Zaporizhzhia Nuclear Power Plant (ZNPP) is Europe’s largest power plant. Following its capture by Russian forces on 4 March 2022, there have been drastic disruptions to safe energy production and a heightened global concern for nuclear safety.

ZNPP, located in the Ukrainian city of Enerhodar, was built by Soviet design in the 1980s. Amongst the ten largest nuclear facilities in the world, ZNPP consists of six water-cooling and water-moderating pressurised reactors.

A global nuclear scare started on 24 February 2022, when Ukraine informed the International Atomic Energy Agency (IAEA) that “unidentified armed forces” took control of all facilities of Chornobyl Nuclear Power Plant located in the exclusion zone. The IAEA appealed for maximum restraint to avoid any action that may put the country’s nuclear facilities at risk and stressed the IAEA’s 2009 General Conference decision that “any armed attack on and threat against nuclear facilities devoted to peaceful purposes constitutes a violation of the principles of the United Nations Charter, international law and the Statute of the Agency.” Later that week, Russian military forces took control of the territory around ZNPP.

By 4 March, Ukraine had informed the IAEA that ZNPP was shelled, and a fire broke out onsite. Although no essential equipment was affected, the military action resulted in the activation of the IAEA’s Incident and Emergency Centre. At the end of the day, Ukraine announced that Russian forces had taken control of ZNPP, but the plant continued to be operated by its regular staff. At the time, two of the plant’s reactor units had undergone controlled shutdown, two were held in low power mode, one was shut down for maintenance, and one was operating at 60 percent power. The biggest worry was that Ukraine would suffer a sustained power grid failure, an increased likelihood during a conflict.

ZNPP’s dire situation

Disruptions in the electricity supply quickly followed the invasion. Less than two weeks after Russian forces seized the plant, ZNPP lost one of its three power lines. Since then, mainly due to shelling or other military action nearby, ZNPP has suffered numerous power cuts. Although it has emergency diesel generators to provide backup power, a secure off-site power supply from the grid is integral to ensuring nuclear safety.

Following the first complete external power outage in August, IAEA Director General Rafael Mariano Grossi initiated the IAEA Support and Assistance Mission to Zaporizhzhia to undertake vital safeguards activities at the plant. In October, ZNPP lost its last remaining external power source due to renewed shelling and had to rely on finicky diesel generators several times to cool the reactor and support other nuclear safety and security functions. This continued through November, as Grossi continued to urge demilitarisation of the zone.

Source: Authors

Cold shutdown of the ZNPP reactors doesn’t remove the risk

The fission reaction that generates heat in a nuclear power plant is produced by positioning uranium fuel rods in close proximity. Shutting down a nuclear reactor involves inserting control rods between the fuel rods to stop the fission reaction. The reactor is then in cooldown mode as the temperature decreases. Once the temperature is below 93 Celsius and the reactor coolant system is at atmospheric pressure, the reactor is in cold shutdown. When the reactor is operating, it requires cooling to absorb the heat and keep the fuel rods from melting together, which would set off a catastrophic chain reaction. When a reactor is in cold shutdown, it no longer needs the same level of circulation.

On 11 September 2022, Energoatom, the operator of the ZNPP, announced it was shutting down the last operating reactor. ZNPP is now in cold shutdown, which has mitigated risk.

However, spent fuel pools also need constant circulation of water to keep cool. Without electricity to run the cooling system, spent fuel overheats, and its zirconium cladding can cause hydrogen bubbles. Without ventilation, these bubbles explode, spreading radiation, much like what happened in Fukushima Daiichi nuclear power plant in Japan after the earthquake and tsunami of 2011.

The cooling pumps for the spent fuel pools need much less electricity than the cooling pumps on the reactor’s primary and secondary loops, and the spent fuel cooling system could tolerate brief electricity outages. Now, if the plant loses offsite power, the operators don’t have to worry about cooling an operating reactor with cranky diesel generators. However, the plant still needs a reliable source of electricity to cool its six huge spent fuel pools and remove residual heat from the shutdown reactors.

There is also a dry spent fuel storage facility at ZNPP. Dry spent fuel storage involves packing spent fuel rods into massive cylinders, or casks, which require no water or other coolants. The casks are designed to keep the fuel rods contained for at least 50 years. However, the casks are not under the containment structures at the plant, and though they were designed to withstand being crashed into by an airliner, it’s not clear whether artillery shelling and aerial bombardment, particularly repeated attacks, could crack open the casks and release radiation.

What can be done?

There has been a certain reticence to acknowledge that Ukraine, despite being the “aggrieved” country, must be willing to make concessions to achieve peace. Russia is not the sole provoker of hostilities at ZNPP. It is illogical for Russia to shell the plant after it seized control, unless there are provocations from the Ukrainian side. For example, according to credible news sources, Ukrainian special forces launched an attack on ZNPP, deploying US-provided HIMARS rockets at the site — an attempt that ultimately failed because of a stronger Russian counteroffensive. Any projectiles nearing the site of a nuclear power plant are an inherently hazardous and potentially catastrophic assault, regardless of the origin of the launch.

Given the high stakes and the potential for irreparable harm, it is imperative for Ukrainian forces to prioritise nuclear safety and refrain from any military action near ZNPP, even though it is under Russian control.

As the memory of the 1986 Chornobyl disaster lingers, the potential danger posed by ZNPP far surpasses that of the single reactor that caused the Chornobyl disaster. Ukrainians should not shame their military officers if they retreat from ZNPP, but rather commend them for their strategic investment into the future prosperity of their country, and possibly their planet. A true measure of a hero lies not in their victories, but in their willingness to fight for what is right, even in the face of overwhelming odds. Right now, accepting the status quo at ZNPP is, in our opinion, what is most right.

The IAEA has called on Russia and Ukraine to set up a “safety and security protection zone” around the plant. However, negotiating and establishing a protection zone in a war zone is entirely unprecedented and totally different from all past IAEA efforts. Establishing a protection zone requires negotiations and approvals at the highest political and military levels in Kyiv and Moscow. It could be accomplished through backchannel engineering diplomacy. In the meantime, the IAEA needs strong support from the United Nations Security Council in the form of a resolution or special mandate. In parallel, the Security Council should immediately empower a special commission to address ZNPP’s precarious status and mediate between the warring parties.

War, in our opinion, is the worst enemy of nuclear safety. This is an unprecedented and volatile situation. Only through active, pragmatic engineering and nuclear safety diplomacy can an amenable and lasting solution to this vexing problem be found.

Najmedin Meshkati is a Professor of Civil/Environmental Engineering, Industrial & Systems Engineering; and International Relations at the University of Southern California (USC). He is an Associate (ex-Research Fellow) with the Project on Managing the Atom at Belfer Center for Science and International Affairs at Harvard Kennedy School, and was a Jefferson Science Fellow and a Senior Science and Engineering Advisor, Office of Science and Technology, Adviser to the Secretary of State, US State Department, Washington, DC (2009-2010). Email: meshkati@usc.edu

Zhamilya Mussaibekova, a freshman from Kazakhstan, who attended high school in Switzerland, is a Computer Science and Cognitive Science major at USC. She has interdisciplinary interest and experience in the field of foreign service, having interned at an embassy in Rome, Italy; and is a student of Professor Meshkati’s Engineering Diplomacy course, Spring semester 2023. Email: zmussaib@usc.edu

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