Harmonization of Methodological Approaches and Real Time Radiological Consequence Forecasting Tools

Determination of urgent countermeasures to protect the public in early phase of the accident at NPP requires providing of radiological impact assessment at different distances in real time. These activities involve current meteorological forecast data and information about source term parameters as one of the main part of the emergency сenters functioning worldwide for prompt notification about the radiological or nuclear event in the country, as well as abroad in the case of transboundary impact. Experts’ background in the assessment and forecasting of radiological consequences area may vary from country to country in terms of methodological approaches, the use of atmospheric dispersion models, doses assessment models, databases, organization procedures, calculation process etc. Possible deviations in the results of assessments performed by experts from different countries may be caused by a number of factors. Their reasons can vary from the use of different information sources to the specifics of protective actions criteria in accordance with national requirements. These factors should be identified both in practice and scientifically. Radiological consequence assessment activities are harmonized at the international level. It is the target of a wide range of international projects. The paper provides information on modern scientific initiatives aimed at improving assessments and forecasts of radiological consequences to determine urgent countermeasures to protect the public at early phases of an accident at nuclear power plant, in particular, approaches to the initial data preparation and the conduct of assessments and forecasting. A review of international benchmarking activities as well as past emergency exercise overview is presented in the paper. Relevant problems of forecasting radiological consequences in real time are highlighted.

Evaluation on Radiological Consequence Induced by MSLB Accident With Alternative Source Term

The major threat that nuclear power plants (NPPs) pose to the safety of the public comes from the large amount radioactive material released during design-basis accidents (DBAs). Additionally, many aspects of Control Room Habitability, Environmental Reports, Facility Siting and Operation derive from the design analyses that incorporated the earlier accident source term and radiological consequence of NPPs. Depending on current applications, majority of Chinese NPPs adopt the method of TID-14844, which uses the whole body and thyroid dose criteria. However, alternative Source Term (AST) are commonly used in AP1000 and some LWRs (such as Beaver Valley Power Station, Units No. 1 and No. 2, Calvert Cliffs Nuclear Power Plant, Unit Nos. 1 And 2, Kewaunee Power Station and so on), so it is attempted to adopt AST in radiological consequence analysis of other nuclear power plants. By introducing and implementing the method of AST defined in RG 1.183 and using integral safety analysis code, a pressurized water reactor (PWR) of 900 MW nuclear power plant analysis model is constructed and the radiological consequence induced by Main Steam Line Break (MSLB) accident is evaluated. For DBA MSLB, the fractions of core inventory are assumed to be in the gap for various radionuclides and then the release from the fuel gap is assumed to occur instantaneously with the onset of assumed damage. According to the assumptions for evaluating the radiological consequences of PWR MSLB, dose calculation methodology is performed with total effective dose equivalent (TEDE) which is the criteria of dose evaluation. Compared with dose criteria of RG 1.183, the dose of control room, exclusion area boundary and outer boundary of low population zone are acceptable.