Optimisation des programmes de surveillance systématique de l’exposition interne

Optimisation of routine monitoring programmes of internal contamination. To optimise the protection of workers against ionising radiation, French regulation imposes the use of limits and dose constraints and the progressive decrease of exposition, in line with the recommendations of the International Commission on Radiological Protection. To verify the compliance of the means of protection with these values when a risk of internal contamination exists, monitoring programmes based on periodic bioassay measurements are performed. However, uncertainties in the dose evaluation arise from the variability of the activity measurements and from incomplete knowledge of the exposure conditions. These uncertainties were taken into account by means of Bayesian statistics. The developed methodology was applied to the analysis of the monitoring programme of workers purifying plutonium in the AREVA NC La Hague reprocessing plant. From the decision threshold of the measurement, the minimum dose detectable (MDD) by the programme with a given confidence level can be calculated through the software OPSCI. It is shown to be a useful support for the optimisation of monitoring programmes by seeking a compromise between their sensitivity and their cost.