Review of the effectiveness of internal dosimetry monitoring regimes.

Routine monitoring is an important element of any occupational radiation protection programme to be able to determine how effective this protection is in practice. As well as providing information on normal operational conditions and routine worker dose uptakes, these programmes are also required to be able to detect the occurrence of abnormal or unexpected exposures to radionuclides, where these risks are deemed to be present in the workplace. Various monitoring techniques and methods are available and can be applied to the direct monitoring of workers or of the workplace. For many of the less radio-toxic radionuclides simple monitoring programmes are often more than sufficient to demonstrate compliance with operational and regulatory controls; however, multiple programmes, operated in parallel, are often required for the more radio-toxic radionuclides-e.g. Plutonium and americium-to be able to provide assurance that the potential risks of exposure are reliably and adequately controlled. When a potential exposure event is detected then further investigations are instigated to confirm whether an intake has occurred and to estimate the resultant dose. This paper presents an empirical review of the records of all such investigations over an eighteen-year period at the Harwell site, Oxfordshire, UK. The purposes of this review were to determine the relative effectiveness of different monitoring methods in being able to detect potential exposure events; and how efficient each method was in detecting potential exposures which, following investigation, were confirmed as real intakes. The analyses revealed that routine faecal sampling provided the better performance characteristics in terms of combined effectiveness and efficiency; and that the ability to detect potential exposures (at levels of up to 6 mSv) in the absence of any routine monitoring programme was limited. There was a very low incidence of potential exposures being detected by more than one monitoring technique, which emphasises the importance of operating multiple monitoring methods in order to optimise the probability and confidence of detecting potential exposures.