The dilemma facing engineers at the plant is this: keeping the reactors cool has required pumping in vast amounts of water, much of which turns to steam, which has to be vented--a process nicknamed"feed and bleed "But the radiation released in e steam and in water that leaks out has made it increasingly difficult to work on storing regular cooling systems. United States government engineers sent to help with the crisis in Japan warned that the troubled nuclear plant there is facing a wide array of fresh threats that could persist indefinitely, and that in some cases are expected to increase as a result of the very measures being taken to keep the plant stabl On April 12, Japan raised its assessment of the accident at the crippled Fukushima Daiichi nuclear power plant from 5 to 7, the worst rating on an international scale putting the disaster on par with the 1986 Chernobyl explosion, in an acknowledgement that the human and environmental consequences of the nuclear crisis could be dire and long-lasting. While the amount of radioactive materials released so far from Fukushima Daiichi so far has equaled about 10 percent of that released at Chernoby, officials said that the radiation release from Fukushima could in time, surpass levels seen in 1986 Here is the status of the six reactors at the Fukushima Daiichi plant as of April12 Reactor No. 1: An explosion on March 12 ripped the top off of the reactor building after a presumed partial meltdown in the reactor core produced hydrogen gas that Powerwas re-established for the control room lighting, an important first step oQ e/ was vented as part of the struggle to cool the reactor. The primary containment ves is said to be intact. Radioactive isotopes have been found in its seawater discha toward turning on the cooling system, but the reactor's temperature has shown a worrisome increase On March 27, cesium was found in the water in the turbine building attached to the reactor. On April 6, engineers prepared to inject nitrogen into the containment vessel to reduce the chance of a hydrogen explosion. Reactor No 2: On March 14, the pumps sending seawater into the reactor to coolit failed temporarily, leading to a partial meltdown. On March 15, an explosion breached the containment vessel and the torus, an enclosed pool of water surrounding the reactor into which steam is released The damage meant that radioactive steam was escaping. A high-voltage cable was extended to its pumps on March 20, but was not powerful enough to restore operation. Radioactive isotopes have been found in its seawater discharge. On March 26, a worker measurin radiation in puddles outside the reactor finds levels too high for his instrument to gauge. The highly radioactive water was found to be pouring from a crackin a pit a cement. On April 6, the Nuclear Regulatory Commission said that some ofthe Gh near the reactor The leak was plugged on April 5 using sodium silicate, which acts as reactor core had probably leaked from its steel pressure vessel into the bottom of the containment structure, implying that the damage was even worse than previouslyThe dilemma facing engineers at the plant is this: keeping the reactors cool has required pumping in vast amounts of water, much of which turns to steam, which has to be vented -- a process nicknamed "feed and bleed." But the radiation released in the steam and in water that leaks out has made it increasingly difficult to work on restoring regular cooling systems. United States government engineers sent to help with the crisis in Japan warned that the troubled nuclear plant there is facing a wide array of fresh threats that could persist indefinitely, and that in some cases are expected to increase as a result of the very measures being taken to keep the plant stable. On April 12, Japan raised its assessment of the accident at the crippled Fukushima Daiichi nuclear power plant from 5 to 7, the worst rating on an international scale, putting the disaster on par with the 1986 Chernobyl explosion, in an acknowledgement that the human and environmental consequences of the nuclear crisis could be dire and long-lasting. While the amount of radioactive materials released so far from Fukushima Daiichi so far has equaled about 10 percent of that released at Chernoby, officials said that the radiation release from Fukushima could, in time, surpass levels seen in 1986. Here is the status of the six reactors at the Fukushima Daiichi plant as of April 12: Reactor No. 1: An explosion on March 12 ripped the top off of the reactor building after a presumed partial meltdown in the reactor core produced hydrogen gas that was vented as part of the struggle to cool the reactor. The primary containment vessel is said to be intact. Radioactive isotopes have been found in its seawater discharge. Power was re-established for the control room lighting, an important first step toward turning on the cooling system, but the reactor's temperature has shown a worrisome increase. On March 27, cesium was found in the water in the turbine building attached to the reactor. On April 6, engineers prepared to inject nitrogen into the containment vessel to reduce the chance of a hydrogen explosion. Reactor No. 2: On March 14, the pumps sending seawater into the reactor to cool it failed temporarily, leading to a partial meltdown. On March 15, an explosion breached the containment vessel and the torus, an enclosed pool of water surrounding the reactor into which steam is released. The damage meant that radioactive steam was escaping. A high-voltage cable was extended to its pumps on March 20, but was not powerful enough to restore operation. Radioactive isotopes have been found in its seawater discharge. On March 26, a worker measuring radiation in puddles outside the reactor finds levels too high for his instrument to gauge. The highly radioactive water was found to be pouring from a crack in a pit near the reactor. The leak was plugged on April 5 using sodium silicate, which acts as a cement. On April 6, the Nuclear Regulatory Commission said that some of the reactor core had probably leaked from its steel pressure vessel into the bottom of the containment structure, implying that the damage was even worse than previously thought