A review of the occurrence and behaviour of neptunium in the Irish Sea

This paper presents a review of research into the occurrence and behaviour of neptunium, principally 237Np, in the Irish Sea. This research has lagged behind that of other radionuclides due to the combination of 1. the relative difficulties in the analysis of 237Np compared with other transuranic elements including separation problems and yield monitor selection and measurement; 2. the relatively low activity of 237Np discharged to the Irish Sea particularly during the 1970s and 1980s when discharges of other radionuclides peaked; and 3. the consequent low dose risk from 237Np in the short term. Consideration of the increasing proportion of 237Np in the Sellafield discharges and the need for knowledge about this isotope for high level waste studies has seen a gradual increase in research during the late 1980s and 1990s. This research shows that 237Np contamination is widespread throughout the Irish Sea and suggests that although neptunium is more mobile in the environment than other transuranics it is generally less bioavailable. Despite these studies, knowledge of 237Np occurrence and behaviour in the Irish Sea is still very limited.