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Title: The Development of a Methodology to Assess Population Doses from Multiple Sources and Exposure Pathways of Radioactivity
Author: J J Hancox
Author: S J Stansby
Author: M C Thorne
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1095, Representation ID: 345, Object ID: 2364
Background The Environment Agency (EA) has new duties in accordance with the Basic Safety Standards Directive under which it is required to ensure that doses to individuals received from exposure to anthropogenic sources of radioactivity are within defined limits. In order to assess compliance with these requirements, the EA needs to assess the doses to members of the most highly exposed population groups (acriticala groups) from all relevant potential sources of anthropogenic radioactivity and all relevant potential exposure pathways to such radioactivity. The EA has identified a need to develop a methodology for the retrospective assessment of effective doses from multiple sources of radioactive materials and exposure pathways associated with those sources. Under contract to the EA, AEA Technology has undertaken the development of a suitable methodology as part of EA R and D Project P3-070. The methodology developed under this research project has been designed to support the EA in meeting its obligations under the Euratom Basic Safety Standards Directive and is consistent with UK and international approaches to radiation dosimetry and radiological protection. The development and trial application of the methodology is described in this report. Main Objectives/Aims In order to develop a suitable methodology for assessing compliance with the regulatory requirements, the scope of the required assessment procedure was defined through review of the relevant regulatory documents. The scope of the assessment methodology is as follows: a Exposure Routes The dose limits apply to doses received from all exposure routes except: a exposures to natural radiation; a radon in dwellings; and a medical exposures. a Types of Dose The assessment methodology is essentially restricted to the retrospective estimation of effective dose to representative members of critical groups. Methodology The assessment methodology has been developed with a theoretical approach to the definition of critical groups. In particular, the developed methodology differs from previous assessment methods in that the critical groups are defined by their estimated doses (from a range of pathways) rather than from their habits. As such, the critical groups are effectively composites of those that would be defined using a more traditional approach of homogeneity in terms of behaviour affecting the dose that they receive. The methodology enables assessment of critical group doses from both licensed nuclear facilities (around which significant levels of environmental monitoring and habit survey data are available) and non-licensed sites (around which monitoring data are at best limited and for which critical groups may not typically have been previously identified). To facilitate efficient assessment of sites, such that the level of effort involved in their assessment is R and D TECHNICAL REPORT P3-070/TR iii commensurate with their radiological significance, the assessment methodology has been developed as a three-stage process: a preliminary screening assessment; a generic regional assessment; a detailed site/region specific assessment. The assessment methodology has been used in two trial assessments: a an assessment of critical group doses local to the BNFL Sellafield facility in Cumbria; and a an assessment of critical group doses in the EA Thames region due to discharges from both licensed and non-licensed sites in the region. Results The trial assessment of the doses around Sellafield produced individual annual effective dose estimates for representative members of the acompositea critical group broadly comparable to the high marine food consumer critical group doses estimated by, for example, the Food Standards Agency. Hence, the application of the new methodology provides confidence that, not only have the key critical group habits previously been identified, but also that the taking into account of multiple sources for a variety of exposure pathways does not lead to the dose limit for the representative member of the critical group being exceeded. Conclusions The assessment methodology for licensed sites relies on the availability of sufficient suitable environmental monitoring and habit survey data. In particular, the approach is best served by the availability of integrated habit survey data in which all surveyed individuals provide details of habits that relate to all possible exposure routes. This type of integrated survey has not yet been undertaken and, for the trial assessments reported here, an approach has been developed to show how integrated habit survey datasets may be generated from a synthesis of partial surveys by the use of assumed/derived correlations between habits. Nonetheless, the use of integrated surveys is recommended and it is noted that the main organisations funding the gathering of such data, i.e. the EA and FSA, are now moving towards this goal. For assessment of the individual doses that may result from the discharge of radioactivity from non-licensed sites, a conservative, modelling-based assessment approach was developed. This methodology has been implemented within a spreadsheet format and applied to the Thames region. For the Thames region, it has been demonstrated that, under strictly conservative assumptions, the doses to members of the public comply with the limit on annual effective dose of 1mSv. The implementation of the methodology within a spreadsheet tool facilitates the application of the approach to other regions. Were this to show that doses from certain non-licensed sites or combinations of such sites, challenged the dose limit, then environmental monitoring and the collection of habit survey data would be merited in order to allow a more rigorous assessment to be undertaken (in a manner similar to that for licensed sites). It is noted, also, that the assessment method for non-licensed sites would benefit from future development onto a GIS-based system. R and D TECHNICAL REPORT P3-070/TR iv 1
Publisher: Environment Agency
Subject Keywords: Radiation; Dose; Public; Retrospective; Aggregated total exposure
Extent: 84
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