Opinion guest column

Facts about the safety and security of nuclear power plants in Ukraine

As members of the MIT Faculty, we are committed to providing unbiased, technical information

The war in Ukraine is heart-breaking. Combining the words “war” and “nuclear” adds fear and raises a host of questions amid uncertainty and sadness. Ukraine is a country that derives over half of its electricity from nuclear energy and has 15 reactors generating electricity. Ukraine is also the location of the decommissioned Chernobyl power plant, which was the site of the worst nuclear accident in history. [Here is a video about what happened at Chernobyl, by Professor Mike Short, as taught in 22.01 (Introduction to Nuclear Engineering and Ionizing Radiation), Fall 2016: https://www.youtube.com/watch?v=Ijst4g5KFN0.]

The mission of the Department of Nuclear Science and Engineering (NSE) includes educating students and informing public discussion of nuclear science and technology. As members of MIT’s faculty, we are committed to both the Institute and NSE's shared mission to provide unbiased, technical information. This mission motivates our open letter, with some answers to the most commonly asked questions we have received.

Is the spent fuel in storage at the Chernobyl site a danger due to loss of power?

The International Atomic Energy Agency (IAEA) has noted that while a loss of power at the Chernobyl site is a concern, it does not mean that the spent fuel storage facility becomes immediately more dangerous. The loss of power was considered in a series of post-Fukushima analyses of the Chernobyl spent fuel storage facility , and it was found that loss of cooling systems would not lead to an urgent risk of significant radioactivity release. This is because the temperature of the spent fuel can be managed by ensuring that adequate water remains in the pool. We estimate that enough water to cool down the spent fuel can be maintained manually for a duration of seven to eight months with water supplies on-site. The physical reason behind this conclusion is that the release of some radioactive gases to the environment will occur only if the temperature of the spent fuel is high enough to cause the fuel cladding to rupture. The temperatures at which the leakage of gases occurs varies based on details of the cladding, but a typical range would be 300 to 650 degrees Celsius. Since water boils at 100 degrees Celsius, as long as there is water in the pool, the spent fuel temperatures stay below temperatures where radioactive gas leakage occurs. If loss of power occurred, the water would have to be replaced faster than it evaporates away. How quickly the water evaporates depends on the heating power of the spent fuel, which in turn depends on many factors, but primarily the burn up of the fuel and the time since the fuel was used in a reactor. Using published values for the spent fuel in the storage pool, we estimate around 1 megawatt of heat in the spent fuel. At this power, water would boil away at a rate of about 8 gallons per minute. That is the flow rate of a garden hose, making replacement of the water by hand possible. The site has about 10,000 cubic meters (or 2.6 million gallons) of makeup water available, good for seven to eight months of water replacement.

Are nuclear power plants (NPPs) more vulnerable or less vulnerable than other kinds of power plants to a military or terrorist attack?

Overall, NPPs are less vulnerable but an attack could have high consequences. NPPs are among the most robust civilian infrastructures on the planet, with multiple layers of protection. NPPs must, by law, be able to withstand terrorist attacks as well as a broad range of natural disasters, such as earthquakes, tornadoes, wildfires, and floods. Ukraine’s NPPs have multiple layers of protection. In the event of an attack, the nuclear reactors can be rapidly shut down. There are also emergency diesel generators and batteries that would ensure the reliable operation of critical equipment, such as pumps, valves, and instruments, as well as continued adequate cooling for the reactor cores if power were lost. These diesel generators and batteries sit behind thick reinforced concrete walls that cannot be penetrated by light weapons. However, it should be made clear that no backup is completely infallible. Even the most robust backups can be disrupted by direct actions of an invading force. The results of such actions could then lead to a release of radioactivity from the nuclear plants, as we explain next.

What happens if power is lost to an operating NPP, like Zaporizhzhia? Should we be worried about a meltdown and release of radiation similar to what happened at Fukushima?

A similar sequence of events would be very unlikely. This is because after the 2011 accident at the Fukushima Daiichi site in Japan, Ukraine’s NPPs were retrofitted with additional layers of protection. For example, if the emergency diesel generators and batteries were to fail simultaneously, there are now mobile backup diesel generators and pumps that can keep the reactor cores cool. In other words, there are backups for the backup.

An attack that damaged the emergency diesel generators and batteries as well as the backup equipment might reduce cooling of the reactor core and lead to damage to the nuclear fuel, up to fuel melting. In this scenario, the plant would be unlikely to operate ever again; however, the vast majority of the radioactivity would be retained within the containment structure of the plant. Some radioactivity might leak from the containment structure and disperse locally, but health effects would be almost certainly undetectable even near the structure. Among people further away, exposure would be below that routinely encountered in diagnostic medical procedures by millions of people worldwide.

NPPs are designed to adhere to national and international safety standards in order to be licensed for operation. This means that all NPPs worldwide are subject to very similar standards and are continuously monitored and reviewed by national regulators and international organizations such as the World Association of Nuclear Operators and the IAEA. Each NPP is peer-reviewed every couple of years, lessons are learned from mishaps, and operating experience is shared widely. The system has further improved after Fukushima. But no system will be perfect, which is why risks are always being assessed and a process of continuous improvement is in place. All industries that involve complex engineered systems and involve risk of hazards (oil, gas, and chemical sectors; hydropower, rail, aviation, and maritime transport; and, of course, nuclear power) use data from accidents and near-accidents to inform the continuous improvement of safety systems. The goal is to avoid a similar accident or near-accident ever happening again.

Where can I find real-time, fact-based updates about the nuclear situation in Ukraine?

An American Nuclear Society (ANS) Rapid Response Taskforce exists to provide information about nuclear safety and security around the world. For the past several weeks, the Taskforce has been focused on Ukraine. The NSE encourages everyone who has concerns or questions about the nuclear situation in Ukraine to reference the ANS Rapid Response Taskforce website and sign up for updates at https://www.ans.org/response. Additional expert resources are linked from the Taskforce webpage. Media and stakeholders with specific information or questions can contact the Taskforce directly at https://www.ans.org/contact/form/?r=response. MIT faculty member Professor Jacopo Buongiorno is a member of the ANS Taskforce.

Anne White, Jacopo Buongiorno PhD ’01, Areg Danagoulian ’99, and Scott Kemp are professors in the Department of Nuclear Science and Engineering.