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DEVELOPMENT OF FUNDAMENTAL DATA FOR RADIATION PROTECTION . PHASE II

Objective

The radiation protection standards recommended by the International Commission on Radiological Protection (ICRP, hereafter called the Commission) have formed the basis for most radiation protection guidelines and regulations which have been issued by international and national institutions or authorities, respectively. They have also been applied in the past by the Commission of the European Community and its member states. Thus the work of ICRP has contributed effectively to an international harmonization of protection standards in this field.

Developments in the last few years have now made it necessary to issue a completely new set of recommendations. In doing so, the Commission has had three aims in mind:
to take account of the new biological information and of trends in the setting of safety standards;
to improve the presentation of the recommendations;
to maintain as much stability in the recommendations as is consistent with the new information.
Adoption of the 1990 Recommendations in radiological protection necessitates a revision of the Commission's secondary limits contained in Limits for Intake of Radionuclides by Workers. New values of Annual Limits on Intake which incorporate the new dose limits, radiation weighting factors and tissue weighting factors, but retaining the metabolic and biokinetic data, have been calculated.

The report discusses radiation effects in the skin, the experimental and epidemiological evidence for radiation induced skin cancer and deterministic effects.
The Commission will recommend an annual limit for workers of 500 mSv for the skin averaged over any 1 cm{2} regardless of the area exposed. This annual equivalent dose is reduced by a factor of 10 for members of the public.

The report on age dependent doses to members of the public from intake of radionuclides will include 12 elements not previously included. Work will proceed on the computation of doses following inhalation of radionuclides, based upon the new tissue weighting factor values and the new respiratory tract model.

A new human respiratory tract model was designed to permit biologically meaningful radiation doses to be estimated, taking into account the effects of smoking, air pollutants and respiratory diseases. Separate parameters are included for deposition, and clearance is considered as 2 competing processes (mechanical clearance in mucus from the airways and translocation through lung tissue to blood and thence to organs of deposition). The report will address the relative radiosensitivity of different regions of the respiratory tract and regional doses within the respiratory tract will be calculated. This approach may necessitate a subdivision of the tissue weighting factor value for lung as used in the 1990 Recommendations. A new dosimetric model will be used to calculate dose in adults, children and infants.

An update will include an appendix on data for nonwestern man. It will give details on elemental and cellular composition of body tissues, andanatomical and physiological parameters for all the major body systems. In particular, data on the fetus and children will be included.

The report will include guidance for the development of procedures to be applied to potential exposures and to the planning of intervention in the event of a nuclear accident or a radiological emergency. Guidance will be given on intervention levels of radon in homes and in the workplace. A particular issue will be the definition of the level of annual exposure to radon at work that leads to workers being considered occupationally exposed.
Task group activities

Several task groups, through the Committees, are aiding the ICRP Main Commission. They include task groups with the following interests.
Risk estimates for cancer and genetic effects at doses appropriate to radiation protection. The data will quantify risks for site-specific cancers related to age and sex and will allow the ICRP to derive tissue weighting factors reflecting the sensitivity of different organs to developing radiation-induced cancers.
Information on the effects of radiation on skin and how this is related to the type of radiation, its penetrative properties, the area of skin involved and the cells at risk. This is relevant to the problem of skin contamination and the recommendation of dose limits in the nuclear industry.
Dosimetry of incorporated radionuclides as a function of age at exposure, thus allowing a prediction of the doses to tissues resulting from accidental exposure of members of the public following a major radionuclide release into the environment. A report on isotopes of hydrogen, carbon, strontium, zirconium, niobium, ruthenium, iodine, caesium, cerium, plutonium, americium and neptunium has already been published. An impending second report will include age-dependent biokinetic data for the elements sulphur, cobalt, nickel, zinc, silver and tellurium.
A critical examination of particle deposition in the human respiratory tract and the doses associated with the subsequent mechanical clearance of particulates and the translocation of radioactive materials to blood and to eventual sites of deposition. This study will update the current ICRP lung model used for dosimetry.
New information on the mass, dimensions and elemental composition of tissues and organs paying particular attention to normal variations at different ages and in different races. This information is necessary for dosimetric modelling of incorporated radionuclides.
A set of logical principles on protecting the public in the event of a major radiation accident, considering the consequences in the long term as well as immediately after the accident, and in the far field as well as the near field.
The application of principles of radiation protection and safety in considering exposures not intended to occur (potential exposure).
Measures for protection against radon, considering the establishment of intervention levels in houses and workplaces, and the various remedial measures available with their cost and effectiveness.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

International Commission on Radiological Protection (ICRP)
Address

OX11 0RJ Didcot
United Kingdom