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• Unique computational routes for safety assessment and radiological risk estimation. • High-fidelity coupled tools based on Monte Carlo with static and dynamic capability. • ICoCo multiphysics coupling codes for improved core analysis. • ICoCo multiscale coupled system TH, subchannel, and CFD codes for improved plant analysis. • Validation of severe accident codes using data from QUENCH (VVER, BWR, ATF) This paper describes the main research lines of the Karlsruhe Institute of Technology (KIT) relevant to Light Water Reactors (LWR) that permit both the safety evaluation of different reactor designs and the prediction of the radiological source term including its impact in the case of hypothetical severe accidents. The numerical tools for core analysis, nuclear power plant analysis of design basis and severe accidents, and the estimation of the radioactive dispersions of fission products after a core meltdown accident are described and selected results are discussed. The analytical investigations at KIT are complemented by experimental investigations at two facilities, namely the COSMOS-H/-L and the QUENCH facilities devoted to safety-relevant Thermal-Hydraulic (TH) phenomena and in-vessel severe accident early-phase for different kinds of fuel rods including Accident Tolerant Fuel (ATF). These data are crucial for the validation of the numerical tools used for safety demonstration. The paper is complemented by a brief description of the in-house tools under development for improved core/plant analysis based on the multi-physics/-scale coupling methodologies, where the in-house tools are combined with external system TH, Monte Carlo, and thermo-mechanic code to increase the prediction accuracy of the core/plant behaviour under stationary and accidental conditions. Selected results are presented and discussed. It can be stated that the long-lasting safety research activities at KIT devoted to LWR led to the development of a computation route combining external with in-house codes that is very much appropriate for safety evaluations and risk assessment; it includes unique multi-physics/-scale coupled tools for improved core and plant analysis of different reactor designs, e.g. PWR, VVER, BWR, SMR, and research reactors. [ABSTRACT FROM AUTHOR]

The JRODOS ( J ava-based R eal-time O nline D ecisi O n S upport) is a decision support system for off-site emergency management for releases of radioactive material into the environment. This paper documents the application of JRODOS by the Hong Kong Observatory in accident consequence assessment and emergency preparedness studies. For operational considerations, the most computational efficient dispersion model in JRODOS, ATSTEP, is adopted. Verification studies for JRODOS's ATSTEP model have been conducted. Comparison with tracer experiment results showed that under neutral atmospheric conditions and distances up to 50 km, the JRODOS simulation outputs were in general of the same order of magnitude with the tracer data. To further evaluate the capability of JRODOS in short-range simulation, a case study on the Fukushima nuclear power plant accident was also carried out. JRODOS was able to produce realistic simulation results which were comparable to the actual airborne monitoring data of the Cs-137 ground deposition from the Fukushima accident. Furthermore, the results of a comprehensive study to assess the potential consequences of accidents at a nearby nuclear power station are presented. Simulation using the French S3 source term for the Guangdong Nuclear Power Station at Daya Bay showed that the projected effective doses within Hong Kong remain far below the IAEA generic criteria of projected dose for urgent protective actions in sheltering/evacuation, while the projected equivalent dose in thyroid may meet the IAEA generic criteria for use of thyroid blocking agent at some areas in the northeastern part of Hong Kong, at distances of up to about 40 km from Daya Bay depending on the prevailing weather conditions in different seasons. [ABSTRACT FROM AUTHOR]

The goal of this work was to develop a methodology for risk assessment in case of an accident originating from a nuclear power plant, and consequently, to improve the relevant radiation monitoring network. In specific, the study involved risk estimation in Greece from a transboundary nuclear power plant accident. The tool employed was JRODOS (Java-based Real-time Decision Support), which is a system for off-site emergency management of radioactive material in the environment. This tool, widely used to generate and study scenarios for nuclear accidents worldwide, provides valuable insight to facilitate emergency preparedness and response. The probability of the plume arriving at numerous regions within the country was calculated, along with the maximum dose rates in case of transport. A risk assessment was performed, and geographical regions were prioritized in terms of risk-based environmental radioactivity burden. A total of 29 administrative districts were identified as low to medium-risk regions. Acquired results were used to determine the optimal spatial distribution of detectors for upgrading the existing monitoring network of environmental radioactivity. • Using JRodos to study daily release scenarios for a whole year, from an NPP near Greece. • Calculation of plume transport probabilities and maximum dose rates for different administrative districts. • Development of a methodology for risk assessment. • Categorization of the country's administrative districts according to risk. • Determination of spatial distribution of radiation monitoring stations. [ABSTRACT FROM AUTHOR]

Ambient gamma dose rate (GDR) is the primary observation quantity for nuclear emergency management due to its high acquisition frequency and dense spatial deployment. However, ambient GDR is the sum of both cloud and ground shine, which hinders its effective utilization. In this study, an automatic method is proposed to identify the radioactive plume passage and to separate the cloud and ground shine in the total GDR. The new method is evaluated against a synthetic GDR dataset generated by JRODOS (Real Time On-line Decision Support) System and compared with another method (Hirayama, H. et al., 2014. Estimation of I-131 concentration using time history of pulse height distribution at monitoring post and detector response for radionuclide in plume. Transactions of the Atomic Energy Society of Japan 13:119–126, in Japanese (with English abstract)). The reconstructed cloud shine agrees well with the actual values for the whole synthetic dataset (1451 data points), with a very small absolute fractional bias (FB = 0.02) and normalized mean square error (NMSE = 2.04) as well as a large correlation coefficient ( r = 0.95). The new method significantly outperforms the existing one (more than 95% reduction of FB and NMSE, and 61% improvement of the correlation coefficient), mainly due to the modification for high deposition events. The code of the proposed methodology and all the test data are available for academic and non-commercial use. The new approach with the detailed interpretation of the in-situ environment data will help improving the ability of off-site source term inverse estimation for nuclear accidents. [ABSTRACT FROM AUTHOR]

In case of a nuclear accident, the source term is typically not known but extremely important for the assessment of the consequences to the affected population. Therefore the assessment of the potential source term is of uppermost importance for emergency response. A fully sequential method, derived from a regularized weighted least square problem, is proposed to reconstruct the emission and composition of a multiple-nuclide release using gamma dose rate measurement. The a priori nuclide ratios are incorporated into the background error covariance (BEC) matrix, which is dynamically augmented and sequentially updated. The negative estimations in the mathematical algorithm are suppressed by utilizing artificial zero-observations (with large uncertainties) to simultaneously update the state vector and BEC. The method is evaluated by twin experiments based on the JRodos system. The results indicate that the new method successfully reconstructs the emission and its uncertainties. Accurate a priori ratio accelerates the analysis process, which obtains satisfactory results with only limited number of measurements, otherwise it needs more measurements to generate reasonable estimations. The suppression of negative estimation effectively improves the performance, especially for the situation with poor a priori information, where it is more prone to the generation of negative values. [ABSTRACT FROM AUTHOR]

JRODOS was used to simulate the dispersion of airborne radioactive material from a point source over the period 2012–2015. In total, 1331 radioactive plumes were simulated with the objective to investigate the influence of changes in meteorological conditions in the performance of the monitoring network. For this purpose, the existing set of 84 monitoring stations included in the EUropean Radiological Data Exchange Platform (EURDEP) system in an area of 200 km around the source point is taken as reference. A methodology is presented for quantitative evaluation of the variability of the number of stations affected, the time of the first detection, the maximum registered and differences between the maximum values match in the network and in the simulated plumes. The results show seasonal differences in all of these parameters according to changes in the size and shape of the affected area due to meteorological conditions. There are large differences in the number of monitoring stations affected by the plumes, from 2 to 74; in the timing and location of the first alert given by the network, from 1 to more than 5 h and faster along the west-east axis from the source; and in level of maximum gamma dose rate detected by the monitoring stations, from 0.17 nSv/h in summer to 0.22 nSv/h in autumn. These results show the need to consider this type of analysis over the years in the design of monitoring networks and in the development of nuclear emergency preparedness and response (EP&R) plans. [ABSTRACT FROM AUTHOR]

This work is dedicated to a study of routine atmospheric discharges from the Dukovany Nuclear Power Plant (NPP), Czechia. Radionuclide discharges and their transport in the environment were simulated using the JRODOS system. JRODOS was originally designed to forecast the atmospheric transport of radionuclide releases. However, the potential of JRODOS can be widened with the use of external scripts. Routine discharges can be simulated as 1-h immediately following discharges when they are summed and rescaled in accordance with the actual discharged activities. For calculations of routine discharges, we selected artificial radionuclides measured in the spectra of aerosol filters originating from the vicinity of the Czech NPPs. According to the simulated map of volumetric activities integrated over a longer period, new aerosol sampling sites can be proposed in the surroundings of the NPP of interest. The simulations have also been compared with the detection levels of selected radionuclides detected on aerosol filters. • A methodology for simulating routine discharges using JRODOS has been proposed. • JRODOS has been automated, with the use of scripts and third-party components. • A map of volumetric activities after routine discharges has been obtained. • Simulations have been compared with detection levels for aerosol filters. [ABSTRACT FROM AUTHOR]

Calculating atmospheric dispersion in a hypothetical nuclear accident plays an essential role as a predictive tool in nuclear emergency planning. The Nuclear Accident Consequence Analysis Code (NACAC) has been developed as an in-house code by the Thailand Institute of Nuclear Technology to develop its capability for understanding the transboundary radiological effect of a hypothetical nuclear accident. To verify the performance of the NACAC, a comparison between the calculated results using the NACAC with those from the well-developed Java-based Real-time On-line Decision Support (JRODOS) code is performed with representative cases of all seasons in a year. Two hypothetical severe accidents at the Fangchenggang pressurized water reactor, namely, (i) a loss of off-site power and (ii) a large-break loss of coolant, are utilized as the initial boundary conditions. The air concentration characteristic maps obtained from both codes are analyzed, revealing that the dominant radionuclide dispersion pathways are similar in all study cases. The air concentration, ground concentration, and total effective dose rate at several locations up to 500 km away from the release point are directly compared. Typically, the calculated results from the two codes are in reasonable agreement. However, for specific locations and directions, the NACAC predictions of the concentrations and total effective dose rate are lower than those from the JRODOS. These differences may be influenced by the different trajectory calculations between the two codes, which resulted in varying plume densities in certain areas. However, it does not significantly affect the radiation effect assessment. The NACAC still provides a total effective dose rate corresponding to the JRODOS, lower than one mSv throughout the main dispersion direction. • Differences in the calculation process of NACAC and JRODOS codes were investigated. • Influences of the data preparation system on simulated results were examined. • The effects of different advection calculations on simulated results were clarified. • An agreement of calculated results by NACAC and JRODOS codes was found. [ABSTRACT FROM AUTHOR]

This study aims at analysing the performance of the European Radiological Data Exchange Platform (EURDEP) at identifying, delineating, and tracking different radioactivity clouds moving across a territory. To this purpose, the atmospheric dispersion of 21 hypothetical STs, calculated by the Modular Accident Analysis Program (MAAP) code, has been simulated under the same meteorological scenario by the JAVA-based RODOS decision support system (JRODOS). EURDEP's performance is evaluated using spatial and temporal parameters. The present analysis shows a large impact of the total amount of activity and the timing of the release peak on EURDEP's performance. Monitoring stations are able to detect quite rapidly the release (first alarm), and presents more variation in the time needed to detect the peak, and to delineate and track the plume. A two-dimensional analysis is suggested to illustrate strengths and weaknesses of EURDEP to face different types of STs. These results highlight the need to link the understanding of ST characteristics with meteorological conditions to limit the environmental and health effects associated with radioactive emissions into the atmosphere. The present study aims at presenting a methodology to analyse the performance of EURDEP in other territories. • Evaluation the performance of the EURDEP system under different model predictions. • Atmospheric dispersion of 21 source terms combining JRODOS and MAAP. • Evaluation the network design in the early detection of radioactivity in the atmosphere. • Methodology to evaluate gamma dose rates networks. [ABSTRACT FROM AUTHOR]

In this work, we present a method to use the European nuclear emergency response system RODOS for analysis of potential sources of airborne radioactivity of an unknown origin. The method is based on a solution of adjoint equations, without modification of the code of long-range atmospheric dispersion model MATCH used in RODOS. The method has been successfully applied to the Ru-106 accident of 2017. The obtained spatial distribution of the correlation between simulations and measurements which could be achieved with source located in a given place, is in a qualitative agreement with analogous results published in other works. The high correlation is centered on the Ural Mountains; this is explained by a very wide expansion of the plume. However, the location of the maximum correlation obtained in this work is in the northern part of Russia, close to a military test site on Novaya Zemlya. This location is far away from the reprocessing plant Mayak in the South-Eastern Urals mentioned in other investigations as the most probable location of the source. In the results presented here, the correlation at the source location corresponding to the Mayak plant is still quite high (0.49); release inventory from this source of about 300 TBq could explain the observed measurements. • Method to analyse possible sources of radioactivity from an unknown origin with the RODOS system. • Results applied to the 2017 Ru-106 accident are in a qualitative agreement with other studies. • Possible sources include the Mayak reprocessing plant and a military test site on Novaya Zemlya. [ABSTRACT FROM AUTHOR]