Mapping of the distribution of 137Cs in Irish Sea sediments

The Sellafield nuclear fuel reprocessing plant released a total of 41 PBq of 137Cs into the Irish Sea in the period 1952-1998. The present work integrates a series of surveys of the 137Cs distribution in sediment Sellafield which was aimed at obtaining a detailed picture of the patterns of sediment contamination and their time evolution, and an estimate of the 137Cs inventory in sediment. The authors applied NaI(TI)-based underwater γ-ray spectrometry to record a series of 1800 one-minute spectra along 14 transects totaling 160 Nm. The dominant feature of the contamination pattern obtained from this survey remains a stripe extending northwestwards along the coast from the discharge point, as reported for previous surveys. Steep gradients are observed perpendicular to the coast, with 137Cs countrates decreasing to half the recorded maximum over a distance of less than 2000 m. (author)