The operator of the crippled Fukushima Daiichi nuclear power plant said that high densities of hydrogen have built up in pipes connected to the No. 1 reactor. Tokyo Electric Power Company said that an explosion is unlikely as there is no oxygen in the pipes, but that it will begin work to drain the gas starting on Thursday. TEPCO began measuring the density of the gas on Wednesday after finding it accumulating in pipes connected to the reactor\'\'s containment vessel late last week, Japan\'\'s NHK World website reported. It found that the density of hydrogen was high, at between 61 to 63 percent. TEPCO said the hydrogen is likely the remains of gas that caused explosions at the plant in March, following the quake and tsunami disaster. The utility has also promised to check the density of hydrogen in pipes in the No. 2 and No. 3 reactors, in line with instructions from Japan\'\'s nuclear safety agency.