129I from nuclear fuel reprocessing facilities at Sellafield (U.K.) and La Hague (France); potential as an oceanographie tracer

On the basis of measurements made on archived seaweed samples, together with available release data, we tentatively estimate that the input of 129I (half-life 16 m.y.) to the oceans from the nuclear fuel reprocessing facilities at La Hague, France and Sellafield, Great Britain, during the past 25 years has been ˜ 5 X 1027 atoms, or ˜ 1.2 ton of 129I. This is an order of magnitude larger than the total estimated 129I in the pre-nuclear era ocean, approximately 25 times the input due to nuclear weapons testing, and several hundred times that released by Chernobyl. Most of this 129I is transported up the West European coastline and into the North Atlantic and Arctic oceans. The technique of accelerator mass spectrometry (AMS) is capable of measuring 106 atoms of 129I, thus offering an extremely sensitive method of tracing this isotope in the oceans. We show, for example, that one can detect the reprocessing signal in 11 seawater samples from virtually anywhere in the North Atlantic. It thus should be possible to monitor not only surface circulation but also deep water formation in this latter area, which is believed to have considerable climatic influence. Given its high sensitivity for detection, and the well defined temporal and spatial distribution of its source function, 129I is a potentially attractive addition to the available suite of oceanographie tracers. We also discuss the potential of using this isotope to trace other possible intentional or accidental releases of fission products in the oceans.