SPATIAL RISK ASSESSMENT METHOD WORKABLE UNDER LIMITED ATMOSPHERIC DATA AVAILABILITY AND ITS APPLICATION TO NINH THUAN NUCLEAR POWER PLANT ZONE PLANNING by HO QUOC DUNG Supervisor Professor YOSHIKI MIKAMI A dissertation submitted in partial fulfilment of the requirement for the degree of Doctor of Engineering in Information Science and Control Engineering March 2015, Japan ABSTRACT Vietnamese government has a nuclear energy program with the goal of building 14 units of nuclear reactor by 2030 Ninh Thuan has been the location approved by the government for the construction of the first nuclear power plants (NPP) Estimating the risk of radionuclide releases in the atmosphere is currently the most essential task for Vietnamese authorities in order to regulate the area-zones around the NPP facilities and to propose the policies to protect public health and safety There is, however, no existing documented work on such critical assessment and this study is an attempt to fill this gap In the first stage, the study has proposed the Simplified Wind Transport Model that overcomes the restriction of meteorological data availability as important input requirements for the other current atmospherics dispersion models This model aims to estimate the transport paths of the radioactive materials in the atmosphere based on the widely available data of the wind speed and wind direction More than forty thousand simulations for the entire weather conditions in Ninh Thuan during 14 year period (1996-2009) were carried out and combined to build up the spatial risk maps around the Ninh Thuan NPP site In the second stage of the study, a practical methodology based on conventional and historical data approach to assess the offsite dose of radioactivity releases in airborne that enter the human body through inhalation exposure pathway was developed Based on the offsite dose estimations, the research seeks to recommend to the government authorities the plan for arranging the critical zones around the NPP and the evacuation policy to minimize the risk of the radionuclide release to the public and to the surrounding environment ACKNOWLEDGEMENTS This PhD thesis is the summary of research activities in Doctoral course at Professor Mikami’s laboratory, Nagaoka University of Technology, Japan I would never have been able to finish my dissertation without the guidance of my Professor, help from friends, and support from my family First and foremost, I would like to express my deepest gratitude to my supervisor, Professor Yoshiki Mikami, for the insightful guidance and tremendous support of my study and research, for his patience, encouragement, enthusiasm, and immense knowledge It is my honour to be a student under his supervision I would like to thank Professor Yuichi Otsuka and Professor Tatsuya Suzuki for their helpful advice and comments during my research work I would like to sincerely thank Professor Li Zhidong, Professor Koichi Yamada for their valuable comments and discussions to improve my research and modify this thesis I would like to thank all members in Mikami laboratory for their kind help and support, for creating good research environment and friendships I also thank Nagaoka University of Technology because of the good support for all international students I would like to give many thanks to my family members There is no word to acknowledge the encouragement and love of my family members I could not have finished the long journey of my study without their love and encouragement Finally, I would like to thank my beloved wife, Le Thi Quynh Lien and my lovely son, Ho Le Minh Nhat They are always behind me through the good and bad times Sincerely, HO Quoc Dung March 2015 TABLE OF CONTENT CHAPTER INTRODUCTION 1.1 RESEARCH MOTIVATION 1.2 RESEARCH OBJECTIVES 1.3 OUTLINE OF THE RESEARCH CHAPTER TECHNICAL BACKGROUND 11 2.1 RADIONUCLIDE SOURCE TERM 11 2.1.1 Fission Product Characteristics 12 2.1.2 Radionuclide Source Terms 13 2.2 ATMOSPHERIC TRANSPORT OF RADIONUCLIDES 17 2.2.1 The Characteristics of Atmospheric Releases 17 2.2.2 Modelling of Atmospheric Transport 29 2.3 OFFSITE DOSE ASSESSMENT THROUGH DIFFERENT EXPOSURE PATHWAYS 34 2.3.1 Exposure pathways 34 2.3.2 Inhalation pathway 35 2.3.3 Ingestion pathway 36 2.3.4 External exposure pathway 37 CHAPTER RESEARCH SITE CHARACTERISTICS 39 3.1 OVERVIEW OF VIETNAM NUCLEAR POWER PLANT PROGRAM 39 3.2 DEMOGRAPHIC AND GEOGRAPHY CHARACTERISTICS OF NINH THUAN 44 CHAPTER METEOROLOGICAL DATABASE 49 4.1 METEOROLOGICAL DATABASE COLLECTION 49 4.2 METEOROLOGICAL DATABASE ANALYSIS 52 CHAPTER SIMPLIFIED WIND TRANSPORT MODEL 55 5.1 MODELLING RADIONUCLIDE TRANSPORT 55 5.1.1 Transport Estimation 55 5.1.2 Dispersion Estimates 59 5.2 APPLICATION FOR NINH THUAN NPP SITES 62 5.2.1 SWTM Simulation 62 5.3 DISCUSSIONS 69 5.4 CONCLUSIONS 70 CHAPTER REVISED SIMPLIFIED WIND TRANSPORT MODEL 73 6.1 SOLAR ALTITUDE ANGLE 73 6.2 ESTIMATING ATMOSPHERIC STABILITY CLASS BY TURNER METHOD 77 CHAPTER OFFSITE DOSE ASSESSMENT AND ZONE PLANNING 81 7.1 HYPOTHETICAL ACCIDENT SCENARIO 83 7.1.1 Source Term 83 7.1.2 Released Radionuclide Concentration 85 7.1.3 Offsite Dose Assessment 88 7.2 OFFSITE ZONE PLANNING 89 7.2.1 Criteria for Area Zoning Plan 91 7.2.2 Zone Planning by Conventional Approach 92 7.2.3 Zone Planning by Historical Data Approach 93 7.3 CONCLUSION 100 CHAPTER DISCUSSION AND CONCLUSION 103 8.1 APPLICATIONS AND LIMITATIONS OF RESEARCH RESULTS 103 8.2 CONCLUSION AND FUTURE PLAN 105 REFERENCES 107 LIST OF ACHIEVEMENTS 113 LIST OF TABLES TABLE 1.1: THE METEOROLOGICAL INPUT DATA REQUIREMENT FOR GPM AND PTM TABLE 1.2: THE COMPARISON OF WEATHER INDICATOR RECORD BETWEEN SURFACE AND UPPER-AIR STATION IN VIETNAM AND JAPAN TABLE 2.1: RADIONUCLIDE CLASSIFICATION SCHEME USED IN THE REACTOR SAFETY STUDY 12 TABLE 2.2: ABWR SOURCE TERMS – RADIONUCLIDE ACTIVITY RELEASE TO THE ENVIRONMENT DURING A LOCA 15 TABLE 2.3: APWR SOURCE TERMS – RADIONUCLIDE ACTIVITY RELEASE TO THE ENVIRONMENT DURING A LOCA 17 TABLE 2.4: VALUES OF THE POWER LAW VARIABLE M AS A FUNCTION OF SURFACE ROUGHNESS AND ATMOSPHERIC STABILITY 20 TABLE 2.5: DEFINITION OF PASQUILL ATMOSPHERIC STABILITY CATEGORIES 24 TABLE 2.6: INTERPRETATION OF FOUR DIFFERENT ATMOSPHERIC STABILITY SCHEMES 25 TABLE 2.7: STABILITY CLASS AS A FUNCTION OF NRI AND WIND SPEED 26 TABLE 2.8: HEIGHT OF MIXING HEIGHT FOR DIFFERENT ATMOSPHERIC STABILITY CATEGORIES 28 TABLE 3.1: PLAN CONSTRUCTION NINH THUAN AND NUCLEAR POWER PLANT 43 TABLE 5.1: COMPARISON OF PUFF AND PLUME DIFFUSION 61 TABLE 5.2: THE TOTAL COLORED AREA AT DIFFERENT SEASON 66 TABLE 6.1: DEFINITION OF PASQUILL ATMOSPHERIC STABILITY CATEGORIES 78 TABLE 6.2: INSOLATION AS A FUNCTION OF SOLAR ALTITUDE 78 TABLE 6.3: STABILITY CLASS AS A FUNCTION OF NRI AND WIND SPEED 79 TABLE 7.1: RADIONUCLIDE CLASSIFICATION SCHEME 83 TABLE 7.2: INVENTORY OF IODINE ISOTOPES 84 TABLE 7.3: AMOUNT OF IODINE RELEASE TO THE ENVIRONMENT 85 TABLE 7.4: VALUES FOR STANDARD DEVIATION ΣY, ΣZ 86 TABLE 7.5: ADULT INHALATION THYROID DOSE CONVERSION FACTORS 89 TABLE 7.6: DEFINITION OF PASQUILL ATMOSPHERIC STABILITY CATEGORIES 95 TABLE 7.7: WEATHER CASE AND ITS OWN PROBABILITY AT 16 DIRECTIONS 96 TABLE 7.8: STATISTICS OF THE SIMULATION FOR 16 DIRECTIONS 99 Figure 7.6 is the map showing the LPZ defined by the conventional approach as compared to that defined by the historical data approach The difference in the shapes of the LPZ resulting from the two different approach suggest the useful information for the government in planning the critical zones around NPP site and the emergency action in case of NPP accident 45,000 30,000 15,000 -15,000 -30,000 -45,000 -45,000 -30,000 -15,000 15,000 30,000 45,000 Figure 7.6: The comparative low population zone in conventional (solid line) and historical data approach (dotted line) 7.3 Conclusion This study aims to provide the offsite dose assessment methodology of a hypothetical NPP accident and applied it to the case at the Ninh Thuan NPP in Vietnam The total radiation dose to the thyroid from iodine exposure through inhalation exposure pathway is primarily focused and estimated The estimation of the offsite dose is then used as the criteria for the planning of the critical zones around the NPP, including the EZ and the LPZ, by applying two different approaches: the conventional approach and 100 our proposed historical data assessment Conventional approach is the scheme based on the assumption that the weather condition is at steady state along the pathway of radionuclide release In this approach, the estimation of dose is performed under hypothetical worst-case of atmospheric condition when the weather remains at atmospheric stability class F and the wind speed m s−1 From another perspective, our proposed historical data approach takes into account the probabilities of different atmospheric patterns based on our collection of the historical meteorological data in the period from the year of 1996 to 2009 The attempt is to provide a more practical scheme The comparative results in estimating the distance of LPZ show that the merit point of our proposed historical data approach is that it reflects the more reality of the NPP accident situation than the conventional one by considering the huge historical weather conditions of the research site The LPZ boundary by historical data approach covers the area of 250 km2 , accounting for only 6.25% as compared with the results from conventional approach (4000 km2 ), while it still can be represent for 95% of weather conditions during the accident These comparative results of LPZ by two different methods suggest the useful information for authorities and government planners in arranging the critical zones around the NPP The results can also be used by the government to produce the evacuation policy and the preparedness plan in case of NPP accident to limit and minimize the consequence of the radionuclide to the public and the environment The critical zones distance giving by conventional approach does not give to the public a practical implication The public not recognize exactly how the threats of NPP accident distributing By using historical data approach, the zone area is created based on the real hourly historical data from 14 years duration The low population zone by history data approach is an area had the highest probability appearing the threats if the NPP accident happens The public policy makers should much more consider on the zone area calculated by history data approach 101 102 Chapter DISCUSSION AND CONCLUSION 8.1 Applications and Limitations of Research Results In this research, the atmospheric dispersion model, namely, SWTM that overcomes the limitations of meteorological data is proposed to estimate the spread of radioactive materials based on the widely available historical data of the wind speed and direction STWM is designed by efforts not only to decrease meteorological input data demands but also to keep computational cost and mathematical simplicity to a minimum SWTM can be used to create the spatial risk maps of radionuclide around the NPP site However, along with its merit as a simplified and fast simulation model, the limitation of SWTM is estimation of radionuclide concentration In order to improve the SWTM model, the revised SWTM is introduced The revised SWTM can achieve better output results by taking account the effective wind speed and the atmospheric stability class factors for their estimations Based on that, it can reduce the error gap of the estimation of radionuclide concentration compared with the real radionuclide concentration in the atmosphere In order to demonstrate the usefulness and applicability of SWTM and revised SWTM model, the simulation of the large-scale (more than 100km) dispersion of radionuclides in the atmosphere for Ninh Thuan NPP site in Vietnam through a total of 40,904 meteorological conditions over an fourteen-year period (1996 - 2009) is implemented for creating spatial risk maps Furthermore, we combine the estimations of radionuclide release by using the revised SWTM under the historical weather conditions over fourteen-year period with the offsite dose assessment to provide the 103 planning for the low population zone area around the Ninh Thuan NPP Our proposed approach for NPP zone planning is named as the historical data approach, is then compared with the conventional approach which is based on the assumption of the worst case of meteorological conditions and works under the Gaussian estimations The comparative results of low population zone by two different approaches suggest the useful information for authorities and government authorities in arranging the critical zones around the NPP However, our proposed method for spatial risk assessment of radionuclide release remains one big demerit point in verifying the accuracy of the output results Although it took account the meteorological conditions of the research site, these meteorological conditions are merely the kind of historical data and are focused only on the wind factors The other factors of atmospheric conditions and topographic characteristics are discarded due the limitation of the input data Therefore, the output results should not guarantee for any important decisions related to the implementation of the Ninh Thuan NPP The critical decisions by government authorities, such as the evacuation plan or long-term preparedness plans in case of NPP accident, or the policies on safety and environment, should be made based on the more reliable and sophisticated estimations over the whole-range of atmospherics conditions of the real NPP locations Despite of this limitation, our proposed model can provide the useful information for government planners and Vietnamese residents, especially during the current situation when the NPP program in Vietnam is just starting the very first steps and the residents are worried about the impacts of this program In these circumstances, even the well-equipped meteorological station is not started to be built in Ninh Thuan and no available assessment of radionuclide release in the atmosphere in case of NPP accident is carried out by VINATOM (Vietnam Automic Energy Institute), our model can be seen as the only way to provide the brief picture about the range of impact in case of radionuclide releasing in the atmosphere The spatial risk maps and the critical zone planning around the Ninh Thuan NPP site provided by our proposed method not only can provide the suggestions for planners during the first-round risk assessment, 104 but also be useful information for government to persuade the residents about the feasibility of the nuclear program in Ninh Thuan Province 8.2 Conclusion and Future Plan In summary, this research provides a method for assessing the radiological risk that can work under the limitation of meteorological data The method not only estimates the probability release of radionuclide but also 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Transport in The Atmosphere – A Case Study of Hypothetical Reactor Accident in Ninh Thuan Province, Vietnam”, Transactions on GIGAKU, GIGAKU Press, Nagaoka University of Technology, Vol.2, No.1, October 2014 113 CONFERENCES (1) Dung Quoc Ho, Yoshiki Mikami, “Geospatial Risk Assessment of Nuclear Power Plant Accidents and It’s Implication to Area Zoning Plant and Emergency Plan - A Case of Ninh Thuan Nuclear Power Plant, Vietnam”, The 3rd International GIGAKU Conference, Nagaoka University of Technology, 20-22 June, 2014 (2) Dung Quoc Ho, Yoshiki Mikami, “Spatial Risk Map of Radionuclide - A Case Study of Hypothetical Reactor Accident in Ninh Thuan Province, Vietnam”, The 1st International Conference on Energy Environment and Human Engineering, Yangon, Myanmar, 21-23 December, 2013 (3) Dung Quoc Ho, Yoshiki Mikami, “Estimating the Transport of Radioactive Materials Released to the Atmosphere - A Case Study of Hypothetical Reactor Accident in Ninh Thuan Province, Vietnam”, The 10th National Nuclear Science and Technology Conference in Vietnam, Vietnam Atomic Energy Association, 15-16 August, 2013 (4) Dung Quoc Ho, Yoshiki Mikami, “An Assessment of Early Radionuclide Doses to Human - A Case Study of Hypothetical Reactor Accident in Ninh Thuan Province, Vietnam”, The 2nd International GIGAKU Conference, Nagaoka University of Technology, 21-23 June, 2013 114