What is uranium-based ammo US is handing to Ukraine against Russia?

The US is sending depleted uranium anti-tank rounds to Ukraine, following Britain's lead in sending the controversial munitions to help Kiev push through Russian lines in its gruelling counteroffensive.

The 120 mm rounds will be used to arm the 31 M1A1 Abrams tanks the US plans to deliver to Ukraine in the fall.

Such armour-piercing rounds were developed by the US during the Cold War to destroy Soviet tanks, including the same T-72 tanks that Ukraine now faces in its counteroffensive.

Depleted uranium is a byproduct of the uranium enrichment process needed to create nuclear weapons.

The rounds retain some radioactive properties, but they can't generate a nuclear reaction like a nuclear weapon would, RAND nuclear expert and policy researcher Edward Geist said.

Here is look at depleted uranium ammunition:

What is depleted uranium?

Depleted uranium is a byproduct of the process to create the rarer, enriched uranium used in nuclear fuel and weapons.

Although far less powerful than enriched uranium and incapable of generating a nuclear reaction, depleted uranium is extremely dense — more dense than lead — a quality that makes it highly attractive as a projectile.

"It's so dense, and it's got so much momentum that it just keeps going through the armour — and it heats it up so much that it catches on fire," Geist said.

When fired, a depleted uranium munition becomes "essentially an exotic metal dart fired at an extraordinarily high speed," RAND senior defence analyst Scott Boston said.

In the 1970s, the US Army began making armour-piercing rounds with depleted uranium and has since added it to composite tank armour to strengthen it.

What has Russia said?

In March, Putin warned that Moscow would "respond accordingly, given that the collective West is starting to use weapons with a 'nuclear component.'"

Putin followed up several days later by saying Russia would respond to Britain's move by stationing tactical nuclear weapons in neighbouring Belarus.

There was no immediate reaction from the Kremlin to the US announcement, which came late on Wednesday during a visit to Kiev by Secretary of State Antony Blinken.

The Pentagon has defended the use of the munitions.

The US military "has procured, stored, and used depleted uranium rounds for several decades, since these are a longstanding element of some conventional munitions," Pentagon spokesperson Marine Corps Lieutenant Colonel Garron Garn said in a statement in March in response to a query from The Associated Press.

The rounds have "saved the lives of many service members in combat," Garn said, adding that "other countries have long possessed depleted uranium rounds as well, including Russia."

Garn would not discuss whether the M1A1 tanks being readied for Ukraine would contain depleted uranium armour modifications, citing operational security.

Not a bomb, still a risk

While depleted uranium munitions are not considered nuclear weapons, their emission of low levels of radiation has led the UN nuclear watchdog to urge caution when handling and warn of the possible dangers of exposure.

The handling of such ammunition "should be kept to a minimum, and protective apparel [gloves] should be worn," the International Atomic Energy Agency cautions, adding that "a public information campaign may, therefore, be required to ensure that people avoid handling the projectiles."

"This should form part of any risk assessment, and such precautions should depend on the scope and number of ammunitions used in an area."

The IAEA notes that depleted uranium is mainly a toxic chemical, as opposed to a radiation hazard.

Particles in aerosols can be inhaled or ingested, and while most would be excreted again, some can enter the bloodstream and cause kidney damage.

"High concentrations in the kidney can cause damage and, in extreme cases, renal failure," the IAEA says.

The low-level radioactivity of a depleted uranium round "is a bug, not a feature" of the munition, Geist said, and if the US military could find another material with the same density but without the radioactivity, it would likely use that instead.

Depleted uranium munitions, as well as depleted uranium-enhanced armour, were used by US tanks in the 1991 Gulf War against Iraq’s T-72 tanks and again in the invasion of Iraq in 2003, as well as in Serbia and in Kosovo.

US troops have questioned whether some of the ailments they now face were caused by inhaling or being exposed to fragments after a munition was fired or their tanks were struck, damaging uranium-enhanced armour.