The simplest way to produce an atomic explosion is to slam together two sizeable chunks of high-enriched uranium (HEU) in what is commonly called a “gun-type nuke”. The approach might sound crude, and it is. No country currently uses this design for its nuclear weapons.

But it is worth remembering two things. First, that it was an HEU gun-type nuclear weapon that killed more than 70,000 people at Hiroshima. Second, that terrorists tend to be less focused on elegance of design than on results. This brings us to a critical question: after nearly five years of living under the threat of sophisticated terrorism – and with clear signs of terrorists trying to acquire nuclear material through criminal networks – why are we still moving so sluggishly to get rid of global HEU stockpiles and to minimise civilian uses of HEU?

Much attention is currently being given to the control of uranium enrichment technology, and rightly so. If all enrichment operations were brought under multinational control, it would become far more difficult for any country to divert enriched uranium for use in weapons. But it makes equal sense to protect – or, better, eliminate – the bomb-grade HEU that already exists.

Experts say there are about 1,850 metric tonnes of HEU in global stockpiles, enough to make tens of thousands of nuclear weapons. The great bulk of this is in military use. On the civilian side, the numbers are much smaller – but the level of security is uneven. Nearly 100 civilian facilities around the world operate with small amounts of weapon-grade HEU – that is, uranium that has been enriched to 90 per cent or greater. These facilities, primarily research reactors, provide important benefits. The isotopes they produce are vital to medical treatments, industrial productivity, water management and many other humanitarian uses. Research conducted at these facilities has greatly enhanced our quality of life.

But most if not all of these benefits could also be achieved using low-enriched uranium (LEU). As far back as the late 1970s, the US and other countries began efforts to convert such facilities from HEU to LEU, to reduce the proliferation risk. In recent years, good progress has been made. Many research reactors have been converted. Large quantities of HEU reactor fuel, both used and unused, have been removed from vulnerable locations and returned to the countries of origin.

Civil society has become involved, raising awareness of the problem and supporting change. A good example is the Nuclear Threat Initiative. Just last year it completed a project with the government of Kazakhstan that successfully “downblended” nearly 3,000kg of fresh HEU fuel to LEU and placed it in secure storage.

But more successes such as these are needed. Many vulnerabilities remain. We need to ratchet up the sense of urgency. We need more coherent global action. First, the countries involved should join forces to minimise and eventually eliminate the civilian use of HEU. Joint research should be conducted to address the remaining technical hurdles involved in converting from HEU to LEU operations. The commercial interests of the companies concerned should be protected. Financing should be made available where needed to assist countries with conversion operations. The HEU fuel should be sent back to the countries of origin for downblending and reuse.

Second, all countries should agree to stop producing fissile material for use in nuclear weapons. The elements are already in place for such an agreement, in the form of a Fissile Material Cut-off Treaty. It is high time to negotiate and conclude such a treaty.

Third, to build trust, countries with civilian and military HEU stockpiles should be encouraged to release clear inventories of those stockpiles and to publish a schedule under which the remaining HEU will be verifiably downblended.

By investing in these straightforward measures, we could reduce substantially the risk of nuclear terrorism. The work could be done jointly, as an international community; this is one initiative in which all countries – nuclear weapon states and non-nuclear weapon states alike – could play a role and from which all would clearly benefit.

Mohamed ElBaradei is the director-general of the International Atomic Energy Agency and the winner of the 2005 Nobel Peace Prize. Jonas Gahr Støre is the Norwegian minister of foreign affairs. An International Symposium on the Minimisation of HEU in the Civilian Nuclear Sector begins at the Nobel Peace Centre in Oslo on Saturday