Optimization of Routine Monitoring of Workers Exposed to Plutonium Aerosols.

In case of incidental confinement failure, mixed oxide (MOX) fuel preparation may expose workers to plutonium aerosols. Due to its potential toxicity, occupational exposure to plutonium compounds should be kept as low as reasonably achievable. To ensure the absence of significant intake of radionuclides, workers at risk of internal contamination are monitored by periodic bioassay planned in a routine monitoring programme. From bioassay results, internal dose may be estimated. However, accurate dose calculation relies on known exposure conditions, which are rarely available when the exposure is demonstrated by routine monitoring only. Therefore, internal dose calculation is subject to uncertainty from unknown exposure conditions and from activity measurement variability. The present study calculates the minimum detectable dose (MDD) for a routine monitoring programme by considering all plausible conditions of exposure and measurement uncertainty. The MDD evaluates the monitoring quality and can be used for optimization. Here, MDDs were calculated for the monitoring of workers preparing MOX fuel. Uncertain parameters were modelled by probability distributions defined according to information provided by experts of routine monitoring, of workplace radiological protection and of bioassay analysis. Results show that the current monitoring is well adapted to potential exposure. A sensitivity study of MDD highlights high dependence on exposure condition modelling. Integrating all expert knowledge is therefore crucial to obtain reliable MDD estimates, stressing the value of a holistic approach to worker monitoring.

Cancer mortality among two different populations of French nuclear workers.

PURPOSE: The aim of this paper is to study the effect of external photon radiation on the mortality of two populations of French nuclear workers: workers exposed only to external photon radiation and workers potentially exposed also to internal contamination or to neutrons. METHOD: External photon radiation has been measured through individual dosimeters. Potential exposure to internal contamination or to neutrons has been assessed by experts on the basis of quantitative measurements or of worksite and type of activity. The mortality observed in each population was compared with that expected from national mortality statistics, by computing standardized mortality ratios. Dose-effect relationships were analyzed through trend tests and log-linear Poisson regressions. RESULTS: 14,796 workers were exposed only to external photon radiation; 14,408 workers were also potentially exposed to internal radiation or to neutrons. Between 1968 and 1994, the number of deaths is respectively, 645 and 1,197. The mean external photon dose was respectively, 3.7 and 12.9 mSv. Similar Healthy Worker Effects were observed in the two populations (SMR = 0.59). SMR of 2.41 90% CI [1.39-3.90] was observed for malignant melanoma among workers of the second population. Significant dose-effect relationships were observed: among workers exposed only to external photon radiation for leukemia except CLL and in the other population, for cancers and other diseases related to tobacco or alcohol consumption. CONCLUSIONS: Results differed between the two populations. The increase in leukemia risk with dose in the first population will have to be confirmed with extended follow-up. In the other population, results may have been confounded by alpha-emitters inhalation, tobacco, or alcohol consumption.

Lung cancer risk associated to exposure to radon and smoking in a case-control study of French uranium miners.

A case-control study nested in the cohort of French uranium miners took smoking information into account in investigating the effect of radon exposure on lung cancer risk. This study included 100 miners who died of lung cancer and 500 controls matched for birth period and attained age. Data about radon exposure came from the cohort study, and smoking information was retrospectively determined from a questionnaire and occupational medical records. Smoking status (never vs. ever) was reconstructed for 62 cases and 320 controls. Statistical analyses used conditional logistic regression. The effect of radon exposure on lung cancer risk was assessed with a linear excess relative risk model, and smoking was considered as a multiplicative factor. Mean cumulative radon exposures were 114.75 and 70.84 Working Level Months (WLM) among exposed cases and controls, respectively. The crude excess risk of lung cancer per 100 WLM was 0.98 (95% CI: 0.18-3.08%). When adjusted for smoking, the excess risk was 0.85 per 100 WLM (95% CI: 0.12-2.79%), which is still statistically significant. The relative risk related to smoking was equal to 3.04 (95% CI: 1.20-7.70). This analysis shows a relative risk of lung cancer related to smoking similar to that estimated from previous miners' cohorts. After adjustment for smoking, the effect of radon exposure on lung cancer risk persists, and its estimated risk coefficient is close to that found in the French cohort without smoking information.

An update of cancer mortality among the French cohort of uranium miners: extended follow-up and new source of data for causes of death.

The follow-up of the French cohort of uranium miners has been extended to 1994, and a new source of information for causes of death has been used. The paper presents the new results regarding the risk of death among the cohort, and analyses the impact of the methodological changes on these results. The extension of the follow-up results in a substantial increase in statistical power compared with previous analysis (+25% for person-years and +74% for the number of deaths). The use of the National Mortality Database as the principal source for causes of death allows to reduce the potential bias in the calculation of standardized mortality ratios (SMR). As a consequence, an excess risk of deaths from laryngeal cancer, suggested in the first analysis, is not confirmed. The analysis shows the existence of an excess risk of deaths from lung cancer among French uranium miners (85 observed deaths, SMR = 1.9, 95% confidence interval CI: 1.5-2.3), and an increase of this risk with cumulative exposure to radon (excess relative risk per 100 working level month = 0.6, 95% CI: 0.1-1.2). These results confirm the existence of a risk of death from lung cancer in a population chronically exposed to relatively low levels of radon.