Windscale , accident

Clarke, R. H. 1974. An analysis of the Windscale accident using the WERRIE code. American Nuclear Science Engineering, 1, 73-74. 

Table 2.3 shows the estimated releases of 90Sr, 131I, 137Cs and 144Ce in the Nevada tests, the thermonuclear tests (H tests), the 1957 Windscale accident, the 1957 accident at a separation plant in the Urals... 

In Fig. 2.5 the fallout of the 137Cs in the pre-1957 oxide particles, is compared with the fallout in the Windscale accident of October 1957. 

Table 2.4. Activities relative to 137Cs after Windscale accident... 

On 29 September 1957, eleven days before the Windscale accident, there was a chemical explosion in a Soviet plant treating active wastes, situated in the Urals. No mention of the accident was made in Soviet media at the time, but an exiled scientist, Z. A. Medvedev collected information and published it in the west (Medvedev, 1976, 1979). A further study, using Medvedev s data and oblique references to the effects of the disaster in Soviet ecological literature, was made by scientists at Oak Ridge (Trabalka et al., 1980). After the elapse of 32 a,... 

In the UK, rainfall of 10-20 mm on 2-4 May gave heavy fallout in the coastal region of Cumbria and Galloway (Clark Smith, 1988). By a coincidence, there was particularly heavy deposition in the hills 20 km SSE of Sellafield, which were also in the path of the emission of October 1957. In this area, there was about 12 kBq m-2 of 137Cs from the Windscale accident (Fig. 2.5), 6 kBq m-2 from distant bomb tests, 1955-65, and 20 kBq m-2 from Chernobyl. Clark Smith estimated the total fallout of 137Cs over the UK at 300 TBq. This compares with about 10 TBq from the Windscale accident and 1000 TBq from weapons tests. 

Table 2.10 shows a comparison of the fallout at Seascale, Cumbria, from the Windscale accident and the fallout in the Munich area from Chernobyl, together with estimates of the effective dose equivalent received by people in those areas at the relevant time (Crick Linsley, 1982,1983 Doerfel Piesch, 1987). The doses at Seascale are extrapolated to 50 a from the accident to allow for long-term contributions, mainly from 137Cs. The doses at Munich are for the first year only, and should be increased by about 50% to give the life-time dose (Clarke, 1987). 

Crabtree, J. (1959) The travel and diffusion of the radioactive material emitted during the Windscale accident. Quarterly Journal Royal Meteorological Society, 85, 362-70. 

Crooks, R.N., Glover, K.M., Haynes, J. W., Osmond, R.G. Rogers, F.J.G. (1959) Alpha activity on air filter samples collected after the Windscale accident. AERE Report R-2952. HMSO, London. 

Crouch, E.A.C. Swainbank, I.G. (1958) Radiochemical and physical examination of debris from the Windscale accident. AERE Report C/R 2589. Harwell, Oxon. 

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). 

Seascale, Cumbria and Leeds after the Windscale accident (Booker, 1958 Burch, 1959) and near Seascale and Harwell after Chernobyl (Fulker, 1987 Cambray et al., 1987). The values are lower than the theoretical curve, especially those derived from the Chernobyl fallout, which mostly occurred in heavy rain. As another example, in the Karlsruhe district of Germany, the fallout of 131I in the first few days of May 1986 was 10 kBq m-2. The peak activity in the milk of cows feeding outdoors was 47 Bq l-1 (Doerfel Piesch, 1987), giving a normalised Ci max) of only 5 x 10-3 m21-1. 

Fig. 3.6. Normalised concentration of 131I in milk after fallout. A, theoretical (Burton et al., 1966) B,C, Seascale and Leeds milk after Windscale accident D,E, Seascale and Berkshire milk after Chernobyl accident.

Fig. 3.7. 131I in thyroids of Leeds residents after Windscale accident (O), and in London residents after Chernobyl accident (A). Points at day zero are calculated from dosage in air. 

If vg is taken as 3 mm s-1, then a dosage of 1 Bqs m-3 of 131I in air gives 3 x 10-3 Bq m-2 fallout. The ratio of thyroid doses from milk compared with inhalation are then as shown in Table 3.9. The calculated ratio of 20 for adults compares with an increase of about 10 in the thyroid activity of Leeds residents attributed to consumption of milk in the days after the passage of the plume of activity from the Windscale accident (Fig. 3.7). The transfer factor fallout/milk in the Leeds area was lower than that assumed in the calculations leading to Table 3.8... 

In Cumbria, after the Windscale accident, a ban on the sale of local milk was made effective within 3 d. If vg for1311 in the area of maximum fallout downwind of Windscale was 3 mm s-1, then the measured deposition of 1 x 106 Bq m-2 corresponds to an air dosage of 3 x 10s Bqs m-3. From Table 3.7, this would give a theoretical thyroid dose to a child of 40 mSv which corresponds to the lower end of the range given in the first row of Table 3.10. If there had been no ban, and if the transfer from fallout to milk had followed the theoretical curve A in Fig. 3.6, then from Table 3.8 a child drinking 0.92 1 of milk per day would have received a thyroid dose of 1.4 Sv. 

Knapp also sought to deduce the maximum concentration C/(max) of 131I in milk resulting from the fallout, using records of tests in the 1960s where gamma dose and C/ were both measured, Garner s (1960) data on transfer from cattle feed to milk, and Booker s (1958) measurements after the Windscale accident. 

Table 3.11.1311 in milk from weapons tests and Windscale accident... 

Knapp s calculations showed the possibility of a public health hazard from the Nevada tests, which, in retrospect, would have justified a ban on the sale of local milk, similar to that applied in Cumbria after the Windscale accident. The calculations were criticised as speculative. However, a further comparison can be made of the consequences of the Harry test and the Windscale accident. St George is 200 km from the Nevada Test Site. Leeds is 150 km from Windscale. In Table 3.11, the calculated Cj(max) levels at Leeds (Burch, 1959) are compared with the respective emissions of 131I. 

The Harry test released about 140 times as much 131I as the Windscale accident, and Knapp s calculated Cj(max) at St George is 50-100 times greater than the measured Cj(max) at Leeds. Burch estimated that the dose to the thyroid of a four-year-old Leeds boy, drinking 0.71 per day of local milk was about 0.8 rad. An infant consuming a similar amount of milk would receive a higher dose because of its smaller thyroid mass. Thus Knapp s estimate of thyroid dose at St George is not unreasonable. 

Dunster, H.J., Howells, H. Templeton, W.L. (1958) District surveys following the Windscale accident of October 1957. Proceedings Second International Conference on Peaceful Uses of Atomic Energy, vol. 18, pp. 296-308. Geneva United Nations. 

Many lessons were learnt during the period 1955-1965 by analysis of dispersion and fallout from bomb tests and also from the Windscale accident, but some of these had been forgotten by 1986 when the Chernobyl accident happened, so no apology is made for describing some work which is now 30 years old. 

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. 

This, the Windscale accident, was for many years the most serious reactor accident it had more radiological consequences than the Three Mile Island accident of 1979. Clearly the accident had the salutary effect of making designers and operators safety conscious in the UK. 

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