The transport to and deposition of americium in intertidal sediments of the ravenglass estuary and its relationship to plutonium

Abstract

The distributions of 241Am in four cores of intertidal sediment from the Ravenglass estuary near to the Windscale nuclear fuel reprocessing facility, northwest England, are reported. Maximum 241Am activities (up to ∼200 pCi g −1) are found at depth in the sediments, and this pattern of accumulation is compared with annual discharges to the sea from Windscale. The results indicate a slow transit of americium to the depositing sediments when the sedimentation rates derived from two independent methods are applied to the cores. This feature is interpreted, and further confirmed, by consideration of plutonium: americium isotopic ratios, as the result of a lag-time of transit from Windscale to the sediments of ∼2·5 years. This slow movement is consistent with earlier theoretical and field data which indicate that americium is rapidly removed to sediments on release, and subsequently transported with bed-loads in the coastal environment.