| TOKYO, March 20, Kyodo Progress to contain the crisis at the Fukushima Daiichi nuclear power plant experienced ups and downs Sunday as operations to cool down the boiling spent fuel pools by throwing water proceeded smoothly, while authorities at one point found the need to tackle the rising pressure in the No. 3 reactor's containment vessel. The process of reducing the pressure by releasing steam from the vessel, a step already taken in the past to deal with the troubles of the No. 3 and other reactors, may mean that radioactive steam could be further released outside. But the plant operator Tokyo Electric Power Co. said later that it would not take the measure for a while because the pressure has stabilized. The imminent task of cooling the overheating spent fuel pools by throwing thousands of tons of water at the No. 3 and No. 4 reactor buildings appear to be continuing relatively smoothly. In the morning, the Ground Self-Defense Force shot water at the No. 4 unit spent fuel pool for the first time, with the amount of water totaling about 80 tons. The mission lasted for nearly one hour, according to the Defense Ministry. The move came after the Tokyo Fire Department shot water into a spent-fuel storage pool at the No. 3 reactor in an overnight operation that lasted more than 13 hours until 3:40 a.m. Cooling the spent fuel tank of the No. 3 reactor building took precedence because smoke was detected from the unit Wednesday, indicating that the pool situated outside the containment vessel may be boiling. A rise in water temperature, usually to 40 C, causes the water level to fall, thus exposing the spent nuclear fuel rods, which could then heat up further, melt and discharge highly radioactive materials in the worst-case scenario, experts say. More than 2,000 tons of water is believed to have been put into the No. 3 reactor pool, exceeding the pool's capacity of 1,400 tons. Fuel rods used at the reactor were plutonium-uranium mixed oxide fuel, known as MOX, said to be harder to control than normal fuel rods made from uranium. On a positive sign, Tokyo Electric said the radiation level about 0.5 kilometer northwest from the No. 2 reactor dropped to 2,579 microsievert per hour as of 11:00 a.m., compared from 3,443 microsievert per hour at 2 p.m. Saturday. But the International Atomic Energy Agency chief Yukiya Amano, who returned to Vienna after a two-day visit to Japan, indicated to reporters on Saturday that it was premature to be optimistic about the future of the troubled plant. ''I hope that safety, stability will be recovered as soon as possible...But I still don't think it is time to say that I think they are going in a good direction or not,'' he said in Vienna. Around noon in Tokyo, the Nuclear and Industry Safety Agency told a press conference that the pressure in the No. 3 reactor's containment vessel is increasing and that it would like to take steps to address the situation ''swiftly.'' But Tokyo Electric said later that it would not immediately take the step to reduce the pressure. While efforts to prevent the situation from further worsening continued, Tokyo Electric is making preparations to bring a stable source of electricity to the No. 1, 2, 5, 6 reactor buildings in the hope of restoring the cooling functions, lost after the magnitude 9.0 quake and the ensuing massive tsunami that hit the plant on March 11. The company said it plans to check the No. 2 reactor's system first as the building housing its containment was not damaged, which means it is hard to cool it down using water from outside. The fuel rods partially melted in the reactor but it is unknown how much water is left in its fuel storage pool. The company has said it will try to restore the systems Sunday to monitor radiation and other data, light the control room and cool down the reactor and the reactor's spent-fuel storage pool. The Fukushima Daiichi Nuclear Power Station is located on the Pacific coast of Fukushima Prefecture about 220 kilometers northeast of Tokyo. The No. 1, No. 2 and No. 3 reactors, which were operating at the time of the quake, automatically halted but lost its key reactor cooling functions because the quake and the tsunami cut off electricity to the plant. Their cores are believed to have partially melted. The No. 5 and 6 units have been relatively less troubled than the other units, but their situation appears to be improving as backup power sources were restored. Tokyo Electric said the temperature of spent-fuel storage pools of the No. 5 and No. 6 units returned to around normal level, to 37.1 C and 41.0 C, respectively, as of 7 a.m. Sunday. ==Kyodo |