Characterisation of airborne uranium and thorium contamination in Northern England through measurement of U, Th and 235U/238U in tree bark

Abstract

Samples of tree bark were collected from four locations in Northern England (a typical rural site, a coal-fired power station, a uranium (isotopic) enrichment plant and a nuclear fuel fabrication facility), to assess the nature and extent of airborne uranium and thorium contamination. The U and Th concentrations of bark were determined by inductively coupled plasma mass spectrometry after conventional nebulisation of bark digests, whilst measurement of 235U/238U isotopic ratio utilised high efficiency nebulisation. Uranium concentrations varied between and within the sites (range, 0.01-12 micrograms g-1), with maximum values recorded within 1 km of the nuclear fuel fabrication plant (Springfields). In comparison, the concentration of Th in bark was low (mean, 0.018 microgram g-1) at all sites with the exception of the area affected by coal combustion (0.2-0.8 microgram g-1). The U/Th ratio varied from 0.5 to 3900 compared with the average crustal ratio of 0.3. Low values (< 2) were recorded at the 'coal' and 'rural' sites whilst Capenhurst and Springfields showed high values indicating the relative magnitude of uranium elevation. Significant enrichment of the natural 235U/238U ratio (0.00725) was observed near the nuclear installations, in particular, the enrichment plant (Capenhurst).

Preliminary results of spatial distribution of uranium and thorium in soil profiles near a uranium industrial site, Guangdong province, China

“…In particular, the U/Th ratio may distinguish U resulting from the artifi cial sources such as manufacture of nuclear fuels, coal--combustion or from natural sources and indicate the relative level of U elevation [12]. In the present study, as shown in Fig.…”

“…Many researchers use concentration ratios of U/Th to illustrate the U-related enrichment or contamination [12,13]. In particular, the U/Th ratio may distinguish U resulting from the artifi cial sources such as manufacture of nuclear fuels, coal--combustion or from natural sources and indicate the relative level of U elevation [12].…”

Characterization of radionuclide activity concentrations and lifetime cancer risk due to particulate matter in the Singrauli Coalfield, India

“…This range is different from the average crustal ratio of 3.5, indicating that 238 U concentrations were elevated in this region relative to Th (Cowart and Burnett 1994); these events are the main factors in the increase of the concentration of 232 Th. The lower ratio of 232 Th/ 238 U is a potential indicator of the source and relative elevation of U concentrations (Bellis et al 2001), due to none of above factor has changed levels of 232 Th. The hypothesis is reinforced that the core of uranium growth in PM comes from atmospheric degradation.…”

Utilisation des isotopes de l’uranium et du rapport U/Th pour évaluer le marquage des végétaux consécutif aux rejets d’uranium des installations du cycle du combustible

“…En effet, les variations des rapports 235 U/ 238 U et 236 U/ 238 U en fonction de l'activité en uranium dans l'environnement peuvent permettre de distinguer les deux laurent.pourcelot@irsn.fr sources principales de l'uranium : l'uranium provenant des rejets des installations, lorsque les process industriels modifient les rapports isotopiques de l'uranium et l'uranium provenant du fond radiologique. Ainsi, l'augmentation de l'activité en uranium est proportionnelle à l'anomalie du rapport massique 235 U/ 238 U (la valeur du fond radiologique est de 0,72 %), attestant, selon le cas, de la présence d'uranium appauvri ou d'uranium enrichi (Pettersson et Holm, 1992 ;Bellis et al, 2001 ;Howe et al, 2002 ;Pourcelot et al, 2011b). De la même façon, une matrice de l'environnement influencée par les rejets de l'uranium de retraitement (URT) est marquée par la pré-sence de l' 236 U (isotope artificiel) (Ketterer et al, 2003 ;Lloyd et al, 2009 ;Pourcelot et al, 2011c ;Tortorello et al, 2014).…”