Q+A: Obama's big summit on preventing nuclear terrorism

WASHINGTON (Reuters) - Nearly 50 world leaders meet in Washington next week for a summit aimed at preventing nuclear terrorism. It will be one of the largest such gatherings on U.S. soil since World War Two.

WHAT IS THE GOAL OF THE SUMMIT?

In a speech in Prague last year, U.S. President Barack Obama warned that nuclear terrorism was the "most immediate and extreme threat to global security." He wants to use the summit to galvanize countries to take the issue more seriously.

The goal of the summit is to reach a common understanding on the threat posed by nuclear terrorism and to agree on steps to secure all loose nuclear material within four years to stop it falling into the hands of groups like al Qaeda.

U.S. Secretary of State Hillary Clinton says the April 12-13 gathering of 47 nations is possibly the largest assembly of world leaders in the United States since 1945. Two countries not on the guest list are Iran and North Korea, both of which are locked in their own nuclear standoffs with the West.

WHAT ARE COUNTRIES DOING TO SECURE NUCLEAR MATERIAL?

The effort to secure weapons-grade material has focused mainly on Russia and former Soviet republics. The United States has helped fund efforts to better protect such materials.

There is a patchwork of ad hoc international agreements aimed at combating theft, smuggling and non-proliferation, including the Global Initiative to Combat Nuclear Terrorism and the Convention on the Physical Protection of Nuclear Material. Washington wants more countries to sign up to them.

Non-proliferation experts do not expect the summit to single out countries that are failing to make the grade. For example, Pakistan is due to attend, but no mention is likely of Abdul Qadeer Khan, the disgraced Pakistani scientist who was at the center of the world's biggest nuclear proliferation scandal.

Experts say the biggest area of risk is Pakistan, which has a heavily guarded stockpile of weapons-grade material but faces huge internal security threats from the Taliban and al Qaeda.

REALISTICALLY, WHAT CAN THE SUMMIT ACHIEVE?

Leaders will pledge to toughen prosecution of traffickers, improve accounting for weapons-grade nuclear material and better protect vulnerable stocks, according to sources with access to a draft communique.

The communique may urge nations to convert nuclear reactors using highly enriched fuel into reactors using low-enriched fuel, which is harder to adapt to produce nuclear weapons. It also calls for strengthening the role of the International Atomic Energy Agency in enforcing nuclear treaties.

Individual countries may also make announcements at the summit about specific steps they are taking to reduce the risk of nuclear terrorism.

WHAT IS 'LOOSE NUCLEAR MATERIAL' AND WHERE IS IT KEPT?

Loose nuclear material refers to stockpiles of highly enriched uranium and plutonium that are typically kept in military installations, nuclear reactors, research reactors and defense laboratories.

Non-proliferation experts say it does not appear the summit will address the issue of securing radioactive material that, for example, can be found in diagnostic equipment in hospitals and could be used to make so-called dirty bombs.

There are about 1,600 tons of highly enriched uranium and 500 tons of plutonium worldwide, enough to make 120,000 nuclear bombs, according to non-governmental groups.

HOW CREDIBLE IS THE THREAT OF NUCLEAR TERRORISM?

Experts describe the threat of a crude fissile nuclear bomb, which is technically difficult to manufacture and requires hard-to-obtain bomb-grade uranium or plutonium, as a "low probability, high consequence act." In other words, unlikely but with the potential to cause massive harm to life and property.

On the other hand, a "dirty bomb", where conventional explosives are used to disperse radiation from a radioactive source, is a "high probability, low consequence act" with more potential to terrorize than cause large loss of life.

U.S. concerns about nuclear terrorism are not shared by everyone, especially developing countries facing more pressing issues, including rising energy demands that may require greater reliance on nuclear reactors in the future.

WILL IRAN, NORTH KOREA BE DISCUSSED AT THE SUMMIT?

Iran and North Korea are not on the agenda of the summit, but Obama is expected to meet leaders on the sidelines to discuss the way forward in imposing tough new sanctions on Iran over its refusal to stop uranium enrichment and getting North Korea to return to nuclear disarmament talks.

HOW IMMINENT IS THE DANGER?

Nuclear experts say there is no sign that terrorists have got their hands on weapons-grade nuclear material but note there have been at least 18 recorded cases of such material being stolen or going missing since the early 1990s.

"There have been repeated al Qaeda attempts to either get stolen nuclear materials or recruit nuclear expertise," says Matthew Bunn, a nuclear expert at Harvard University.

Experts say making a crude nuclear bomb is technologically challenging for terrorist groups but not impossible. They would need about 110 pounds (50 kg) of highly enriched uranium and a machine shop to cast it into metal form. One mass of uranium would then be fired at high speed at another mass of uranium in a "gun-type" bomb to cause a nuclear explosion.

(Editing by Mohammad Zargham)