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Sellafield Discharges
The British Nuclear Fuels reprocessing plant
at Sellafield remains the largest single cause of exposure to
artificial radionuclides. Doses resulting from operational discharges
are low and, on the basis of current scientific understanding,
do not pose a significant health risk at this time. However, the
potential risk of contamination which might occur as a result
of accidents remains a cause for concern.
Radiological Protection Institute of Ireland
Since the early 1950s, low-level liquid radioactive wastes have
been discharged into the north-eastern Irish Sea from the British
Nuclear Fuels Plc (BNFL) Sellafield establishment formerly known
as Windscale.
Initially, the major source of these discharges was the processing
of nuclear fuel for the production of nuclear weapons. Since the
late 1950s, operations have been dominated by the reprocessing
of fuel from commercial nuclear power programmes.
The most significant low-level radioactive wastes result from
water used to purge the cooling ponds used for keeping spent fuel
elements (Magnox), and from the reprocessing plant where low-level
liquid waste is collected and neutralised in "sea tanks"
before being discharged to sea at around high tide.
Authorised discharges take place through a series of pipelines
extending 2.5km seaward of the high-water mark, with a very much
smaller level of radioactivity being discharged via Sellafield's
sewers.
Discharges from Sellafield have always been subject to controls
by governmental departments or regulatory agencies in the UK.
Currently, authorisation to discharge is granted to BNFL by the
UK Environment Agency.
Over the years, the Sellafield discharges have acted as a large
point source of alpha (α), beta (β) and gamma (γ)
emitting radionuclides originating from both fission and neutron
activation processes. This has resulted in significant increases
of artificial radionuclide concentrations in parts of the Irish
Sea marine environment and beyond, with minute traces detectable
as far away as the Central Arctic Ocean.
The environmental impact of Sellafield's discharges depends mainly
on the way in which discharged radionuclides are dispersed and
accumulate in the Irish Sea.
The spatial and temporal distributions of Sellafield-derived
radionuclides are governed by a number of complex mechanisms.
Some important factors that influence their behaviour include
the rate of input from authorised discharges, their chemical speciation
on the effluent and upon contact with seawater, prevailing hydrographic
conditions, and their interactions with suspended particles, sediments
and biota.
Effects of Sellafield discharges
on harbour porpoises
A 1999 study by the Radiological
Protection Institute of Ireland and University
College Cork to assess radionuclide contamination in harbour
porpoises (Phocoena phocoena) in the Irish Sea waters found
the radioactivity dose to be insignificant.
As top-level predators, harbour porpoises and other cetaceans
receive radioactive contamination via transfer up through the
food web of radionuclides present in the marine environment.
Muscle samples from 25 porpoises stranded on the coasts of Britain
and Ireland or from fisheries bycatch in Irish coastal waters
were analysed for artificial caesium-137 and naturally occurring
potassium-40 radionuclides. The average levels of caesium-137
measured were some ten times higher in porpoises from the Irish
Sea (17.8 Becquerels per kilogram-¹) compared to those from
the Atlantic (1.9 Bq/kg-¹), Celtic Sea (1.7 Bq/kg-¹)
and North Sea (2.4 Bq/kg-¹).
These results are consistent with monitoring studies that show
that levels of caesium-137 are higher in marine life from the
Irish Sea than from the Atlantic, Celtic and North Seas.
Average levels of potassium-40 (94.7 Bq/kg-¹) in porpoises
were much greater than those of caesium-137 and did not vary between
the different sampling locations.
The average level of caesium-137 measured in fish landed at
Irish Sea ports during the same period was about 3.0 Bq/kg-¹.
Porpoises consume a range of fish species; their average dose
level (17.8 Bq/kg-¹) shows that the levels of caesium-137
increase with trophic level (the different feeding levels within
an ecosystem).
The study concluded that the dose to porpoises from radioactivity
in the marine environment was calculated and found to be insignificant.
"Thus, despite the elevated levels of caesium-137 in Irish
Sea porpoises relative to those from the Atlantic, Celtic and
North Seas, the resulting radiation dose is unlikely to have had
a detrimental effect on their health."
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