Report Says a Shortage of Nuclear Fuel Looms WASHINGTON - Most nuclear reactors in the United States rely on a type of lithium that is produced only by China and Russia, and the supply may be drying up, according to a study to be released on Wednesday. The Government Accountability Office said the looming shortage of a material critical to the operation of 65 out of 100 American nuclear reactors "places their ability to continue to provide electricity at some risk," a conclusion echoed by outside experts. The problem reflects the withering away of the American industrial infrastructure of all things nuclear, and the nation's dependence on distant places for "energy-critical materials," including "rare earth" materials used in high-efficiency motors, and other materials used in solar cells. Producing these generally involves environmentally damaging processes, one reason that production has moved abroad. The material in potentially short supply is specifically lithium-7, which is what is left over when it is separated from another form, lithium-6, which can be used to make tritium, the hydrogen in the hydrogen bomb. The two forms, called isotopes, are chemically identical, although lithium-7 has one additional neutron. The equipment needed to separate lithium-6 from lithium-7 is mostly a cold war leftover. The United States shut down almost all of its machinery in 1963, when it had a huge surplus, now mostly consumed. It has not had to make much tritium in the last few years because its nuclear weapons inventory is shrinking. China and Russia apparently still have their equipment in place, but because it is related to their weapons program, outsiders do not know how much capacity they might have. At the same time, Chinese domestic demand for lithium-7 is likely to increase soon because they are working on a new type of nuclear reactor that uses vastly larger quantities of the material, according to independent experts. Per Peterson, the chairman of the nuclear engineering department at the University of California, Berkeley, said it would be "pragmatic" for the United States to re-establish the ability to separate lithium-6 from lithium-7 - although the G.A.O. report said it would take five years and $10 million to $12 million. Dr. Peterson said the American utilities could protect themselves by soliciting bids from companies that could do the work in this country, and signing purchase agreements. So far, though, according to the G.A.O., no government entity has taken the lead to assure a supply, and the utilities, having seen no problem so far, do not appear concerned. The reactor industry could also find a substitute material, although Keith P. Fruzzetti, a reactor chemistry expert at the Electric Power Research Institute, a nonprofit utility consortium, said that a change like that "typically takes many years to accomplish." The type of nuclear reactor that uses lithium-7 heats water under high pressure to keep it from boiling and then transfers the heat through heat exchangers that are prone to corrosion. The reactors use lithium to counteract another chemical they add to the water that makes it corrosive, boric acid. The boric acid is needed to sop up excess neutrons, the subatomic particles that are released when uranium is split, and which sustain the chain reaction. The report also cited the recent failure of the federal government to foresee the shortage of another isotope, a type of helium that the Department of Homeland Security wanted to use in detectors looking for smuggled bomb materials. The G.A.O. report was requested by Representative Dan Maffei of New York, who is the ranking Democratic member of the House Science Committee's subcommittee on oversight. A staff member said that because of the government shutdown, Mr. Maffei's office would have no comment. The G.A.O., which produced the report before the shutdown began, is also mostly closed.