Recent research towards integrated deterministic-probabilistic safety assessment in Korea

Heo, Gyunyoung,Baek, Sejin,Kwon, Dohun,Kim, Hyeonmin,Park, Jinkyun Korean Nuclear Society 2021 Nuclear Engineering and Technology Vol.53 No.11

For a long time, research into integrated deterministic-probabilistic safety assessment has been continuously conducted to point out and overcome the limitations of classical ET (event tree)/FT (fault tree) based PSA (probabilistic safety assessment). The current paper also attempts to assert the reason why a technical transformation from classical PSA is necessary with a re-interpretation of the categories of risk. In this study, residual risk was classified into interpolating- and extrapolating-censored categories, which represent risks that are difficult to identify through an interpolation or extrapolation of representative scenarios due to potential nonlinearity between hardware and human behaviors intertwined in time and space. The authors hypothesize that such risk can be dealt with only if the classical ETs/FTs are freely relocated, entailing large-scale computation associated with physical models. The functional elements that are favorable to find residual risk were inferred from previous studies. The authors then introduce their under-development enabling techniques, namely DICE (Dynamic Integrated Consequence Evaluation) and DeBATE (Deep learning-Based Accident Trend Estimation). This work can be considered as a preliminary initiative to find the bridging points between deterministic and probabilistic assessments on the pillars of big data technology.

Design evaluation of emergency core cooling systems using Axiomatic Design

Heo, Gyunyoung,Lee, Song Kyu Elsevier 2007 Nuclear engineering and design Vol.237 No.1

<P><B>Abstract</B></P><P>In designing nuclear power plants (NPPs), the evaluation of safety is one of the important issues. As a measure for evaluating safety, this paper proposes a methodology to examine the design process of emergency core cooling systems (ECCSs) in NPPs using Axiomatic Design (AD). This is particularly important for identifying vulnerabilities and creating solutions. Korean Advanced Power Reactor 1400MWe (APR1400) adopted the ECCS, which was improved to meet the stronger safety regulations than that of the current Optimized Power Reactor 1000MWe (OPR1000). To improve the performance and safety of the ECCS, the various design strategies such as independency or redundancy were implemented, and their effectiveness was confirmed by calculating core damage frequency. We suggest an alternative viewpoint of evaluating the deployment of design strategies in terms of AD methodology. AD suggests two design principles and the visualization tools for organizing design process. The important benefit of AD is that it is capable of providing suitable priorities for deploying design strategies. The reverse engineering driven by AD has been able to show that the design process of the ECCS of APR1400 was improved in comparison to that of OPR1000 from the viewpoint of the coordination of design strategies.</P>

Reverse Estimation for Particle Deposition of UO2F2 (holdup) Using Numerical Simulation: Survey and Research Status

Sungmin Yang,Gyunyoung Heo,Seungmin Woo,Changwoo Kang,Yeongchan Kim 한국방사성폐기물학회 2021 한국방사성폐기물학회 학술논문요약집 Vol.2021 No.11

Tritium Productivity Evaluation of Graphite-moderated Reactor Using MCNP6

Sungmin Yang,Gyunyoung Heo,Seung Min Woo 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

North Korea claimed to have tested a hydrogen bomb in its fourth nuclear test in 2016, and declared that the hydrogen bomb was completed after the sixth nuclear test in 2017. North Korea’s operation of Yongbyon Graphite-moderated reactor has been thought to be aimed at producing plutonium, but it has been strongly argued that the restart of the Graphite-moderated reactor is, indeed, aimed at supplying tritium recently. Tritium can be used not only to manufacture hydrogen bombs, but also to miniaturize nuclear weapons, making it as a key material for nuclear weapon capability. Since upgrading nuclear weapons and developing hydrogen bombs through the use of tritium by North Korea could pose a major threat to the security of the Korean Peninsula, it is important to accurately evaluate North Korea’s nuclear weapon capabilities through the analysis of nuclear material production scenarios based on its nuclear facilities. However, researches on North Korea’s nuclear materials such as HEU (Highly Enriched Uranium) and Pu production has been actively conducted, while no research has been shown on tritium production yet. Therefore, this study aims to evaluate the tritium productivity based on the analysis of hypothetical nuclear material production facilities and possible tritium production scenarios. Basic research was conducted about the existing theoretical methodology for tritium production, the analysis of the global tritium production history, and the analysis of nuclear facilities. Based on this basic investigation, feasible tritium production scenarios were constructed. Subsequently, based on design criteria of an hypothetical Graphite-moderated reactor, possible tritium production scenario was modeled by applying the TPBAR (Tritium Production Burnable Absorber Rod). In addition, the factors such as 6Li concentration, design parameters, material compositions, and the number of TPBARs, which may affect tritium throughput were analyzed in terms of sensitivity study such that the maximum and minimum throughput can be predicted.

Online Cross Calibration Technique Considering Missing Data for Redundant Sensors in Research Reactor

Moath Kassim,Gyunyoung Heo 대한전자공학회 2016 대한전자공학회 학술대회 Vol.2016 No.4

For better accuracy and healthy monitoring, redundant signals usually used in nuclear power reactors and research reactors to measure plant conditions. A Cross Calibration (CC) method is widely used to evaluate sensors performance and help operators and maintenance staff to determine the proper time for sensor calibration. This paper presents an online calibration monitoring technique that can check sensors’ signals deviation including wide range of missing data, particularly for small-size research reactors which have a weak signal validation algorithm comparing with large-size power reactors. The HANARO (Hi-flux Advanced Neutron Application Reactor) which is an operating research reactor at KAERI (Korea Atomic Energy Research Institute) provided data sets to be analyzed, and then a statistical algorithm was built to solve the problem using the Weighted Average (WA) method by assigning weight percentage for each sensor’s signal point independently, and skipping the unknown values. For making it more dynamic and flexible, points of signal were averaged with their weigh percentage to avoid including the number of sensors in the calculation. It is assumed that at least one sensor is functioning well within its operation limits, so averaging was done and an acceptable averaging band was proposed to be compared with all sensors’ signals, where the out of band signal identified as a sensor defect. And, as it is expected, the in-house code developed will analyze HANARO data or any data that has missing values problem, and then alarm message will be initiated as a result to show if any sensor really needs calibration. This code excluded the case that all sensors are deviated together.

A Study on North Korea’s Denuclearization Policy Suggestion Through Ukraine-Russia War Analysis

Sungmin Yang,Gyunyoung Heo 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.2

Since the 1992 ‘Joint Declaration of South and North Korea on the Denuclearization of the Korean Peninsula’ was agreed, various negotiations and policies have been conducted. There were policies such as CVID, Strategic Patience, Top-Down Approach, Calibrated Practical Approach, Audacious Initiative and the Geneva Agreement, and 9.19 Joint statement by the six-party talks were signed to denuclearize Korean Peninsula. However, starting with the first nuclear test in 2006, North Korea conducted six nuclear tests to develop atomic bombs, boosted fission bombs, ICBMs, and SLBMs to enhance its weapon capabilities. In addition, nuclear security crisis on the Korean Peninsula has been rising day by day as signs of restarting the North Korea’s Yongbyon 5MWe Graphite-moderated reactor were observed and the possibility of a seventh nuclear test have been increased. Since North Korea’s nuclear issue has a lot of influence on international security, especially on the Northeast Asian countries, a realistic denuclearization policy that reflects North Korea’s current domestic situation along with the international situation is needed. It’s been six months since Russia invaded Ukraine on February 24, 2022. The war between Russia, which has nuclear weapons, and Ukraine, which gave up its possession of nuclear weapons due to the Cooperative Threat Reduction (CTR) program known as the Nunn-Lugar program, is expected to have a significant impact on North Korea, which is considering denuclearization due to UN sanctions on North Korea. Therefore, in this study, based on the war patterns of Russia-Ukraine war, perspective on how it could affect North Korea’s denuclearization is analyzed. Also, significance and limitations of the previous nuclear negotiations, the North Korea’s political regime, the ‘five-year strategy for North Korea’s economic development’ and the ‘five-year plan for North Korea’s economic development’ were analyzed to suggest practical DPRK’s denuclearization policy.

Online Cross Calibration Technique Considering Missing Data for Redundant Sensors in Research Reactor

Moath Kassim,Gyunyoung Heo 대한전기학회 2016 정보 및 제어 심포지엄 논문집 Vol.2016 No.4

For better accuracy and healthy monitoring, redundant signals usually used in nuclear power reactors and research reactors to measure plant conditions. A Cross Calibration (CC) method is widely used to evaluate sensors performance and help operators and maintenance staff to determine the proper time for sensor calibration. This paper presents an online calibration monitoring technique that can check sensors’ signals deviation including wide range of missing data, particularly for small-size research reactors which have a weak signal validation algorithm comparing with large-size power reactors. The HANARO (Hi-flux Advanced Neutron Application Reactor) which is an operating research reactor at KAERI (Korea Atomic Energy Research Institute) provided data sets to be analyzed, and then a statistical algorithm was built to solve the problem using the Weighted Average (WA) method by assigning weight percentage for each sensor’s signal point independently, and skipping the unknown values. For making it more dynamic and flexible, points of signal were averaged with their weigh percentage to avoid including the number of sensors in the calculation. It is assumed that at least one sensor is functioning well within its operation limits, so averaging was done and an acceptable averaging band was proposed to be compared with all sensors’ signals, where the out of band signal identified as a sensor defect. And, as it is expected, the in-house code developed will analyze HANARO data or any data that has missing values problem, and then alarm message will be initiated as a result to show if any sensor really needs calibration. This code excluded the case that all sensors are deviated together.

Solving partial differential equation for atmospheric dispersion of radioactive material using physics-informed neural network

Gibeom Kim,Gyunyoung Heo Korean Nuclear Society 2023 Nuclear Engineering and Technology Vol.55 No.6

The governing equations of atmospheric dispersion most often taking the form of a second-order partial differential equation (PDE). Currently, typical computational codes for predicting atmospheric dispersion use the Gaussian plume model that is an analytic solution. A Gaussian model is simple and enables rapid simulations, but it can be difficult to apply to situations with complex model parameters. Recently, a method of solving PDEs using artificial neural networks called physics-informed neural network (PINN) has been proposed. The PINN assumes the latent (hidden) solution of a PDE as an arbitrary neural network model and approximates the solution by optimizing the model. Unlike a Gaussian model, the PINN is intuitive in that it does not require special assumptions and uses the original equation without modifications. In this paper, we describe an approach to atmospheric dispersion modeling using the PINN and show its applicability through simple case studies. The results are compared with analytic and fundamental numerical methods to assess the accuracy and other features. The proposed PINN approximates the solution with reasonable accuracy. Considering that its procedure is divided into training and prediction steps, the PINN also offers the advantage of rapid simulations once the training is over.

Urban Zone Discovery from Smart Card-Based Transit Logs

JUNG, Jae-Yoon,HEO, Gyunyoung,OH, Kyuhyup INSTITUTE OF ELECTRONICS, INFORMATION & 2017 IEICE TRANSACTIONS ON INFORMATION AND SYSTEMS E SE Vol.100e.d No.10

<P>Smart card payment systems provide a convenient billing mechanism for public transportation providers and passengers. In this paper, a smart card-based transit log is used to reveal functionally related regions in a city, which are called zones. To discover significant zones based on the transit log data, two algorithms, minimum spanning trees and agglomerative hierarchical clustering, are extended by considering the additional factors of geographical distance and adjacency. The hierarchical spatial geocoding system, called Geohash, is adopted to merge nearby bus stops to a region before zone discovery. We identify different urban zones that contain functionally interrelated regions based on passenger trip data stored in the smart card-based transit log by manipulating the level of abstraction and the adjustment parameters.</P>

Cyber attack taxonomy for digital environment in nuclear power plants

Kim, Seungmin,Heo, Gyunyoung,Zio, Enrico,Shin, Jinsoo,Song, Jae-gu Korean Nuclear Society 2020 Nuclear Engineering and Technology Vol.52 No.5

With the development of digital instrumentation and control (I&C) devices, cyber security at nuclear power plants (NPPs) has become a hot issue. The Stuxnet, which destroyed Iran's uranium enrichment facility in 2010, suggests that NPPs could even lead to an accident involving the release of radioactive materials cyber-attacks. However, cyber security research on industrial control systems (ICSs) and supervisory control and data acquisition (SCADA) systems is relatively inadequate compared to information technology (IT) and further it is difficult to study cyber-attack taxonomy for NPPs considering the characteristics of ICSs. The advanced research of cyber-attack taxonomy does not reflect the architectural and inherent characteristics of NPPs and lacks a systematic countermeasure strategy. Therefore, it is necessary to more systematically check the consistency of operators and regulators related to cyber security, as in regulatory guide 5.71 (RG.5.71) and regulatory standard 015 (RS.015). For this reason, this paper attempts to suggest a template for cyber-attack taxonomy based on the characteristics of NPPs and exemplifies a specific cyber-attack case in the template. In addition, this paper proposes a systematic countermeasure strategy by matching the countermeasure with critical digital assets (CDAs). The cyber-attack cases investigated using the proposed cyber-attack taxonomy can be used as data for evaluation and validation of cyber security conformance for digital devices to be applied, and as effective prevention and mitigation for cyber-attacks of NPPs.