Monte-Carlo prediction of changes in areas of west Cumbria requiring restrictions on sheep following the Chernobyl accident

Abstract

Following the 1986 Chernobyl accident radiocaesium levels in sheep meat in some upland areas of the United Kingdom were above the national intervention limit. West Cumbria was one of these areas and restrictions are currently still in place. In addition to deposition from the Chernobyl accident, Cumbria has been subject to radiocaesium deposition from atmospheric nuclear weapons tests, the 1957 Windscale accident and routine releases from the Sellafield nuclear reprocessing plant. A Monte-Carlo approach has been used to try to predict areas in west Cumbria where radiocaesium activity concentrations in lamb meat would require the imposition of restrictions at different times after the Chernobyl accident. The approach models the transfer of radiocaesium from soil to vegetation, based upon soil organic matter, and from vegetation to lamb meat. Spatial inputs are soil organic matter and total post-Chernobyl (137)Cs and (134)Cs deposition; a ratio of Chernobyl (137)Cs to (134)Cs deposition has been used to differentiate Chernobyl and pre-Chernobyl (137)Cs deposition. Comparisons of predicted radiocaesium transfer from soil-vegetation and the spatial variation in lamb (137)Cs activity concentrations are good and predicted restricted areas with time after Chernobyl compare well to the restricted areas set by UK government. We predict that restrictions may be required until 2024 and that in some areas the contribution of pre-Chernobyl (137)Cs to predicted lamb radiocaesium activity concentrations is significant, such that restrictions may only have been required until 1994 as a consequence of Chernobyl radiocaesium deposition alone. This work represents a novel implementation of a spatial radioecological model using a Monte-Carlo approach.

Observations of Fukushima fallout in Great Britain

“…The highest concentrations were from areas which received comparatively high levels of 137 Cs from previous sources (i.e. above ground weapons tests, the 1957 Windscale accident and the 1986 Chernobyl accident) (Wright et al, 2003).…”

Inter-varietal variation in caesium and strontium uptake by plants: a meta-analysis

“…These radionuclides are of particular concern as they have relatively long half-lives ( 137 Cs z 30 years; 134 Cs z 2 years; 90 Sr z 29 years) and relatively high biological availability. Radioisotopes of caesium were the primary long-term contributors to human doses received after the Windscale (1957;Wright et al, 2003) and Chernobyl (1986;IAEA, 2006) accidents, and are now the principal radiological concern in areas affected by the accident at Fukushima in 2011 (Nakanishi and Tanoi, 2013). Strontium-90 is a major contributor to doses in areas contaminated by the Mayak accident (1957;Balanov et al, 2007) and is present in soils of the Chernobyl Exclusion Zone at activity concentrations approaching those of 137 Cs (Kholosha, 2008).…”

Factors contributing to radiocaesium variability in upland sheep flocks in west Cumbria (United Kingdom)

“…At the time of sampling this would result in a Chernobyl 137 Cs: 134 Cs ratio of circa 12 as a result of physical decay (the exact ratio varying between farms depending upon sampling time). Wright et al (2003) derived this radiocaesium ratio from 156 measurements of cow milk collected within Cumbria in the aftermath of the Chernobyl accident (MAFF/WO, 1987); the 137 Cs: 134 Cs ratios ranged from 1.08 to 2.54 in individual samples and the value used is in agreement with other estimates from more restricted data sets for Cumbria (see Wright et al, 2003 for comparison).…”

“…To determine the contribution of these 'aged' sources the total 137 Cs activities determined in soil and vegetation samples a 137 Cs: 134 Cs ratio of 1.7 in Chernobyl fallout in west Cumbria as derived by Wright et al (2003) for Cumbria was assumed. At the time of sampling this would result in a Chernobyl 137 Cs: 134 Cs ratio of circa 12 as a result of physical decay (the exact ratio varying between farms depending upon sampling time).…”