Publication Abstract

Temporal variations and behaviour of radionuclides in a shoreline location

D. McCubbin and K.S. Leonard

Seawater and sediment samples were collected from a tidal site close to the BNFL reprocessing plant at Sellafield, Cumbria (UK), to determine the behaviour of 137Cs, 231Np, 239+240Pu and 241 Am. The selected site, Whitehaven Harbour, drains almost completely at low tide and refills at high water. To assess the contribution from the most recent discharges sampling was carried out on both tides, and on two separate occasions; initially during a period concurrent with greatly reduced effluent releases and again to coincide with normal discharge operations. Moreover, since the suspended particulate concentration varies considerably during the tidal cycle, this site provides an ideal opportunity to study radionuclide particlewater interactions.

Results indicate that the concentrations of radionuclides in the dissolved phase varied on each sampling occasion and over tidal cycles. The fluctuations were found to be quite considerable (e.g. up to 3-fold for 239+240Pu) over a 6 hour period. However, as a result of decreased effluent discharges over a number of years, it is suggested that Sellafield no longer provides the major contribution for 137Cs, 239+240Pu and 241Am at Whitehaven Harbour. Nevertheless, discharges of 231Np from Sellafield have not decreased to the same extent and it is likely that current releases continue to provide the predominant source term in local seawater. Particle-water interactions were different for each radionuclide. 137Cs levels showed a tendency to increase with suspended particulate concentration, possibly due to remobilisation. In contrast, no simple correlation was observed for dissolved 241Am. 231Np exhibited conservative behaviour with concentrations remaining relatively constant over the range of sampling conditions. Some evidence of scavenging was observed for 239+240Pu(V) as shown by the decrease of concentrations concomitant with suspended load.

Reference:

D. McCubbin and K.S. Leonard, 1997. Temporal variations and behaviour of radionuclides in a shoreline location.Radioprotection, 32(C2): 197-204