单选题：A.Does the world need more nuclear power or less? Scared by

A.Does the world need more nuclear power or less? Scared by the disaster at theFukushima nuclear plant in March 2011, Japan has now taken all its commercialreactors offline. The last was powered down on September 16th,2013.
B.Meanwhile, measures are underway in Germany and Switzerland to stop their nuclearstations. Another 11 European countries, plus Australia and New Zealand, remainstrongly opposed to nuclear power. In recent years, more reactors around the worldhave closed than opened.
C.Yet nuclear reactors do one thing no other mainstream source of electricity can boast:they generate large blocks of power without producing carbon dioxide in the process.Hydro-electricity is largely carbon-free, but most suitable sites have long since beenexploited. Certainly, renewables like solar, wind and biomass can deliver powerlargely free of greenhouse gases. But renewables are nowhere near reliable nor cheapenough to displace conventional fuels--be they coal, natural gas, oil or nuclear. Norcan they be scaled up fast enough to meet the world's greedy demand for electricity.
D.Overall, opposition to nuclear power--despite the graphic footage of the nucleardisaster in Fukushima--seems to gradually decline. Last year, The Economist heldan online debate on whether the world would be better off without nuclear power.Readers voted 61% to 39% in favor of keeping it.
E. All told,40-odd countries--mainly in the Middle East and Asia--have nowcommitted themselves to building their first atomic-power plants, or to adding newones to their existing nuclear capacity. Today, the nuclear industry's prospects lookbrighter than at any time since 1979. That was when a partial meltdown at the ThreeMile Island plant in Pennsylvania sent shockwaves around the world--and furtherorders for nuclear generating capacity began to dry up. The latest reactor designs arefar safer. The AP1000, an "advanced passive" reactor from Toshiba's Westinghousedivision, has a huge pool of water above the reactor, which is dumped by gravityinto the core in an emergency. Westinghouse claims the AP1000 is 100 times saferthan present reactors. The broadly similar European Pressurised Reactor, designed byAreva, a French firm, has four safety systems instead of the more usual two or three.
F.But to my mind, the question is not whether their "passive" designs can make themsafer. Of that there is no doubt. The question, rather, is why such an inherently flaweddesign as the light-water reactor (LWR) is still, after all these years, the preferredtechnology?
G. Most of today's reactors, whether they use boiling water or pressurised water, tracetheir ancestry back to the USS Nautilus, the world's first nuclear submarine, launchedin 1954. At the time, the LWR was just one of many reactor designs that existed eitheron paper or in the laboratory--using different fuels, different coolants and differentmoderators.
H. The light-water reactor of the day, with its solid uranium-dioxide fuel and water forboth moderator and coolant, was by no means the best. But Admiral Hyman Rickover,the father of America's nuclear navy, chose it because it could be put into use fasterthan any of the others, making it possible for Nautilus to be launched on time. TheLWR also appealed to Rickover because it produced a lot of bomb-making chemicalelements as a by-product.
I.After that, the die was cast. America's first commercial reactor, the 60-megawatt Shippingport station in Pennsylvania, the rest of America's commercial reactors followed suit. Other countries subsequently copied or licensed much the same light- water technology.
J.In hindsight, that was a terrible mistake. Producing large quantities of plutonium isjust about the last thing a commercial reactor needs to do. It creates huge handling and storage problems as well as all manner of security and spread headaches. On top of that, the LWR's other drawbacks ensured that commercial reactors would henceforth be more expensive to build and costlier to operate than might otherwise have been thecase.
K.Another problem concerns the bundles of rods that contain the uranium-dioxide fuel.These have to be removed from the core after only a few years of burning and storedin cooling ponds, even though no more than 3-5% of the energy in their uranium hasbeen consumed. Their zirconium ( 锆 ) cladding swells and distorts as a result oftemperature differences and radiation damage. There is always the danger of fuel rodscracking if left in the reactor too long.
L.Within the fuel rods themselves, the nuclear fuel becomes steadily poisoned by short-lived by-products. This causes dangerous instabilities that make managing the reactortricky.
M.Passive safety features aside, the new generation of reactors being promoted aroundthe world are still basically old-fashioned light-water reactors with solid-fuel coresthat are cooled and moderated by water. "Maddeningly," say two leading light-watercritics, "historical, technological and regulatory reasons conspire to make it hugelydifficult to distinguish from our current path of solid-fuel, uranium-based plants."
N.In what has become a classic account of America's missed opportunity to makenuclear power cleaner, safer and potentially an alternative to coal, Robert Hargravesof Dartmouth College and Ralph Moir, formerly of Lawrence Livermore NationalLaboratory, have made the most compelling case yet for reactors that use a liquid fuelinstead of a solid one.
O.One advantage of liquid fuels is that they are not subjected to the radiation damage orstructural stresses that cause the fuel rods in conventional reactors to swell and distort.Also, because they use a liquid fluoride ( 氟化物 ) salt for a coolant, there is no high-pressure water to deal with. Operating at atmospheric pressure, no containment vesselis therefore needed. The xenon ( 氙) gas that poisons the fuel rods in a conventionalreactor simply bubbles out of a liquid fuel, while other fission products ( 裂变产物 )separate out and cease absorbing neutrons from the chain-reaction underway.
P.The spent fuel from a light-water reactor contains radioactive plutonium with a half-life of over 24,000 years. The fuel used in a liquid-fuel reactor is liquid fluoride lacedwith thorium ( 钍) . The toxicity of what little waste it produces is 10,000 times lessthan that from a conventional reactor. Overall, the half-life of a liquid-fuel reactor'sby-products is measured in hundreds rather tens of thousands of years.
Q.The liquid-fluoride thorium reactor, developed at Oak Ridge National Laboratory inTennessee during the late 1960s, ran successfully for five years before being axedby the Nixon administration. The reason for its cancellation: it produced too littleplutonium for making nuclear weapons. Today, that would be seen as a distinctadvantage. Without the Cold War, the thorium reactor might well have been the powerplant of choice for utilities everywhere.
R.Today,' things are different. Being plentiful and cheap, thorium is the only fuel thatstands a chance of generating electricity as cheaply as burning coal. As such, it is theonly fuel capable of making the world get rid of the biggest single polluter of all.
Because of its huge storage and cheap price, thorium may be the only fuel that canreplace coal to produce electricity at a low cost.