Carbon-14 discharges from the nuclear fuel cycle: 2. Local effects

Abstract

Environemtnal 14C levels around various types of nuclear installations within the UK have been monitored during recent years. Enhanced 14C levels have been detected around both the nuclear fuel reprocessing plant as Sellafield and the thermal nuclear power station complex at Hunterston. From these measurements, the radiological impact of the 14C discharges on the local population is assessed. It is conservatively estimated that the 14CO 2 emissions from Sellafield between 1952 and 1985 could have delivered an 8·4 man Sv collective effective dose equivalent commitment to the population living within 40 km of the site. The maximum possible collective dose to the population within 15 km of Hunterston in 1984 was 15 × 10 −3 man Sv. Conservative estimates of maximum annual effective dose equivalents to individuals around Sellafield and Hunterston are 0·2 mSv (in 1982) and 12 μSv (in 1984), respectively. These dose levels do not exceed the limits recommended by ICRP but the former value clearly indicates that, for the larger discharges at least, consideration and optimisation of 14C releases are fully justified. The same 14C measurements are also used to test the validity of two atmospheric dispersion models, the Gaussian plume and the so-called ‘hyperbolic’ models. The former is excellent in predicting downwind 14C levels around Hunterston but is unsatisfactory when applied to Sellafield, whereas the latter proves reliable at both sites. Further investigations suggest that the Gaussian plume model's poor performance at Sellafield can be explained by inaccurate input data.