The arms control crowd has wanted a fissile material control treaty (FMCT) for a very long time, and President Obama agrees. Such a treaty would prohibit the manufacture of fissile material (mainly enriched uranium and plutonium) for use in weapons.
The FMCT has been discussed in the United Nations Conference on Disarmament (more here), not that body's liveliest forum, although it was instrumental in developing the Comprehensive Nuclear Test-Ban Treaty. The history of the FMCT has been of blocking by one nation or another, to a point where it is barely discussed.
Why should that be? The purpose of the treaty is to end the manufacture of fissile material for nuclear weapons. Whose interests this serves is obvious. The United States and Russia have far more than they need; in fact, they are now burning excess weapons uranium in reactors and arguing about how to dispose of the plutonium - in reactors or by mixing with much more radioactive stuff and burial. They don't need any more.
The other NPT nuclear weapon states are also pretty well fixed for fissile material: the United Kingdom and France have plenty, and China may want a bit more, but probably not much. In any case, China hasn't been saying much on an FMCT.
The nations that have signed up to the NPT as non nuclear weapon states have essentially signed on to an FMCT: they've agreed not to make nuclear weapons, so they're not producing fissile material to that end.
The outliers are the three outside the NPT: India, Israel, and Pakistan; along with North Korea, which has withdrawn and tested two nuclear devices, and Iran, which remains within the NPT but has been developing the capability to produce fissionable material with some indications that it may be or may have been interested in using those materials in weapons.
An FMCT would not affect the behavior of the NPT nuclear five, nor of most of the non nuclear weapon states. So presumably it is directed at the five outliers. I say "directed at" because none of those states has pressed for an FMCT, although India reluctantly agreed to follow the US lead on the subject as part of its obligations in the nuclear trade pact negotiated under the Bush administration.
I keep wondering what makes anyone think that any of these five would eagerly (or reluctantly) sign on to an FMCT. We've sort of got India's agreement, yes, although during the discussions of the trade pact, there was strong resistance to any limits on India's nuclear material production, which continues.
Perhaps the benefit of an FMCT would be codification of increased surveillance of fissile material in the nuclear weapon states, which will be needed anyway as the numbers of nuclear weapons are negotiated down. That surveillance could be extended to other states as well.
Couldn't the time and effort toward an FMCT be spent more constructively? Why does anyone think that the states of concern would sign up? What does an FMCT do that the NPT doesn't?
We hear today that Pakistan is blocking progress on an FMCT in the Conference on Disarmament. Well, duh. Given that Pakistan is building two new reactors to furnish weapons plutonium and has repeated that it needs to counterbalance India's nuclear force, why did anyone expect anything else?