[en] This report presents the results of the marine radioactivity monitoring programme carried out by the Radiological Protection Institute of Ireland (RPII) during 2000 and 2001. The primary objective of the programme is to assess the exposure of the Irish population resulting from radioactive contamination of the Irish marine environment and to estimate the risks to health from this exposure. Discharged radioactive waste from the British Nuclear Fuels plc (BNFL) reprocessing plant at Sellafield in Cumbria in the North West of England continues to be the dominant source of this contamination. In particular, the remobilisation from sediments of historic discharges makes an important contribution to the levels of radioactivity in the seawater of the western Irish Sea. Approximately 300 samples of fish, shellfish, seaweed, seawater and sediment were collected in 2000 and again in 2001. Both the Marine Institute and the Department of Communications, Marine and Natural Resources assisted the Institute with this sampling. The samples were analysed for a range of radionuclides at the Institute's radio-analytical laboratory. The results show that the artificial radionuclide of greatest dosimetric significance continues to be caesium-137. The activity concentration of this radionuclide in the Irish marine environment has remained relatively stable since the mid 1990s but at a lower level than that observed during the previous two decades. Along the Irish coastline the highest activity concentrations observed are in the north-east. Since 1994 the commissioning and operation of new facilities at Sellafield have resulted in an increase in the discharges of technetium-99 to the Irish Sea. This has been reflected in an increase in the activity concentrations of this radionuclide at all east coast sampling sites. However, the low radiotoxicity of technetium-99 means that it is generally of lesser radiological significance than caesium-137. The main pathway contributing to the exposure of the Irish public is the consumption of seafood. The committed effective dose to heavy consumers of seafood due to measured artificial radionuclides was 1.18 Sv in 2000 and 1.20 Sv in 2001. Caesium-137 is the dominant radionuclide, accounting for approximately 60-70% of the total dose. The dose to the Irish population due to this radionuclide has declined significantly over the last two decades. For example, in 1982 the dose due to caesium-137 to heavy consumers was estimated to be approximately 70 Sv. This had fallen to 0.73 and 0.81 Sv in 2000 and 2001, respectively. These doses may be put into context by comparing them with the dose attributable to the presence of the naturally occurring radionuclide, polonium-210, in seafood. This has been estimated to be 148 aeSv for heavy seafood consumers. The estimated doses may also be compared with the annual average dose of approximately 3620 aeSv from all sources of radiation received by members of the Irish public. The dose received in 2000 and 2001 by a heavy seafood consumer corresponds to a risk of developing a fatal cancer of approximately 1 in 17 million. The doses incurred by people living in Ireland today as a result of the routine operations at Sellafield are now very small and do not constitute a significant health risk. The Institute therefore advises that from a radiological perspective it is safe to eat seafood landed at Irish fishing ports and to enjoy the amenities of the Irish maritime area. Further reductions in these doses are being pursued through the implementation of the OSPAR Strategy with regard to Radioactive Substances. All signatories to the Strategy are committed to progressive and substantial reductions in radioactive discharges from their facilities. Compliance with the objectives of the OSPAR Strategy should ensure that the radiation doses attributable to the operations at Sellafield and other nuclear facilities are even further reduced in future years. The rate of reduction in radiation doses will be influenced by the remobilisation of radionuclides bound to sediments in the Irish Sea. The Institute takes the view that the very highest possible standards of safety and waste management should apply to nuclear facilities including the implementation of best available techniques for the further reduction of discharges with a view to minimising their environmental impact

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[en] This report presents the results from ten current meter moorings deployed in the eastern Irish Sea during 1986, as part of a field programme investigating local sediment dynamics. The main aim of the moorings was to provide long-term estimates of residual current flow, for use in a numerical box model which will simulate the distribution and behaviour of radionuclides with a high affinity for sediments, such as plutonium. (author)

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[en] A selection of marine samples collected in the vicinity of Dublin Bay on the East Coast of Ireland and Galway Bay on the West Coast have been analyzed with a high resolution Compton suppression spectrometer designed for the analysis of low-level environmental samples. Radiocaesium levels in these samples are compared and some preliminary conclusions presented. The principal components of the spectrometer, which is described in detail, are (I) an upward-locking Ge(Li) detector mounted in a special NPR-type cryostat, (II) active shielding in the form of a well detector fashioned from NE102A scintillator and a NaI(T1) detector, (III) an anti-Compton analyzer and (IV) a multichannel analyzer. The multichannel analyzer is interfaced with a 32K microcomputer to a Digital VAX-11/780 computer where up-to-date gamma spectroscopy techniques are employed for the deconvolution of spectra, search and identification of each line and estimation of the activity of each radionuclide. (author)

[en] A long-term transport model for conservative substances in the marine environment is presented. It has been successfully applied to the simulation of salinity, river water discharges and ¹³⁷Cs dispersion in the Irish Sea. The use of salinity data for calibration of advection and diffusion processes has been shown to be a powerful tool for the development of the model. This mechanism can be considered as a universal calibration method for dispersion models. It could be very useful for the development of models which describe marine scenarios for which very little radiological information is available. (author)

[en] Uptake experiments were successfully undertaken for polonium and plutonium in the marine diatom Skeletonema costatum. Experiments were complemented with a field study which yielded concentration factors for these radionuclides for plankton samples collected in the eastern Irish Sea. The uptake experiment produced uptake half times of 0.8 and 0.6 days for plutonium and polonium, respectively. Concentration factors of 3.1 x 10⁵ l kg^-1 for plutonium and 2.4 x 10⁵ l kg^-1 for polonium were consistent with those suggested by the IAEA for phytoplankton. Concentration factors derived from the field study were 2 x 10³ l kg^-1 for plutonium and 1.4 x 10⁴ l kg^-1 for polonium and were more consistent with IAEA values for zooplankton rather than phytoplankton. The maximum calculated dose rate due to Po and Pu in plankton sampled in the field was 0.12 μGy h^-1. In applying the laboratory-derived phytoplankton CF values for Po and Pu, higher dose rates, in the range 6-11 μGy h^-1, were calculated. The latter values are well below the UNSCEAR and IAEA review value of 400 μGy h^-1, and are also below the Environment Agency marine action level of 40 μGy h^-1.

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