The Fukushima Daiichi nuclear accident.

Abstract

1. Introduction I remember vividly the event in 1986 when the Unit 4 reactor at (1) exploded, since I was working in Russia during the weeks following it. Largely, this was a preventable occurrence, and was caused by a combination of circumstances, but principally through an unscheduled and ill-conceived experiment involving the full withdrawal of the majority of the control rods from the reactor, actually in defiance of standing rules and after deliberately disabling safety systems. In part, the reason for the withdrawal of so many of the control rods was an attempt to compensate for the loss of power caused by a build-up of xenon, which acts as a neutron absorber. Various factors contributed to a loss of cooling water which heightened the already unstable condition of the reactor, due to an increase in the production of steam in the cooling channels (positive void coefficient). By this stage, there was nothing that could be done to avert a calamity, since inherent positive feedback effects rendered the initial rise in power unstoppable, leading to an overwhelming power surge, estimated to be 100 times the nominal power output of the reactor. There is much speculation as to how many deaths might eventually cause, but the initial recorded number was 562 (including 47 liquidators and nine children who died of thyroid cancer). Estimates of the ultimate number range from 4,0002 up to nearly one million (3) fatalities from radiation-induced cancers. is the third really serious nuclear accident to occur in the civilian nuclear industry. There was very little information made available within the USSR, and my Russian colleagues learned most about what had happened from their counterparts in the West. I have mentioned Chernobyl to various of my friends and acquaintances recently, and from this small survey it seems that no-one under the age of about 50 is aware of even the name of the place, let alone what happened there. Apparently, a worker at a Swedish nuclear power plant (NPP) set the alarms off when he went into work on a Monday morning, having been hiking over the weekend. Naturally, this was a surprise since someone working at an NPP might be expected to be contaminated by exposure inside the installation, but in this case, the radioactive plume had contaminated Sweden (and the NPP worker) along with much of Western Europe, which alerted that the event had taken place. Along with Chernobyl, there have been major accidents at Three Mile Island and Windscale (subsequently renamed Sellafield). That said, the nuclear industry has a fairly impeccable safety record, albeit that the long-term storage of its waste remains an unresolved dilemma. To the above list of three, which occurred some decades ago, can now be appended the Fukushima Daiichi nuclear accident (4). In the latter instance, the tsunami following the Tohoku earthquake on 11 March 2011 resulted in failures of equipment and a loss-of-coolant event, with nuclear meltdowns (overheating and damage to the reactor core, with melting of fuel rod components and the potential for escape of radionuclides), and the egress of radioactive isotopes, commencing on 12 March 2011. Fukushima and are the only NPP accidents to measure Level 7 on the International Nuclear Event Scale (5) (described below), and it is estimated that the Fukushima accident has released (6) 10-30% of the amount of radiation resulting from that at Chernobyl, although the emissions continue, and it is not clear how and when they may be stemmed entirely. The Fukushima NPP (7) had six separate boiling water reactors which were made by General Electric (GE) and maintained by the Tokyo Electric Power Company (TEPCO). Reactor 4 had been de-fuelled when the incident took place, and reactors 5 and 6 were in cold shutdown with the intention of a planned maintenance effort. When the earthquake hit, reactors 1-3 were automatically shut down by the insertion of control rods, i. …