LONDON - GE Hitachi Nuclear Energy has proposed an alternative nuclear fuel recycling system, which could reduce radioactive waste and avoid extraction of plutonium that can be used for making weapons.

Nuclear experts say while the proposed Advanced Recycling Center (ARC) could help to solve some of the biggest worries as more countries build nuclear reactors, high costs are drawbacks.

Here is what is happens about spent nuclear fuel at present:

-- What happens to spent nuclear fuel?

Nuclear fuel elements are discharged and cooled down in a water pool for up to 50 years at reactor sites. Many countries plan to put them in repositories in deep geological sites afterwards. Finland or Sweden may become the first to put such waste into repository after 2020.

-- What happens in countries that have opted to recycle spent nuclear fuels?

Used nuclear fuel is reprocessed to extract the remaining uranium and plutonium generated during irradiation of the fuel in the reactor.

Uranium accounts for about 95 percent of the volume, while plutonium is about 1 percent and about 3 percent is fission products or nuclear waste.

Uranium can be re-enriched and used as fuel in nuclear reactors. At present, it is stored in most countries. France has reactors that can use such fuel after it is re-enriched in Russia. Plutonium is processed into mixed oxide fuel, or MOX, for use in reactors.

Separated highly-radioactive waste is vitrified and put into heavy stainless containers and mostly stored at reprocessing plants.

-- Which countries have opted for the closed fuel cycle or to reprocess spent nuclear fuel?

China, France, India, Japan, the Netherlands, Russia and Britain. The United States is reconsidering its policy and could in future treat spent nuclear fuels.

-- Where are such reprocessing capacity?

Major facilities include those in La Hague in France, Sellafield in Britain, Ozersk in Russia, and Rokkasho in Japan. (Source: World Nuclear Association)

(Reporting by Nao Nakanishi; editing by James Jukwey)