An incident occurred in a materials science and metallurgy laboratory during the examination of an irradiated sample of reactor fuel assembly. The incident leads to a puncture point contamination of the operator at the end of the 3rd finger of the left hand. The contaminant was mainly Ru-106 with its daughter Rh-106. The paper reports the activity and dose assessment, which have been performed by several methods.
The activity measurement has been obtained using a conventional device based on a germanium detector. The results were confirmed using a software developed in our laboratory based on reconstruction of voxel phantom associated to the Monte-Carlo N-Particle code (MCNP) for in vivo measurement. The software discussed here enables automatic creation of an MCNP input data file based on scanning data. The utility includes the specification of the nature and the configuration of both the source and the detector. The segmentation of the images, obtained either with computed tomography (CT) or with magnetic resonance imaging (MRI), is realised by distinguishing tissues according to their signal (brightness). The results obtained by this method, in the cases of a calibration phantom and of biological samples, were in good agreement with the corresponding measurements. The study presented here is the first application of this technique on a real human contamination case.
Concerning the dose estimation, three calculations have been performed using both analytical and Monte Carlo methods. The first one, which is used as a reference method in France, deals with a homogeneous skin contamination either superficial or in depth. This approach lies on the analytical calculation of the dose experimented by the basal cells. This method calculates the dose using the value of the activity expressed per centimetre square. To deal with local contamination, the model assumes a contaminated surface of 1cm², which is not completely satisfying in case of punctual contamination. To improve the calculation in such case and to be able to deal with wound contamination cases, the last two methods have been developed. They are based on the voxelisation of the contaminated tissue coupled with the MCNP code, which calculates the radiation transport and allows dose recording within each voxel. One of those methods considers the contaminated tissue as a homogeneous medium, the other one takes into account the personal numerical phantom of the contaminated people (phantom already introduced above for the activity assessment).
The results are compared together and the suitability of the tools described in this study is discussed. This case of contamination shows the potential of the presented methods as a basis for wound monitoring.
(1) IRSN (Institut de Radioprotection et de Sûreté Nucléaire), Département de Protection de la santé de l'Homme et de Dosimétrie, BP17, 92262 Fontenay-aux-Roses Cedex, France.
(2) Service de Radiologie, HIA Percy - 92141 Clamart cedex, France
(3) Electricité de France (EDF-GDF), SCAST, Immeuble Becquerel, 6, rue Ampère F- 93203 Saint-Denis, France