Rupert Cornwell: It's that rare thing – a big summit that could produce results

Two iron laws usually govern international summits. Gridlock on the surrounding streets rises in direct proportion to the number of participants, while the likelihood of significant results moves in the opposite direction. The summit on nuclear security in Washington may just be the exception that proves the rule.

On the first count, early signs were that Washingtonians had heeded warnings, and traffic was flowing reasonably smoothly downtown, despite what is said to be the largest gathering of world leaders hosted by an American president since the 1945 San Francisco conference that founded the United Nations.

Far more important, there were also signs the 47 national delegations may come up with something beyond the pre-cooked and platitudinous communiqué normal on such occasions – all the more so since the summit proper lasts little more than 24 hours.

The encouraging aspect is that not only the US, but also every other participant nation, appears to recognise the overwhelming importance of the subject. There is broad agreement that the most dangerous threat facing the world is not of nuclear war between two nation states, but the risk of crucial nuclear technology and materials, in particular highly enriched uranium or plutonium, falling into the hands of a terrorist group.

The conference cannot ensure that all such materials will instantly be placed beyond the reach of al-Qa'ida at the stroke of a pen – not least because the nuclear "rogue states" of Iran and North Korea have not been invited.

What it can do though, is to produce real commitments from those present – not just vague statements of intent, but concrete undertakings. These could include an action plan, with specific dates for agreement on key issues like minimum security and storage standards for every aspect of the nuclear business, civilian and military. A follow-up conference should also be agreed, to monitor progress and hold laggards to account.

This week's gathering is but one of several events promoting President Obama's perhaps utopian vision of a nuclear-free world. Next month sees a UN conference aimed at limiting nuclear proliferation. But in terms of making it less likely that anyone will ever use a nuclear weapon, this summit could make the biggest contribution of all.