Feature: Nuke terrorism haunts in shadow of Brussels attacks

Walking on the streets of Washington D.C. on a March morning, one can still feel some coldness in a gust of early spring wind.

This provides an apt metaphor for the global nuclear security landscape: danger lurks while the international community works to secure a world free of nuclear terrorism.

As progress grows, so does the threat of nuclear terrorism, experts said.

It is a grim reality that 50-plus world leaders and heads of international organizations will bear in mind when they gather in the U.S. capital for the Nuclear Security Summit (NSS) to be held from Thursday to Friday.

The summit is the fourth and probably the last of the series since its launch by U.S. President Barack Obama in 2010 with an aim of raising the profile of the nuclear security issue.

The summit comes as the extremist group Islamic States (IS) extends its deadly grasp, which now reaches far beyond Syria and to the heart of Europe.

Last week, synchronized bombings in Brussels killed at least 35 people and injured more than 300 others. Months ago, the carnage in Paris, capital of France, killed 130.

The most disturbing fact is that an unverified report claims the Brussels terrorists had planned to target a nuclear power plant, bringing the prospect of a nuclear attack by terrorist groups into sharp focus.

The IS, commanding more recruits, money and expertise than other terrorist groups, has caused widespread alarm.

"I regard them as a worrisome potential threat," Matthew Bunn, a specialist in nuclear security at Harvard's John F. Kennedy School of Government, told Xinhua.

A surveillance video showing that IS operatives closely monitored a senior staff with a Belgian nuclear facility for many hours is the most worrisome indicator of potential IS interests in nuclear matters, Bunn said.

Three men linked to the video had a hand in the Paris or Brussels attacks.

Out of the danger will emerge strong global actions against nuclear terror, experts said, adding that more concerted efforts to prevent nuclear materials from falling into the hands of the IS will undoubtedly factor into the talks at the session.

"Because of the expectation of the rise of such a threat, there have been such NSS to make a response," said Shen Dingli, a member of the Global Council of the New York-based Asia Society and a nuclear security expert with China's Fudan University.

During the two-day summit, there will be a special session focusing on the IS, including bolstering security in urban centers and preventing the terror group from obtaining chemical or radiological materials.

According to government reports in countries including the United States, it is very possible that if an extremist group like the IS got hold of highly-enriched uranium or plutonium, they might be able to make a crude, unsafe but nonetheless very dangerous nuclear bomb, or "dirty bomb."

Nuclear experts warn that the global nuclear security architecture is far from seamless and that terrorists are seeking the loopholes of the chain.

"It looks that the IS is unlikely to make a nuclear bomb yet, but no one can be sure it could not make a 'dirty bomb.' So it is important to control radioactive materials which are widely available in hospitals, among others," Shen said.

Meanwhile, he said, nuclear security will cover not only nuclear materials security, but also focus on the safety of nuclear facilities, including the physical protection and loyalty of staff.

Another way to prevent extremist groups such as the IS from making a dirty bomb is to convert highly-enriched uranium to low-enriched uranium as fuel in reactors, said Zhang Hui, who heads the Harvard Kennedy School's research initiative on China's nuclear policies.

The low-enriched uranium fuels -- enriched to less than 20 percent -- are unsuitable for weapons.

Meanwhile, after the release of the surveillance video, nuclear facilities in Belgium have been put on high alert and tighter regulations have been introduced for the staff, he said. Endi