Without external electricity, it has been impossible to operate the cooling pumps and circulate water to keep spent fuel rods cold
The central problem behind almost every hurdle faced by the workers at the Fukushima nuclear power plant has been ? and remains ? a lack of power supply. Since electricity was knocked out by the tsunami it has been impossible to run the pumps that cool the reactor cores and circulate water around storage pools used to keep spent fuel rods cold.
Last week engineers succeeded in connecting power to some of the reactors, but three remain in a dangerous and precarious state. The fuel rods inside reactors one, two and three are at least partially exposed but should be covered by water at all times to prevent a meltdown. The fuel in all three reactors is believed to have melted to some degree.
This week engineers began pumping fresh water into the reactors amid fears that the previous tactic ? to flood them with seawater and vent off steam ? was leading to a build-up of salt deposits that could block the coolant pipes.
Spent fuel rods in the storage pools are another serious concern. The Japanese authorities do not know the condition of 2,724 waste fuel rods kept in ponds in the top levels of reactor buildings one to four and there are concerns that the pool at building four boiled dry. The rods pose a potentially greater threat than the overheating reactors, because they could catch fire and release radiation directly into the air.
The pool at reactor four has been stacked beyond its original design capacity and there is a slim chance that damage to the rods could restart nuclear reactions, producing enormous amounts of radiation.
The Japanese authorities have gathered all the water-pumping equipment they can muster, from military trucks to fire engines and concrete pumping apparatus, to keep the storage pools filled with water, but without external power there can be no let-up in dousing the rods.
"If you take a fuel rod bundle out of a reactor and put it in a pool, you have to leave it for five years before you can take it out. They don't produce a lot of heat, but it is unrelenting," said Richard Lahey, who was General Electric's head of safety research for boiling water reactors when the company installed them at Fukushima.
The latest setback engineers face is the discovery of highly radioactive water in and around the turbine building at reactor two. Radiation detectors measured the level at 1,000 millisieverts per hour and as workers are allowed an exposure of 250 millisieverts a year, raised from 100 millisieverts before the crisis, they could only be in the contaminated area for 15 minutes before reaching the maximum dose.
Engineers cannot resume work on connecting the power to reactor two until they have drained the water pools and scrubbed the area clean, an effort now underway.
Officials at Tepco, who run the plant, say it is not clear where the radioactive water came from, but it escaped from the reactor core, either directly through a breach in the containment vessel or through a crack or hole in pipework.
Lahey believes that molten fuel inside reactor two has begun to leak out of its containment vessel, meaning it may be too late to save that reactor.
The troubles on site are compounded by fears that radioactive material, including plutonium, is leaching into the soil and has washed into the sea. So far, these problems are localised: most radioactive material leaked onto land will bind to soil and stay there, while radioactive material in the sea will be diluted and disperse. "They are doing all the right things now, but this is a tight horse race," Lahey said.
Source: http://www.guardian.co.uk/world/2011/mar/28/japan-fukushima-nuclear-reactors-electricity
Comedy Economic growth (GDP) US foreign policy Television industry Economic policy Mark Bright
No comments:
Post a Comment