Suzuki spoke the words from his own mouth. It wasn't the ABC speaking! Doh! I didn't see B1 and B2 whispering into his ear either!
"Radiation exposure following the nuclear accident at Fukushima-Daiichi did not cause any immediate health effects. It is unlikely to be able to attribute any health effects in the future among the general public and the vast majority of workers," concluded the 60 th session of the Vienna-based United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR).
•Following a major earthquake, a 15-metre tsunami disabled the power supply and cooling of three Fukushima Daiichi reactors, causing a nuclear accident on 11 March 2011. All three cores largely melted in the first three days. •The accident was rated 7 on the INES scale, due to high radioactive releases over days 4 to 6, eventually a total of some 940 PBq (I-131 eq). •Four reactors are written off – 2719 MWe net. •After two weeks the three reactors (units 1-3) were stable with water addition but no proper heat sink for removal of decay heat from fuel. By July they were being cooled with recycled water from the new treatment plant. Reactor temperatures had fallen to below 80ºC at the end of October, and official 'cold shutdown condition' was announced in mid-December. •Apart from cooling, the basic ongoing task was to prevent release of radioactive materials, particularly in contaminated water leaked from the three units. This task became newsworthy in August 2013. •There have been no deaths or cases of radiation sickness from the nuclear accident, but over 100,000 people had to be evacuated from their homes to ensure this. Government nervousness delays their return
Inside the Fukushima Daiichi reactors: Major fuel melting occurred early on in all three units, though the fuel remains essentially contained except for some volatile fission products vented early on, or released from unit 2 in mid-March, and some soluble ones which were leaking with the water, especially from unit 2, where the containment is evidently breached. Cooling still needs to be provided from external sources, now using treated recycled water, while work continues to establish a stable heat removal path from the actual reactors to external heat sinks. Temperatures at the bottom of the reactor pressure vessels have decreased to well below boiling point and are stable. Access has been gained to all three reactor buildings, but dose rates remain high inside. Nitrogen is being injected into all three containment vessels and pressure vessels. Tepco declared "cold shutdown condition" in mid-December when radioactive releases had reduced to minimal levels.
Fuel ponds: developing problems: The spent fuel storage pools survived the earthquake, tsunami and hydrogen explosions without significant damage to the fuel or significant radiological release, or threat to public safety. The new cooling circuits with external heat exchangers for the four ponds are working well. Temperatures are normal. Analysis of water has confirmed that most fuel rods are intact. Fuel assemblies are now ready to be removed from unit 4 pool.
Radioactive releases to air: Major releases of radionuclides, including long-lived caesium, occurred to air, mainly in mid-March. The population within a 20km radius had been evacuated three days earlier. Considerable work was done to reduce the amount of radioactive debris on site and to stabilise dust. The main source of radioactive releases was the apparent hydrogen explosion in the suppression chamber of unit 2 on 15 March. A cover building for unit 1 reactor has been built and commissioned, a more substantial one for unit 4 is under construction. Radioactive releases in mid-August 2011 had reduced to 5 GBq/hr, and dose rate from these at the plant boundary was 1.7 mSv/yr, less than natural background.
Radiation exposure on the plant site: Six workers received radiation doses apparently over the 250 mSv level set by NISA, but at levels below those which would cause radiation sickness.
Radiation exposure beyond the plant site: There have been no harmful effects from radiation on local people, nor any doses approaching harmful levels. However, some 160,000 people were evacuated from their homes and only in 2012 were allowed limited return.
Return of evacuees: Many evacuated people remain unable to fully return home due to government-mandated restrictions based on conservative radiation exposure criteria. However, over 1000 premature deaths have been caused by maintaining the evacuation beyond a prudent week or so. Decontamination work is proceeding while radiation levels decline naturally. The October 2013 IAEA report makes it clear that many evacuees should be allowed to return home.
Managing contaminated water: A large amount of contaminated water had accumulated on site, but with the commissioning of a new treatment plant in June 2011 this was progressively being treated and recycled for reactor cooling. However, the main plant is not performing as well as expected, and a supplementary plant was installed. In 2013 a further, more sophisticated plant was commissioned. The persistence of tritium limits the potential to release treated water to the sea. Some radioactivity has been released to the sea, but this has mostly been low-level and it has not had any major impact beyond the immediate plant structures. Concentrations outside these structures have been below regulatory levels since April 2011.
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