Sellafield Discharges Research Articles

The potential role of biofilms in promoting fouling formation in radioactive discharge pipelines

Nuclear facility discharge pipelines accumulate inorganic and microbial fouling and radioactive contamination, however, research investigating the mechanisms that lead to their accumulation is limited. Using the Sellafield discharge pipeline as a model system, this study utilised modified Robbins devices to investigate the potential interplay between inorganic and biological processes in supporting fouling formation and radionuclide uptake. Initial experiments showed polyelectrolytes (present in pipeline effluents), had minimal effects on fouling formation. Biofilms were, however, found to be the key component promoting fouling, leading to increased uptake of inorganic particulates and metal contaminants (Cs, Sr, Co, Eu and Ru) compared to a non-biofilm control system. Biologically-mediated uptake mechanisms were implicated in Co and Ru accumulation, with a potential bioreduced Ru species identified on the biofilm system. This research emphasised the key role of biofilms in promoting fouling in discharge pipelines, advocating for the use of biocide treatments methods.

129I in sediment cores from the Celtic Sea by AMS through a microwave digestion process

Radiochemical methods before measurement are indispensable to determine Iodine-129 by Accelerator Mass Spectrometry (AMS) in environmental samples. In particular, in sediments, iodine is associated with both inorganic and organic matter, and it presents in several chemical forms. Therefore, the radiochemical procedure must be designed to extract all the different iodine species from the matrix, whilst being as robust and time effective as possible. In this work, different microwave digestion methods, together with the processing of the iodine species to be measured by AMS, were tested and their performances are presented here. Two sediment cores, one with muddy sediment (core A) and one with permeable sandy sediment (core I), collected in the Celtic Sea, were used and the results were evaluated to determine an optimized iodine extraction. The method consisted of a microwave digestion with concentrated nitric acid followed by a double liquid–liquid extraction and the final precipitation of silver iodide (AgI), required to measure iodine by AMS. Back extraction of iodine in a reducing solution during purification was carried out with hydrazine (NH2-NH2). Subsequent additional steps were added to optimize all iodine species extraction. First, hydrochloric hydroxylamine (NH2OH·HCl) and sodium bisulfite (Na2S2O5) were used to homogenize all iodine species before extraction through a redox process. Second, sodium hypochlorite (NaOCl) was added to remove any final organic matter after digestion. The final method incorporated sodium hydroxide (NaOH) combined with NaOCl to facilitate reduction of iodine in solution and enhance the NaOCl effect. The different methods were validated against an internal standard and the last method was chosen, as it showed the most reproducible and accurate results. As practical application, Iodine-129 concentration from both cores were compared, showing concentrations between 0.19 × 1012 at/kg and 7.16 × 1012 at/kg for core A and between 0.28 × 1012 at/kg and 2.40 × 1012 at/kg for core I. Despite the 129I diffusion detected in the deeper layers, depth profiles accurately reproduced Sellafield discharges, which is the nuclear fuel reprocessing plant closest to the cores.

200-year industrial archaeological record preserved in an Isle of Man saltmarsh sediment sequence: Geochemical and radiochronological evidence

The Isle of Man, situated in the central Irish Sea, was a significant centre for Pb and Zn mineral extraction during the Industrial Revolution. Comminuted mining debris from the East Snaefell and North Laxey mining areas was transported, through hydrological action, from upland catchments to the coast. This study focuses on an eastern coastal sediment sink and a salt marsh sediment sequence from Port Cornaa. A sediment monolith was excavated, sub-sampled and geochemically investigated using Itrax scanning, WD-XRF analysis and radionuclide methods. Since the island is only 55 km from one of the world's major nuclear reprocessing sites (Sellafield), it was anticipated that a record of these radionuclide discharges (1951-present) would be identifiable and contribute clear chronological markers. The 137Cs profile shows a Sellafield discharge component and also a larger component that is attributed to the 1986 Chernobyl airborne plume. This contribution in the salt-marsh sediment would be derived from the erosion and transport of Chernobyl-labelled upland soils into the marsh. Sediment depth was converted to age using natural (210Pb) and anthropogenic radionuclides (137Cs and 239, 240Pu) and a compelling age vs depth relationship was obtained. The ability to reliably date the overall sediment section shows that sediment accumulation is uniform for the top 25 cm (5 mm/y) and from −25 to −70 cm (3.2 mm/y). The robust age-depth model allows features in the geochemical profiles for S, As, Pb, Zn and Cu to be dated and used to infer events at the East Snaefell and North Laxey mines. These include start-up of mining, introduction of more-efficient mining practises (i.e. water-wheel technology), change in the intensity of mining and final mine closure. The study provides a 200-year industrial archaeological record for the east coast of the Isle of Man. It demonstrates the benefits offered by a combined study involving non-destructive, high resolution Itrax scanning, conventional WDXRF and radionuclide dating.

Deposition of artificial radionuclides in sediments of Loch Etive, Scotland

The nuclear fuel reprocessing plants on the Sellafield site (UK) have released low-level effluents into the Irish Sea under authorisation since 1952. This has led to the labelling of nearby offshore sediments with a range of artificial radionuclides. In turn, these sediments act as a long-term secondary source of both soluble and particle-associated radionuclides to coastal areas. These radionuclides are of interest both in assessing possible environmental impacts and as tracers for marine processes. Here we present results from a study of the geochemistry of natural (234, 238U) and artificial (137Cs, 241Am, 238Pu, 239+240Pu, and 236U) radionuclides and their accumulation in sediments from Loch Etive, Scotland. The data are interpreted in the context of the historical radioactive discharges to the Irish Sea and biogeochemical processes in marine sediments. Loch Etive is divided into two basins; a lower, seaward basin where the sedimentation rate (∼0.6 cm/yr) is about twice that of the more isolated upper basin (∼0.3 cm/yr). These accumulation rates are consistent with the broad distribution of 137Cs in the sediment profiles which can be related to the maximum Sellafield discharges of 137Cs in the mid-1970s and suggest that 137Cs was mainly transported in solution to Loch Etive during that period. Enrichments of Mn, Fe, and Mo in sediment and porewater from both Loch Etive basins result from contemporary biogeochemical redox processes. Enrichments of 238U and 234U in the lower basin may be a result of the cycling of natural U. By contrast, the Sellafield-derived artificial isotope 236U does not seem to be affected by the redox-driven reactions in the lower basin. The 238Pu/239,240Pu ratios suggest contributions from both historical Sellafield discharges and global fallout Pu. The uniform sediment distributions of Pu and Am, which do not reflect Sellafield historical discharges, suggest the existence of a homogenous secondary source. This could be the offshore ‘mud patch’ in the vicinity of Sellafield from which the supply of radionuclides reflects time-integrated Sellafield discharges. This source could also account for the continuing supply of Cs to Loch Etive, even after substantial reductions in discharge from the Sellafield site.

An estimate of the inventory of technetium-99 in the sub-tidal sediments of the Irish Sea

Published results from earlier studies have provided indications that measurable quantities of technetium-99 (99Tc) have accumulated in the sub-tidal sediments of the Irish Sea. This is due to the enhanced discharges from the Sellafield nuclear reprocessing plant in Cumbria, UK (between 1994 and 2004). Depth distributions of 99Tc concentrations in sub-tidal sediments have been determined from a limited number of Irish Sea sites, following the collection of deep sediment cores (up to 2 m in depth), sampled in two research cruise surveys in 2005 and 2006. Vertical concentration profiles of 99Tc from a range of substrates in the Irish Sea are presented here and these have been used to produce an estimate of the total inventory of 99Tc residing in the sub-tidal sediments of the Irish Sea. Significant variation was observed between 99Tc concentrations in the sediment samples, as well as in the shape of individual depth profiles. As anticipated, concentrations tended to be greater on fine-grained (muddy) substrates and showed a general decrease with distance from Sellafield. Vertical concentration profiles of 137Cs, and 137Cs data from published work, have also been considered to evaluate the use of the relatively few 99Tc core data (upon which to determine the 99Tc inventory).The inventories of 99Tc and 137Cs are estimated to have been of the order of 30 and 455 terabecquerels (TBq), respectively, or ∼2% of the total cumulative Sellafield discharge for each of the two radionuclides. The residence half-time of 137Cs in the sub-tidal sediments of the Irish Sea is estimated to be in the order of ∼16 years. Therefore, as the Kd values for 99Tc and 137Cs are similar, this also provides an indicative value to predict future losses of 99Tc from the sediment reservoir.

Temporal record of Pu isotopes in inter-tidal sediments from the northeastern Irish Sea

A depth profile of 239Pu and 240Pu specific activities and isotope ratios was determined in an inter-tidal sediment core from the Esk Estuary in the northeastern Irish Sea. The study site has been impacted with plutonium through routine radionuclide discharges from the Sellafield nuclear reprocessing plant in Cumbria, NW England. A pronounced sub-surface maximum of ~ 10 kBq kg -1 was observed for 239 + 240 Pu, corresponding to the peak in Pu discharge from Sellafield in 1973, with a decreasing trend with depth down to ~ 0.04 kBq kg -1 in the deeper layers. The depth profile of 239 + 240 Pu specific activities together with results from gamma-ray spectrometry for 137Cs and 241Am was compared with reported releases from the Sellafield plant in order to estimate a reliable sediment chronology. The upper layers (1992 onwards) showed higher 239 + 240 Pu specific activities than would be expected from the direct input of annual Sellafield discharges, indicating that the main input of Pu is from the time-integrated contaminated mud patch of the northeastern Irish Sea. The 240Pu/ 239Pu atom ratios ranged from ~ 0.03 in the deepest layers to > 0.20 in the sub-surface layers with an activity-weighted average of 0.181. The decreasing 240Pu/ 239Pu atom ratio with depth reflects the changing nature of operations at the Sellafield plant from weapons-grade Pu production to reprocessing spent nuclear fuel with higher burn-up times in the late 1950s. In addition, recent annual 240Pu/ 239Pu atom ratios in winkles collected during 2003–2008 from three stations along the Cumbrian coastline showed no significant spatial or temporal differences with an overall average of 0.204, which supports the hypothesis of diluted Pu input from the contaminated mud patch.

Accumulation, solid partitioning and remobilisation of 99Tc in subtidal and intertidal sediments in the Irish Sea

Recent studies have shown that accumulation of 99Tc in seabed sediments labelled by authorised radioactive liquid discharges into the NE Irish Sea from the Sellafield reprocessing complex is greater than previously thought. In this paper, new data on 99Tc concentration profiles in subtidal and intertidal sediments from the eastern and western Irish Sea are provided with a view to elucidating the processes responsible for the incorporation and retention of 99Tc in the seabed. The data show that substantial amounts of 99Tc have accumulated in the fine-grained subtidal sediments off the Cumbrian coast, particularly after increased releases from Sellafield following the commissioning of the Enhanced Actinide Removal Plant (EARP) in 1994. In all the cores taken in this area, 99Tc has been found to be present to depths in excess of 30 cm. Analysis of 137Cs and 241Am profiles, together with other supporting geochemical data, show a high degree of homogenisation of the sediments down to these depths as a result of physical and biological processes, and confirm that incorporation of 99Tc into the sediment compartment is actually the result of mixing and reworking, rather than active sediment accumulation. In contrast, active deposition of material transported from this mixed pool of sediment appears to be the dominant mechanism controlling 99Tc profiles in intertidal areas close to the Sellafield discharge outfall. Data obtained from the analysis of subtidal sediment cores from the western Irish Sea mud basin suggest that similar mixing processes to those occurring in the subtidal sediments of the eastern Irish Sea are also active in this area. Time-series data on 99Tc concentrations in surficial sediments from this basin, gathered in the period 1988–2004, inclusive, show a clear increase in concentrations, by a factor of ∼2, between samples collected pre-EARP and post-EARP. The constancy of 99Tc concentrations in surface sediments throughout the 1980s and the early-1990s suggests that little redissolution and export of 99Tc occurred over this extended period. A similar observation applies to the post-EARP period, when concentrations remained relatively constant despite the reported steady decrease in 99Tc concentrations in the overlying waters. This apparent lack of remobilisation is consistent with data from sequential extraction analyses, which indicate that the bulk of the 99Tc is strongly bound to non-labile geochemical phases, with only a small proportion associated with exchangeable and acido-soluble phases. Further, these analyses show that 99Tc is not associated with oxygen-sensitive and highly-reactive acid-volatile sulphides (AVS) to any significant extent.

Changing patterns of radionuclide distribution in Irish Sea subtidal sediments

This paper presents new data on the distribution of long-lived radionuclides in Irish Sea subtidal sediments, contaminated as a result of the BNFL Sellafield discharges. The results from different sampling campaigns in 1999 have been combined to assess the extent of radionuclide mobility relative to earlier surveys, in both the eastern and western Irish Sea areas, and to investigate changes in radionuclide distribution over time. The results appear to confirm the trend of continuing re-distribution and transfer of contamination away from the English coast. West of the Isle of Man, radionuclide concentrations and inventories have remained more or less constant. The inventory of radionuclides in sandy sediments in the eastern Irish Sea is still under-represented by current sampling, but could be improved by deeper and more extensive vibrocoring.

Distribution of Technetium-99 in sub-tidal sediments of the Irish Sea

To date, relatively little attention has been given to the accumulation of 99Tc discharged from Sellafield in the subtidal sediments of the Irish Sea. The potential implications for secondary seafood contamination from contaminated sediment has driven the UK Food Standards Agency to commission further research into this pathway. The work reported here reviews existing data and provides new measurements of 99Tc specific activity in surface and sub-surface sediments of the Irish Sea, together with environmental K d values. The results are used to assess the spatial and temporal evolution of 99Tc in the seabed after 8 years of enhanced Sellafield discharges (between 1994 and 2002), of the aforementioned radionuclide. The information is discussed with reference to other studies, in an attempt to infer the processes controlling 99Tc uptake and release from seabed sediments. The average environmental K d value for 99Tc in the Irish Sea (1.9×10 3) was more than an order of magnitude greater than the presently recommended value of 10 2 [IAEA, 2004. Sediment distribution coefficients and concentration factors for biota in the marine environment. Technical Report Series No. 422, IAEA, Vienna]. Comparison with results from laboratory studies indicates that the observed distribution may represent metastable binding rather than thermodynamic equilibrium. Activities in surface sediments decreased with increasing distance from Sellafield but were also dependent upon the nature of the underlying substrate, being greater on muddy material. Preliminary measurements of grain-size distribution indicated that the observed variation in activities was probably not due to surface area effects. There is an emerging body of evidence from other studies that indicate the differences were most likely due to variations in redox regimes between the different substrates. Vertical profiles were significantly irregular, probably due to the effects of variable sediment mixing processes. Comparison of profiles, close to the Sellafield pipeline, with a core taken over 20 years earlier (pre-EARP) indicated that the increase in the cumulative Sellafield discharge and redissolution from surficial sediment were required to explain the temporal variation. Since the surveys reported here were completed, substantial progress has been made in reducing 99Tc discharges from Sellafield. Assuming that the rate and extent of 99Tc remobilisation follows a similar pattern to that previously observed for caesium ( 137Cs), then the half-time for redissolution of 99Tc bound to sedimentary material in the Irish Sea is likely to be of the order of several tens of years. It is probable that small but nevertheless measurable 99Tc contamination of local seafood will persist for several decades, due to this secondary source.

Tracer-derived transit time of the waters in the eastern Nordic Seas

The spatial-temporal distribution of the anthropogenic radionuclide 137Cs originating from nuclear bomb testing and the Sellafield reprocessing plant in the Irish Sea is simulated using a global version of the Miami Isopycnic Coordinate Ocean Model (MICOM). The physical model has a horizontal resolution of about 40 km, and it is forced with daily atmospheric reanalysed fields for the period 1948 to 2002. A comparison of the temporal evolution of observed and simulated concentrations of 137Cs has been conducted for the regions east of Scotland, west of central Norway and at the entrance of the Barents Sea. It follows that the annual mean 137Cs concentration signal from the Sellafield discharge reaches the southwestern Barents Sea region in 5 yr, in accordance with available observations. To more accurately assess the age of the caesium-tagged water masses, three additional experiments were performed with an Eulerian age coupled to the evolution of the tracer concentration. It is demonstrated that the transit time depends on the duration of the tracer release history, on the dynamical ocean state and on whether the transit time is derived from the time difference between the release history and the concentration evolution downstream of the release, or as an explicit Eulerian age tracer. The Eulerian age tracer gives a transit time for a Sellafield-like discharge to reach the Barents Sea of 56 months in the 1970s, 52 months in the 1960s and 51 months in the 1980s, and that this difference is strongly governed by the ocean dynamics in the Faeroe—Scotland region.

Application of a magnetic extraction technique to assess radionuclide?mineral association in Cumbrian shoreline sediments

An assessment has been made of the association of 239+240 Pu, 241 Am and 210 Po (in secular equilibrium with 210 Pb) with iron minerals using a magnetic extraction technique. Grab samples of beach sand from the Cumbrian (UK) coastline were subjected to successive extractions with a ~0.1 T ferrite magnet and a ~0.3 T rare-earth magnet procedure to separate magnetic iron oxide minerals. Radionuclide concentrations in the magnetic extracts were enhanced (by ~4–6-fold) relative to the residue. Those in the ~0.1 T magnet extracts were broadly similar to those in the antiferromagnetic material extracted by the ~0.3 T magnet, despite the very large differences in magnetic property values between the two fractions (one to two orders of magnitude). The percentage of magnetic material in terms of mass was small and therefore, the majority of these radionuclides (on average 88%) were associated with the residue. Removal of stable Fe was incomplete. Given that the radionuclides may also bind to paramagnetic (nonmagnetic) Fe minerals, the data were extrapolated by normalising the results to quantitative Fe removal. This yielded average values of 37%, 45% and 46% for 239+240 Pu, 241 Am and 210 Po( 210 Pb), respectively, as upper limits for the fraction associated with magnetic+nonmagnetic Fe minerals. There are significant uncertainties inherent in quantifying data from this extraction technique. Nevertheless, it seems reasonable to conclude that radionuclide association with Fe minerals is unlikely to have a significant impact upon the physical dispersion of sediment contaminated by Sellafield discharges in the Irish Sea. However, it may be an important factor in governing Pu redox and redissolution behaviour.

Redox-dependent behaviour of technetium-99 entering a permanently stratified anoxic fjord (Framvaren fjord, Norway)

Two sampling expeditions were undertaken at the highly stratified, anoxic Framvaren fjord to investigate the behaviour of redox sensitive 99Tc in the water column, its uptake onto particulate matter and removal to the sediments. Peak 99Tc concentrations from recent Sellafield discharges were observed at the fjord on both expeditions. Maximum 99Tc concentrations were observed at 6–8 m (salinity of 12.5–15) in Framvaren, indicating that inflowing water interleaves predominately at this depth. Below this, 99Tc transport down to the oxic/anoxic interface was found to be limited by the density gradient as, within error, all 99Tc above the interface is in the <10 kDa fraction. High Kd values were observed below the interface and therefore 99Tc uptake onto particulate matter occurred to the greatest extent at the particle concentration maximum. Particle-bound Tc was carried to the sediments, and the sediments hold a blurred record of European reprocessing discharges. However, a maximum of only 41% of the 99Tc was associated with particles and 20% with colloids, thus an observed minimum of 39% was present as “soluble” species in these strongly reducing waters. This is the first observation of “soluble” Tc species under highly reducing conditions in the natural environment. Subsequent uptake onto particles or colloids was not observed below this depth, and “soluble” Tc(IV) species persist in this system.

Spatial and Temporal Impacts of 14C Releases from the Sellafield Nuclear Complex On the Irish Coastline

The Sellafield nuclear fuel reprocessing plant is estimated to be the largest single source of global anthropogenic radiocarbon discharge. This study addresses the impact of these releases on the Irish coastal marine environment. Spatial trends in the 14C content of seaweed (Fucus spp.) were assessed by collecting and analyzing samples from well-distributed locations around the Irish coastline. Temporal trends were studied by comparing 14C concentrations in present-day samples with levels found in archive material collected at the same locations during research campaigns conducted in the mid-1980s and mid-1990s. The impact of 14C discharged from Sellafield was found to be most apparent in seaweeds from the northeastern Irish coast. This indicates that the pattern of residual currents and, in particular, the south to north transfer of water known to predominate in the Irish Sea, largely controls the spatial distribution of 14C releases. Maximum 14C discharge levels to the marine environment from Sellafield (between 12 and 13 TBq yr-1) were mirrored by peak concentrations found in seaweed from the mid-1990s and in present-day samples (highest recorded value of 130.4 pMC). Concentrations of 14C in seaweed from the west coast of Ireland correspond closely with values measured for seaweeds from the Atlantic coast of northwest Spain and do not appear to be significantly affected by Sellafield discharges.

Application of a magnetic extraction technique to assess radionuclide–mineral association in Cumbrian shoreline sediments

An assessment has been made of the association of 239+240Pu, 241Am and 210Po (in secular equilibrium with 210Pb) with iron minerals using a magnetic extraction technique. Grab samples of beach sand from the Cumbrian (UK) coastline were subjected to successive extractions with a ~0.1 T ferrite magnet and a ~0.3 T rare-earth magnet procedure to separate magnetic iron oxide minerals. Radionuclide concentrations in the magnetic extracts were enhanced (by ~4–6-fold) relative to the residue. Those in the ~0.1 T magnet extracts were broadly similar to those in the antiferromagnetic material extracted by the ~0.3 T magnet, despite the very large differences in magnetic property values between the two fractions (one to two orders of magnitude). The percentage of magnetic material in terms of mass was small and therefore, the majority of these radionuclides (on average 88%) were associated with the residue. Removal of stable Fe was incomplete. Given that the radionuclides may also bind to paramagnetic (nonmagnetic) Fe minerals, the data were extrapolated by normalising the results to quantitative Fe removal. This yielded average values of 37%, 45% and 46% for 239+240Pu, 241Am and 210Po( 210Pb), respectively, as upper limits for the fraction associated with magnetic+nonmagnetic Fe minerals. There are significant uncertainties inherent in quantifying data from this extraction technique. Nevertheless, it seems reasonable to conclude that radionuclide association with Fe minerals is unlikely to have a significant impact upon the physical dispersion of sediment contaminated by Sellafield discharges in the Irish Sea. However, it may be an important factor in governing Pu redox and redissolution behaviour.

Accumulation of technetium-99 in the Irish Sea?

An assessment has been carried out to determine the impact of continued 99 Tc discharges into the Irish Sea from the nuclear fuels reprocessing plant at Sellafield. Samples of surface and bottom seawater and sediment have been collected from the Irish Sea and analysed for 99 Tc. The information has been used, together with supporting data, to determine the effect of summer stratification upon the seawater concentrations and to evaluate whether sediments provide a sink for 99 Tc. Hydrographic data provide clear evidence of thermal stratification of waters above the muddy sediment in the western Irish Sea. Surface water contained higher 99 Tc concentrations than bottom water, and concentrations were inversely related to water salinity. This inverse relationship was not observed in the eastern Irish Sea close to Sellafield. 99 Tc activities in surficial sediments were greatest (>20 Bq/kg) at sites closest to the Cumbrian coastline. Activity, from equivalent sampling sites, remained similar between surveys carried out in 1995 and 1998. The muted response of the seabed sediments, to fluctuations in the Sellafield discharges, compared with the water column is to be expected given that they reflect the integrated radionuclide discharge history.

Accumulation of technetium-99 in the Irish Sea?

An assessment has been carried out to determine the impact of continued 99Tc discharges into the Irish Sea from the nuclear fuels reprocessing plant at Sellafield. Samples of surface and bottom seawater and sediment have been collected from the Irish Sea and analysed for 99Tc. The information has been used, together with supporting data, to determine the effect of summer stratification upon the seawater concentrations and to evaluate whether sediments provide a sink for 99Tc. Hydrographic data provide clear evidence of thermal stratification of waters above the muddy sediment in the western Irish Sea. Surface water contained higher 99Tc concentrations than bottom water, and concentrations were inversely related to water salinity. This inverse relationship was not observed in the eastern Irish Sea close to Sellafield. 99Tc activities in surficial sediments were greatest (>20 Bq/kg) at sites closest to the Cumbrian coastline. Activity, from equivalent sampling sites, remained similar between surveys carried out in 1995 and 1998. The muted response of the seabed sediments, to fluctuations in the Sellafield discharges, compared with the water column is to be expected given that they reflect the integrated radionuclide discharge history.

Simulating transport of non-Chernobyl 137Cs and 90Sr in the North Atlantic–Arctic region

The spatial and temporal distributions of the anthropogenic radionuclides 137Cs and 90Sr, originating from nuclear bomb testing and the Sellafield reprocessing plants in the Irish Sea, are simulated using a global version of the Miami Isopycnic Coordinate Ocean Model (MICOM). The physical model is forced with daily atmospheric re-analysed fields for the period 1950 to present. Comparison of temporal evolution of observed and simulated concentrations of 137Cs have been conducted for the regions east of Scotland, west of central Norway and at the entrance of the Barents Sea. It follows that the radionuclides from the Sellafield discharge reach the Barents Sea region after 4–5 years, in accordance with observations. The simulation provides a detailed distribution and evolution of the radionuclides over the integration time. For the Atlantic waters off the coast of Norway and in the southern Barents Sea, the atmospheric fallout dominates over the Sellafield release up to the mid 1960s and from the early 1990s, whereas Sellafield is the main source for the two radionuclides in the 1970s and 1980s. It is furthermore argued that model systems like the one presented here can be used for future prediction of radioactive contaminations in the Nordic Seas and the Arctic Ocean, for instance under various global warming scenarios.

Further studies of the distribution of technetium-99 and caesium-137 in UK and European coastal waters

Data on the temporal and spatial variations of 99Tc and 137Cs in UK coastal waters are provided from surveys carried out over the period 1993–1998; prior to and post the discharge of elevated quantities of 99Tc from the nuclear fuel reprocessing plant at Sellafield (Cumbria, UK). 99Tc seawater concentrations in the Irish Sea increased by more than an order of magnitude within the study period concomitant with the increase in discharges. 137Cs discharges were relatively low (∼0.3% of their peak values in the 1970s). Simplistically, the 137Cs distribution reflected varying hydrographic conditions superimposed upon the residual concentrations of a system approaching steady state. Differences between the 137Cs/ 99Tc ratio in Sellafield discharges and seawater indicate that 137Cs remobilisation, from sediments contaminated by large discharges in the 1970s, is presently the predominant (∼90%) source term to the water column. The 137Cs/ 99Tc ratio in the Irish Sea decreased significantly within the period of these surveys (e.g. reduced from ∼14 in 1993 to 0.4 in 1996, within the vicinity of Sellafield). However, it is difficult to extrapolate this information to assess the contribution from Sellafield in distant waters because the low levels of 137Cs are continuously perturbed by additional inputs during transit (e.g. remobilisation from sediments outside the Irish Sea). Examination of 99Tc data for the North Sea indicates that the leading edge of the first EARP pulse, entering via the Scottish coastal current, may have migrated to the limit of the current flowing south along the British coastal margin within 9 months. The estimated transfer factor (TF) for Sellafield discharges in this current is 52 Bq m −3/PBq annum −1 with transit times from Sellafield to the Pentland Firth and Lowestoft of ∼9 and ∼24 months, respectively. These transit times, derived from the 99Tc data, are significantly shorter than previous estimates based on 137Cs and 90Sr data from the 1970s and 1980s.

Records of radionuclide deposition in two salt marshes in the United Kingdom with contrasting redox and accumulation conditions

Single cores from two salt marshes in the United Kingdom located near different nuclear facilities were investigated to compare chronostratigraphic estimates derived from the natural radionuclide 210Pb excess with estimates from the known times of introduction of artificial radionuclides to the environment. Both cores selected had clear visual indications of redox zonation, and evidence for diagenetic redox perturbation of the radionuclide records was also sought. In the core from Beaulieu Marsh on the south coast of England, the redox zonation was revealed by the profiles of the redox-sensitive elements Mn + I, Fe + P + As, and S, and the records of nuclear discharges were entirely contained within oxidized conditions in the upper 40 cm. The constant flux/constant sedimentation 210Pb excess accumulation estimate was 76% of that derived from the 1963 fallout 137Cs level (0.35 vs. 0.46 g cm −2 yr −1 dry mass), but the constant flux 210Pb excess method indicated that accumulation rates were lower at Beaulieu before ∼1950. On any timescale, 137Cs appears earlier in the sediment record than its introduction to the environment, but although downward diffusion of 137Cs relative to 241Am has clearly occurred, the 137Cs peak still appeared in place and there was negligible penetration of 137Cs into underlying reduced conditions. This core also contained a peak of the 60Co discharges from either or both the Winfrith and La Hague nuclear plants that peaked in 1980 and 1984, respectively. The sediments in the core from Wyre Marsh on the eastern coast of the Irish Sea had accumulated more rapidly than those at Beaulieu, and in this case the redox zonation could be established only from Mn and S profiles. Here, the constant initial activity 210Pb excess accumulation rate estimate was 125% of that derived from the 137Cs peak correlated with the 1975 Sellafield discharge maximum (0.79 vs. 0.64 g cm −2 yr −1). Sellafield discharge 137Cs swamps fallout or Chernobyl 137Cs signals in this core, but the 137Cs and 241Am sediment records are well separated and remain consistent with the slightly different discharge patterns over time. This is so despite the fact that the maximum activity levels of both isotopes are now located well into reducing conditions out of which Mn must have migrated. The 210Pb profile appeared similarly unaffected by the oxidized/reduced boundary in this case. This core was too short to define the limits of any downward 137Cs migration. 210Pb excess accumulation rate estimates for salt marshes should be viewed with some caution because of the steady-state assumptions inherent in all 210Pb excess methods and the potential for fluctuating accumulation conditions and open system behavior in salt marshes.

Assessment of prospective foodchain doses from radioactive discharges from BNFL Sellafield

This paper presents the method used by the UK Food Standards Agency (FSA) to assess the potential impact of proposed radioactive discharges from the Sellafield nuclear site on food and determine their acceptability. It explains aspects of a cautious method that has been adopted to reflect the UK government policy and uncertainties related to people's habits with regard to food production and consumption. Two types of ingestion doses are considered in this method: ‘possible’ and ‘probable’ doses. The method is specifically applied to Sellafield discharge limits and calculated possible and probable ingestion doses are presented and discussed. Estimated critical group ingestion doses are below the dose limit and constraint set for members of the public. The method may be subject to future amendments to take account of changes in government policy and the outcome of a recent Consultative Exercise on Dose Assessments carried out by FSA. Uncertainties inherent in dose assessments are discussed and quantified wherever possible.