PC-based probabilistic safety assessment in Japan

The role of PC-based programs is becoming important in the area of PSA. The PC-based program QUEST has been developed to perform level-1 PSA at PNC. This program is an effective tool to examine the effects of the change in the plant design and/or operational procedures. Also, as a part of the full scope PSA activity for the prototype liquid metal fast breeder reactor, a systems analysis code network, which involves some PC-based programs, was developed and has been utilized to perform level-1 PSA with less manpower and more consistency. Further, a living PSA tool is currently being developed for the purpose of maintenance of or improvement in operational safety.     

Development and application of a Risk Assessment Tool

Probabilistic Safety Assessment (PSA) is a powerful method for evaluating the safety of nuclear facilities. PSA models are the basis of risk monitors, which can be utilized for monitoring the plant risk. The objective of this work was to develop a risk monitoring software tool, which could match the requirements for a risk monitor, according to standard reference documents. We tried to implement all required features in a user-friendly interface. In this paper a newly developed risk monitor called Risk Assessment Tool (RAT) is presented, and its main features and capabilities are introduced. Some of these features are: graphical event/fault tree developing interface, a 30-day risk profile, performing importance analysis, different administrative levels, and handling time-dependent failure data. In order to have an actual application, a case study is performed for Tehran Research Reactor, and the results are compared to the results obtained from a well-known reliability software package. In most cases, the results from two software tools match well.     

International survey on PSA figures of merit

Probabilistic safety assessment (PSA) figures of merit represent one of the most interesting topics in the use of PSA for safety-related applications. This is all the more interesting as the viewpoints and opinions of different experts on the use of importance factors could diverge. Even when the experts agree, the use of these measures is likely to involve a number of difficulties or pitfalls, especially if they are used too “mechanically”, without proper care. EDF considered the topic to be sufficiently important and controversial to justify exploratory studies as part of the scientific and technical monitoring program and to get advice, comments, and critical viewpoints from a number of international PSA experts and practitioners. This report presents a synthesis of the results of this international survey.     

Current status of methodologies for seismic probabilistic safety analysis

This report is a review of the methodology for conducting a seismic-probabilistic safety analysis (PSA) at a nuclear power station. The objective of this review is to provide an up-to-date review of the state-of-the-art of the various sub-methodologies that comprise the overall seismic-PSA methodology for addressing the safety of nuclear power stations, plus an overview of the whole methodological picture. In preparing this review, the author has had in mind several categories of readers and users: policy-level decision-makers (such as managers of nuclear power stations and regulators of nuclear safety), seismic-PSA practitioners, and PSA practitioners more broadly. The review concentrates on evaluating the extent to which today's seismic-PSA methodology produces reliable and useful results and insights, at its current state-of-the-art level, for assessing nuclear-power-station safety. Also, this review paper deals exclusively with seismic-PSA for addressing nuclear-power-station safety. Because the author is based in the U.S., it is natural that this review will contain more emphasis on U.S. experience than on experience in other countries. However, significant experience elsewhere is a major part of the basis for this evaluation.     

Software Assurance Using Structured Assurance Case Models

Software assurance is an important part of the software development process to reduce risks and ensure that the software is dependable and trustworthy. Software defects and weaknesses can often lead to software errors and failures and to exploitation by malicious users. Testing, certification and accreditation have been traditionally used in the software assurance process to attempt to improve software trustworthiness.In this paper, we examine a methodology known as a structured assurance model, which has been widely used for assuring system safety, for its potential application to software assurance. We describe the structured assurance model and examine its application and use for software assurance. We identify strengths and weaknesses of this approach and suggest areas for further investigation and testing.     

REX: An intelligent decision and analysis aid for reliability and risk studies

A review of the role of expert system technology in performing Probabilistic Risk Assessments (PRA) is presented. Important aspects of the system analysis part of PRA studies are discussed. Intensive human activities in system analysis are studied and represented in a rule based expert system called REX. Object oriented programming method is used to develop REX. All important aspects of REX development including its structure and important rules used are described. Finally our experience with REX is presented.     

Methods and practices used in incident analysis in the Finnish nuclear power industry

According to the Finnish Nuclear Energy Act it is licensee's responsibility to ensure safe use of nuclear energy. Radiation and Nuclear Safety Authority (STUK) is the regulatory body responsible for the state supervision of the safe use of nuclear power in Finland. One essential prerequisite for the safe and reliable operation of nuclear power plants is that lessons are learned from the operational experience. It is utility's prime responsibility to assess the operational events and implement appropriate corrective actions. STUK controls licensees' operational experience feedback arrangements and implementation as part of its inspection activities. In addition to this in Finland, the regulatory body performs its own assessment of the operational experience. Review and investigation of operational events is a part of the regulatory oversight of operational safety. Review of operational events is done by STUK basically at three different levels. First step is to perform a general review of all operational events, transients and reactor scram reports, which the licensees submit for information to STUK. The second level activities are related to the clarification of events at site and entering of events' specific data into the event register database of STUK. This is done for events which meet the set criteria for the operator to submit a special report to STUK for approval. Safety significance of operational events is determined using probabilistic safety assessment (PSA) techniques. Risk significance of events and the number of safety significant events are followed by STUK indicators. The final step in operational event assessment performed by STUK is to assign STUK's own investigation team for events deemed to have special importance, especially when the licensee's organisation has not operated as planned. STUK launches its own detail investigation once a year on average. An analysis and evaluation of event investigation methods applied at STUK, and at the two Finnish nuclear power plant operators Teollisuuden Voima Oy (TVO) and Fortum Power and Heat Oy (Fortum) was carried out by the Technical Research Centre (VTT) on request of STUK at the end of 1990s. The study aimed at providing a broad overview and suggestions for improvement of the whole organisational framework to support event investigation practices at the regulatory body and at the utilities. The main objective of the research was to evaluate the adequacy and reliability of event investigation analysis methods and practices in the Finnish nuclear power industry and based on the results to further develop them. The results and suggestions of the research are reviewed in the paper and the corrective actions implemented in event investigation and operating experience procedures both at STUK and at utilities are discussed as well. STUK has developed its own procedure for the risk-informed analysis of nuclear power plant events. The PSA based event analysis method is used to assess the safety significance and importance measures associated with the unavailability of components and systems subject to Technical Specifications. The insights from recently performed PSA based analyses are also briefly discussed in the paper.     

Non-productive tool path optimisation for four-axis milling using the simulated annealing algorithm

The paper concerns the development of generic computer aided optimisation techniques for the minimisation of residence time of a multi-component pallet in a horizontal machining centre. A general methodology has been established to take a part program for a multi-faced pallet, that involves many components, typically 20–30, and tool changes, segment it to extract the position and machining conditions embedded in it, automatically re-sequence the machining operations to find the optimum total tool path, and regenerate a new part program with the optimised machining sequence. A range of case studies has been used to: validate the software, and to demonstrate its ability to minimise the total pallet residence time. The techniques developed can be used for semi-automatic part programming of the entire pallet with multi-components, and with an auto-selection multi-tool facility. The software is capable of achieving a large reduction in part programming time, as well as reducing the non-machining time. It is shown that the use of the optimisation package with a range of part programs reduces the total pallet residence time by a factor between 9.5 and 36%, and consequently has the potential to achieve considerable economic gains.     

A probabilistic safety analysis of incidents in nuclear research reactors

This work aims to evaluate the potential risks of incidents in nuclear research reactors. For its development, two databases of the International Atomic Energy Agency (IAEA) were used: the Research Reactor Data Base (RRDB) and the Incident Report System for Research Reactor (IRSRR). For this study, the probabilistic safety analysis (PSA) was used. To obtain the result of the probability calculations for PSA, the theory and equations in the paper IAEA TECDOC-636 were used. A specific program to analyse the probabilities was developed within the main program, Scilab 5.1.1. for two distributions, Fischer and chi-square, both with the confidence level of 90 %. Using Sordi equations, the maximum admissible doses to compare with the risk limits established by the International Commission on Radiological Protection (ICRP) were obtained. All results achieved with this probability analysis led to the conclusion that the incidents which occurred had radiation doses within the stochastic effects reference interval established by the ICRP-64.     

Level-1 probability safety assessment of the Iranian heavy water reactor using SAPHIRE software

The main goal of this review paper is to analyze the total frequency of the core damage of the Iranian Heavy Water Research Reactor (IHWRR) compared with standard criteria and to determine the strengths and the weaknesses of the reactor safety systems towards improving its design and operation. The PSA has been considered for full-power state of the reactor and this article represents a level-1 PSA analysis using System Analysis Programs for Hands-On Integrated Reliability Evaluations (SAPHIRE) software. It is specifically designed to permit a listing of the potential accident sequences, compute their frequencies of occurrence and assign each sequence to a consequence. The method used for modeling the systems and accident sequences, is Large Fault Tree/Small Event Tree method. This PSA level-1 for IHWRR indicates that, based on conservative assumptions, the total frequency of accidents that would lead to core damage from internal initiating events is 4.44E−05 per year of reactor operation.     

Probabilistic risk analysis for the NASA space shuttle: a brief history and current work

While NASA managers have always relied on risk analysis tools for the development and maintenance of space projects, quantitative and especially probabilistic techniques have been gaining acceptance in recent years. In some cases, the studies have been required, for example, to launch the Galileo spacecraft with plutonium fuel, but these successful applications have helped to demonstrate the benefits of these tools. This paper reviews the history of probabilistic risk analysis (PRA) by NASA for the space shuttle program and discusses the status of the on-going development of the Quantitative Risk Assessment System (QRAS) software that performs PRA. The goal is to have within NASA a tool that can be used when needed to update previous risk estimates and to assess the benefits of possible upgrades to the system.     

事故序列评估程序:核电厂事故后人的可靠性分析技术

核电厂事故后人的可靠性分析(HRA)是核电厂概率安全评价和核电厂安全运行的重要组成部分。人因可靠性分析事故序列评估程序技术(ASEP)是对于传统的人的失误率预测技术(THERP)方法的改进和规范。文章介绍了事故序列评估程序技术的应用程序和应用，并给出某核电厂的一个全厂断电(LOOP)应用实例。     

A Microprocessor-based Traffic Light Simulator

A microprocessor has been incorporated into a traffic light simulator. It is being used to teach undergraduate industrial engineers about software development and basic concepts of interfacing. The simulator combines hardware, software, and documentation into a compact portable package which can be locally constructed. It provides a useful part of the study program required to develop the skills industrial engineers need for industrial control.     

Living PRAs made easier with IRRAS

The Integrated Reliability and Risk Analysis System (IRRAS) is an integrated PRA software tool that gives the user the ability to create and analyze fault trees and accident sequences using an IBM-compatible microcomputer. This program provides functions that range from graphical fault tree and event tree construction to cut set generation and quantification.

IRRAS contains all the capabilities and functions required to create, modify, reduce and analyze event tree and fault tree models used in the analysis of complex systems and processes. IRRAS uses advanced graphic and analytical techniques to achieve the greatest possible realization of the potential of the microcomputer. When the needs of the user exceed this potential, IRRAS can call upon the power of the mainframe computer.

The role of the Idaho National Engineering Laboratory in the IRRAS program is that of software developer and interface to the user community. Version 1.0 of the IRRAS program was released in February 1987 to prove the concept of performing this kind of analysis on microcomputers. This version contained many of the basic features needed for fault tree analysis and was received very well by the PRA community. Since the release of Version 1.0, many user comments and enhancements have been incorporated into the program providing a much more powerful and user-friendly system. This version is designated ‘IRRAS 2.0’. Version 3.0 will contain all of the features required for efficient event tree and fault tree construction and analysis.     

Living PSA program: LIPSAS development for safety management of an LMFBR plant

During construction and subsequent operation of a nuclear power plant, many changes occur in components, systems and operating procedures, which continuously modify the configuration of the power plant. The unique ability of PSA techniques to effect of possible changes to baseline system configurations has been noted. A living PSA program can assess and manage safety-related operations and plant changes by adequately reproducing plant models and structured databases corresponding to the changes in system configuration. A living PSA system, LIPSAS, has been developed for the Japanese prototype liquid metal-cooled fast-breeder reactor (LMFBR), Monju, which is in the preoperation functional test stage. In order to utilize the LIPSAS as a risk management tool, equations for the schematic time history of the plant risk level and the relative risk criteria have been developed. Experience with LIPSAS shows that this program is a prospective tool to support decisions that affect plant safety, although a continuing and significant resource commitment of the operations staff at the site is still required.     

Managing Security-Risks for Improving Security-Durability of Institutional Web-Applications: Design Perspective

The advanced technological need, exacerbated by the flexible time constraints, leads to several more design level unexplored vulnerabilities. Security is an extremely vital component in software development; we must take charge of security and therefore analysis of software security risk assumes utmost significance. In order to handle the cyber-security risk of the web application and protect individuals, information and properties effectively, one must consider what needs to be secured, what are the perceived threats and the protection of assets. Security preparation plans, implements, tracks, updates and consistently develops safety risk management activities. Risk management must be interpreted as the major component for tackling security efficiently. In particular, during application development, security is considered as an add-on but not the main issue. It is important for the researchers to stress on the consideration of protection right from the earlier developmental stages of the software. This approach will help in designing software which can itself combat threats and does not depend on external security programs. Therefore, it is essential to evaluate the impact of security risks during software design. In this paper the researchers have used the hybrid Fuzzy AHP-TOPSIS method to evaluate the risks for improving security durability of different Institutional Web Applications. In addition, the e-component of security risk is measured on software durability, and vice versa. The paper’s findings will prove to be valuable for enhancing the security durability of different web applications.     

冲击响应谱控制系统的开发

冲击响应谱试验规范已在航天产品的研制中被普遍采用，针对冲击响应谱试验规范的特点，研制开发了一套基于PC机下的冲击响应谱控制系统，包括系统的功能分析、组成、核心算法的研究、软件实现及试验结果等。解决了磊击响应谱控制系统研制中的两个关键问题，即根据规范生成时域驱动信号及依据响应实现谱控制，并通过自闭环和使用电动振动台联机试验两种方式验证了系统的有效性。     

Software Architecture for a Virtual Environment for Nano Scale Assembly (VENSA)

A Virtual Environment (VE) uses multiple computer-generated media to let a user experience situations that are temporally and spatially prohibiting. The information flow between the user and the VE is bidirectional and the user can influence the environment. The software development of a VE requires orchestrating multiple peripherals and computers in a synchronized way in real time. Although a multitude of useful software components for VEs exists, many of these are packaged within a complex framework and can not be used separately. In this paper, an architecture is presented which is designed to let multiple frameworks work together while being shielded from the application program. This architecture, which is called the Virtual Environment for Nano Scale Assembly (VENSA), has been constructed for interfacing with an optical tweezers instrument for nanotechnology development. However, this approach can be generalized for most virtual environments. Through the use of VENSA, the programmer can rely on existing solutions and concentrate more on the application software design.     

An Optimized Algorithm for CR-MIMO Wireless Networks

With the rapid development of wireless communication technology, the spectrum resources are increasingly strained which needs optimal solutions. Cognitive radio (CR) is one of the key technologies to solve this problem. Spectrum sensing not only includes the precise detection of the communication signal of the primary user (PU), but also the precise identification of its modulation type, which can then determine the a priori information such as the PU’ service category, so as to use this information to make the cognitive user (CU) aware to discover and use the idle spectrum more effectively, and improve the spectrum utilization. Spectrum sensing is the primary feature and core part of CR. Classical sensing algorithms includes energy detection, cyclostationary feature detection, matched filter detection, and so on. The energy detection algorithm has a simple structure and does not require prior knowledge of the PU transmitter signal, but it is easily affected by noise and the threshold is not easy to determine. The combination of multiple-input multiple-output (MIMO) with CR improves the spectral efficiency and multi-path fading utilization. To best utilize the PU spectrum while minimizing the overall transmit power, an iterative technique based on semidefinite programming (SDP) and minimum mean squared error (MMSE) is proposed. Also, this article proposed a new method for max-min fairness beamforming. When compared to existing algorithms, the simulation results show that the proposed algorithms perform better in terms of total transmitted power and signal-to-interference plus noise ratio (SINR). Furthermore, the proposed algorithm effectively improved the system performance in terms of number of iterations, interference temperature threshold and balance SINR level which makes it superior over the conventional schemes.