Fukushima No. 1 reactor plant is built on the coast of northern Japan partly so it can utilise seawater to keep it cool (see http://en.wikipedia.org/wiki/Nuclear_reactor_coolant ) and partly for safety. Most of the water, with no radioactive increase or contact is circulated and discharged back into sea. Some water however, circulates through to the reactor becoming radioactive.
This water as expanding steam is a major issue. Expanding steam mixed with hydrogen gas (which ignited) apparently blew the top off the containment building.
Another more serious threat is that one or more of the 6 reactor cores (consisting of red hot fissioning fuel rods) at Fukushima 1 will overheat/melt down - which may have occurred in 3 reactors. Larger meltdowns could cause explosions that could project highly radioactive fragments or dust over a wide area - in a disaster equivalent to a dirty bomb http://en.wikipedia.org/wiki/Dirty_bomb . Fortunately "dirty bombs" are non-nuclear (non-fission or non-fusion) explosions. There is no large-scale heat or blast effects but a severe problem is widely spread radioactive material.
The bias of many Australian experts, many of whom act as consultants for the nuclear industry, is obvious. Like many Japanese politicians and power company executives they are presenting a limited and optimistic gloss on an ongoing disaster.
Its even more extreme amongst "experts" and perhaps journalists paid by the British nuclear industry see:
http://www.theregister.co.uk/2011/03/14/fukushiima_analysis/ headed "Fukushima is a triumph for nuke power: Build more reactors now!
Analysis Japan's nuclear powerplants have performed magnificently ..."
It is interesting to look at the results of the Three Mile Island disaster, which appears to be a lesser meltdown event than Fukushima.
Three Mile Island (TMI) had profound effects on the US nuclear industry for decades. See
http://en.wikipedia.org/wiki/Three_Mile_Island_accident#Effect_on_nuclear_power_industry
"The Three Mile Island accident is one of the factors cited for the decline of new reactor construction...51 American nuclear reactors were cancelled from 1980–1984."
The clear and present danger to the Japanese public (some already irradiated) over more than a 30 kilometre radius speaks louder than pro-industry experts.
The Japanese Government will no doubt be organising a multi-year committee of industry experts to talk away responsibility and dumb down public fears. Its notable that many national Japanese politicians, including the PM are often in power for less than 12 months - so they'll be long gone when the committee issues recommendations. As with the Canberra Fire
http://en.wikipedia.org/wiki/2003_Canberra_bushfires#Official_responses committees remove responsibility.
But the inherent danger of building reactors in Japan will not be addressed until a full megadeath reactor meltdown occurs on the scale of radiation from a nuclear explosion.
Map courtesy of ABC News Online, World Nuclear Association and The Federation of Electric Power Companies of Japan. Location of multiple reactor plants damaged by the earthquake and tsunami including the disaster at Fukushima No. 1 plant.
This blog is just doing brief summaries about the rapidly changing Fukushima nuclear disaster - detailed updates round the clock are best read at http://en.wikipedia.org/wiki/Fukushima_I_nuclear_accidents .
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BACKGROUND
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The Australian, March 14, 2011 has produced a
clear explanation about the problems of cooling reactors and cause of physical events if a major meltdown occurred:
"...Nuclear reactors produce heat in two ways: one is simple fission, where atoms are split to produce heat that generates electricity plus the neutrons that keep the nuclear chain reaction going. This process can be shut down in an instant by pushing control rods into the fuel.
However, there are far less controllable processes at work in all reactors.
According to Robin Grimes, director of the Nuclear Energy Centre at Imperial College London, "when you split an atom you get heat and radiation, but you also get two new atoms which then undergo further radioactive decay.
That decay produces about 10 per cent of a reactor's heat output, and there is nothing we can do to stop it. It generates an incredible amount of energy and it takes days to die down."
So, even when a reactor has been technically shut down it is essential that cooling continue. If it does not, the heat will build up and melt the reactor core. At Fukushima that meant engineers had to keep pumping water through the core or face disaster. Initially all appears to have worked as intended. Three of the plant's six reactors were in operation when the quake hit and they automatically shut down. But then their normal cooling system stopped, too.
The plant operators started to remove the heat caused by nuclear decay with emergency diesel generators. But these failed about an hour later, perhaps because of flooding. When the hydrogen-filled steam was vented from the reactor vessel, the hydrogen reacted with oxygen, either in the air or water outside the vessel, and exploded. A similar "hydrogen bubble" concerned officials at the 1979 Three Mile Island nuclear disaster in Pennsylvania until it dissipated.
If the temperature inside the Fukushima reactor vessel continued to rise it could eat through the bottom of the reactor vessel. Next, it would eat through the floor of the already-damaged containment building. At that point, the uranium and dangerous by-products would start escaping into the environment.
At some point in the process, the 15cm stainless steel walls of the reactor vessel would melt into a lava-like pile, slump into any remaining water on the floor, and potentially cause an explosion much bigger than the one caused by the hydrogen. Such an explosion would enhance the spread of radioactive contaminants. If the reactor core became exposed to the external environment, officials would likely begin pouring cement and sand over the entire facility, as was done at the 1986 Chernobyl nuclear accident in the Ukraine, Peter Bradford, a former commissioner of the US Nuclear Regulatory Commission, said in a briefing for reporters.
Ken Bergeron, a physicist and nuclear waste expert, added that as a result of such a meltdown the surrounding land would be off-limits for a considerable period of time, and "a lot of first responders would die".
As the authorities battle to avert a meltdown at the Fukushima plant, it emerged that a senior figure in Japan's nuclear community had resigned in protest from a safety panel saying guidelines to protect atomic power plants from earthquake damage were too lax.
Ishibashi Katsuhiko, a professor at Kobe University, said seismic guidelines brought in to protect Japan's 55 reactors in 2006 were "still seriously flawed".
He pointed out that big quakes had taken place in "close proximity" to three nuclear power plants in Japan from 2005 to 2007. In each case, the ground motion caused by the quake was stronger than that for which the plants had been designed. A tremor at the Kashiwazaki-Kariwa plant, less than 320km across the main island from Fukushima, had experienced a tremor with ground motion of 993 gal (a measure of ground movement), far beyond its design value of 450 gal. "Not only are the new design guidelines defective but the system to enforce them is in a shambles," wrote Katsuhiko after his resignation. He said it was just a matter of luck that the epicentre of each earthquake had not been nearer.
...In Australia. the federal government and the opposition have both refused to buy into a debate on nuclear energy following Fukushima.
However, ALP president and
Queensland premier Anna Bligh, who called for a debate on domestic nuclear power in December said the explosion was "cause for some pause and consideration before we see anybody jumping to invest in that sort of energy, particularly here in Australia".
The Australian Greens say Fukushima is another pointed reminder for Australia not to go down the nuclear route.
Greens leader Bob Brown used the incident as an argument against nuclear, which he labelled a delicate and unsafe technology.
"It's the potential for terrorism, you can't have it in flight paths, it needs to be built next to big areas of population . . . it takes up a lot of water, it's enormously expensive," he told Sky News.
"We have much better alternatives, thank God.
WHOLE ARTICLE"
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COMMENT
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Building reactors in a highly active seismic/earthquake areas like Japan is intrinsically dangerous, hence longterm plans to build reactors in Indonesia in an equally active zone are dangerous. Very low earthquake areas like Australia are much safer places to build reactors, oil refineries or any other types of large factories.
Japan's heritage of nuclear bombing both of Hiroshima and Nagasaki make Japanese people highly sensitive to nuclear safety - yet Japanese companies have built more than 50 reactors in their earthquake prone country
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Pete
Russian R-36 Missile (at right) used to boost the Fractional Orbital Bombardment System (FOBS)
into Space 
