ukrainian nuclear links.

ZNPP two years on

The Zaporizhia nuclear power station was captured by Russian troops on 4 March, 2022, with shelling of the site and important electrical equipment. No significant damage to the units was registered. Before the war, all six units were in operation but half a year later, in September 2022, the last two operating units were shut down.

Since then – for almost a year and a half – all reactors have remained shut down. Russia cannot supply electricity to its territory and does not want to supply it to the territory of Ukraine. Instead, electricity from the Ukrainian grid is used to maintain one unit (earlier two units) in the hot shutdown state. All other units are now in the cold shutdown state.

Cold shutdown relates to a fuelled reactor with the following parameters of the sealed and filled primary circuit – temperature up to 70°C, pressure up to 35 kg/cm2. The core is being cooled through the outage cooling system. It’s a three-train safety system with flow up to 800 m3/hour and maximum pressure of 23 kg/cm2. The heat sink is the sprinkler ponds located on the station territory. During power generation, this safety system is designed for the emergency injection of a low-pressure boric acid solution.

Hot shutdown relates to a fuelled reactor and nominal parameters of the primary circuit – temperature more 260°C and pressure 160 kg/cm2. The main circulation pumps are in operation. The heat of the core and the pumps is removed by the secondary circuit that needs the operation of the main turbine systems including the feed water, steam, condensate systems and circulation pumps.

In 2023, the State Nuclear Regulatory Inspectorate of Ukraine issued an order to maintain all the plant units in a cold shutdown state. However, in reality this is a hollow regulation as Energoatom can’t access the site to meet this requirement.

The official Russian explanation for keeping one of the units in the hot state is that it is necessary to produce low parameter steam for the plant water treatment facilities and to heat the town. The town is 6 km from the plant and heat supply from the operating units was normal although using pumps consuming electricity from the grid is an unusual operating mode.

Furthermore, a number of movable heating installations were delivered to the town by Russia and connected to houses during the first winter of the war. Several mobile steam generating installations were also delivered to the station but it still keeps one power unit in the hot state consuming around the same amount of electricity as an operating unit – up to 50 MWe.

Spent fuel pools are located at every unit and form a common space with the reactor during refuelling. Their three-train cooling system is always in operation, in any reactor state, and uses the same cooling water as the reactor cooling system.

The plant turbine cooling pond (about 11 km2) is separated from the Dnipro River and now is not used due to the plant shutdown. Following the destruction of the Kakhovskaya HPP dam in June 2023 – the Kakhovka water reservoir (52 km3) emptied and the plant lost the ability to fill the cooling pond. However, while that is not currently a problem as the plant is not in operation, possible damage to the cooling pond dam could lead to loss of the water and with it the opportunity to make up the safety system sprinkler ponds. Nonetheless, the cooling pond dam proved to be reliable – no leaks were detected, evaporation is minor and its level has been stable for months.

The plant drilled several wells on the site and reported on its ability to make up the safety sprinkler ponds. Ukrainian experts reported that this drilling and pumping of the water can impact the site’s ground stability, especially given that some units had problems with inclination in the past.

Evaporation from the sprinkler ponds is insignificant, especially in winter. But the main mitigating factor is a long, almost 1.5-year, shutdown of all reactors therefore having low decay heat of less than 1 MWt per reactor.

It’s worth noting another nuclear provision located at the plant – the spent nuclear fuel dry storage facility holding 173 casks of 24 cassettes each. No changes or damage was detected and mesh fences were mounted above the storage site to protect the casks against shell fragments and debris. No new additions are anticipated.

Before the war, the plant had four 750 kV power lines plus an auxiliary 330 kV line connected to the Zaporizhia thermal power plant. This represents a good level of power supply redundancy in the event of an emergency. In recent months, the plant has been supplied through a single main line and the auxiliary one. From time to time, due to missile attacks, even hundreds of kilometres from the plant, one of the lines is disconnected, leaving only one line remaining – in peacetime this situation would be considered almost critical although almost normal since the war began.

During the occupation, the station experienced eight complete blackouts, two of them when two units were operating at full capacity and the rest when the units were shut down. The plant had no reportable problems during these periods although a complete blackout is considered a dangerous situation for nuclear safety. During these blackouts emergency diesel generators (20 x 6kV units in total) started and supplied the safety systems.

Shelling and incidents

For much of the last two years, the station has suffered several shelling attacks, with missiles and mines hitting buildings and landing in the station grounds. No critical damage or injuries have been reported and in recent months there has been no shelling of the station or surrounding areas.

In November 2023 Energoatom announced a primary- to-secondary reagent leak incident at unit 5 in the hot shutdown state, “due to the incompetence of the Russian staff” and improper operation of water clean-up filters. The borated water of the primary circuit entered the turbine deaerator and all steam generators. This incident was not a steam generator leak.

Over the last year, Energoatom has reported steam generator leaks at the units in hot state shutdown several times. Russia didn’t report this and didn’t comment.

While the plant in shutdown mode doesn’t create the considerable radiation and nuclear risks associated with an operating unit, long-term risks to the equipment remain.

Significantly, there were some 11,000 employees at the plant before the war. Now only about 2,600 employees have signed contracts with Rosatom to work at the plant. In recent months it was known about 800 employees refused to sign the contracts and continue to work for Ukraine.

This staff situation is unsatisfactory given there were regular cases reported in the autumn when only one operator was working in a main control room and sometimes for more than one shift.

Many of the staff who refused to cooperate with Rosatom were replaced and banned from the plant. In early February, it was reported that the last staff disloyal to Rosatom – about 400 qualified and licensed employees – have been dismissed from the station.

Meanwhile, Russian military and civil staff – more than 1000 people – live in the plant premises while military vehicles are also on the site and even within the turbine halls.

The radiation situation at the station is within normal limits and without change, that is natural for a station that was completely shut down more than a year ago. Since September 2022 there have been permanent IAEA monitoring missions at the plant. The 16th group of 2-3 experts arrived at the plant in January this year. They can only go to locations permitted by Russia and recently the inspectors were not allowed to visit the reactor halls. They are shown the plant’s maintenance activities plan without receiving a copy for a detailed review. They can visit the main control rooms but can’t ask questions about qualifications and experience of the staff. Sometimes they report sounds near the plant similar to the sound of launching missiles from multiple launch rocket systems. There are similar IAEA missions at other Ukrainian plants.

The Zaporizhia nuclear plant is now a Russian enterprise located on Russian territory under the amended Russian constitution and in the view of the Russian president. In interviews the general director of Rosatom has reportedly referred to the titanic efforts of Russia to reduce any risks at the site to zero, under the control of the IAEA, and its efforts to protect the plant and its staff from the armed intervention of the Ukrainian armed forces.

An uncertain future

Russia currently has limited prospects for starting up the plant given it has no powerful consumers in the region. The Ukrainian power community waits for the liberation of the territories and hopes that the main plant equipment will not be damaged before or after the Russian’s leave. Ukrainians believe that the Zaporizhia plant will become a bargaining chip for Russia and will maintain its integrity through to the end of these dark times. It’s also understood that logic does not necessarily apply to such forecasts during a period of conflict.

But even in such a favourable case, the prospects for Ukraine and the role of Zaporizhia are not especially favourable. It may take one to two years to start up one or two units given the cooling pond can’t withstand more without considerable making up from the Dnipro river. The state of the cooling pond is unknown; the biology of the water may be not good for effective cooling of the turbines and it may need years to restore it. Certainly, building the new Kakhovka dam and filling the Kakhovka reservoir will take years.

It’s a very long road and it’s unknown when the first step towards an operating Zaporizhia can begin.

Author: Olexiy Kovynyev