Occupational exposures worldwide and revision of international standards for protection.

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) has become the world authority on the levels and effects of ionising radiation. Since 1975, UNSCEAR has evaluated inter alia the level of occupational exposure worldwide. Based on revised questionnaires, more detailed information is now available. The results of the last evaluation (1995-2002) will be shown in the paper. Lessons learned from the responses by UN Member States will be given, as well as an outline of plans for data collection in future cycles. The requirements for protection against exposure to ionising radiation of workers, the public and patients are established in the International Basic Safety Standards for Protection against Ionising Radiation and for the Safety of Radiation Sources (BSS), published in 1996. As a result of a review of the BSS in 2006, the International Atomic Energy Agency (IAEA) started a process for the revision of these standards in 2007. International organisations including the joint sponsoring organisations of the BSS-IAEA, FAO, ILO, OECD/NEA, PAHO and WHO--as well as potential new joint sponsoring organisations of the revised BSS--the European Commission and UNEP-were involved from the beginning in the revision process. The paper also provides a summary of the status of the Draft Revised BSS and describes the new format. The paper focuses, in particular, on requirements for the protection of workers as well as recordkeeping requirements, which provide the legal basis for the collection of specific data; these data are of the type that can be used by UNSCEAR.

Derived emergency reference levels for the introduction of countermeasures in the early and intermedia phases of accidental releases to atmosphere

When an unplanned release of radioactive material to atmosphere is identified or suspected, environmental survey teams under the direction of the operator of the nuclear installantion are sent into the anticipated path of the plume of activity to make measurements and take samples. In the case of external dose, measurements can be easily related to projected doses to individual memebers of the public. However, the radiological interpretation of measurements of airbonrne activity concentrations, of activity levels on soil, pasture grass and crops, and of radionuclide levels in milk and drinking water requieres the use of quantities which relate the appropriate environmental concentration to an implied dose. The derivation of these quantities is not a simple procedure, particularly when they are to be generally applicable. It involves interpretation of the primary dose criteria which have been established for planning the introduction of countermeasures, making assumptions about the habits of the group of people who could receive the highest doses, and using mathematical models to obtain a relationship between dose and activity concentrations in environmental materials. The paper describes recent work by the National Radiological Protection Board (NRPB) to provide guidance on derived quantities for use in the United Kingdom (UK). While some of the numerical values obtained are specific to UK condiditons, the methods are more generally applicable. (AU)

An assessment of the radiological impact of the Windscale reactor fire, October 1957.

On the 10th and 11 October 1957 a fire in the No 1 Pile at the Windscale establishment in Cumbria led to an uncontrolled release of activity to the atmosphere. The resultant cloud subsequently dispersed and radionuclides could be detected over England, Wales and parts of northern Europe. The extensive environmental measurements which were made during and after the release enabled a fairly accurate estimate to be made of the radiation doses to the most exposed individuals in the local population. Until recently, no estimates of the population dose resulting from the release had been published. This paper describes assessments which have been made by the NRPB of the population or collective dose from the release and of the possible associated health impact. In addition to the fission products that escaped, radionuclides were released from materials undergoing irradiation in the pile at the time of the fire. The assessment has included the results of a review of previously unpublished data which established the quantity of these nuclides released and considers their impact on both individual and population doses. The collective effective dose equivalent commitment from the release is estimated to have been 2.0 x 10(3) man Sv. The route of exposure which contributed the most to the collective dose was the inhalation pathway. Iodine-131 was the most important radionuclide, contributing nearly all of the collective dose to the thyroid and a large part of the collective effective dose. Polonium-210 and caesium-137 also made significant contributions; that from caesium-137 came in the longer term via external irradiation from ground deposits and the ingestion of contaminated foodstuffs. The methodology used in the study has been validated to a certain degree by comparing the predicted levels of individual thyroid activity and those measured directly in the weeks following the accident in London, Leeds and Cumbria.

Models for the transfer of radionuclides in cattle for use in radiological assessments.

In performing assessments of the radiological impact of releases of radioactive materials to the environment, mathematical models are required to enable the transfer through various parts of the environment and hence the dose to man to be predicted. The nature of the models and their degree of complexity depend largely upon the particular applications in which they are to be used. Two types of model of differing degrees of complexity for predicting the transfer of strontium, caesium and iodine in cattle have been developed at NRPB . They form part of a general model for the transfer of radionuclides through terrestrial foodchains . The first is a relatively simple model based on the use of equilibrium transfer factors, while the second is an improved but more complex model which incorporates the extra features necessary to provide a reasonable representation of the time dependence of transfer to milk and to meat. Comparisons of the results using the two types of model in some situations of radiological interest have been performed. From these comparisons conclusions have been drawn about the adequacy and pertinence of the use of each model type in different situations.