The Fissile Material Cut-off Treaty (FMCT) is a proposed arms control
treaty, that would ban the the production of fissile material for
nuclear weapons or other nuclear explosive devices, such as weapon grade
uranium or
plutonium.
The FMCT would not cover material enriched only for non-explosive materials, nor non-fissile material like tritium or the components of warheads or missiles. Nor would the treaty address existing stockpiles. It has an advantage over the Nuclear Non-Proliferation Treaty (NPT) which is explicitly discriminatory in prohibits countries other than five designated Nuclear Weapon States (NWS) (United States, Russia, China, the United Kingdom and France) from possessing nukes. The FMCT instead would be universally applied, and thus could provide some form of control over these and other states that have developed nuclear weapons outside the authority of the NPT, like India, Pakistan and North Korea (and if you wish, Israel).
The idea of banning the production of weapon grade material dates back to 1946. Occasionally throughout the Cold War the idea was mooted as something that would indirectly cap the number of nuclear weapons that could be built. However instead the Cold War ended with more nuclear weapons than what either side needed, and the US began to promote the FMCT in international fora. In the United Nations General Assembly a resolution adopted by consensus that called for negotiation of a "non-discriminatory multilateral and internationally and effectively verifiable treaty banning the production of fissile material for nuclear weapons or other nuclear explosive devices."
Negotiations commenced in 1995 at the United Nation's principle arms control venue, the Conference on Disarmament (CD). However negotiations only lasted until the end of the year when the session's negotiation mandate expired, and save for a short period in 1998 the CD has not resumed. The CD operates on the basis of concensus, so only one country needs to chuck a whobbly to disrupt an arms control process.
Firstly, it is not much of a priority in the post-Cold War environment. Terrorism and rogue states are a greater concern, and arms control treaties are now being used to counter the proliferation of weapons. Indeed many countries are dismantling their stockpiles anyway - 10% of all electricity in the United States comes from a nuclear reactor that is feeding off downblended fissile material that was previously enriched to be weapons grade. Certainly the states with nuclear ambitions aren't interested, unless they can get something in return.
The Bush administration has not publically outlined the reasons to its opposition, although verification could be their main sticking point. Verification would be expensive, possibly inconclusive and would necessarily involve the international community sticking its nose in American nuclear facilities. And I doubt even the bravest weapons inspector wants to crawl through the service ducts of the most radioactive zones on the planet.
Another problem of the treaty have been some parties wanting the treaty to cover more ground than what other people are comfortable with. Some states want existing stockpiles to be included in the Treaty. Some NGOs want the treaty to ban plutonium separation outright, a position that most states oppose.
The main states have varying positions similar to the US line, or different to concord with their own priorities. Russia supports the FMCT in principle, but has proposed that the agreement be limited to weapon-grade plutonium (most of its reprocessing plants use uranium). China was a supporter, but now would only consider the Treaty if other arms control treaties that are in its interest (like PAROS and missile defence) are given equal weighting. Britain and France continue support the treaty, if unenthusiastically.