Theoretical and practical aspects of a free-atmosphere tritium exposure system

Autor: W.J.G. Workman, P.A. Davis, F.L Johnston, B.D. Amiro
Rok vydání: 1997
Předmět:
Zdroj: Journal of Environmental Radioactivity. 36:141-156
ISSN: 0265-931X
DOI: 10.1016/s0265-931x(96)00085-9
Popis: A free-atmosphere release system was designed to expose an experimental area continuously to tritiated hydrogen (HT) over periods of days to weeks. The system was constructed of four 19-m-long line sources arranged in a square to fumigate the central area containing plants and soil, irrespective of wind direction. The line sources were operated in the upwind direction only to conserve HT, and the release rate was adjusted in proportion to the wind speed. Both the wind-direction and wind-speed adjustments were controlled by a datalogger in the field and were updated every 5 min. Sulphur hexafluoride (SF 6 ) was also released as a tracer to measure spatial and temporal variability. The system operated satisfactorily over a 12-day experimental period and achieved a relatively uniform concentration of HT across the experimental plot. The temporal variability was about 25% based on daily averages, but 4-h averages varied more. Mean horizontal spatial variability was about 20% across the plot, and there was little vertical variability at lower heights where soil and vegetation were exposed. Measured ratios of HT to SF 6 did not vary much over time, but were about 20% less than calculated from the source term. The experimental data were used to study the oxidation of HT to tritiated water vapour (HTO) by micro-organisms in the soil and the subsequent environmental transfer of the HTO.
Databáze: OpenAIRE