It used to be that people were either pro or anti nuclear power — and that they would let you know which through a sticker on their car bumper. Now the debate is shifting. As evidence for global warming mounts, getting rid of nuclear power, with its very low carbon emissions, looks harder to justify in today's world than it did in the 1970s; hence the talk of a ‘nuclear renaissance’. But there is a difference between keeping today's nuclear-power capacity (about 365 GW of capacity, which is responsible for generating roughly 16% of the world's electricity) and greatly increasing it. With extensive nuclear expansion depending on reprocessing spent nuclear fuel, whether or not to reprocess is now shaping up to be a new dividing line in the nuclear debate.

Reprocessing retrieves plutonium and unused uranium from used nuclear fuel. If you want to make sophisticated nuclear weapons, you need to have a reprocessing capacity, and the world's main nuclear-weapon powers all do. But not all of them have the capacity to reprocess spent fuel for civilian purposes. The United States has eschewed reprocessing as a way of making reactor fuel for the past 30 years. Now it is reconsidering it, sparking a reappraisal of the technology around the world.

Reprocessing makes usable fuel out of unusable waste, and in doing so reduces the volume and activity of what's left behind. The proposed conversion to civil reprocessing in the United States is being spurred in part by a desire to limit the amount of waste that needs to be put into long-term storage at the contentious Yucca Mountain site in Nevada. Supporters point to the reduction of waste and the increase in the amount of energy that can be extracted from a fixed amount of fuel as ‘green’ credentials for the technology. They also point out that the world's uranium supplies may not be sufficient to support an aggressive expansion of nuclear power unless fuel is reused.

But reprocessing is also accident-prone, expensive and makes available the sort of stuff that can be used to build bombs. No country has yet managed to make reprocessed fuel cheaper than the enriched uranium that is used in most reactors, undercutting any economic rationale at today's uranium prices.

The reprocessing method the US Department of Energy proposes, called UREX+, aims to reduce the possibility of reprocessed plutonium being used in weapons by leaving it mixed with other highly radioactive metals. This supposedly leaves it too radioactive for malefactors to handle. But many opponents believe that the methods being discussed are still a security risk.

The issues are a little too complex to get on to a bumper sticker. But the current state of play can be displayed on a map.

The United States is mulling over a proposal from the Bush administration to return to reprocessing, which the country has abjured due to proliferation concerns since India tested a bomb made from extracted plutonium in 1974. The new scheme, called the Global Nuclear Energy Partnership (GNEP), would have nuclear-weapons states plus Japan sending fuel to other states for use in their standard reactors. The donor countries would then take the fuel back for reprocessing. The idea has been received frostily in some quarters. The House of Representatives allocated about half of the funds requested by the administration to the project, saying there was too little detail in the plan to warrant a $250-million investment. Many scientists and activists — both pro and anti nuclear power — have criticized the economics, timing and safety of the plan.

The image has been created in high resolution format. This is available as a PDF file online. Credit: M.BOND/SPL

The United Kingdom is home to the Sellafield site, where a reprocessing plant called Thorp has been inoperative since the discovery in April 2005 of a broken pipe that was leaking uranium and plutonium in a sealed-off cell. The incident renewed talk of shutting down the plant, which has been charged with polluting the Irish and North Seas. The publicly owned contractor that runs the whole Sellafield site, including two reprocessing plants and a hodgepodge of retired infrastructure needing clean-up, is up for sale.

France is the king of reprocessing (the United Kingdom's Thorp plant never ran at capacity). Nuclear company Areva has plants at La Hague that have reprocessed waste from France's own extensive nuclear-power industry, as well as from Belgium, Switzerland, the Netherlands and Japan. In 2004 and 2005, weapons-grade plutonium that the United States promised Russia it would get rid of was reprocessed at Areva's Cadarache fuel plant into mixed-oxide (MOX) fuel. The MOX fuel was then used at the Catawba Nuclear Station in South Carolina.

Sweden is now thinking of reprocessing the waste from its nuclear-power industry for the first time in 20 years. A shipment of waste will set sail for Sellafield in the summer of 2007, if all goes as planned.

India reprocesses at three small plants. Famously, it got the technology from the United States, then used the plutonium it extracted to make a nuclear bomb, which it tested in 1974. India was affronted when asked to join the GNEP not as a provider of reprocessing power but as a client.

Australia's prime minister, John Howard, announced on 6 June that the nuclear-free country will study the possibility of building some nuclear power plants, and of becoming a reprocessing nation. Howard visited US energy secretary Sam Bodman last month to discuss the GNEP reprocessing scheme.

Russia reprocesses its waste to form uranium, which it uses again as fuel, and plutonium, which it stores. Plans to build fast reactors that could burn pure plutonium have been edging forwards for years. Russia would like to import waste from other countries to stake a claim in a future ‘plutonium economy’, in part because it has little domestic uranium. According to Russian news reports, the head of the Mayak reprocessing plant, Vitaliy Sadovnikov, was charged with polluting the river Techa in March, but given amnesty in May because it was the 100th anniversary of the national state legislature.

Japan has just begun a 17-month test phase at the brand-new Rokkasho reprocessing plant, which is far larger than the Tokai pilot reprocessing plant, now headed for retirement. The new plant's capacity will be 800 tonnes per year. Japan has also agreed, on paper, to join the GNEP, but a 1988 agreement banning the transfer of reprocessing technology between Japan and the United States is standing in the way.