At a meeting 23 and 24 March in Belgrade, US and Russian members of the Elbe Group – retired general officers from the military and intelligence services – declared that the risk of terrorism, both conventional and nuclear, is growing.  They urged that special attention must be given to preventing Daesh, al Qaeda, and other terrorist organizations which have declared openly their desire to gain weapons of mass destruction, from obtaining them.

As world leaders gather for the fourth nuclear security summit this week, in the aftermath of the horrifying terrorist attacks in Brussels, it seems likely that Belgian Prime Minister Charles Michel will have more to say than anyone else — both about real nuclear terrorist dangers and about real steps taken to improve nuclear security.

The history of nuclear security has been described as an example of “punctuated equilibrium” -- long periods of inaction and complacency followed by events that catalyze action. U.S. history is rife with examples where the discovery of vulnerabilities or major incidents led agencies to strengthen nuclear security requirements.

There is no shortage of terrorist groups – homegrown and international alike – that see opportunity in China’s nuclear enterprise, the fastest-growing in the world. Some would like to steal radioactive material for nuclear or dirty bombs; others may be pondering ways to breach a facility’s containment walls or even induce a Fukushima-style meltdown.

World leaders face a stark choice at the final Nuclear Security Summit later this week: Will they commit to efforts that continue to improve security for nuclear weapons, fissile materials, and nuclear facilities, or will the 2016 summit be seen in retrospect as the point at which attention drifted elsewhere, and nuclear security stalled and began to decline? The answer will shape the chances that terrorist groups, including the Islamic State, could get their hands on the materials they need to build a crude nuclear bomb.

They cut through four fences, set off sensors and alarms, hammered on the outside of the storage building, and defaced it with paint and human blood. They remained on the site for over an hour before a guard finally arrested them.

The history of nuclear security has been described as one of punctuated equilibrium, long periods of inaction and complacency followed by events that catalyze action. U.S. history is rife with examples where the discovery of vulnerabilities or major incidents led to the strengthening of nuclear security requirements.

Last week, a National Academies of Sciences, Engineering, and Medicine panel affirmed the goal of eliminating highly enriched uranium (HEU) from civilian use, while recommending step-wise conversion of high performance research reactors using weapon-grade uranium fuel and that the White House coordinate a 50-year national roadmap for neutron-based research. (Full disclosure:  I sat on that committee, and oversaw the NNSA reactor conversion program from 2006-9; this post, however, represents my views, not necessarily those of the committee or NNSA.)

With the fourth and final nuclear security summit approaching in March, the 2016 edition of the Nuclear Threat Initiative (NTI) Nuclear Security Index raises red flags about the international community’s implementation of the important measures needed to protect against catastrophic nuclear terrorism and to build an effective global nuclear security system. More importantly, it raises the question, how will leaders sustain momentum and high-level political attention on the need to secure dangerous nuclear materials once the summits come to an end?

In 1998, in Operation Auburn Endeavor, the U.S. government helped fly 4.3 kilograms of highly enriched uranium (HEU) and low-enriched uranium (LEU) from vulnerable facilities in war-torn Georgia to the Dounreay reprocessing plant in the United Kingdom. At the time, those in the U.S. government involved in the project, myself included, thought that was all the HEU there was in Georgia. So it was a surprise when the IAEA announced the removal of another 1.83 kilograms of HEU from Georgia – apparently now really the last of the HEU there.