The distribution of a range of artificial radionuclides, derived from the authorised discharges of the Sellafield nuclear fuel reprocessing plant, have been determined in a core sampled from the intertidal sediments in the Esk Estuary. The plutonium-alpha activity profiles qualitatively resemble the Sellafield discharge histories for these isotopes, suggesting that the plutonium is largely immobile in the sediments. The beta-emitting 241Pu isotope activity profile was also determined for the sediments using the beta/alpha discriminator on a low-level liquid scintillation counter and qualitatively resembles the Sellafield discharge history. The 241Am activity profile represents the sum of americium both from Sellafield discharges and from the decay of its parent isotope 241Pu. The 244Cm activity profile was examined to see if its relationship to 241Am could be used as a marker of the Sellafield "discharge only" 241Am but this proved to be unsuitable. The 241Pu measurements were therefore used to calculate the amount of 241Am ingrowth and a deconvolved 241Am profile was estimated. The presence of the short-lived isotope 242Cm in the core can only be due to the precursor isotope, 242mAM, supporting its production. The first direct environmental sample measurements of the anthropogenic isotope of uranium, 236U, have been made using accelerator mass spectrometry. Coupled with 238U/235U atom ratios, and the known operational history of Sellafield, these data provide evidence that uranium has limited movement within the core. 237Np activity profiles in cores from west Cumbrian area are limited and the concentrations determined here are very similar to findings of other authors who have sampled close to this sampling site. The profile does not resemble the known Sellafield discharges suggesting that some redistribution of neptunium in the core is occurring. Finally, a quantitative model has been developed to examine the relationship between the Sellafield discharge histories and the sediment profiles, in terms of transport to the sampling site via an offshore mud patch which acts as a buffer. A prediction of the Sellafield discharge history for 236U, which is unknown, has been made, and the model has also been used to evaluate the potential mobility of the actinides that have been studied. A long-term prediction of the transfer of radionuclides to the intertidal sediments has also been made.