[en] In this study, we performed an importance analysis of the in-service testing(IST) components for Ulchin Units 3 using the PSA and the integrated importance analysis method developed in this study. The quantitative importance analysis using PSA was performed through Level 1 and 2 internal PSA, external PSA, and shutdown/low power operation PSA. The integrated importance analysis method developed in this study was applied to the importance analysis of components neither modeled nor identified as high safety significant components (HSSCs) in PSA. It is basically aimed at having a PSA expert perform an importance analysis using PSA and its related information. It is a substitute for an expert panel in the risk-informed IST. It consists of the simplified failure modes and effects analysis, the quantitative evaluation for the component failure mode assumed to have the most significant effect, and the integrated evaluation procedures of components importance analysis. The final importance analysis results of valves show that 167 (26.55%)of the 629 IST valves is HSSCs and 462(73.45%) is low safety significant components (LSSCs). The final importance analysis of pumps results also show that 28 (40%)of the 40 IST pumps is HSSCs and 12(30%) is LSSCs

[en] As part of the Probabilistic Safety Assessment of safety grade digital systems used in Nuclear Power plants research, measures and methodologies applicable to quantitative reliability assessment of safety critical software were surveyed. Among the techniques proposed in the literature we selected those which are in use widely and investigated their limitations in quantitative software reliability assessment. One promising methodology from the survey is Bayesian Belief Nets (BBN) which has a formalism and can combine various disparate evidences relevant to reliability into final decision under uncertainty. Thus we analyzed BBN and its application cases in digital systems assessment area and finally studied the possibility of its application to the quantitative reliability assessment of safety critical software

[en] Current reliability assessments of safety critical software embedded in the digital systems in nuclear power plants are based on the rule-based qualtitative assessment methods. But practical needs require the quantitative features of software reliability for Probabilistic Safety Assessment (PSA) that is one of important methods being used in assessing the whole safety of nuclear power plant. This paper discusses a Bayesian Belief Nets(BBN) based quantification method that models current qualitative software assessment in formal way and produces quantitative results required for PSA. Commercial Off-The-Shelf(COTS) software dedication process was applied to the discussed BBN based method for evaluating the plausibility of the method in PSA

[en] Digital I and C systems are being used widely in the Non-safety systems of the NPP and they are expanding their applications to safety critical systems. The regulatory body shifts their policy to risk based and may require Probabilistic Safety Assessment for the digital I and C systems. But there is no established reliability prediction methodology for the digital I and C systems including both software and hardware yet. This survey report includes a lot of reliability prediction methods for electronic systems in view of hardware. Each method has both the strong and the weak points. This report provides the state-of-art of prediction methods and focus on Bellcore method and MIL-HDBK-217F method in deeply. The reliability analysis models are reviewed and discussed to help analysts. Also this report includes state-of-art of software tools that are supporting reliability prediction

[en] This paper describes the overall methods to handle the dependencies between human errors showed in shutdown PSA based on the insights from low power and shutdown PSA. This paper includes an evluation method of human dependencies in the context of human reliability analysis and how to model them in accident sequence analysis and quantify them. Many human actions are modeled in shutdown PSA because almost safety systems are manually operated during shutdown. Those human actions greatly affect the core damage frequency. In particular, it is very important to treat properly the dependencies of multiple human errors in the cutest level in the shutdown PSA

[en] Digital I and C systems are being used widely in the non-safety systems of the NPP and they are expanding their applications to safety critical systems. The regulatory body shifts their policy to risk based and may require Probabilistic Safety Assessment for the digital I and C systems. But there is no established reliability prediction methodology for the digital I and C systems including both software and hardware yet. This survey includes a lot of reliability prediction methods for electronic equipment in view of hardware. Each method has both the strong and the weak points. This report provides the state-of-art of prediction methods and focus on Bellcore TR-332 method and MIL-HDBK-217 method extensively

[en] Current reliability assessments of safety critical software embedded in the digital systems in nuclear power plants are based on the rule-based qualitative assessment methods. Then recently practical needs require the quantitative features of software reliability for Probabilistic Safety Assessment (PSA) that is one of important methods being used in assessing the whole safety of nuclear power plant. But conventional quantitative software reliability assessment methods are not enough to get the necessary results in assessing the safety critical software used in nuclear power plants. Thus, current reliability assessment methods for these digital systems exclude the software part or use arbitrary values for the software reliability in the assessment. This reports discusses a Bayesian Belief Nets (BBN) based quantification method that models current qualitative software assessment in formal way and produces quantitative results required for PSA. Commercial Off-The-Shelf (COTS) software dedication process that KAERI developed was applied to the discussed BBN based method for evaluating the plausibility of the proposed method in PSA

[en] This report is prepared to suggest a practical Probabilistic Safety Assessment (PSA) methodology of safety-critical digital instrumentation and control (I and C) systems. Even though conventional probabilistic safety assessment methods are immature for applying to microprocessor-based digital systems, practical needs force to apply it because the result of probabilistic safety assessment plays very important role in proving the safety of a designed system. Microprocessors and software technologies make the digital system very complex and hard to analyze the safety of their applications. The aim of this is: (1) To summarize the factors which should be represented by the model for probabilistic safety assessment and to propose a standpoint of evaluation for digital systems. (2) To quantitatively presents the results of a mathematical case study which examines the analysis framework of the safety of digital systems in the context of the PSA. (3) To show the results of a sensitivity study for some critical factors

[en] This report describes the review results of the safety assessment and reliability analysis techniques of digital instrumentation and control (I and C) systems. The techniques are far from that of analog I and C systems because of the characteristics of digital systems. This report categorizes the current issues related to the safety assessment of digital I and C systems into three groups as follows: 1. The methodologies which could integrate the characteristics of hardware and that of software. 2. The methodologies which effectively represent safety improvement due to the fault-tolerant mechanisms embedded in digital I and C systems. 3. The methodologies which could effectively represent the phased-mission systems. (author)

[en] Enhancement of public understanding on the nuclear safety charter - Framing draft of preamble and articles in nuclear safety charter - Collection of professionals' concerns in the field of nuclear - Completion of explanatory text on the preambles and articles in charter. Enhancement of public confidence on the nuclear safety - Setting new publicity strategy involving animation technic to improve harmony with public - Development of public information prototype and materials about preamble and articles in the nuclear safety