Blackout at Zaporizhzhia nuclear plant: dirty bomb risk?

Read more in the article by Espreso TV.

Contents:

1. What does “cold shutdown” of nuclear power units mean?
2. What will happen at ZNPP in case of blackout?
3. Rosatom workers don’t know how ZNPP works
4. A “second Chornobyl” at ZNPP is impossible
5. Russian forces could turn ZNPP into a dirty bomb

What does “cold shutdown” of nuclear power units mean?

Zaporizhzhia NPP is the largest nuclear power plant in Europe and one of the five largest in the world. It has six VVER-1000 reactors, each with a capacity of 1,000 MW. According to Oleh Dudar, Head of the R&D Center's Department for Global Innovative Technologies in Nuclear Energy and former Head of ZNPP's Operations Division until September 2022, all six reactors are currently in a "cold shutdown" state.

As of today, all units have been placed in cold shutdown. The International Atomic Energy Agency (IAEA) reports that the last reactor, Unit 4, was put into cold shutdown in April this year. IAEA Director General Rafael Grossi described this as a positive move for nuclear safety, as cooling the reactor provides an additional safety buffer in case of an accident.

"A cold shutdown means that the nuclear fuel is no longer active - the chain reaction of atomic fission has stopped. This is the safest state for the reactors," says Oleh Dudar. "However, this doesn’t mean you can just turn off the lights and walk away. Even in a cold shutdown, some heat is still generated, and the nuclear fuel needs to be cooled. During cold shutdown, the fuel temperature is maintained at 30-35°C. The plant still requires electricity to keep the cooling systems and other critical operations running."

According to Dmytro Humeniuk, Head of the Safety Analysis Department at the State Scientific and Technical Center for Nuclear and Radiation Safety, Zaporizhzhia NPP, which was once Ukraine's largest electricity producer, has now become one of its largest consumers.

"When the plant was operating, it generated electricity for its own needs and supplied power to Ukraine’s unified grid. Now, it relies on these power lines to receive electricity in order to keep security systems running and to cool the fuel. Without this, the fuel could overheat and melt, as happened at Fukushima," Dmytro Humeniuk told Espreso TV.

What will happen at ZNPP in case of blackout?

According to Oleh Dudar, there are currently only two power lines supplying ZNPP: the Dniprovska 750 kV and the Ferosplavna-1 330 kV lines. Both of these pass through the Kakhovka Sea, which no longer exists. If either of these power lines is damaged - often due to Russian shelling - it poses a significant threat to the plant.

"We must recognize that the Ukrainian power engineers working to restore these lines are doing heroic work. They’re essentially operating in a war zone, under constant shelling," says Oleh Dudar. "If both power lines are cut and the plant loses external power, diesel generators will automatically kick in."

In total, ZNPP has 20 powerful diesel generators: three for each power unit and two station-wide.

“By regulations, the diesel fuel reserves at the plant should be enough to sustain autonomous operations for 10 days. If used sparingly, they could last up to two weeks,” explains Dudar.

However, the biggest concern is that no one can say for certain whether the plant still has enough fuel reserves or if the generators have been properly maintained.

“One generator is enough to power one unit, and there were three generators per unit. In fact, the greatest threat to Zaporizhzhia NPP is the presence of Russian forces at the plant,” says Dmytro Humeniuk. “But we don’t know if the Russians have drained and sold the diesel fuel or dismantled the generators for spare parts.”

A blackout, in the true sense, means the plant loses external power and the generators fail to start. In this scenario, the fuel could overheat and potentially release radiation. If the reactors are operational, fuel overheating can begin in about three hours. In a cold shutdown, this process takes longer - up to several days.

According to Oleh Dudar, during a cold shutdown, the fuel will gradually warm up. If a complete blackout occurs, irreversible processes will begin in about 20 days.

Rosatom workers don’t know how ZNPP works

According to Oleh Dudar, who was at ZNPP when it was seized by Russian forces, one of the most critical issues is the plant's staffing.

"Before the full-scale invasion, Zaporizhzhia NPP employed 11,500 people. Now, there are just over 2,000, but the exact number is unclear. We know that most of the staff are Rosatom workers. We don’t have precise data on how many of the original ZNPP staff are still there," says Oleh Dudar. "The problem is that Rosatom workers are unfamiliar with our equipment - they don’t know the operating procedures or regulations. They won’t be able to manage the consequences of core overheating, which could lead to a radiation accident.”

"I’m convinced that the nuclear workers at the plant won’t deliberately sabotage it, even if they are Russians. After all, we’re talking about their own lives and health, as well as the lives of their families, who are probably also in Enerhodar. They’re sitting on a powder keg themselves," says Dmytro Humeniuk. "In case of emergency at a nuclear power plant, there are clear instructions on how to handle the situation. The instructions developed in Ukraine were based on the approach provided to us by Westinghouse, which is an American system. It’s different from the one originally used in the Soviet Union and the one adopted by Russia. I’m not sure how Rosatom specialists will handle these instructions."

A “second Chornobyl” at ZNPP is impossible

Despite Zaporizhzhia NPP being the largest nuclear power plant in Europe, the consequences of a potential accident would not be comparable to the Chоrnobyl disaster. At Chornobyl, the reactors were RBMK (High Power Channel Reactors), which are much more dangerous than the VVER (Water-Water Power Reactor) units used at ZNPP. The VVER reactors have addressed the key issues of the RBMK reactors, specifically the risk of uncontrolled power surges in the reactor core, which was the cause of the Chornobyl disaster.

“In general, Zaporizhzhia NPP is one of the safest in Europe,” says Dmytro Humeniuk. “However, the presence of Russian forces at the plant is already a significant risk. There are reports that part of the plant’s territory has been mined, and a potential emergency at the facility, combined with ongoing military operations, could result in a radiation leak.”