The Determination of when Routine Internal Dosimetry Monitoring Is Required

Routine internal dose exposures are typically (in the UK nuclear industry) less than external dose exposures: however, the costs of internal dosimetry monitoring programmes can be significantly greater than those for external dosimetry. For this reason decisions on when to apply routine monitoring programmes, and the nature of these programmes, can be more critical than for external dosimetry programmes. The UK Ionising Radiations Regulations [1] require that all significant doses are assessed and recorded, and the Approved Code of Practice [2] advise that decisions on when monitoring is required is determined by the expected magnitude and variability of personal dose. This leaves the practical problem of how to quantify the expected dose while avoiding the “Catch-22” situation of implementing extensive monitoring programmes simply to provide evidence that they were not required. This paper describes various internal dosimetry risk assessment methods which are employed by Nuvia Limited Approved Dosimetry Services to attempt to provide an objective assessment of when routine internal dosimetry monitoring should be considered. It also discusses the possible shortcomings of these process and potential future development. The paper argues that, for most instances in the nuclear industry, the principle objective of routine internal monitoring programmes is not to monitor exposure to internal dose, but to monitor for the risk of exposure; thereby indicating when more thorough investigations and dose estimation is required, and also providing important feedback to the efficacy of radiological protection measures.