On 11th March 2011, a very large earthquake and one of the worst ever recorded tsunamis caused enormous devastation and loss of life in north-eastern Japan. Eleven reactors at four nuclear power stations in the region shut down safely when struck by the earthquake but the tsunami level that then occurred was far in excess of the design-base events. At the Fukushima Daiichi nuclear power station, the emergency diesel power generators were inundated. The consequent loss of power caused inadequate cooling of reactor fuel in the reactor cores and cooling ponds. This, in turn, caused damage to the fuel and release of fission products. Hydrogen, generated by chemical reaction of the fuel cladding with coolant water, caused explosions which damaged the reactor buildings.

In a presentation to the Nuclear Engineering Panel of the Sydney Branch at Chatswood on 25 May 2011, Tony Irwin (Chairman of the Panel) reviewed the features of the boiling water reactors (BWRs) involved in the incident, explained the sequence of events and showed the roadmap for restoration. Don Higson (Secretary of the Panel) then discussed the radiological and human aspects including radiation levels and discharges, doses received, evacuation decisions, risk implications and comparisons with the Chernobyl reactor accident.

Four reactors at Fukushima, all approaching 40 years old, have been severely damaged and will be written off – like many other industrial installations in that part of Japan. The loss of power generation and the trauma of the nuclear emergency have been devastating for Japan.

However, the announcement on 12 April of an increase of the Fukushima event from 5 to 7 on the International Nuclear Event Scale has given the impression that it is as bad as the Chernobyl accident, which is misleading because:

• There have actually been no deaths caused by radiation exposure at Fukushima, whereas there have been around 50 at Chernobyl.
• Although some workers at Fukushima have received significant doses and two have received radiation burns, none has incurred a dose anywhere near high enough to cause acute radiation sickness. At Chernobyl, 134 workers were hospitalised with radiation sickness and 28 of them died.
• The reactor containments appear to have been at least partially effective at Fukushima. Releases of radioactivity outside the site boundary have reached levels at which emergency measures had to be implemented but were much less than at Chernobyl (less than 10% of the Chernobyl releases of iodine-131 and caesium-137).
• Members of the general public have not been harmed by radiation at Fukushima, although inadequate understanding of radiation has caused extreme and unnecessary anxiety.
• Even if evacuation had not occurred (except perhaps from the first 2km outside the site boundary), it is unlikely that there would have been any physically discernible public health effects from radiation

The PowerPoint Presentations are available on the EA website:
.    The Radiological Impact of the Japanese Nuclear Emergency by Dr Don Higson
.    Japan's Nuclear Emergency by Dr Tony Irwin

Dr Don Higson
Secretary
Nuclear Engineering Panel - Engineers Australia sydney Division