Most of the fuel rods that melted in the pressure vessel of the No. 1 reactor of the stricken Fukushima nuclear power plant dripped into the containment vessel and ate into it, according to Tokyo Electric Power Co.
Most of the fuel rods that melted in the pressure vessel of the No. 1 reactor of the stricken Fukushima nuclear power plant dripped into the containment vessel and ate into it, according to Tokyo Electric Power Co.It said on Nov. 30 the melted fuel did not breach the containment vessel but partially eroded its concrete floor.As for the No. 2 and No. 3 reactors, most of the melted fuel stayed within the pressure vessel, TEPCO added.Water levels have submerged the fuel rods at all three reactors, which is helping to cool them, the plant operator said.TEPCO said its latest findings were based on water levels in the containment vessels, temperature readings and other data.It admitted earlier that melted fuel partially breached the reactors, a potentially catastrophic development.During the 1979 accident at the Three Mile Island nuclear power plant in the U.S. state of Pennsylvania, a core meltdown occurred but the pressure vessel was not breached.TEPCO now faces the challenge of developing new technologies to recover the melted fuel for when eventual decommissioning of the reactors gets under way. According to TEPCO's analysis, the cooling equipment in the No. 1 reactor halted immediately after the Great East Japan Earthquake struck March 11. The fuel rods became exposed three hours after the cooling equipment stopped.It took days before water could be pumped in from the outside. The damage to the pressure vessel was more severe there than at the No. 2 and No. 3 reactors, where it took two to three days before the fuel rods became exposed.According to the latest analysis of the No. 1 reactor, all the fuel rods melted and ate through the pressure vessel to the containment vessel. The melted fuel filled pits on the concrete floor of the containment vessel, eroding it to a depth of about 65 centimeters.It would still have to eat through 37 cm of concrete to reach the steel casing of the containment vessel. Thus, a catastrophic meltdown on the scale of a theoretical "China syndrome" did not take place, TEPCO said.The coolant water in the containment vessel is only about 30 cm deep, but that is sufficient to submerge and cool the melted fuel and is preventing further erosion, TEPCO officials added.TEPCO said few of the melted fuel rods in the No. 2 and No. 3 reactors leaked into the containment vessel. However, an expert commissioned by the Japan Nuclear Energy Safety Organization to analyze what happened said that the situation could be much worse."About 70 percent of the melted fuel could have leaked to the containment vessel, although there is room for uncertainties," the expert said.TEPCO's latest findings were aimed at preparing for the eventual decommissioning of the reactors. It also wanted to verify whether it could declare, by the end of the year, that a state of cold shutdown has been achieved. But the accuracy of the findings is difficult to determine, given the difficulty of obtaining data.TEPCO is considering the use of a special camera, resembling an endoscope, to monitor the interior of the reactors in the future.