Monitoring intakes of radionuclides by nuclear power plants workers in France: materials, methods and results

EDF (Electricite de France) owns 57 operating reactors distributed on 20 sites. Individual monitoring for intakes of radionuclides is done by whole body gamma countings and excretion bioassays. This monitoring concerns all EDF workers (about 20,000), and also subcontractor personnel (about 40,000 people per year). The aim of monitoring is to detect any intake above the recording level and to assess, as precisely as possible, internal doses. ICRP publications no.30 and 54 are used for internal dose calculations. Whole body countings (approximately 200,000 per year) are made by occupational health services on each nuclear site. The equipment consists of: 1. two whole body counters with two large NaI detectors, the approximate detection limit is 150 Bq in Co-60 for a 1-minute count. 2. one shielded chair with two smallers NaI detectors (one for thyroid and one for thoraco-abdominal region), specially designed for iodine contamination case, or casualties on stretchers. A special medical software program incorporates: 3. an operating system containing a module to ensure the quality control of measurements. 4. a measurement interpretation system with a screening histogram facility for activity alarm levels and spectrometry gamma analysis. 5. an administrative database for nationwide monitoring of all EDF and non-EDF workers. An EDF central radiotoxicology laboratory, located in the suburbs of Paris, analyses all the biological samples (about 8,000 per year, urines, faeces or nose blows) and centralises the results. At the occupational health service's request, the following analyses can be done: 1. tritium activity measurements (liquid scintillation) with a detection limit of 75 Bq per litre, 2. gamma spectrometry (HPGe detectors) on urines and faeces ash samples with a detection limit of 0.5 Bq per sample for one hours of counting. 3. alpha spectrometry (after chemical treatment) on urines and faeces ash samples with a lower detection limit of 0.2 mBq per sample for 72 hours of counting, 4. Beta and alpha total counts (ZnS scintillators) on nose blows used for monitoring alpha risks. 5. Quality assurance programs are applied for measurements and also for dose assessments. For the measurements, especially for low activities of alpha emmiters, yearly comparison exercises are organized by PROCORAD association (CEA and COGEMA laboratories). More than 50 European and American laboratories have participated in recent years. By another way, OPRI, the radiation protection office of the Ministry of Health, organises intercomparison measurements of laboratories. For the quality control on dose assessment, the EDF laboratory participates in the comparison exercises planned by EURADOS-CENDOS Working Group 6. Routine, operational and special monitoring programs are carried out. The results are given with the dominant radionuclides indicated. These results shows that the collective effective dose is extremely low: 257 man-mSv for 90 cases over 16 years. The protection methods used appear to be effective. Nethertheless, in some special cases, adding effective dose to external exposure doses could lead to a total dose higher than the regulatory limits. (author)