Tracer Applications of Sellafield Radioactivity in British West Coastal Waters

Nuclear chemistry, Chemical oceanography, Hydrologic sciences

Economides, Beatrice

University:University of Glasgow

关键词: Nuclear chemistry, Chemical oceanography, Hydrologic sciences;   

Others  :  http://theses.gla.ac.uk/77419/1/10991881.pdf

来源: University of Glasgow

【 摘 要 】

In this research study, Sellafield - discharged radioactivity, in particular radiocaesium, is used to trace water movement in west British coastal waters. Data on radiocaesium levels in surface waters of the Hebridean Sea Area, Clyde Sea Area, North Channel and Irish Sea are interpreted along with salinity and other hydrographic results. These data provide information on spatial and temporal property distributions whilst subsurface radiocaesium levels help to improve knowledge of the three-dimensional transport of these waters. In parallel, seaweeds from the west coast of Britain (including N. Ireland, the Isle of Man and the Outer Hebrides) have been analysed for their radionuclide contents. Matching of radiocaesium time-trends at various sites has provided estimates of water transit times between stations (e. g. 4.8 months from Sellafield to the Firth of Clyde) and thus has allowed calculation of nuclide Appearance (Ea) Factors. A 14.4 months' residence time for water in the Irish Sea / Clyde Sea Area system and a maximum decay-time of 17 months between Sellafield and the Clyde Sea Area have been estimated; evidence from sea water and seaweed radionuclide levels suggests that most of this residence occurs in the north eastern Irish Sea. It is proposed that a fraction of the Sellafield - discharged material, particularly in the Irish Sea and probably in surface waters, remains relatively undiluted during transport of the radioactive plume from Sellafield to The Minches, whilst some extensive mixing may occur in deeper and surrounding waters. Restriction of the radioactive plume to the Scottish coast is observed when Atlantic water incursion into the Hebridean Sea Area is strong and the Islay Front attains an easterly position. When Atlantic water influence in the area is weak, the front has a more westerly position and coastal confinement of the plume is less obvious. Observations show that, when the gradient across the front is strong, nearby current velocities are slow and vice versa; current velocity is found to show good correlation with wind speed. Radiocaesium dilutions estimated from Ea values and measured sea water and / or seaweed radiocaesium levels indicate relatively high (twentyfold) dilutions from Sellafield to the North Channel and the Clyde Sea Area but slow dilutions (two-threefold) from the North Channel to The Minches. This finding is confirmed by the observation from radiocaesium and plutonium half-distances, of higher (13 and 4 times) dilution rates within the Irish Sea and Clyde Sea Area (respectively) relative to those in the Scottish coastal current. From the observed Sellafield-Clyde Sea Area transit time, a mean velocity of 1.7 km day-1 is obtained and is applied to the north flowing water of the North Channel to estimate a northwards water flux as 5-10 km 3day-1. The corresponding radiocaesium flux, taking account of reduced subsurface radiocaesium levels, is 1.2 - 4.2 x 10.