e-Digest Statistics about: Radioactivity
Artificial Sources of Radiation
Exposure from liquid effluents
Most of the liquid effluents are discharged to the sea following treatment to remove as much radioactivity as practicable. Some liquid discharges are made to inland waters. Sea water, and to a lesser extent fresh water, are already naturally radioactive with uranium, 210Po and 40K species. Even distilled water contains the naturally occurring radionuclide ³H produced in the atmosphere by cosmic rays. However, traces of artificial radionuclides are detected in the biota in the waters receiving the liquid effluents.
The table 'Annual emissions of radioactive liquid discharges by site' shows liquid discharges for each nuclear site. Authorisations setting annual numerical limits to the levels of radioactivity in liquid discharges cover all the major establishments (see footnotes to this table). In 2000 and 2001, liquid discharges at all sites were within the authorised limits. There were increases in liquid discharges from Sellafield for 14C and 99Tc in 1995 as a result of the resumption of processing wastes which had been stored pending the availability of the, now operational, Enhanced Actinide removal plant (EARP); discharges of 14C and 99Tc have since fallen. The Thermal Oxide Reprocessing Plant (THORP) began a period of active commissioning in 1994 and has been operational since 1997. Liquid discharges from THORP are relatively low, although it does add to ³H discharges and is the main source of cobalt-60 discharges from the site since 1997.
The Key Fact 'Discharges for the nuclear industry' shows total discharges since 1983 to water, for the sites listed in the table 'Annual emissions of radioactive liquid discharges by site', and to air, for the sites listed in the table 'Annual emissions of radioactive atmospheric discharges by site'. As different radionuclides have different toxicities, the discharge data have been weighted, using discharges of 137Cs as the baseline, to take account of the relative toxicities. These totals have been indexed, with 1985 as the base year. This shows that discharges have reduced over this period.
Discharges from Sellafield are the main source of artificial radioactivity in the UK marine environment. The figure Concentration of caesium-137 in the Irish Sea shows the concentrations of 137Cs in the Irish Sea for 1980, 1990, 1995 and 1996. the figures Concentration of caesium-137 in the North Sea and Concentration of tritium in the North Sea show respectively, for 2000, 137Cs and ³H concentrations in the North Sea. The figures Concentration of caesium-137 in surface water in the Irish Sea and Concentration of tritium in the Irish Sea show respectively 137Cs and ³H concentrations in the Irish Sea for 2000 and 2001. The concentrations data were obtained using samples of seawater collected during research vessel cruises undertaken every 2-3 years by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) an agency of Defra. The large decrease in concentrations of 137Cs in the Irish Sea between 1980 and 1996 reflects the reduction from 3,000 TBq to 10 TBq in annual marine discharges of 137Cs from Sellafield over the same period. Marine discharges of 137Cs from Sellafield have fluctuated slightly since 1996 but have remained at less than 10TBq during that period (see table 'Annual emissions of radioactive liquid discharges by site'). Average concentrations of 137Cs in the large volume of the Irish Sea changed little between 1990 and 2001.
Consumption of fish and shellfish, and external exposure at intertidal pathways, are the main sources leading to radiation exposure from liquid discharges. Radioactivity levels in fish and shellfish, and external exposure in the intertidal areas in the vicinity of the major nuclear establishments and further afield, were monitored independently formerly by MAFF/Defra and now by CEFAS on behalf of the Food Standards Agency. This is carried out to verify the satisfactory control of radioactive waste discharges to the aquatic environment and to ensure that the resulting public radiation exposure, in particular the exposure of critical groups, is within nationally accepted limits. The table 'Radioactivity concentrations in some samples of fish ...' shows concentrations in fish and shellfish sampled at or around nuclear installations. The table 'Estimates of public radiation exposure to radioactive liquid discharges' shows trends in estimated radiation exposure from radioactive liquid discharges to critical groups. Details of the critical groups, the pathways through which they are exposed, the levels of exposure of such groups and the top two contributors to dose in 1999 from discharges of radioactive liquid waste from nuclear sites are given in Table 'Estimates of public radiation exposure from discharges of liquid radioactive waste in the UK'. Discharges from more than one site may contribute to the exposure of the critical group and thus the levels of exposure given in the tables may, in some cases, include a contribution from more than one site. Discharges from Sellafield give rise to the highest exposures from artificial radionuclides and contribute to exposures near many other nuclear sites around the United Kingdom. However, discharges of radioactivity, excluding ³H, to the marine environment from Sellafield in 2000 were around 1 per cent of the peak levels in the 1970s. As a result, the radiation dose to the local critical group (consumers of large quantities of local seafood) from marine discharges has fallen. The estimated dose of 0.15 mSv in 2001 is well within the dose limit of 1 mSv/year from artificial radiation.
Wastes discharged as part of an industrial process from a chemical works in Whitehaven, Cumbria are also a source of radiation exposure of the public (see the table 'Estimates of public radiation exposure to radioactive liquid discharges'). These wastes contain natural radionuclides, in particular 210Po, that results in exposure levels above background ones. From mid-1992, changes in the manufacturing process, combined with operation of an effluent treatment plant, resulted in a large decrease in the quantities of radionuclides discharged. In 2001, exposures of local fish and shellfish consumers were assessed as between 0.19 and 0.42 mSv. Details of other radioactive liquid discharges and associated environmental impacts are reported in "Radioactivity in Food and the Environment, 2001" [18].
Trends in the collective dose to the UK population from liquid discharges, between 1976 and 1997, are shown in the table 'Estimated collective dose from consumption of fish and shellfish'. Dose estimates were calculated by combining annual data on fish and shellfish landings in the UK, with concentrations of radionuclides sampled in fish and shellfish in the appropriate areas and the amounts of fish and shellfish consumed annually by the population. The collective dose was mainly from fish (via radiocaesium) because the consumption of shellfish, and hence its contribution to the collective dose, was relatively minor. The annual collective dose calculation for the UK population was not continued beyond 1997.
In Detail:
Exposure to the public through discharges from nuclear installations
Further Information:
- Key Facts:
- Sources
- Artificial sources:
- Occupational radiation
- Medical
- Fallout
- Products
- Direct shine
- Discharges
Data Tables:
- Figures:
- 8 Concentration (Bq kg-1) of caesium-137 in the Irish Sea: 1980, 1990, 1985 and 1996
- 9 Concentration (Bq kg-1) of caesium-137 in the North Sea: 2000
- 10 Concentration (Bq kg-1) of tritium in the North Sea: 2000
- 11 Concentration (Bq kg-1) of caesium-137 in surface seawater from the Irish Sea: September 2001
- 12 Concentration (Bq kg-1) of tritium in the Irish Sea: 2001
- References, further reading and links to other resources:
- [1] Hughes, J S, National Radiological Protection Board (1999). Ionising Radiation Exposure of the UK Population: 1999 Review, NRPB-R311. TSO.
- [18] Food Standards Agency, Scottish Environment Protection Agency (2000). Radioactivity in Food and the Environment, 2001 (RIFE-7) FSA/SEPA
- Amersham plc: Environment and social report - radioactivity
- Department for Environment Food and Rural Affairs (Defra): UK Strategy for radioactive discharges 2001-2010
- Food Standards Agency (FSA): Radioactivity in Food
- OSPAR Commission for the protection of the marine environment of the North East Atlantic
- OSPAR (2002) Publications 158: ISBN 0 946956 91 XLiquid discharges from nuclear installations in 2000
- OSPAR (2002) Publications 161: ISBN 0 946956 90 1Discharges of radioactive substances into the maritime area by non-nuclear industry
- Internet Links:
- British Nuclear Fuels plc (BNFL)
- British Energy Generation
- Centre for Environment, Fisheries and Aquaculture Science (CEFAS)
- United Kingdom Atomic Energy Authority (UKAEA)
- National Dose Assessments Working Group (NDAWG)
- UK Marine Special Areas of Conservation: Radioactive substances
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Page last modified: 16 September 2003
Page published: 10 September 2003