In the wake of North Korea's nuclear-weapons test, little attention has been paid to a revised plan for US nuclear weapons. But details of the scheme emerged on 19 October when officials announced the start of its environmental review. The plan, which focuses heavily on the handling of the plutonium used in nuclear weapons, deserves close scrutiny: it could have wide implications not just for the United States' own nuclear-weapons stockpile, but for the fate of the tattered non-proliferation regime.

The United States currently retains about 50 tonnes of plutonium for military use — enough to fuel some 9,000 warheads. Where it isn't deployed, the plutonium is scattered across the nation's sprawling nuclear-weapons complex.

Last week, officials at the National Nuclear Security Administration (NNSA), the branch of the US Department of Energy that runs the nuclear-weapons programme, announced that it would like to reduce costs by moving nearly all its plutonium into a single facility. The consolidated plutonium centre, as it would be called, would be built at a pre-existing site and would place plutonium-related research, surveillance and manufacturing under a single roof.

That would be a positive move. Plutonium is too widely dispersed under the current arrangement, with significant quantities being held near populated areas, such as Livermore in California. Confining plutonium to a single, remote site therefore makes sense — as do elements of the plan that would consolidate existing high-explosive and hydrodynamic testing facilities.

Other aspects of the plan are more troubling, however. Specifically, the plutonium centre would be equipped to produce around 125 new plutonium 'pits' per year — these are the cores of modern nuclear weapons. NNSA officials say that the new production capability is necessary to help build a “reliable replacement warhead” — a new kind of warhead that is supposed to require less maintenance than existing designs (see Nature 442, 18–21; 2006). They argue that these warheads would replace, rather than augment, the existing stockpile.

But the construction of such a facility is liable to prompt other nations to revisit their own production plans. Although it won't change the course of countries such as Iran, it reinforces the increasingly prevalent view that nuclear weapons are vital to any nation's security. That perception may encourage further development in non-nuclear states, such as Japan and Brazil. It also sends a clear message to the United States' old nemesis Russia, which continues to maintain an unnecessarily large nuclear stockpile of its own.

The United States has not yet made a convincing case that the new warheads are needed — tests on existing plutonium pits suggest that they will last for several decades, and the replacement warhead is in any case still in the design phase. What's more, the United States already has a working pit facility at Los Alamos National Laboratory in New Mexico, which some specialists think could be adapted to produce some 50 pits a year.

Increasing pit production and building new kinds of weapons run contrary to the spirit of the 1970 Nuclear Non-Proliferation Treaty, which calls for existing nuclear-weapons states to take steps towards disarmament. Instead, the United States and other nuclear states should be acting to shrink both their weapons stockpiles and their production complexes. The best thing they could do for their collective future security would be to demonstrate to the world that nuclear weapons are less central to their own defence strategies than they were during the cold war.