GE Hitachi has proposed to build an advanced reactor at Britain's Sellafield nuclear site that would convert the UK's waste plutonium stockpile into a cost-competitive source of power generation.

The U.S.-Japan joint venture company has pitched the UK government a plan to build a multi-billion-pound, 600 megawatt reactor to recycle the world's largest civilian stockpile of plutonium which is currently stored at Sellafield.

The UK government spends 2 billion pounds a year in managing its growing stockpile and is reviewing its options, including long-term storage and reprocessing.

We could take that 100 tonnes of plutonium oxide and put it through our prism reactor to make power, GE Hitachi Nuclear Energy's Danny Roderick said in a telephone interview.

Roderick said the proposed 600-MW plant would recycle the existing plutonium stockpile in about 5 years and at a cheaper cost than building new mixed-oxide fuel (MOX) plants, an alternative method of reusing the stockpile of separated plutonium.

Britain's only MOX plant at Sellafield closed earlier this year after losing its Japanese business following the Fukushima nuclear crisis.

This proposal is still in the consultation process with the UK government. But if the government decided to pursue the reuse option, we want to be there, Roderick said.

According to him, GE Hitachi's prism nuclear reactor is cost-effective and competitive against MOX plants, although he could not give an indication of the potential cost savings.

What we do know at this point is that prism technology is proven, Roderick said.

The company is in talks to export its reactor technology to other countries with plutonium stockpiles, but exports to the UK are the easiest due to preexisting trade agreements with the United States, Roderick said.

Plutonium is a by-product from the use of uranium fuel in reactors. It is found in used or spent fuel when it is removed from a reactor. It can be extracted by reprocessing and can then be reused to make MOX fuel or stored.

MOX fuel is seen as attractive because it is a way to use surplus plutonium which would otherwise be stored as nuclear waste or might be stolen to make nuclear weapons.

(Reporting by Oleg Vukmanovic; editing by Jason Neely)