What is going on at Fukushima?

On 26 April 1986 a reactor at the nuclear power station at Chernobyl in the Ukraine exploded. The Chernobyl reactor had a graphite core, a design not followed in the West although the first reactor built at the University of Chicago had a graphite core. The disaster at Chernobyl was the fire from burning graphite that lifted radioactive dust particles into the atmosphere. About 200 plant workers and firemen got radiation doses that could lead to Acute Radiation Illness and 31 died almost immediately with the delayed deaths of a further 21. But no one in the general public got acute radiation sickness. 650,000 “liquidators” who cleaned up Chernobyl and surroundings were certainly exposed to some radiation. Interestingly, a report by WHO in 2006 on Health Effects of the Chernobyl Accident states that of a group of 61,000 liquidators, 4,995 deaths were recorded between 1991 and 1998 and this death rate was lower but not significantly different from that of the whole Russian population. Of these deaths, 216 were estimated as attributable to radiation. However there were some 2000 reported thyroid cancers with 20 deaths. The tragedy of this was that it was avoidable. However the Soviet authorities did not advise families not to drink local milk for a month and a number of antidotes to iodine were available. For cesium, there is an estimate of 4000 cancer deaths over the next 50 years in the former Soviet bloc. That is 80 a year compared to 6,000 deaths from cancer each year in the United States.

State of the Fukushima Plant

It is clear that at the start of the earthquake, all the operating reactors were rapidly shut down. Power would have fallen from full to about 8% almost immediately and within 10 hours it would have been 1% of full power. Full power in each reactor was of the order of 3000 MW so within ten hours it was 30 MW. Unit 4 does not appear to have been operating as its fuel had been withdrawn some 3 months before the earthquake. Explosions were reported from unit 3 that may have been the venting of hydrogen from the pressure vessel with an explosion following. Smoke was reported from unit 4 but the source is not clear. The loss of back up pumps for cooling water and the delay in pumping sea water into the reactors and cooling pools no doubt exacerbated the situation. A possible explanation for the delay was the time necessary to diagnose the problems and a reluctance to use seawater that would lead to a write off of the plant.

There is so little coherence in reports that it is not clear if any pressure vessels have fractured although it does appear that the outer concrete structures of some units may have cracked.

The safety of the operators appears to be in hand and following radiation procedure limits. It is not clear that the sea water used for cooling is being treated for removal of radioactive products but the reports are not encouraging.

It is too early to make any informed judgement except to think that this remarkable incident, given the magnitude of the earthquake and tsunami, is nearer in consequences to Three Mile Island than to Chernobyl.