Knowing the Difference Between These Nuclear Explosions

The past year has seen an unsettling amount of new interest in nuclear weapons. While the likelihood of nuclear use is still generally agreed to be very low, it is significantly higher than it was this time last year. Russia's invasion of Ukraine and Putin's very unsubtle threats have raised speculation about how far he might be willing to go. Would he resume Russian nuclear tests? Or actually use a tactical nuclear weapon in Ukraine? Those who did not live through the Cold War have probably never given much (or any!) thought to these kinds of questions. Even those who did have now spent decades in a post-Cold-War era, where the idea of intentional nuclear war between the US and Russia felt like a nightmare from the bad old days. The reemergence of such possibilities in the wake of Putin's nuclear threats has created much alarm--and an equal amount of confusion--over what is happening, what could happen, and what it would mean.

In theory, a dirty bomb or nuclear bomb attack could happen anywhere, but the danger presented by an attack on a nuclear power plant is bound to a fixed location.

The alarm is warranted; any time nuclear use of any kind is a realistic possibility you can be sure we have moved into a whole new, and incredibly dangerous, state of the world. The confusion is understandable--for most people there has been no need to think about these kinds of threats for decades and hearing the words "nuclear" and "war" in the same sentence is enough to inspire at least a small degree of panic. Understanding more about what the risks are and what they might mean is one way to begin to deal with this fear and transform it into an impetus for action and change that could help to avert the most dire scenarios.

What types of nuclear risks do we face in Ukraine?

One place to begin sorting out this confusion is in clarifying the distinctions among different types of nuclear risk. Since the beginning of the Ukraine war, experts have discussed several different ways that nuclear weapons or technology might be involved in the conflict. The key ones here are (1) an incident at a Ukrainian nuclear power plant caused--either accidentally or deliberately--by the conflict; (2) a "dirty bomb" attack; and (3) tactical nuclear weapons use.

Attacks on nuclear power plants

Concerns about how attacks--either accidental or deliberate--might affect nuclear power plants in Ukraine arose shortly after the war began. Russian troops first occupied the Chernobyl nuclear power plant, located on Ukrainian territory and site of one of the world's worst nuclear disasters in 1986. They also took control of Ukraine's Zaporizhzhia nuclear power plant after shelling set part of the complex on fire. Ukrainian President Volodymyr Zelensky accused Russia of deliberately attacking the plant to cause "nuclear terror." Due to ongoing shelling, the plant has periodically had to rely on backup diesel generators for power to keep its reactors cool and prevent a meltdown. Zaporizhzhia is one of four nuclear power plants currently operational in Ukraine.

While many have argued that attacks on nuclear power plants are illegal under international humanitarian law, the reality is that this is not as clear cut as it should be. Moreover, such facilities could easily be damaged in the course of an active conflict even if they are not specifically targeted.

The consequences of an attack resulting in damage to a nuclear power plant are the closest to a "known" event, with multiple historical precedents. Major accidents at nuclear power plants such as the 1986 disaster at the Chernobyl nuclear power plant (located within Ukrainian territory and occupied by Russia early in its invasion) or the 2011 Fukushima Daiichi disaster in Japan, would be comparable to the damage that might result in a war. These disasters can result in the release of large amounts of radiation, rendering surrounding areas uninhabitable for many years and requiring extensive and very expensive cleanup efforts that can last decades. Around 200,000 people were evacuated at the time of the Chernobyl accident, and an area of 150,000 square kilometers (almost 58,000 square miles) was contaminated with radioactive material; cleanup of the site is still underway today.

One major difference between an attack on a nuclear power plant and other types of attacks is that the location is known in advance of any potential attack. In theory, a dirty bomb or nuclear bomb attack could happen anywhere, but the danger presented by an attack on a nuclear power plant is bound to a fixed location. Moreover, even outside of wartime, nuclear power plants develop plans to mitigate the effects of various kinds of incidents, including terrorist attacks. So there would likely be pre-existing plans for containment, evacuation, medical assistance to victims in surrounding areas, and other contingencies. Without a doubt, an attack during an active military conflict would make it considerably more difficult--if not impossible--to carry out many of these plans as they were intended, but they might give at least a bit of a head start in preparation.

Dirty bombs

More recently, Russian statements have raised fears about possible use of a "dirty bomb" to spread radiation. The Russian statements expressed concern that Ukraine might use a dirty bomb itself but try to attribute it to Russia in a "false-flag" operation aimed at gaining international support and additional military assistance. But experts have noted that Russia has been known to float ideas accusing others of actions that it plans to take itself and that Russia could use claims that Ukraine had used a dirty bomb as a pretext to further escalate the war.

Some have also suggested that Russia might try to use a very low-yield nuclear weapon and claim that the radiation it gave off was caused by a dirty bomb set off by Ukraine. However, as experts have pointed out, it would be relatively easy to tell the difference between these two types of bombs by both the type of radiation that results and also the blast effects from the initial explosion.

A "dirty bomb," known in more technical terms as a "radiological weapon," or "radiological dispersal device (RDD)" is entirely different from a nuclear bomb. While a nuclear bomb relies on nuclear fission and fusion, a dirty bomb simply uses a conventional explosive--like dynamite--to disperse radioactive materials; there is no nuclear explosion.

This means that the damage done by a dirty bomb is mainly from the explosion, not the radiation. The radiological contamination from a dirty bomb would be spread much less widely than in a nuclear explosion--the Nuclear Regulatory Commission says "within a few blocks or miles of the explosion," rather than the "thousands of square miles" that it could spread if a nuclear bomb were used. Damage and casualties would depend on the size of the explosion; deaths caused by radiation would be rare.

A dirty bomb is intended to achieve different goals than a nuclear weapon. The goal of a dirty bomb is to disperse radioactive materials, harming those who are in the area and contaminating the site to render it unusable for some period of time, and sowing fear among the general public. Dirty bombs are generally weapons of terror, not of conquest. They have been called "weapons of mass disruption," rather than "weapons of mass destruction."

None of this is to say that there would not be serious consequences in the event a dirty bomb was used. While the number of deaths and amount of destruction would be far less than with the use of a nuclear weapon, it would still be unprecedented. A dirty bomb used in a crowded area could kill or injure many people in its explosion, just like other terror attacks, such as the 1995 Oklahoma City bombing. But, unlike an attack with a conventional bomb, radioactive contamination would complicate efforts to aid victims, evacuate the area, undertake a search for the perpetrators, and all the other activities that would normally follow such an incident. The cleanup efforts would be extensive and expensive, and if the attack occurred in an area where active military conflict was taking place, that would add another layer of difficulty.

Use of a dirty bomb, especially for the first time, would also likely have major psychological consequences. This might be even more true in Ukraine, with its historical memory of nuclear disaster at the Chernobyl nuclear power plant. But the impact would be felt worldwide, as the unprecedented use of such a weapon of terror would create widespread fear and likely demands for a military response.

Politically, if it became clear that Russia was behind the use of a dirty bomb, this would further isolate Russia from the international community.

Tactical nuclear weapons

One of the first threats that came up in media reports and expert commentary following the Russian invasion--spurred by dangerous and irresponsible rhetoric from Russian President Vladimir Putin--was the possibility that Russia might use a tactical nuclear weapon to dissuade the US and NATO from further aiding Ukraine. If such a weapon were used, even in symbolic fashion with few casualties, it would break a taboo against the use of nuclear weapons that has not been broken since the US dropped two atomic bombs on Hiroshima and Nagasaki in 1945. There is no guarantee that it would not start an escalatory spiral culminating in all-out nuclear war.

Although they are often thought of as "small," the most important thing to know about tactical nuclear weapons is that they are still full-fledged nuclear weapons. The modifiers "tactical" or "strategic" indicate how these weapons would likely be used, but both operate in the same way, and have the same effects, to greater or lesser degrees.

Modern nuclear weapons work by using conventional explosives to compress nuclear material, causing nuclear fission (this is called the "primary"). This fission releases massive amounts of energy, creating the extremely high temperature and pressure needed to ignite nuclear fusion (the "secondary"). The energy released by these weapons creates a fireball that reaches temperatures of tens of millions of degrees--the same range as the center of the sun.

Characterizing tactical nuclear weapons as "small" is misleading--some so-called "tactical" nuclear weapons have yields as great or greater than that of the bomb dropped on Hiroshima in 1945 (15 kilotons) that killed more than 70,000 people instantly and reduced the city to ruins.

The idea that using a tactical nuclear weapon would be anything other than a catastrophe is inaccurate and unspeakably dangerous. First, even one nuclear explosion could spread radiological contamination over a wide area if weather conditions, such as high winds, allow it.

But even if Russia were to detonate a single low-yield nuclear weapon in an uninhabited area with the intention of simply sending a message; even if there were very few--or even no--casualties and fallout was negligible, this would still constitute a fundamental shift in the entire international security system. It would violate a central norm--that of nuclear non-use--and, in the worst case, could set off a series of escalatory moves that could spin out of control into a full-fledged nuclear war, with civilization-ending consequences.

Even an attack not large enough to cause widespread environmental damage would still create varying levels of uncertainty and panic worldwide. In the immediate area of the attack, chaos would ensue as medical workers and first responders struggled to aid victims and deal with the aftermath of the explosion in a radioactive environment. It is unlikely that sufficient medical help would be available, particularly of the specialized kind that would be in greatest demand (such as burn beds). The most well-resourced cities during peacetime would struggle to meet such needs; the situation would be far worse during an active conflict. Farther afield, people would flee large cities that they imagined might be future targets. Global economic and financial networks would be disrupted.

Understanding and averting risks

While it is undeniably alarming to think of any nuclear involvement in wartime, understanding the differences among possible scenarios can help to understand how we can prevent the worst from happening. In some cases, there are immediate practical steps that could be taken. For example, to avoid a nuclear power plant accident, combatants could create "safe zones" around nuclear power plants as the International Atomic Energy Agency has recommended.

Undoubtedly, use of a tactical nuclear weapon is the scenario with the potential for the most far-reaching consequences. While no one can control Putin's actions, we must work now to ensure that if he does carry out his irresponsible threats, the US and its allies do not act in a way that leads down the path to nuclear war. Most crucially, the United States and NATO must not respond with nuclear weapons. As my colleague Stephen Young has pointed out, "the only fight with Russia that the United States will lose is a nuclear conflict." That goes for the rest of the world as well.