What is a dirty bomb? Russian claims stoke nuclear war fears in Ukraine

There is growing concern that a crude device could be used, raising the risk of full-scale atomic warfare

Smoke rises on the outskirts of the city during a Russian missile attack in Kyiv. Reuters

Workers surround the Monument to the Heroes of the Heavenly Hundred with sandbags against damage from shelling in Mykolaiv. EPA

Russian President Vladimir Putin welcomes Azerbaijan President Ilham Aliyev for talks before a meeting between the Russian president and the leaders of Armenia and Azerbaijan in the Black Sea resort city of Sochi, Russia. AFP

People take water from a water pump in Kyiv. EPA

A woman walks past a damaged building in the town of Nova Kakhovka. Reuters

A woman outside her home, which was destroyed during battles at the start of the conflict, in Yahidne, Chernihiv. Getty Images

People shelter inside a subway station during a Russian missile attack in Kyiv. Reuters

Firefighters at the site of a drone attack in Kyiv, Ukraine. AP

A woman walks past the site of a Russian missile strike in the southern Ukrainian city of Mykolaiv. Reuters

Rescuer workers at a building destroyed in an attack in Mykolaiv. Reuters

Parts of a drone lie on a street in Kyiv. Reuters

A drone flies over the Ukrainian capital during an attack. AFP

Ukrainian servicemen tow a captured Russian armoured vehicle in Rudneve village, Kharkiv. EPA

A partially destroyed residential building in Saltivka, in Kharkiv. AP

Ukrainian servicemen fire a captured Russian howitzer on a front line near Kupyansk city, Kharkiv. EPA

Ukrainian servicemen near the recently retaken town of Lyman in Donetsk region. AFP

An officer from a Ukrainian national police emergency demining team prepares to detonate collected anti-tank mines and explosives near Lyman, in the Donetsk region. AFP

A boy playing on a destroyed Russian tank on display in Kyiv. AFP

A young couple hiding underground during an air alert in Zaporizhzhia. AFP

Ukrainian firefighters looking for survivors after a strike in Zaporizhzhia. AFP

Workers fix a banner reading 'Donetsk, Luhansk, Zaporizhzhia, Kherson - Russia!' to the State Historical Museum near Red Square in Moscow. AFP

Residents try to cross a destroyed bridge in the Kharkiv region of Ukraine. AFP

Alyona Kishinskaya helps to clean up a shop as it prepares to reopen in Balakiya, Ukraine, after a six-month Russian occupation. Getty Images

Alla, 12, has a swinging time in Balakiya, Ukraine, as life goes on despite the war. Getty Images

Ukrainian flags in the town square in Balakiya. Getty Images

A destroyed Russian command centre in Izium, Ukraine. Getty Images

In what may be a final farewell, young Russian recruits - escorted by their wives - walk to a train station in Volgograd before being sent to war in Ukraine. AP

Russian recruits board the train to Ukraine in Volgograd. AP

Ukrainian soliders drive a tank at the recently retaken eastern side of the Oskil River in Kharkiv region, Ukraine. AFP

Volunteers pass boxes of food aid on a destroyed bridge over the Oskil River. AFP

Ukrainian soliders rest on an armoured personnel carrier. AFP

A sign warns of landmines in Izyum, eastern Ukraine. AFP

This crater was left after a missile strike in the Donetsk region of Ukraine. AFP

Russia's Defence Minister Sergey Shoigu held calls with defence ministers from several countries — including the US, UK, France and Turkey — on Sunday and said Moscow had “concerns about possible provocations by Ukraine”, which it claimed was preparing to use a “dirty bomb”.

Mr Shoigu’s remarks sparked concern among some analysts, who said Russia had a history of making similar claims about an enemy’s intention, before doing the same thing.

Britain's Ministry of Defence subsequently issued a statement warning Russia against any further “escalation” while US Defence Secretary Lloyd Austin said Washington “rejected any pretext for Russian escalation”.

US Secretary of State Antony Blinken said in a tweet on Sunday that he spoke to Ukrainian Foreign Minister Dmytro Kuleba to reject Moscow's “false allegations” that Ukraine was “preparing to use a dirty bomb on its own territory”.

But what actually is a dirty bomb and why has the weapon concerned experts for so many years?

What is a dirty bomb?

Also known as a radiological dispersal device, a dirty bomb consists of explosives attached to radioactive material that can be spread over a wide area, contaminating land and posing a long-term radiation risk to anyone who does not evacuate from affected areas.

It is different from a nuclear bomb, which uses specially shaped explosive charges to compress highly enriched uranium or plutonium until it reaches a critical mass, creating a nuclear explosion.

Mastering this process usually requires decades of scientific research and has only been achieved by a handful of countries such as the US, Russia, Pakistan, North Korea, India, China, France and the UK.

Instead, a dirty bomb is a far more crude device and is far easier to make than nuclear weapons, which are much more powerful. In theory, a dirty bomb can make large areas uninhabitable and raise the risk of cancer and other radiation-related illnesses over widespread areas.

However, recent studies on dirty bombs say the risk they pose to human life comes mainly from the massive force of an explosion that could contaminate large areas, rather than any radiation effects, which would be minuscule compared with a nuclear blast, which produces temperatures in the millions of degrees Celsius at the centre and several thousands of degrees in areas near the explosion.

As a result, the bombs have been called “weapons of mass disruption”.

This point was made clear during a US Senate hearing on the threat they posed in 2002, when the US was concerned about terrorist attacks on a scale of the 2001 World Trade Centre bombing.

“If a dirty bomb were to be detonated in the centre of Washington or if a highly radioactive can of powder were emptied from a rooftop, it could kill dozens,” said nuclear expert Richard Meserve, who chaired the hearing, which was also attended by US President Joe Biden, who was a senator at the time.

“It would not be the catastrophic event that many think, but it would have a catastrophic psychological impact on the nation and, even worse, it would contaminate a city that would probably result in evacuations and great difficulty in convincing the American public that it could be reinhabited, even though the increased cause or risk of cancer or other negative health effects would be relatively minimal,” he said.

Have they been used in Ukraine?

The weapons have never been used in any conflict so far. However, in June, Serhii Plokhy, director of the Ukrainian Research Institute at Harvard University, said Russia could destroy nuclear plants in Ukraine, effectively turning them into dirty bombs.

Aside from this warning, the weapons would have little battlefield use in Ukraine. The main impact of the weapon would be psychological and would probably affect civilians who are worried about illness, rather than soldiers who have to contend with the day-to-day risk of death in battle.

Both Ukraine and Russia possess weapons that are readily available and more than capable of turning huge areas of land into extremely hostile environments, including numerous multiple-launch rocket systems that can shower explosives over large areas of land, as well as guided artillery rounds that can hit tanks and soldiers with pinpoint accuracy.

Why are dirty bombs so controversial?

There is currently no treaty banning dirty bombs but their use would probably be considered illegal due to the risk posed to civilians, and might also fall under the Nuclear Non-Proliferation Treaty, which seeks to reduce, among other things, the risk that radiation poses to civilians.

Both sides would probably consider their use too costly in terms of reputational damage, especially considering their limited battlefield benefit.

For Ukraine and Russia, a further consideration would be the risk that radiation could blow towards their own troops and civilian areas. That risk could be higher for Russia in Ukraine, where the prevailing wind blows from the west towards Russian-occupied land.