The recent terrorist attack in Brussels should remind the world that nuclear security has never been more important. Even with the disarmament of many Cold War era weapons, poorly secured stockpiles of weapons-usable uranium and plutonium remain across the globe, several of which have experienced security breaches in recent years. Without action to keep these materials from terrorist groups and other nonstate actors an act of nuclear terrorism becomes all the more likely.

In 2010, the Obama administration convened the first Nuclear Security Summit (NSS) in an attempt to draw high-level political attention to this issue. These Summits reconvened in 2012 and 2014 in Seoul and The Hague, respectively. Each summit, attended by nations across the globe, has been driven by the goal of securing all civilian nuclear materials and creating a global culture of accountability. The NSS process, supported by international experts including many Carnegie Corporation of New York grantees, has raised awareness around nuclear security, reduced the number of worldwide sites containing fissile material, and built support for higher security standards. It has driven home the message that vulnerable nuclear materials anywhere are a threat to citizens everywhere.

We are safer today for this effort, but more must be done. As Matthew Bunn, a Corporation grantee at Harvard University’s Project on Managing the Atom, noted in a recent Q&A, security has improved, but so have the capabilities of the terrorist groups seeking these nuclear materials. “If IS [Islamic State] did turn toward nuclear weapons, they have more money, more people, more territory under their control, and more ability to recruit globally than al-Qaeda ever had.”

This is not idle speculation. In November, authorities recovered video footage from an IS associate in Brussels who had been monitoring a nuclear scientist, potentially in search of radioactive or nuclear materials. Facilities in Belgium house highly-enriched uranium—the most easily weaponized nuclear material—as well as radiological materials that could be used in a radiological dispersal device (or “dirty bomb”). Just this month, eleven workers at Belgium's Tihange nuclear facility had their security access revoked, an action that called to mind an incident in 2014 in which a Belgian nuclear power plant was sabotaged by an insider, causing an estimated $100-200 million in damage.

One of the achievements of the Nuclear Security Summit process has been the reduction in the amount of excess highly-enriched uranium. This reduction, coupled with the strengthening of security procedures in Belgium and other countries with similar risk profiles, is a positive and necessary step toward creating a safer nuclear environment.

However, as we approach the final installment of the NSS process, much work remains to be done.

Historically, as documented in this interactive, these efforts have been led by the United States and Russia. Unfortunately, deteriorating U.S.-Russia relations have contributed to a decision by Moscow to skip the upcoming NSS summit (scheduled for March 31-April 1), an action which Bunn notes may forestall future advances by the initiative. “Russia and the United States have the world’s largest stockpiles of materials, and the largest experiences in learning to account for those stockpiles, and we have a responsibility jointly to figure out ways to work together even in difficult periods.”

The Greatest Threat