Wolsong Nuclear Power Plant Research Articles

Dose analysis of nearby residents and workers due to the emission accident of gaseous radioactive material at the spent resin mixture treatment facility

The dose from a possible accident at a microwave-based spent resin mixture treatment facility that was to be installed and operated at the Wolsong nuclear power plant was analyzed to evaluate the radiological safety prior to its installation and operation. The dose to which workers and nearby residents are likely to be exposed was calculated based on the atmospheric dispersion and deposition factors using the XOQDOQ code. The highest atmospheric dispersion factors were 1.349E-05 s/m3 (workers) and 1.534E-06 s/m3 (residents). The highest doses due to emissions from the mock-up tank before operation were 1.91E-06 mSv (workers) and 1.78E-07 mSv (residents). Even after 3 h of operation, emissions from the mock-up tank had the greatest impact ranging from 4.63E-08 to 1.24E-06 mSv (workers) and 2.74E-10 to 1.16E-07 mSv (residents), respectively. The doses were 7.09E-09–4.55E-07 mSv and 4.18E-11–4.25E-08 mSv at 4–5 h of operation, and the maximum doses after operation reached 5.69E-07 mSv and 5.31E-08 mSv for the workers and residents, respectively.Even at the exclusion area boundary (EAB), 4.76E-08–9.51E-07 mSv (annual dose:9.52E-05–1.90E-03 mSv/y) was below the dose limit of the EAB, and the safety of the facility installation inside the NPP was confirmed.

Multi-Hazard Risk Assessment of South Korean Nuclear Power Plants

Multi-hazard risk assessments of potential earthquake-triggered tsunamis with the positive contribution of climate change-related sea level rise (SLR) are performed for Hanul and Shin-Hanul (originally the Uljin), Kori and Shin-Kori, and Wolsong and Shin-Wolsong Nuclear Power Plants (NPPs) throughout the 21st century. Logic tree approach is used to construct probabilistic tsunami hazard model for evaluating the inundation levels at the coast of each NPP. Hypothetical earthquake sources are generated throughout the East Sea (Sea of Japan) using Monte Carlo Simulations. Epistemic uncertainty of the sea level rises and aleatory variability of the tsunami hazards is considered for stochastic multi-hazard assessment. Tsunami simulations are performed using revised bathymetric levels based on SLR projections of different Shared Socioeconomic Pathways (SSP) revealed by the Intergovernmental Panel on Climate Change (IPCC). Tsunami hazard curves are presented to determine the level of the adverse effects of SLR on tsunami inundations for the projected years. Environmental risk assessment is conducted by evaluating multi-hazard curves. The results show that the effect of SLR will be extremely significant on tsunami inundation levels, especially for the worst-case scenario estimated by IPCC. Depending on the multi-hazard risk assessments, Hanul NPP is the only site to survive against the worst-case scenario. Wolsong and Shin Wolsong NPP is under moderate multi-hazard risk. Whereas, Kori and Shin-Kori NPP may encounter a destructive multi-hazard environmental risk according to the analysis conducted in this study.

Preliminary Evaluation of Derived Concentration Guideline Level for Surface Soil at Wolsong NPP Site Using RESRAD-ONSITE Code

A preliminary derived concentration guideline level (DCGL) was calculated for the soil of the Wolsong nuclear power plant (NPP) (the first commercial pressurized heavy water reactor in South Korea) site using the RESRAD-ONSITE computational code. In total, fourteen selected radionuclides were analyzed after considering the preliminary evaluation information of radionuclides observed in the pressure tube specimen in the Wolsong Unit 1 heavy water reactor and previous NPP decommissioning cases. Furthermore, a geological structure model of the Wolsong NPP site was established according to the safety analysis report of the Wolsong NPP. In addition, the distribution coefficients (Kd) of various radionuclides were derived using the JAEA-SDB and the pH information of the groundwater around the Wolsong NPP site. The DCGL for surface soil of the Wolsong NPP site was derived via the application of criteria for the site release to facilitate unrestricted reuse. Moreover, preliminary dose evaluation and relevant analysis were performed according to the Wolsong NPP site resident scenario. The novelty of this study lies in the first calculation of the preliminary DCGL values for the case of the pressurized heavy water reactor (Wolsong NPP) site. It is expected that further reliable DCGL results might be achievable if more precise radionuclide information and site-specific parameters with respect to the Wolsong NPP site are secured and applied in the future.

Feasibility study of synthesizing graphene quantum dots from the spent resin in a nuclear power plant to reduce disposal cost

The feasibility of synthesizing graphene quantum dots from spent resin in a nuclear power plant that was subject to decommissioning was experimentally analyzed, and the resulting reduction in disposal cost was estimated. Owing to radiation safety and regulatory issues, graphene quantum dots were synthesized using an uncontaminated ion-exchange resin, IRN150 H/OH, prior to its use in a nuclear power plant. The synthesis of graphene quantum dots was attempted, and the characteristics were analyzed using atomic force microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The characterization of synthesized graphene quantum dots showed it was possible to recycle the spent resin into graphene quantum dots. Considering the amount of spent resin at the Wolsong Nuclear Power Plant, it is estimated that 3932 drums of ILW reduce to 1636 drums of LLW and 786 drums of EW, and the disposal cost reduces by 42 310 612 USD, indicating the reduction of 79%.

Preparation of the Applicable Regulatory Guideline on Mixed Waste in Korea Based on the Analysis of US Laws and Regulations

Unit 1 of the Kori Nuclear Power Plant (NPP) and Unit 1 of the Wolsong NPP are being prepared for decommissioning; their decommissioning is expected to generate large amounts of intermediate-level, low-level, and very low level Waste. Mixed waste containing both radioactive and hazardous substances is expected to be produced. Nevertheless, laws and regulations, such as the Korean Nuclear Safety Act and Waste Management Act, do not define clear regulatory guidelines for mixed waste. However, the United States has strictly enforced regulations on mixed waste, focusing on the human health and environmental effects of its hazardous components. The U.S. Nuclear Regulatory Commission and the U.S. Department of Energy regulate the radioactive components of mixed waste under the Atomic Energy Act. The U.S. Environmental Protection Agency regulates the hazardous waste component of mixed waste under the Resource Conservation and Recovery Act. In this study, the laws, regulations, and authorities pertaining to mixed waste in the United States are reviewed. Through comparison and analysis with waste management laws and regulations in Korea, a treatment direction for mixed waste is suggested. Such a treatment for mixed waste will increase the efficiency of managing mixed waste when decommissioning NPPs in the near future.

Sorption behavior of cesium on silt and clay soil fractions

The effect of clay mineral composition on Cs adsorption behavior of silt and clay fractions (SC-fractions) of soil was investigated. Surface soil samples were collected within 2 km of Kori and Wolsong nuclear power plants in South Korea, and SC-fractions (<20 μm) were separated. The physicochemical properties of SC-fractions and types of clay minerals contained in the SC-fractions were analyzed. The cesium adsorption capacity of the SC-fractions, and affinity between the SC-fractions and Cs, were investigated by isothermal adsorption analysis using the dual-site Langmuir adsorption model. To understand selective adsorption of Cs, the radiocesium interception potential and distribution coefficient of the SC-fractions were analyzed in the presence or absence of competing ions. The radiocesium distribution coefficient of the SC-fractions showed a trend similar to that of the Langmuir sorption coefficient of high-affinity binding sites for Cs in the SC-fractions. The SC-fractions of Kori soils that contain only non-expandable clay minerals including highly weathered mica had low Cs adsorption capacity. However, the SC-fractions of Kori soils showed higher Cs adsorption selectivity compared to the SC-fractions of Wolsong soils containing expandable clay minerals and micaceous mineral with a low degree of weathering. It is predicted that the highly weathered micas have high affinity to Cs, and such clay minerals contribute the most to the adsorption process in dilute solutions.

An artificial intelligence-based approach to predicting seismic hillslope stability under extreme rainfall events in the vicinity of Wolsong nuclear power plant, South Korea

Rainfall and earthquakes are two significant triggering factors of mass movement. Since the Gyeongju earthquake on 12 September 2016, which took place near the Wolsong nuclear power plant, many concerns have been raised about the threat posed by landslides during intense rainfall. In this study, we developed a new methodological approach to assess the stability of hillslopes at the catchment scale. We applied a geographical information system (GIS)-based pseudo-static model to 10,000 representative sample points by coupling the steady state infiltration corresponding to extreme rainfall and seismic force. Thus, we obtained the factor of safety of the representative sample points and set it as our target variable. The target variable was divided into two subsets: 80% of the data was used to train the model and 20% was reserved for testing purposes. We then applied a deep learning neural network method to incorporate other spatial geo-environmental data such as topographic, hydrologic, soil, forest, and geology, i.e., independent variables that can be used to predict the factor of safety in the catchment scale. The accuracy of the model was assessed using Pearson’s correlation coefficient, which was 0.97 and 0.98 and root mean square error 0.301 and 0.290 in the cases of the training and testing data, respectively. The prediction results indicate that the integration approach produces reliable, accurate landslide susceptibility maps, which may be helpful to researchers working on landslide management strategies.

Tritium Distribution in the Low-Level and Intermediate-Level Wastes of a Korean CANDU Reactor

Korea Hydro & Nuclear Power Company, Ltd., has operated the Wolsong Tritium Removal Facility (WTRF) since 2007 to reduce tritium concentrations in the moderator and coolant of the Wolsong nuclear power plant. As a result of the WTRF operation, the concentration of tritium in the moderator and coolant significantly decreased from 2320 to 9.3 GBq/kg. In particular, the tritium concentrations of the radioactive waste directly affected by radioactivity in the moderator and coolant were reduced by up to 99% during the WTRF operation. For this purpose, a chemical separation and quantification method for tritium separation was developed, and its average recovery yield was 98%.

Tritium Research and Development Status at KAERI

Korea has 26 nuclear power plants (NPPs). Out of these 26 plants, 4 are Canada Deuterium Uranium (CANDU) reactors at the Wolsong nuclear power site. In CANDU reactors, deuterium oxide is used as a moderator/coolant, and tritium is produced whenever a deuterium oxide nucleus captures a neutron. The Wolsong Tritium Removal Facility was designed to remove tritium generated in CANDU reactors. We are introducing tritium environmental protection not only at the Wolsong NPP but also at the High-Flux Advanced Neutron Application Reactor (HANARO) and in high-temperature gas-cooled reactors (HTGRs). We present a tritium behavior analysis code and assess the concentration of tritium in combustible dry active waste. Advanced techniques are introduced to transfer tritium from tritiated water to the gaseous phase. In addition, research on the nuclear fusion tritium storage and delivery system, which is part of the fuel cycle, has been carried out. In this paper, we present the recent progress in the effort to develop tritium systems at the Korea Atomic Energy Research Institute.

A Shape of the Response Spectrum for Evaluation of the Ultimate Seismic Capacity of Structures and Equipment including High-frequency Earthquake Characteristics

In 2016, an earthquake occurred at Gyeongju, Korea. At the Wolsong site, the observed peak ground acceleration was lower than the operating basis earthquake (OBE) level of Wolsong nuclear power plant. However, the measured spectral acceleration value exceeded the spectral acceleration of the operating-basis earthquake (OBE) level in some sections of the response spectrum, resulting in a manual shutdown of the nuclear power plant. Analysis of the response spectra shape of the Gyeongju earthquake motion showed that the high-frequency components are stronger than the response spectra shape used in nuclear power plant design. Therefore, the seismic performance evaluation of structures and equipment of nuclear power plants should be made to reflect the characteristics of site-specific earthquakes. In general, the floor response spectrum shape at the installation site or the generalized response spectrum shape is used for the seismic performance evaluation of structures and equipment. In this study, a generalized response spectrum shape is proposed for seismic performance evaluation of structures and equipment for nuclear power plants. The proposed response spectrum shape reflects the characteristics of earthquake motion in Korea through earthquake hazard analysis, and it can be applied to structures and equipment at various locations.

Best-estimate severe accident and source term analysis for an ISLOCA scenario of a CANDU-6 plant using the MAAP-ISAAC code

An interfacing system LOCA (ISLOCA) is a bypass accident that results in the release of reactor coolant directly to the outside of a reactor building through a break in part of the low-pressure boundary of the reactor coolant system. Though the core damage frequency resulting from an ISLOCA scenario in the CANDU-6 type Wolsong nuclear power plant is very low, a direct release of radioactive nuclides to the environment could lead to severe radiation exposure among residents near the plant, and cannot be overlooked. For this reason, a quantitative evaluation of the amount of radioactive nuclides to be released to the environment was carried out by applying a best-estimate methodology to the MAAP-ISAAC code11MAAP-ISAAC is a CANDU version of MAAP owned by the Electric Power Research Institute, and a relevant accident management strategy for it was investigated in terms of a deterministic analysis. As part of this, an auxiliary building was additionally modeled to simulate deposition effects in the auxiliary building as well as pool scrubbing effects at the submerged break location following an ISLOCA. The decontamination effect by deposition and so on within the piping following an ISLOCA was evaluated. The analysis results showed that the decontamination factor for other nuclide groups excluding inert gas, Sb and Te2 nuclide groups was about 2.5. The analysis with consideration of all these decontamination effects was identified to yield a 78.4% reduction of Cs released to the environment compared with previous conservative analysis, which did not consider the decontamination effect within the ISLOCA piping and in the auxiliary building. In the case of the Wolsong CANDU plant, prior to external cooling water injection to the reactor vault (which is considered to be a Severe Accident Management Guidance (SAMG) accident management strategy), the amount of Cs-137 released to the environment exceeds the domestic regulatory requirement (100 TBq). In contrast, a sensitivity analysis in which an operator closes the test valve installed in a medium-pressure emergency core cooling system piping path and relieves the pressure of a reactor building using a containment filtered venting system (CFVS), met the aforementioned limitation for the amount of Cs-137 when an operator closes the test valve within 1 h following the accident and operates the CFVS properly (i.e., according to its operating procedure). This means that the appropriate accident management strategy for an ISLOCA scenario in the Wolsong CANDU plant can sufficiently prevent severe radiation exposure around the plant. Moreover, it is expected that these best-estimate methodologies developed from this study can be applied to all CANDU-6 plants.

Construction of Aquatic Environmental Database Near Wolsong Nuclear Power Plant

Radioactive materials are released into the air and deposited on the surface soil after a nuclear accident. Radionuclides deposited in soil are transported by precipitation to nearby environments and contaminate the surface water system. Basic data on surface watershed and soil erosion models have been collected and analyzed to evaluate the behavior of radionuclides deposited on surface soil after a nuclear accident. Data acquisition and analysis in aquatic environment were performed to investigate the physical characteristics and variation of biota in rivers and lakes of the Nakdong river area near the Wolsong nuclear power plant. For these purposes, a digital map, and hydrological, water quality and biota data were gathered and a systematic database (DB) was constructed in connection with them. Constructed aquatic DB will be supplied and used in surface watershed and soil erosion models for investigation of long-term movement of radionuclides in adsorptive form in surface soil. Finally, basic data and established models will be utilized for general radiological impact assessment in aquatic environment.

Study of Soil Erosion for Evaluation of Long-term Behavior of Radionuclides Deposited on Land

The accident at the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) resulted in the deposition of large quantities of radionuclides over parts of eastern Japan. Radioactive contaminants have been observed over a large area including forests, cities, rivers and lakes. Due to the strong adsorption of radioactive cesium by soil particles, radioactive cesium migrates with the eroded soil, follows the surface flow paths, and is delivered downstream of population-rich regions and eventually to coastal areas. In this study, we developed a model to simulate the transport of contaminated sediment in a watershed hydrological system and this model was compared with observation data from eroded soil observation instruments located at the Korea Atomic Energy Research Institute. Two methods were applied to analyze the soil particle size distribution of the collected soil samples, including standardized sieve analysis and image analysis methods. Numerical models were developed to simulate the movement of soil along with actual rainfall considering initial saturation, rainfall infiltration, multilayer and rain splash. In the 2019 study, a numerical model will be used to add rainfall shield effect by trees, evaporation effect and shield effects of surface water. An eroded soil observation instrument has been installed near the Wolsong nuclear power plant since 2018 and observation data are being continuously collected. Based on these observations data, we will develop the numerical model to analyze long-term behavior of radionuclides on land as they move from land to rivers, lakes and coastal areas.

ASSESSMENT OF RADIOLOGICAL DOSES FOR PEOPLE LIVING IN KOREA FOLLOWING ACCIDENTAL RELEASES OF RADIONUCLIDES FROM NUCLEAR POWER PLANTS IN KOREA AND CHINA.

Accidentally released radionuclides are dispersed into the environment and cause human exposure through various pathways. Concerns about radiological impacts of a possible Nuclear power plant (NPP) accident in neighboring countries, especially in China, are increasing in Korea. Dose assessments for the hypothetical nuclear accidents in Korea (Hanbit and Wolsong NPPs) and China (Tianwan NPP) were conducted using the developed Korean code system. The results show that there is a possibility that a Tianwan NPP accident could have a slightly greater or similar impact on certain parts of Korea compared to accidents occurring at domestic NPPs, and could affect Korea within a few days of the accident. This research is expected to be used as basic material for preparing against nuclear accidents in neighboring countries.

Dispersion and removal characteristics of tritium originated from nuclear power plants in the atmosphere

The activities of tritium in water-vapor (n = 649) and precipitation (n = 2404) samples were measured from 1998 to 2015 around the Wolsong nuclear power plant (NPP) site where four pressurized heavy water reactors and two pressurized water reactors operated. The activity concentrations of tritium in the water-vapor and precipitation samples were in the ranges of 2.2–2200 Bq/L and 0.3–1090 Bq/L, respectively. The concentrations of tritium in the water-vapor in spring were approximately 7 times higher than those in fall and winter, mainly owing to the wind directions at the power plant location. The annual geometric mean activities of tritium in the water-vapor and precipitation samples varied within 56% and 83% from the average, respectively, depending primarily on the annual discharge amount of tritium to the atmosphere. The activities of tritium in the water-vapor and precipitation samples rapidly decreased away from the power plant. Approximately 0.5–30% of tritium discharged from the NPP site was removed by precipitation to the ground within an area with a radius of 30 km from the NPP site, which linearly depended on the precipitation amount. Our results suggest that the wind direction and precipitation, in addition to the amount of discharge, are important factors that control the tritium concentrations in air near the NPP site.

Necessity of management for minor earthquake to improve public acceptance of nuclear energy in South Korea

Abstract As public acceptance of nuclear energy in Korea worsens due to the Fukushima accident and the earthquakes that occurred in the Gyeongju area near the Wolsong nuclear power plant (NPP), estimating the effects of earthquakes has become more essential for the nuclear industry. Currently, most countermeasures against earthquakes are limited to large-scale disasters. Minor-scale earthquakes used to be ignored. Even though people do not feel the shaking due to minor earthquakes and minor earthquakes incur little damage to NPPs, they can change the environmental conditions, for instance, underground water level and the conductivity of the groundwater. This study conducted a questionnaire survey of residents living in the vicinity of an NPP to determine their perception and acceptance of plant safety against minor earthquakes. The results show that the residents feel earthquakes at levels that can be felt by people, but incur little damage to NPPs, as minor earthquakes (magnitude of 2.0–3.9) and set this level as a standard for countermeasures. Even if a minor earthquake has little impact on the safety of an NPP, there is still a possibility that public opinion will get worse. This study provides analysis results about problems of earthquake measures of Korean NPPs and specific things that can bring about an effect of deterioration of public acceptance. Based on these data, this article suggests that active management of minor earthquakes is necessary for the sustainability of nuclear energy.

Weibull parameter calculation and estimation of wind speeds for the return period: A case study in the Kori and Wolsong NPP areas

This paper presents the results of a case study on a wind characteristic analysis performed using a probabilistic distribution function to evaluate the meteorology of the Kori and Wolsong nuclear power plants (NPPs) in the Republic of Korea. The return period for daily extreme wind speed considering the wind direction was estimated using a Weibull distribution for the Kori and Wolsong NPP sites. From the directional wind calculation, the Weibull scale parameter c ranged from 5.83 to 9.06 at the Kori site and from 4.53 to 6.79 at the Wolsong site. The shape parameter k ranged from 1.97 to 3.59 at the Kori site and from 2.56 to 4.77 at the Wolsong site. The minimum and maximum directional wind speeds for the return period were 10.29 and 21.00m/s in the WSW and WNW directions, respectively, at the Kori site and 6.54 and 12.07m/s, respectively, at the Wolsong site. The results of this research offer a useful reference to evaluate the site safety assessment for the construction of Shin-Kori units 5 and 6 near the Kori site and a 2nd-stage low-intermediate level radioactive waste depository site near the Wolsong site. The study results can also be utilized to plan an evacuation pathway during unexpected radiation emergency conditions.

Assessment of long-term trend for environmental radioactivity around Wolsong nuclear power plant in Korea

The radiological environment around Wolsong NPP site has been monitored since Wolsong Unit 1 started commercial operation in 1983, as required by regulations in Korea. As a result of the periodic safety review on Wolsong Unit 3 & 4 in 2011, the regulator recommended that an assessment on the long-term accumulation trend of environmental radioactivity around Wolsong Unit 3 & 4 should be performed. In response to this, the assessment was performed based on environmental monitoring data and non-parametric statistical tool (i.e., Mann–Kendall Test). The environmental monitoring data included indicator organisms, soil and marine deposit which were usually monitored for verification of the typical radioactivity level. Most results of the assessment showed no trend and only a few results showed a slight increase. It was concluded that the radioactivity accumulation due to the operation of the plant was insignificant and thus no concern has been raised regarding any effect on the safety and health of the residents around Wolsong NPP site. It is expected that the result of this study could be utilized to establish the plan and policy for environmental monitoring at other NPP sites.

Numerical simulation of air pollutant dispersion using an in situ tracer experiment at a nuclear site

A tracer dispersion experiment was conducted at the Wolsong Nuclear Power Plant, Korea to determine concentrations of airborne radioactive materials under weather conditions unfavorable to dispersion. The observed concentrations were compared with estimates from a Gaussian plume model to determine whether the model provides sufficiently conservative estimation under bad weather conditions and is therefore suited to radiological impact analysis at nuclear power facilities. It was found that the more often the meteorological data was used, the more advantageous it was in helping to understand the diffusion characteristics of radioactive materials.Most of the current computer models for estimating the dispersion of airborne radioactive materials, which are needed to gain construction approval for a nuclear power plant, are based on the Gaussian plume model. Overall, the Gaussian plume model overestimates the concentration of airborne radioactive materials compared with actual observations. This suggests that the model is suitably conservative to enable its use in radiological environmental impact assessment of the health risks to nearby communities.

Uncertainty analysis of CsI distribution for typical CANDU6 station blackout accident

This paper illustrates an application of a severe accident analysis code, ISAAC (Integrated Severe Accident Analysis Code for the CANDU plants), to the uncertainty analysis of fission product behaviors during a severe reactor accident. The ISAAC code is a system-level computer code capable of performing integral analyses of potential severe accident progressions in nuclear power plants, and whose main purpose is to support a level 2 probabilistic safety assessment or severe accident management strategy developments. The code employs lots of user options for supporting sensitivity and uncertainty analyses. The present application is mainly focused on determining an estimate of the fission products in the release and transport processes and the relative importance of the dominant contributors to the predicted fission products. The key modeling parameters and phenomenological models employed for the present uncertainty analysis are closely related to the fission product release correlations, vapor–aerosol equilibrium, vapor–surface equilibrium for a revaporization calculation, and aerosol decontamination factors. A typical CANDU6 type plant, the Wolsong nuclear power plant, was used as a reference plant for the analysis.