Multi external event probabilistic safety assessment framework

Korea has been achieving the world best safety and economic performance of nuclear power plants through continuous technology development and asset management optimization since its first nuclear power reactor was introduced in the late 1970s. While most countries have stopped building new nuclear power plants since the severe accident in TMI nuclear plant in 1979, Korea has been steadily developing its own reactor models and constructing new nuclear plants. In addition, Korea won recent new nuclear plant project of United Arab Emirates (UAE) as a result of these efforts. A nuclear power plant consists of a great variety of complex equipment having state-of-the-art technologies, and the highest nuclear safety and equipment reliability are required. Therefore, the most sophisticated systematic engineering asset management is essential to the nuclear power plant. As a responsible company of operating and constructing all nuclear power plants in Korea, Korea Hydro and Nuclear Power Co. (KHNP) has developed its own asset management model for the nuclear power plants in operation and expanded the model into the new plants under construction. Since the asset management model was developed for the various equipment types in the nuclear power plant, it can be easily utilized in other industries as a highly effective asset management model. This paper presents new and innovative methods to refine and improve existing asset management practices in general plants by diagnosing KHNP’s physical asset management model. It contributes to the development and improvement of an advanced asset management model for general plant industries and utilities to meet the objectives of securing a clean environment, improved public health and safety, and general community well being.

To the Editor: I read with great interest the recent article (1) and subsequent debate (2, 3) regarding the cohort study on cancer risks among those residing near nuclear power plants. Since the issue of health effects among populations living near nuclear facilities is an important topic within public health discourse, further scientific communication would contribute to a more complete understanding of radiation exposure and health. In this light, I would like to add a few comments on this issue. First, the study objective of the original investigation is indeed a fundamental issue which cannot be dismissed as a 'silly question'. If the study purpose is to identify the cancer risk due to radiation exposure from nuclear power plants, then it is difficult to justify why the original study did not include radiation-sensitive subpopulations such as fetuses or children from the beginning of the study. Also, considering that accurate exposure assessment is a vital component of environmental epidemiology, the simple application of a crude exposure index (i.e., distance from nuclear power plant) in this study raises questions related to the study purpose. I would judge that the main purpose of the original study was to build a prospective cohort of adults for cancer and other diseases rather than one focused on radiation exposure and cancer. Therefore, we need to acknowledge that while this is in fact a well-designed general cohort study, the cohort includes certain limitations for drawing causality with radiation exposure and cancer. Therefore, the results must be analyzed with caution. In my opinion, the results of this study should not be misleadingly interpreted as solid null findings rather than as inconclusive. Second, I am convinced that conducting a re-analysis of the existing dataset would be a worthwhile undertaking in order to investigate the association in greater depth. This is not a case of right versus wrong, but a natural process of investigating the truth. Existing and future findings together will contribute to a better understanding of the full scope of the radiation effect. A re-analysis study may provide us with valuable distinct approaches and considerations. Continued monitoring of health outcomes, refinement of exposure assessment, and corresponding updates of analysis are fundamental elements and advantages of cohort studies. Since the government and a number of researchers have dedicated considerable time, effort and funds to this cohort, I believe the existing data, as a national asset, need to be actively applied in support of the public interest. However, we must at the same time acknowledge the limitations of the original cohort which may continue to hinder the investigation of the association between radiation exposure and cancer risk even after applying more sophisticated statistical analyses. Therefore, additional efforts to compensate for the limitations of this study, in particular improving exposure assessment, minimizing exposure misclassification, and conducting new epidemiologic studies focusing on children, are warranted in order to better shed light on the association between radiation exposure from nuclear power plants and the development of cancer. Third, I would like to point out that there remain certain uncertainties in estimating cancer risk associated with exposure to ionizing radiation. Even the Life Span Study of Japanese atomic bomb survivors, which serves as a quantitative basis for radiation risk estimation worldwide, featured drawbacks including selection bias, immortal bias, and missing information (4). It is difficult to state that a low level of measured radiation can on its own completely guarantee no increased cancer risk for those living near nuclear power plant sites. The discrepancy between measured radiation doses and cancer risk remains mainly unexplained, and a possible hypothesis has been suggested (5). Although the majority of previous studies on cancer risks in populations near nuclear facilities have reported null findings except in the case of childhood leukemia (6), it is the role of epidemiology to clarify this issue of whether or not the observed cancer risk is related with radiation. Therefore, I would like to emphasize the importance of epidemiologic study in combination with surveillance data on radiation doses in populations near nuclear power plants. I believe that constructive discussions focusing on research itself can further advance radiation epidemiology in Korea and I hope this journal can serve as a means to accomplish this in its basic role as a scientific journal.

Derivation of dose constraint for the general public around nuclear power plants with operational data of radioactive effluent releases

2017년 6월에 영구정지 된 고리 1호기의 해체는 한국의 상업 원전에 대한 첫 해체 사례가 될 것이다. 해체 과정 중에 발생하 는 폐기물에 대한 처분은 전체 해체 비용의 많은 부분을 차지한다. 따라서 방사화 및 오염된 콘크리트 구조물은 적절한 해체 전략을 수립하여 경제적이고 안전하게 해체되어야 한다. 본 논문에서는 생물학적 차폐체에 대한 최적화된 해체 및 처분 시 나리오를 연구하였다. 해체사례, 폐기물 처분 규정 및 처리 기술을 분석하였다. 그리고 생물학적 차폐체 제거 과정의 폐기물 발생량을 최소화하기 위해서, 최적 해체 시나리오를 제시하였고 폐기물 처분 방안을 도출하였다.

Background: On June 18, 2017, Korea's first commercial nuclear reactor, the Kori Nuclear Power Plant No. 1, was permanently suspended, and the capacity of nuclear power generation facilities will be adjusted according to the governments denuclearization policy. In these circumstances, it is necessary to assess the quality of radiation safety management in nuclear power plants in Korea by evaluating the radiation dose associated with them.

Design modification of a feedwater heater impingement baffle to mitigate shell wall thinning by flow acceleration corrosion

Identifying human failure events (HFEs) for external hazard probabilistic risk assessment

The aim of this study is to verify if the reliability of a digital four-channel RPS under the design phase satisfies the specified target and to identify the weakness of system design and potential solutions for system reliability improvement. The event-tree/fault-tree (ET/FT), which is the method used in the current probabilistic safety assessment (PSA) framework of nuclear power plants (NPPs), was adopted to developed reliability modeling for the RPS with the Top Events defined as the system failure to generate reactor trip signal and the system generating spurious trip signal. The evaluation results indicate that the probability of the system failure on demand and the frequency of spurious trip signal generation are 1.47 × 10−6 with a 95% upper bound of 4.63 × 10−6 and 7.94 × 10−4/year with a 95% upper bound of 2.50 × 10−3/year, respectively. The importance and sensitivity analyses were conducted and it was found that undetected unsafe common cause failures (CCFs) of signal conditioning modules (SCMs) dominate the system reliability. Two preliminary optimization schemes relative to reducing periodic test interval and adapting two kinds of diverse SCMs were proposed. Results of the quantitive evaluation of the schemes show that neither of them could determinedly improve the system reliability to the target level. In the future, more detailed optimization analysis shall be required to determine a feasible system design optimization scheme.

The Reactor Experiment for Neutrino Oscillation (RENO) started data-taking from August 2011 and has successfully measured the smallest neutrino mixing angle $\theta _{13}$ by observing the disappearance of reactor electron antineutrinos. Electron antineutrinos from the six reactors at Hanbit Nuclear Power Plant in Korea are detected and compared by the two identical near-and-far detectors. RENO has published precise values of $\theta _{13}$ and its measurement of $\Delta m^{2}_{ee}$ based on energy dependent disappearance probability. In this paper, we present an updated measurement of $\theta _{13}$ and $\Delta m^{2}_{ee}$ based on roughly 3000 days of data, an independent measured value of $\theta _{13}$ based on 1500 days of data with neutron capture on hydrogen as a delayed signal, and a sterile neutrino search result.

Preparation of Radiological Environmental Impact Assessment for the Decommissioning of Nuclear Power Plant in Korea

A Precise Measurement of Reactor Antineutrino at RENO

Design of condensation heat exchanger for the PAFS (Passive Auxiliary Feedwater System) of APR+ (Advanced Power Reactor Plus)

Derivation of site-specific derived concentration guideline levels at Korea Research Reactor-1&2 sites

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All nuclear power plants must consider external flooding hazards such as local intense precipitation, riverine flooding, flooding due to upstream dam failure, and coastal flooding due to storm surge or tsunami. While external flooding events could potentially interrupt off-site power, threaten plant structures, systems and components important to safety, or limit plant access, they have often been qualitatively assessed as risk insignificant and screened out from detailed evaluation and quantification. Recent lessons learned from the Fukushima seismic/tsunami initiated nuclear accident (2011), the Fort Calhoun (2011), Vermont Yankee (2013), Arkansas Nuclear One (2013), and St. Lucie (2014) flooding events have highlighted the need for more detailed risk analysis. However, incorporating an external flood model into the traditional event tree/fault tree approach used in static probabilistic risk assessment (PRA) models is challenging because it is difficult to accurately represent plant system and component behavior and reliability of manual actions during an ever-progressing flood event. The plant response to external flood may be highly spatial and time dependent, subject to the hydrological and hydraulic characteristics of the flood event. Such unique challenges prompt the investigation of using simulation-based dynamic analysis approaches for external flood risk assessment. Simulation methods can better model the performance of structures, systems, and components during an external flooding event. A general framework to perform a simulation-based dynamic flooding analysis is presented in this paper with the subtasks of flood hazard analysis, flood fragility analysis, plant response modeling, safety margin analysis or PRA quantification. A new type of PRA technique, State-based PRA Modeling, is introduced to incorporate time-related interactions such as those from both 3D physical simulations and random failures into traditional PRA logic models.