This article presents a method for assessing the radionuclide surface contamination density (SCD) on open sites and in premises of a radiation hazardous facility based on measurements of the ambient dose equivalent rate (ADER). The method is intended for use at the initial stage of the assessment of the radiation environment at facilities. The assessed SCD at a given location on the surface can differ from the directly measured SCD at that location, since sources located on the surface and distributed by the depth contribute to the ADER value. The method makes it possible to estimate SCD with reasonable accuracy without increasing the number of measurements, and thus avoid additional occupational exposure and the use of additional resources. SCD and ADER as spatial variables have different support of measurement data. For ADER, measured at a height of 1 m, the support of measurement data can be taken to be a circle in the centre of which a gamma-ray detector is located, with a radius of several tens of meters. In contrast, SCD has the support of measurement data, close to the overall dimensions of the beta detector (100 cm2). To solve the problem of SCD calculation on the basis of ADER measurements, the method of conversion coefficients (MCC) is usually applied, based on the use of conversion factors; however, this method provides an adequate estimate only under conditions of an SCD with low gradient over the surface. The method proposed in this article is applicable for an arbitrary distribution of SCD, and designed to deal with heterogeneous contamination patterns. The developed method is based on the numerical solution of the Fredholm equation of the first kind. The measurement data always contain an error, therefore, the task of the SCD calculation is an ill-posed problem, and the Tikhonov regularisation method (ridge regression) was used to solve it. The article presents the method developed and examples of use. Validation of the method was performed using 38 measurements of the radioactive contamination from 137Cs in soil. It is shown that the method proposed in the article demonstrates a significant superiority in comparison with the MCC method, because it allows more accurate localisation of areas contaminated with radionuclides and is applicable for an arbitrary distribution of SCD.
To estimate thyroid radioactivity in the Ukrainian population from May-June 1986, more than 150,000 individual examinations were carried out by special dosimetric teams. The results of these total measurements were approved to be a basis for assessing individual absorbed doses of infant and adult thyroid irradiation associated with the 131I exposure. The dosimetric radioiodine data bank of thyroid irradiation of the Ukrainian population was created to analyze these measurements. The analysis was performed using the data for eight Ukrainian districts and the town of Pripjat, which were all heavily contaminated due to radioiodine exposure. Results of the dose assessments are given using two models: the more conservative model of "single radioiodine intake" and a more realistic model that considers the individual duration of radioiodine intake. In accordance with the more realistic model, the predictions of late effects have shown that a collective thyro-oncogenic dose is equal to 64,000 person-Gy, stimulating the possibility of the emergence of 300 cases (30 incurable) of thyrocancers. Considering this information for the next 35 y (1991-2026), it is possible to predict a 1.4-fold increase over spontaneous thyroid cancer morbidity for children who lived in the heavily contaminated regions of the Ukraine in 1986 (spontaneous and radiogenic to spontaneous).
Andreeva Bay in northwest Russia hosts one of the former coastal technical bases of the Northern Fleet. Currently, this base is designated as the Andreeva Bay branch of Northwest Center for Radioactive Waste Management (SevRAO) and is a site of temporary storage (STS) for spent nuclear fuel (SNF) and other radiological waste generated during the operation and decommissioning of nuclear submarines and ships. According to an integrated expert evaluation, this site is the most dangerous nuclear facility in northwest Russia. Environmental rehabilitation of the site is currently in progress and is supported by strong international collaboration. This paper describes how the optimization principle (ALARA) has been adopted during the planning of remediation work at the Andreeva Bay STS and how Russian-Norwegian collaboration greatly contributed to ensuring the development and maintenance of a high level safety culture during this process. More specifically, this paper describes how integration of a system, specifically designed for improving the radiological safety of workers during the remediation work at Andreeva Bay, was developed in Russia. It also outlines the 3D radiological simulation and virtual reality based systems developed in Norway that have greatly facilitated effective implementation of the ALARA principle, through supporting radiological characterisation, work planning and optimization, decision making, communication between teams and with the authorities and training of field operators.
In the 1960s two technical bases for the Northern Fleet were created in the Russian northwest at Andreeva Bay in the Kola Peninsula and Gremikha village on the coast of the Barents Sea. They maintained nuclear submarines, receiving and storing radioactive waste and spent nuclear fuel. No further waste was received after 1985, and the technical bases have since been re-categorised as temporary storage sites. The handling of these materials to put them into a safe condition is especially hazardous because of their degraded state. This paper describes regulatory activities which have been carried out to support the supervision of radiological protection during recovery of waste and spent fuel, and to support regulatory decisions on overall site remediation. The work described includes: an assessment of the radiation situation on-site; the development of necessary additional regulatory rules and standards for radiation protection assurance for workers and the public during remediation; and the completion of an initial threat assessment to identify regulatory priorities. Detailed consideration of measures for the control of radiation exposure of workers and radiation exposure of the public during and after operations and emergency preparedness and response are complete and provided in sister papers. The continuing requirements for regulatory activities relevant to the development and implementation of on-going and future remediation activities are also outlined. The Norwegian Radiation Protection Authority supports the work, as part of the Norwegian Government's plan of action to promote improvements in radiation protection and nuclear safety in northwest Russia.
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