The effect of chemical speciation on the impact of ¹²⁹I discharges to atmosphere from BNFL Sellafield, Cumbria

¹ Westlakes Research Institute, International Research and Graduate Centre, Westlakes Science & Technology Park, Moor Row, Cumbria CA24 3JY, U.K.
² T.H. Huxley School of Environment, Earth Sciences and Engineering, Imperial College of Science, Technology and Medicine, Silwood Park, Berkshire SL5 7TE, U.K.

Abstract

¹²⁹I is produced through neutron-induced fission of ²³⁵U and neutron capture reactions with the fission products ¹²⁸Te and ¹³⁰Te in the cores of nuclear reactors. This typically constitutes about 1 % of the total fission products, depending on fuel burn-up. Whilst ¹²⁹I is not released in routine discharges from nuclear power plants it is released during reprocessing. The ability to model ¹²⁹I behaviour (important for prospective assessments) has been relatively poor. This is due both to variability in the reported behaviour of iodine, which may be related to abundance and physico-chemical form, and to the relative paucity of data for ¹²⁹I. The primary aims of this study are to measure environmental concentrations of ¹²⁹l around Sellafield; to establish whether the chemical species of iodine in air differs as a function of the source term, and; to determine concomitant values for model parameters defining ¹²⁹I transport through the environment. Some differences in the environmental transport of ¹²⁹I are observed, albeit slight, apparently related to source term. These findings suggest that a source-specific approach may be appropriate. The critical group dose arising from ¹²⁹l is estimated to be about 1.4 µSv a^-1 to adults and 3.2 µSv a^-1 to infants.