Some aspects of RF radiation safety guidelines on urgent protective measures in case of radiation emergency at NPP

Full text: The work is aimed at developing a decision making strategy and tools for putting into practice the principles of reasonableness and optimization when applying countermeasures in case of a radiation related accident at a nuclear power plant in RF. The presentation discusses results of the study of the legal framework in the RF for decision making to protect the personnel and public in case of a radiation-related accident Consideration is given to issues of methodological support for emergency response systems at NPPs, as required by the RF radiation safety norms to protect personnel and the public. This work was performed as part of methodological support to the national emergency center of Rosenergoatom comprising several technical support centers on the base of leading institutes with large scientific potential in the fields of nuclear power use, environmental and public protection, radioecology etc. Such centers were set up for scientific and technical support to decision making in case of emergency at NPPs. Specialists of die centers are able to quickly assess the emerging situation and propose a set of measures to minimize damage, drawing on expert judgements. The radiation safety guidelines (NRB-99) lays down requirements and criteria for decision making to protect the public in different phases of a radiation accident which should be used when implementing countermeasures and developing emergency response plans with allowance for specific situation and local conditions. These criteria provide a basis for designating areas of emergency response that would be optimum for specific population points, intervention measures etc. Dealing with these tasks requires development of normative and methodological documentation taking into account both the NRB-99 requirements and international recommendations. In accordance with NRB-99: expected and averted radiation doses are the key criteria to be used in application of any protection measures in radiation emergency. Besides, specific activities of radionuclides in foods are also used as criteria; requirements regarding intervention measures depend on whether the predicted dose can bring about deterministic effects. In the case of high doses leading to deterministic effects protection measures are mandatory. If deterministic effects cannot be excluded, then protection measures should be justifiable and optimized. One of the key concepts of emergency response activities is the intervention level. In NRB-99 the intervention level is defined as radiation factor level which when exceeded requires protection measures. The NRB-99 lays down dose levels the excess of which can lead to clinical effects. These are consistent with the IAEA guidelines. The criteria of NRB-99 for shelter and evacuation am different from those of ICRP as far as measurement units are concerned. In NRB-99 doses averted through sheltering and evacuation are proposed to be calculated as absorbed dose, rather than effective dose. The NRB-99 requires prediction of doses averted by sheltering, evacuation and iodine prophylaxis in the first 10 days after a radiation accident. This suggests that a protection measure can be as long as 10 days. The NRB-99 contains no recommendation with regard to consideration of exposure pathways. Also, in the NRB-99 there is no mentioning of population groups for which averted dose should be calculated. The IAEA recommendations specify that averted dose should apply to a population mean value, rather than most exposed persons (critical groups). However, predicted doses for critical groups should be estimated given exposure levels require urgent Intervention (i. e. leading to clinical effects). Method for express assessment of possible intervention areas in the early phase of emergency at a nuclear power plant. The presentation discusses a method for preparing quickly recommendations an emergency measures to protect the personnel and the public in case of emergency at a NPP with V VR or RBMK reactors using the forces of NPP before radiation safety experts become involved. This method was developed with the purpose to 1.) Improve radically fast response in terms of preparation of recommendations an intervention measures in the first hours into an accident. 2.) Reduce stress for the NPP administration and liberate them for efficient management of an accident The task of preparing recommendations an emergency measures in the first hours of an accident by NPP forces can be efficiently executed based on preliminary study of a set of initial data, which am key for radiation consequences of an accident and developing a set of recommendations for each set. The presentation describes a method for selection of a set of initial data and identifying corresponding areas in which emergency measures would be reasonable to implement. The considered key factors influencing the radiation situation in the early phase of an accident at NPP include: the activity of 131I release to the atmosphere (contribution of other iodine radioisotopes can be allowed for by using a correction factor), physical and chemical forms of iodine in the release, a release duration, time of the day during which the release is dispersed in the atmosphere, the population age group, the atmospheric boundary layer stability category, wind speed and the underlying surface roughness length. In selecting a set of initial data preference was given to standard information about meteorological conditions of pollutant dispersion in the atmosphere available to meteorological stations and dosimetry services of NPPs. Analysis was performed for joint realization of atmospheric stability category and classification of wind speed at vane's height. Results of analysis are presented. tab. 1 (author)