Contribution of the French society for radiation protection to the current reflections on the possible improvements of the radiological risk management system. Following the invitation from IRPA to comment on the article written by Professor Roger Clarke entitled "Control of Low Level Radiation Exposure: Time for a Change?", the Board of the French Society for Radiation Protection (SFRP) decided to set up a working group on "controllable dose". The latter, which worked from April 1999 to July 2000, consisted of some twenty members representing the stakeholders involved in radiological protection in France: authorities, experts and professionals from nuclear, medical and research fields as well as associative movement. The present article, which has been approved by the Board of SFRP, summarises the findings of the WG presented during the IRPA-10 Congress in May 2000. The WG first examined the current hypothesis on radiological risk and noted their relevance for a practical management of such a risk. Then, a list of the different exposure situations and their associated characteristic was elaborated in a table form, followed by a discussion on the situations when the system of radiological protection fits well, less well or bad, particularly through the implementation of the general principles of radiological protection. The WG finally made proposals to ICRP for an evolution of the system towards a more operational way.

Radiological impact assessment of very low-level radioactive waste management pathways. Two approaches are currently being adopted for the management of very low-level waste (VLLW): disposal in surface facilities and, for some categories of VLL waste, the implementation of treatment and utilisation channels. In this paper, the orders of magnitude of the radiological consequences which may result from these two options are discussed, in a matter of a description rather than a comparison. As regards disposal, radiological impact is presented through a generic case, along with the uncertainties stemming from the variability of the parameters associated with its design, as well as those associated with the geosphere and the biosphere. In the case of treatment and utilisation channels, such as disposal or recycling of VLL waste oils or VLL wastes containing asbestos, the assessment of radiological consequences deals with the public exposure and with the occupational exposure on the basis of a stage-by-stage breakdown of the industrial process.

In the case of accidental exposure to ionising radiation, estimation of the absorbed dose in the organism is an important indicator for evaluating the biological consequences. To complete the clinical and biological investigations, physical dosimetry methods can be used to provide an estimate of the absorbed dose and its distribution in the organism. This article describes the development of calculation tools in physical dosimetry, in particular a numerical anthropomorphic phantom which can be adapted to each individual. A standard model was developed from the data available in the ICPR Publication 23. A set of tests was carried out with the model dimensions being modified to study the effect of morphology on the dose calculation. A comparison was made with another standard model used in internal dosimetry. These studies highlight the parameters to be taken into account in the model, depending on whether the accident is local or global.

Although great efforts had been made to improve the physical phantoms used for calibrating in vivo measurement systems, for technical reasons they can only provide a rough representation of human tissue. Substantial corrections must therefore be made to calibration factors obtained with such calibration phantoms for extrapolation to a given individual. These corrections are particularly crucial and delicate in low-energy in vivo measurement when absorption in tissue is significant. To improve calibration for such special conditions, the possibility has been raised of using voxelised numerical phantoms associated with Monte Carlo computing techniques. In the method described below, a mathematical phantom, consisting of a voxelised representation derived from scanner images is used, with a specially-designed interface making it possible to not only reconstruct widely-differing contamination configurations and specify associated tissue compositions, but also automatically create an MCNP4b input file. After validation of the different sources and geometries, the complete procedure of reconstruction of the phantom and simulation of 241Am lung measurement was carried out using a tissue equivalent calibration phantom of the type commonly used for lung calibration for actinides. The purpose of this work was to extend the use of this principle to the reconstruction of numerical phantoms on the basis of physiological data of individuals obtained from magnetic resonance and scanner images. The results obtained and the current limitations of this approach in the context are discussed.