Atmospheric Dispersion of Radioactive Material in Radiological Risk Assessment and Emergency Response

Progress in NUCLEAR SCIENCE and TECHNOLOGY, Vol. 1, p.7-13 (2011) REVIEW Atmospheric Dispersion of Radioactive Material in Radiological Risk Assessment and Emergency Response YAO Rentai * China Institute for Radiation Protection, P.O.Box 120, Taiyuan, Shanxi 030006, China The purpose of a consequence assessment system is to assess the consequences of specific hazards on people and the environment. In this paper, the studies on technique and method of atmospheric dispersion modeling of radioactive material in radiological risk assessment and emergency response are reviewed in brief. Some current statuses of nuclear accident consequences assessment in China were introduced. In the future, extending the dispersion modeling scales such as urban building scale, establishing high quality experiment dataset and method of model evaluation, improved methods of real-time modeling using limited inputs, and so on, should be promoted with high priority of doing much more work. KEY WORDS: atmospheric model, risk assessment, emergency response, nuclear accident 11) I. Introduction from U.S. NOAA, and SPEEDI/WSPEEDI from The studies and developments of techniques and methods Japan/JAERI. However, the needs of emergency of atmospheric dispersion modeling of radioactive material management may not be well satisfied by existing models in radiological risk assessment and emergency response which are not well designed and confronted with difficulty have evolved over the past 50-60 years. The three marked in detailed constructions of local wind and turbulence fields, types of dispersion models, which may depict the validity of empirical parameterization, and testing of development of dispersion modeling technique for the confidence-level estimates. It should usually by difficult to application in radiological risk assessment and emergency obtain a dataset of field experiments to test atmospheric response, are Gaussian plume models in the 1960s and dispersion models including meteorological observations 1970s, Lagrangian-puff models and particle random walk and tracer samplings of good quality and high-resolution. models in the 1980s - 1990s, and developing CFD Some typical experiments considered to be of greatest potential value for testing models are Kincaid12) tracer (Computational Fluid Dynamics) models in the 2000s. 13) Current available atmospheric dispersion models range experiment for plat terrain, MADONA field study for complex terrain, URBAN 200014) and Joint Urban 200315) from the relatively simple to the highly complex. In order to 16) determine how dispersion models can be applied most for urban-scale and building-scale, and ETEX for effectively, it is important to identify the needs in long-range transport. radiological risk assessment and emergency response. The studies and developments in China have made great Up to now, Gaussian plume models are applied to risk progress in the functions and techniques of atmospheric assessment and emergence response, typically, such as dispersion modeling and real-time consequence systems for MACCS1) and COSYMA2) for probabilistic risk assessment over a decade. The models applied to emergency response and RASCAL/InterRAS3,4) and HOTSPOT5,6) for are currently involved in with mass consistent diagnostic emergence response. The Gaussian plume model wind field model, quasi-hydrostatic numerical prognostic approximately depicts the distribution of time-averaged model, Lagrangian puff model and particle random walk concentrations over a period of time such as one hour. model. In fact, the same issues mentioned above should be Because of some insuperable inherent vices, new resolved though the existing dispersion models can meet knowledge and processing methods cannot be taken into some needs of the emergency managements. account though empirical corrections have been applied to In this paper, a brief review of the needs of atmospheric model, for instance, terrain modified factor. Such models dispersion models in radiological risk assessment and will face the challenge in the case of complex topographies, emergency response was given. Then the studies on urban environments and buildings, low wind speed or calm nuclear accident consequences assessment in China were conditions, and so on. For the purposes of actual emergency introduced. Finally, some issues calling for attentions in response and real-time consequence assessment, Lagrangian atmospheric dispersion modeling are discussed. puff and particle models are currently used in many advanced emergency response system such as NARAC7,8) II. Needs of Atmospheric Dispersion Models in 9) 10) from U.S. DOE/LLNL, RODOS from EC, HYSPLIT Radiological Risk Assessment and Emergency Response *Corresponding author, Tel.: +86-351-2202230, Fax.: +86-351-7020407, E-Mail: [email protected] Atomic Energy Society of Japan 7 8 YAO Rentai 1. Consequence Assessment and Atmospheric used in characterizing atmospheric dispersion and Dispersion examine how these models are applied operationally There are three types of nuclear accident consequence for emergency response efforts. assessment in the light of purposes of assessment: z Identify deficiencies in the models that limit their (1) Probabilistic Risk Assessment (PRA). The effectiveness and breadth of application; assess the assessment on the risk from the potential accident would research and development needed to enhance the be based upon probabilistic analysis considering the effectiveness and operational use of these models in occurring probability and consequence spectrum of each emergency situations. accident. z Determine the observational data needed to (2) Real-time consequence assessment. The aim is to initialize, test, and use these models effectively, and provide an input for emergence response through assessing identify the ways in which other environmental or predicting and to provide support for emergency measurements can complement these models to response managers before accident releases. In detailed, the provide additional and more accurate information. real-time consequence assessment is divided into early, As for emergency response, it is very important to let intermediate and latent phases. emergency responders understand that there are limits to (3) Over-event or past accident consequence atmospheric dispersion modeling capabilities. Conversely, assessment. That means consequence assessment studies dispersion modelers and meteorologists would be aware of through retracing the transport of radioactive material for how nowcasts and forecasts are used in emergency response the historical releases. situations. Atmospheric dispersion modeling represents one of the valuable tools of effective emergency response for its 3. Types of Atmospheric Dispersion Model and technical support on environment and health prediction and Selection decision-making. Thus, it is important to make models as Models of environmental processes are approximate accurate as possible. The present numerical modeling representations of reality. Each model involves a set of methods focus on providing various best prediction results tradeoffs, taking into account objectives such as whether it not too conservative. will be used to aid understanding, to estimate changes that Errors in numerical modeling are mainly emerged from might occur, or to determine which areas might be affected uncertainties in both the discrete process of transportation if a release were to occur. Now there are six general model equation and the data input. To reduce uncertainties and types (as shown in Table 1), which are compartmentalized develop most realistic atmospheric dispersion model, many in the light of model principle and theory and complexity. details should be validated through meticulous studies. Field experiment should be the most traditional and reliable Table 1 General types of atmospheric dispersion model Level Type Representative models way for the validation and evaluation of atmospheric 6 CFD, LES FEM3MP(LLNL, US) dispersion models. ADREA-DIFF(Demokritos, Three-dimensional Greece) 5 Eulerian grid 2. Consideration for the Needs of Risk Assessment and TRAVELLING(KfK/Univ. model Emergency Response Karlsruhe, Germany) Lagrangian In fact different modeling methodologies are required in MC31(CEA, France) particle model or the risk assessment and different stages of emergency 4 Monte-Carlo response. For the risk assessment and the preparedness ARCO(ENEA, Italy) particle model and latent stages, an model capable of providing RIMPUFF(Riso, Denmark) confidence-level estimates is desired, but model MESODIFF-II(SRC, US) execution time is not important. For the response stage, Lagrange puff RAPTAD(Los Alamos, US) 3 especially for the immediate first response before model SPADE(ENEA, Italy) releases, tradeoff and compromises will be needed HARM(EPA-ATDD, US) between model accuracy and timely predictions. PG&E-Puff Model(PG&E, US) Segmented plume ATSTEP(KfK, Germany) In the wake of the terrorist attacks of September 11, 2001, 2 the U.S. National Academies launched a major new model COSYMA(EC) Gaussian plume initiative to provide guidance to the federal government on 1 RASCAL(NRC, US) model scientific and technical matters related to counterterrorism and homeland security. To address these issues, a steering Part of the problem of model selection is to know the committee was convened that included several members of horizontal scale of the various transport and diffusion the Board on Atmospheric Sciences and Climate (BASC) processes of concern. Another

Load more