title: Should we ignore U-235 series contribution to dose?
abstract: Environmental Risk Assessment (ERA) methodology for radioactive substances is an important regulatory tool for assessing the safety of licensed nuclear facilities for wildlife, and the environment as a whole. ERAs are therefore expected to be both fit for purpose and conservative. When uranium isotopes are assessed, there are many radioactive decay products which could be considered. However, risk assessors usually assume (235)U and its daughters contribute negligibly to radiological dose. The validity of this assumption has not been tested: what might the (235)U family contribution be and how does the estimate depend on the assumptions applied? In this paper we address this question by considering aquatic wildlife in Canadian lakes exposed to historic uranium mining practices. A full theoretical approach was used, in parallel to a more realistic assessment based on measurements of several elements of the U decay chains. The (235)U family contribution varied between about 4% and 75% of the total dose rate depending on the assumptions of the equilibrium state of the decay chains. Hence, ignoring the (235)U series will not result in conservative dose assessments for wildlife. These arguments provide a strong case for more in situ measurements of the important members of the (235)U chain and for its consideration in dose assessments.
authors.affiliation: Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PRP-ENV, SERIS, LM2E, Cadarache, France. Electronic address: karine.beaugelin@irsn.fr.
authors.forename: Karine
authors.initials: K
authors.lastname: Beaugelin-Seiller
authors.affiliation: Canadian Nuclear Safety Commission, P.O. Box 1046, Station B, 280 Slater Street, Ottawa, ON K1P 5S9, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Goulet
authors.affiliation: Canadian Nuclear Safety Commission, P.O. Box 1046, Station B, 280 Slater Street, Ottawa, ON K1P 5S9, Canada.
authors.forename: Steve
authors.initials: S
authors.lastname: Mihok
authors.affiliation: NERC Centre for Ecology & Hydrology, CEH-Lancaster, Lancaster Environment Centre, Library Avenue, Bailrigg, Lancaster LA1 4AP, UK.
authors.forename: Nicholas A
authors.initials: NA
authors.lastname: Beresford
mesh_terms: D000818:Animals; D000835:Animals, Wild / Q000378:metabolism*; D006801:Humans; D060106:Lakes / Q000032:analysis; D011829:Radiation Dosage; D011834:Radiation Monitoring; D011868:Radioisotopes / Q000032:analysis*; D018570:Risk Assessment; D012525:Saskatchewan; D014501:Uranium / Q000032:analysis
chemical_list: D011868:Radioisotopes; D014501:Uranium
keywords: Decay chain; Dose assessment; Uranium; Wildlife