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THE IMPACT OF LIQUID RADIOACTIVE WASTE DISCHARGES FROM SELLAFIELD TO THE IRISH SEA IN RECENT YEARS. B. D. Smith, G. J. Hunt and W. C. Camplin CEFAS, Lowestoft Laboratory, Pakefield Road, Lowestoft, NR33 0HT, United Kingdom Abstract. This paper describes the trends in liquid radioactive waste discharges from British Nuclear Fuels plc (BNFL) Sellafield and in concentrations in local marine environmental media. The 10-year period 1993 to 2002 is covered during which time discharges commenced from the Thermal Oxide Reprocessing Plant (THORP), which reprocesses oxide fuels and from the Enhanced Actinide Removal Plant (EARP), which treats current and historic liquid wastes, particularly to remove transuranic radionuclides. Radionuclides examined in detail include 3H, 14C, 99Tc, 129I, 137Cs, 239 + 240Pu and 241Am. The paper considers the relationship between discharges and environmental concentrations, and relates concentrations to changes in recent discharge patterns, the effects of historic discharges and environmental influences. In view of the interest in 99Tc, more data are included than for the other radionuclides. The effects of environmental concentrations in terms of radiological significance to the potentially critical group of fish and shellfish consumers local to Sellafield are also presented. Doses have varied during the period, partly because of changed radionuclide concentrations in seafoods, but also as a result of the changing patterns in the amounts of seafood eaten by the group. The paper examines these factors. The influence of the OSPAR Radioactive Substances strategy on future discharges and impacts is also discussed. 1. Introduction Since the 1950s, British Nuclear Fuels plc (BNFL) and its predecessors have operated nuclear plants at Sellafield in west Cumbria, UK. Primarily, the site undertakes reprocessing of irradiated nuclear fuel from Magnox and oxide fuel reactors in the UK and abroad. Associated storage of fuel elements in cooling ponds is undertaken prior to reprocessing. The site also includes the Calder Hall nuclear power plant which, until its closure in March 2003, has generated nuclear power since 1956. In more recent times, BNFL has also begun manufacturing mixed oxide fuels, and has increasingly turned its attention to decommissioning redundant plant and facilities, including the Windscale Advanced Gas- cooled Reactor (WAGR). Operations on site generate liquid radioactive wastes which are discharged into the Irish Sea, some of the streams being treated to reduce their radioactive content. These plants include the Site Ion Exchange Effluent Plant (SIXEP), which treats fuel storage pond water, and the Enhanced Actinide Removal Plant (EARP) which treats routine and decay-stored waste streams mainly from the older, Magnox reprocessing plant. The adjacent United Kingdom Atomic Energy Authority (UKAEA) research facilities also discharges minor quantities of liquid wastes via the BNFL site. Under UK legislation, discharges to the environment have to be authorised, and in the period considered by this paper (1993 to 2002), several authorisations have been in force. Discharges in 1993 were covered by a variation in January 1990 to an authorisation granted in 1986 under the Radioactive Substances Act 1960. Discharges in 1994 to 1999 were covered by an authorisation which came into effect in January 1994 under the Radioactive Substances Act 1993. This authorisation took account of the start up of EARP and the Thermal Oxide Reprocessing Plant (THORP), and included consideration of the commissioning periods for these new plants. More details have been published [1]. Both the 1990 variation and the 1994 revision were issued by the Ministry of Agriculture, Fisheries and Food (MAFF) and Her Majesty’s Inspectorate of Pollution (HMIP). Increased 99Tc discharges to the Irish Sea followed the commencement of EARP operations and this attracted © British Crown Copyright, 2004 1 particular attention both nationally and internationally. As a consequence, the Environment Agency (EA) issued a variation which reduced the 99Tc limit applicable from January 2000. Under the Environment Act 1995, the EA, which subsumed HMIP, had become the sole authorising body for radioactive waste discharge authorisations in England. At the same time, MAFF became a Statutory Consultee, though in 2000 this responsibility passed to the Food Standards Agency (FSA) under the Food Standards Act 1999. Table I shows the annual limits in these authorisations in simplified form. Table I. Authorised annual liquid discharge limits for BNFL Sellafield. 1990 Variation 1994 Revision 2000 Variation Radionuclide Limit Limit (in Limit (after 1994) Limit (TBq y-1) 1994) (TBq y-1) (TBq y-1) (TBq y-1) 3H 3500 31000 31000 30000 14C 4 20.8 20.8 20.8 60Co 8 13 13 13 90Sr 35 30 48 48 95Zr/95Nb 180 50 9 9 99Tc 10 200 200 90 106Ru 170 75 63 63 129I 0.4 2 2 2 134Cs 10 6.6 6.6 6.6 137Cs 110 75 75 75 144Ce 22 10 8 8 Pu-alpha 7 4 0.7 0.7 241Pu 170 150 27 27 241Am 3 1.3 0.3 0.3 total alpha 10 4.7 1 1 total beta 500 400 400 400 NB Limits for 3H and 129I from 1994 onwards are upper values. Actual limits within a year are related to reprocessing throughput in THORP. 2. Changes in discharges from 1993 to 2002 The trends in discharges of selected radionuclides from 1993 - 2002 are shown as the histograms in Figures 1-10. Discharges of 3H (Figure 1) and 129I (Figure 5) have gradually increased in the period due to commissioning of THORP. Thus far, the increases in 3H have not been as great as envisaged by BNFL when the 1994 authorisation was set. Carbon-14 discharges (Figure 2) increased from 1994, as expected, with the re-routing from a gaseous waste stream into a liquid one. Increases were greater in the mid-1990s than late-1990s, but discharges were at 13 TBq y-1 by 2002 compared with 2 TBq y-1 prior to the diversion. Discharges of 99Tc (Figures 3 – 4) have increased due to processing of stored wastes through EARP, reaching a peak of 192 TBq y-1 in 1995, substantially above the pre-EARP level of less than 10 TBq y-1. Though subsequently lower, discharges in 2002 were close to the authorised annual limit of 90 TBq. Discharges of 137Cs (Figure 6) decreased over the period, partly due to EARP, but also because of improved performance of the site ion-exchange effluent plant (SIXEP) which treats effluents from fuel element storage ponds. Typically, discharges were less than 10 TBq y- 1 compared with up to 5000 TBq in the 1970s. Discharges of 239Pu + 240Pu (Figure 7) and 241Am (Figure 8) decreased by at least an order of magnitude as a result of EARP operations. Some small increases in discharges of 239Pu + 240Pu are apparent in 2001 – 2002. 3. Concentrations in marine biota On behalf of FSA (and previously MAFF), CEFAS carries out an extensive programme for monitoring radioactivity due to Sellafield in the marine environment. This programme is regularly reviewed to allow for changes in discharges, environmental conditions and the habits of critical groups. Monitoring results are published annually, for example [2] and [3], as well as more frequently on the FSA’s web site (www.foodstandards.gov.uk). Selected results from near Sellafield are presented with the discharge data in figures 1-10. Examples have been chosen for species which are of radiological significance to the critical group of fish and shellfish consumers. Sampling and analytical uncertainties are described in the annual reports, but for the purposes of this paper, the concentration data have representative ±10% error bars. Figure 1 presents annual mean concentrations of 3H in plaice (Pleuronectes platessa) from Ravenglass, about 10 km south of the site. Analyses of 3H in marine biota around Sellafield have begun in recent years and there are insufficient data to suggest trends. However, comparison with 3H in seawater around Sellafield suggests that some bioaccumulation is taking place. Figure 2 presents annual mean concentrations of 14C in plaice and cod (Gadus morhua) from the small ‘Sellafield Offshore Area’ about 5km south of the discharge pipeline outlet. A natural background component of 26 Bq kg-1, typical of levels in these species away from anthropogenic sources, has been subtracted. Concentrations reflect discharges though there appears to be a residual effect of discharges following reductions during the late-1990s. In view of the interest in 99Tc, Figures 3 and 4 show concentrations in winkles (Littorina littorea) and lobsters (Homarus gammarus) around Sellafield. Winkles were collected from Ravenglass and Nethertown. Lobsters were obtained from landings at Ravenglass and from the ‘Sellafield Coastal Area’ (SCA). The latter extends 11km offshore between St Bees Head (about 15 km north of the site) and Selker (about 15 km south of the site), though samples were obtained predominantly from the north of this area. Concentrations reflect discharge patterns and there is a lag between peak concentrations and the peak discharge in 1995. It is interesting to note that Ravenglass lobsters show lower concentrations than SCA lobsters, whereas Drigg winkles show higher concentrations than Nethertown winkles. Data for 129I in the seaweed Fucus vesiculosus from St Bees are shown in Figure 5, and concentrations reflect increasing discharges over the period. This seaweed is not eaten but it can be used as a fertiliser. It also provides a useful indicator species since it concentrates the levels due to the low discharges. Figure 6 presents annual mean concentrations of 137Cs in plaice and cod from the ‘Sellafield Offshore Area’. There appears to be a close correlation between concentrations and discharges, both showing the same reductions over the period. However, this correlation needs some caution since it is known that there is a significant contribution due to remobilisation of 137Cs from historic discharges adsorbed on sediments [4].