Windscale activity released

The release of 131I and other fission products in reactor accidents has been considered in the previous chapter. In the Windscale accident, the temperature in the fire zone reached an estimated 1300°C and 8 tonne of uranium metal melted. Over 25% of the 1311 in the melted fuel escaped to atmosphere. In the Chernobyl accident, the fuel was U02, the temperature exceeded 2000°C, and about 25% of the total reactor inventory of 131I was released to atmosphere, as vapour or particulate aerosol. In the Three Mile Island accident, 131I remained almost completely in the reactor coolant. The activities of 131I released in reactor accidents, including that at Chernobyl, have totalled much less than the activities released from weapons tests (Table 2.3). 

The release of xenon and krypton isotopes at the time of the Windscale accident was not directly measured, but because 4 days intervened between shutdown of the reactor and commencement of the graphite fire during low power running and because most xenon and krypton isotopes have a short radioactive half-life, this component of the activity released would have been small. It is notable that although a search was made for plutonium contamination of the environment after the release, none in fact was found. 

Overall, however, the release of refractory fission products from Windscale was less than the release of volatile elements by two or three orders of magnitude, relative to the inventories in the reactor fuel (Table 2.4). Alpha activity on the stack filters and environmental filters was mainly 210Po, derived from the bismuth irradiated in the isotope channels (Crouch Swainbank, 1958 Crooks et al., 1959). The 210Po/137Cs ratio on the environmental filters was about 0.2, with no significant change with distance, suggesting that both activities were carried on the same fume particles. 

The estimates of release of fission products from Windscale, which are inevitably subject to error, are not essential to the assessment of the radiological effects, which are based on local measurements of activity in milk and other foodstuffs, and in the thyroids of members of the public. 

The fire in the air-cooled graphite-moderated uranium-metal-fueled reactor at Windscale in 1957 led to the release of what was estimated as 20,000 Ci of iodine-131 and much smaller quantities of some other fission products from the top of the 400-ft-high stack. The quantities of activity in the release were estimated by Stewart, Chamberlain, Dunster, and others at the time (J). This estimate was amplified later by Beattie from miscellaneous sources (4). Table I shows the activities of the released isotopes from Beattie s report (4). 

Activities of the Isotopes Released from the Windscale Reactor Accident, 1957... 

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