<P> Recent concerns have been expressed about safety issues affecting a large part of the nuclear fleet of reactors . In 2012, the Union of Concerned Scientists, which tracks ongoing safety issues at operating nuclear plants, found that "leakage of radioactive materials is a pervasive problem at almost 90 percent of all reactors, as are issues that pose a risk of nuclear accidents". The U.S. Nuclear Regulatory Commission reports that radioactive tritium has leaked from 48 of the 65 nuclear sites in the United States . </P> <P> Following the Japanese Fukushima Daiichi nuclear disaster, according to Black & Veatch's annual utility survey that took place after the disaster, of the 700 executives from the US electric utility industry that were surveyed, nuclear safety was the top concern . There are likely to be increased requirements for on - site spent fuel management and elevated design basis threats at nuclear power plants . License extensions for existing reactors will face additional scrutiny, with outcomes depending on the degree to which plants can meet new requirements, and some extensions already granted for more than 60 of the 104 operating U.S. reactors could be revisited . On - site storage, consolidated long - term storage, and geological disposal of spent fuel is "likely to be reevaluated in a new light because of the Fukushima storage pool experience". In March 2011, nuclear experts told Congress that spent - fuel pools at US nuclear power plants are too full . They say the entire US spent - fuel policy should be overhauled in light of the Fukushima I nuclear accidents . </P> <P> David Lochbaum, chief nuclear safety officer with the Union of Concerned Scientists, has repeatedly questioned the safety of the Fukushima I Plant's General Electric Mark 1 reactor design, which is used in almost a quarter of the United States' nuclear fleet . </P> <P> About one third of reactors in the US are boiling water reactors, the same technology which was involved in the Fukushima Daiichi nuclear disaster in Japan . There are also eight nuclear power plants located along the seismically active West coast . Twelve of the American reactors that are of the same vintage as the Fukushima Daiichi plant are in seismically active areas . Earthquake risk is often measured by "Peak Ground Acceleration", or PGA, and the following nuclear power plants have a two percent or greater chance of having PGA over 0.15 g in the next 50 years: Diablo Canyon, Calif.; San Onofre, Calif.; Sequoyah, Tenn.; H.B. Robinson, SC.; Watts Bar, Tenn.; Virgil C. Summer, SC.; Vogtle, GA.; Indian Point, NY.; Oconee, SC.; and Seabrook, NH . </P>

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