In a drab one-storey building in Bellevue,Washington,dozens of engineers,physicists and nuclear experts are chasing a radical dream of Bill Gates: a new kind of nuclear reactor that would be fueled by todays nuclear waste,supply all the electricity in the United States for the next 800 years and,possibly,cut the risk of nuclear weapons proliferation around the world. The people developing the reactor work for a start-up,TerraPower,led by Gates and a fellow Microsoft billionaire,Nathan Myhrvold. Building a prototype reactor could cost $5 billiona reason Gates is looking for a home for the demonstration plant in rich and energy-hungry China. The hope is that well find a country that would be able to build the demo plant, Gates said last year in a conversation with energy expert Daniel Yergin. If that happens,then the economics of this are quite a bit better than the plants we have today. Perhaps one of the most intriguing arguments supporters make about the reactor is that it could eliminate several routes to weapons proliferation. Iran,for example,says its nuclear programme is for peaceful purposes,but it is enriching far more uranium than it needs for power generation. Todays nuclear reactors run on concentrations of 3 to 5 per cent uranium 235,an enriched fuel that leaves behind a pure,mostly natural waste,uranium 238. (A uranium bomb runs on more than 90 percent uranium 235.) In reactors,some uranium 238 is converted to plutonium that is used as a small,supplemental fuel,but most of the plutonium is left behind as waste. In contrast,the TerraPower reactor makes more plutonium from uranium 238 for use as fuel,and so would run almost entirely on uranium 238. It would need only a small amount of uranium 235. The result,TerraPowers supporters hope,is that countries would not need to enrich uranium in the quantities they do now. TerraPowers concept would also blunt the logic behind a second route to a bomb: recovering plutonium from spent reactor fuel,which is how most nuclear weapons are built. Since so much uranium 238 is available,there would be no reason to use that plutonium,TerraPower says. Countries that do not have nuclear weapons will still need electricity,said John Gilleland,chief executive of TerraPower,and we would like to see them build something that allows us to sleep at night. No one disputes that this is a very long-term bet. Even optimists say it would take until at least 2030 to commercialise the technology. What the competition would look like thenwind,solar,natural gas or some other technologyis not clear. If you could pick just one thing to lower the price ofto reduce povertyby far you would pick energy, Gates said as he introduced the reactor idea in a speech in 2010. TerraPower is a spinoff of Intellectual Ventures and focuses on inventing new products and techniques. But its critics call it a patent troll because it buys large portfolios of technology patents and uses them,they say,to sue software designers,smartphone makers and others. TerraPower is not alone in pursuing a reactor that will turn waste uranium into energy. General Atomics,which has decades of experience in nuclear power,is pursuing what it calls an energy multiplier reactor module on the same general principle. Based in San Diego,they would use helium,not sodium,however,potentially simplifying some problems. Like TerraPower,General Atomics is courting the Chinese. Matthew L Wald
