Dose distribution measurements and calculations for Dounreay hot particles

AS Aydarous, Monty Charles, PJ Darley

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

Discrete fragments of irradiated nuclear fuel have been discovered on the foreshore at the Dounreay nuclear site in Scotland, offshore on the seabed and at nearby beaches which have public access. The fragments contain mainly Cs-137 and Sr-90/Y-90 and for particles recovered to date, Cs-137 activities are within the range of 10(3) to 10(8) Bq. The most active particles found at Sandside Beach contain similar to 3x10(5)Bq Cs-137. Direct measurements of the spatial dose distributions from 37 fuel fragments were measured in detail for the first time using radiochromic dye film as part of a national evaluation of the associated potential radiological hazard. Monte Carlo code calculations of the doses are in good agreement with measurements, taking into account variations to be expected due to differences in shape and the increasing importance of self-absorption for the larger, more active fragments. Dose measurements provide little evidence for wide variations in the Cs-137:Sr-90/Y-90 ratio between fragments. Specific attention is given to the evaluation of skin dose, averaged over an area of 1 cm(2) at a depth of 0.07 mm, since this is of major radiological concern. There is no obvious dependence of skin dose on the site of origin of the fragments (foreshore, seabed or beaches) for a given Cs-137 activity level. A dose rate survey instrument (SmartION) was shown to provide a rapid and convenient method for skin dose assessment from fuel fragments in the Cs-137 activity range measured (2x10(5) to 2x10(7) Bq). A conversion factor multiplier of 240 can be applied to the open window SmartION scale reading to estimate the skin dose rate within +/- 25%.
Original languageEnglish
Pages (from-to)146-158
Number of pages13
JournalRadiation Protection Dosimetry
Volume128
Issue number2
DOIs
Publication statusPublished - 1 Jan 2008

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