Radiotherapy reliability analysis based on PSA method

The reliability of radiotherapy was evaluated and effective approaches were obtained in order to improve radiotherapy quality by using the Probabilistic Safety Assessment(PSA) method. This study investigated the feasibility of the PSA method being applied to radiotherapy through Image-guided Radiotherapy(IGRT) and chest tumor irradiation. A fault tree has been constructed after analyzing causal relationship of the events.After calculating Risk A, a total inaccuracy radiotherapy probability and the importance of all base events were obtained. The probability of inaccurate radiotherapy was 2.87%. Under the condition that the target delineation was perfectly right, the accuracy of radiotherapy significantly improved. With the calculation without Conebeam Computed Tomography(CBCT) being corrected before irradiation, the accuracy significantly decreased.The most important events were connected with the human factor. Improving human technical level could enhance radiotherapy quality control efficiently.

Probabilistic approach for open pit bench slope stability analysis——A mine case study

The geotechnical slope design of an open pit wall starts at the bench scale configuration.At this scale,the rock slope stability is governed primarily by the geological discontinuities within the rock mass and as a result,structurally-controlled failures(e.g.planar,wedge or toppling)are most likely to occur.The probabilistic approach offers a major advantage over the traditional deterministic method in that it accounts for the different degrees of variability and uncertainty often encountered in rock properties.This paper presents a bench slope stability assessment for an open pit mine in Peru using a probabilistic-based approach by coupling a kinematic analysis based on stereographic projection techniques followed by a kinetic analysis by means of the limit equilibrium method.Finally,these two probabilities are combined to provide an overall measure of the probability of failure(PoF)of the bench slope system.The case study is characterized by significant scatter in the geometrical and mechanical properties of the joints.Extensive surface mapping was conducted at 36 different sites following the ISRM suggested procedures.Several direct shear tests were carried out.It is shown that by combining field and laboratory measurements and engineering judgment,the probability density functions(PDF)of the discontinuity parameters can be obtained.These are then used in a Monte Carlo simulation process to compute both kinematic and kinetic probabilities of failure.The overall probability of failure aims to provide the design engineer with a tool to critically evaluate the bench performance from a geotechnical risk perspective and to provide a basis for future bench design optimization.

Success criteria analysis in support of probabilistic risk assessment for nuclear power plants: application on SGTR accident

Success criteria analysis(SCA) bridges the gap between deterministic and probabilistic approaches for risk assessment of complex systems. To develop a risk model,SCA evaluates systems behaviour in response to postulated accidents using deterministic approach to provide required information for the probabilistic model. A systematic framework is proposed in this article for extracting the front line systems success criteria. In this regard, available approaches are critically reviewed and technical challenges are discussed. Application of the proposed methodology is demonstrated on a typical Westinghouse-type nuclear power plant. Steam generator tube rupture is selected as the postulated accident. The methodology is comprehensive and general; therefore, it can be implemented on the other types of plants and complex systems.

Determination and stability analysis of ultimate open-pit slope under geomechanical uncertainty

In open-pit mines,pit slope as one of the important parameters affects the mine economy and total minable reserve,and it is also affected by different uncertainties which arising from many sources.One of the most critical sources of uncertainty effects on the pit slope design is rock mass geomechanical properties.By comparing the probability of failure resulted from deterministic procedure and probabilistic one,this paper investigated the effects of aforesaid uncertainties on open-pit slope stability in metal mines.In this way,to reduce the effect of variance,it implemented Latin Hypercube Sampling(LHS)technique.Furthermore,a hypothesis test was exerted to compare the effects on two cases in Middle East.Subsequently,the investigation approved high influence of geomechanical uncertainties on overall pit steepness and stability in both iron and copper mines,though on the first case the effects were just over.

A Framework for Modern Risk-Informed Root Cause Analysis Process

The paper discusses the framework for a risk-informed root cause analysis process.Such process enables scaling of the analysis performed based on the risk associated with the undesired event or condition,thereby creating tiers of analysis where the greater the risk,the more sophisticated the analysis.In a risk-informed root cause analysis process,a situation is normally not analyzed at a level less than what actually occurred.However,a situation may be investigated as though the consequence were greater than actually happened,especially if only slight differences in circumstances could result in a significantly higher consequence.While operational events or safety issues are normally expected to result only with negligible or marginal actual consequences,many of those would actually have certain potential to develop or propagate into catastrophic events.This potential can be expressed qualitatively or quantitatively.Risk-informing of root cause analysis relies on mapping the event or safety issue into a risk matrix which,traditionally,is a two-dimensional probability-consequence matrix.A new concept employed in the risk matrix for root cause analysis is that,while the probability reflects the observed or expected range of values(retaining,thus,its“traditional”meaning),the consequence reflects not only the observed or materialized impact(such as failure of equipment)but,also,its potential to propagate or develop into highly undesirable final state.The paper presents main elements of risk-informed root cause analysis process and discusses qualitative and quantitative aspects and approaches to determination of risk significance of operational events or safety issues.

A novel refined dynamic model of high-speed maglev train-bridge coupled system for random vibration and running safety assessment

Running safety assessment and tracking irregularity parametric sensitivity analysis of high-speed maglev train-bridge system are of great concern,especially need perfect refinement models in which all properties can be well characterized based on various stochastic excitations.A three-dimensional refined spatial random vibration analysis model of high-speed maglev train-bridge coupled system is established in this paper,in which multi-source uncertainty excitation can be considered simultaneously,and the probability density evolution method(PDEM)is adopted to reveal the system-specific uncertainty dynamic characteristic.The motion equation of the maglev vehicle model is composed of multi-rigid bodies with a total 210-degrees of freedom for each vehicle,and a refined electromagnetic force-air gap model is used to account for the interaction and coupling effect between the moving train and track beam bridges,which are directly established by using finite element method.The model is proven to be applicable by comparing with Monte Carlo simulation.By applying the proposed stochastic framework to the high maglev line,the random dynamic responses of maglev vehicles running on the bridges are studied for running safety and stability assessment.Moreover,the effects of track irregularity wavelength range under different amplitude and running speeds on the coupled system are investigated.The results show that the augmentation of train speed will move backward the sensitive wavelength interval,and track irregularity amplitude influences the response remarkably in the sensitive interval.

核电站PSA分析中可靠性数据处理的贝叶斯方法

可靠性数据是进行核电站概率安全分析 (PSA)分析的一个非常重要的方面。对于一些运行时间较短的核电站而言，综合考虑同型电站的先验数据和本电站的运行数据是必不可少的。贝叶斯方法是进行这种数据处理方式的一种重要方法。在贝叶斯处理中，必须确定先验分布的类型和分布参数。本文用数值计算的方法，得到了先验数据的分布参数。并将这种方法作为计算核心，形成贝叶斯处理程序 INETBAYES。利用大亚湾核电站一些特有数据，以同型电站的可靠性数据作为先验数据，用 INETBAYES数据对其进行了处理，并给出了处理后的结果。

认知失误定量分析方法及其在PSA中的应用

认知可靠性和失误分析方法(CREAM)是第二代人的可靠性分析方法中的代表方法之一。以CREAM的核心思想为基础,对定量分析方法进行了改进,给出了共同绩效条件(CPC)对人的可靠性影响的量化指数。提出了用环境影响指数来定量计算情景环境迫使人的认知失误的发生概率,给出了概率安全评价(PSA)中人误概率的分析方法,并用于诊断核电站蒸汽发生器传热管破裂和蒸汽发生器隔离时的人误概率分析。

高温气冷堆概率安全分析(PSA)报告审评的思考

高温气冷堆是我国重大专项的先进核电厂项目,高温气冷堆PSA报告是其执照申请文件的重要组成部分。简要介绍了高温气冷堆PSA报告的审评情况,并对高温气冷堆PSA审评过程中的有关问题进行了初步的探讨。

基于GO法的船用反应堆设备冷却水系统DPSA研究

DPSA(dynamic PSA)与传统的PSA相比,能够很好的解决包含时间、过程变量以及人员操作行为等动态因素方面的问题。根据船用反应堆设备冷却水系统的原理和运行特点,基于GO法原理创建了操作符互备自投门,并导出互备自投门的可靠性参数随时间变化的状态转移方程,从而建立了设备冷却水系统的DPSA动态计算模型。分析结果表明:该模型可以合理地分析计算设备冷却水系统的不可用度随时间的变化。

核电厂丧失通风系统的PSA分析

通风系统(HVAC)是核电厂重要的支持系统之一,通风系统的丧失对核电厂安全的威胁是不容忽视的。根据国外核电厂的概率安全分析(PSA)的工程经验反馈,丧失通风系统的风险对核电厂堆芯损坏频率(CDF)的贡献高达25%。本文结合国内外调研和工程实践,开发了一套适用于核电厂丧失通风系统的PSA分析方法,并基于某核电厂开展系统性的丧失通风系统风险分析。分析结果表明,丧失通风系统对核电厂堆芯损坏频率的贡献是不容忽视的。通过识别出的通风系统设计的薄弱项,能够为核电厂通风系统设计及优化提供指引,以进一步提升核电机组的安全水平。

PSA技术在“华龙一号”核电机组运行优化中的应用研究

本文将PSA模型分析应用于电站运行管理工作梳理中,提出了基于PSA风险见解的风险薄弱项查找方法与管理优化流程,并且在“华龙一号”运行机组上进行应用实践,提出并实施“应急硼注入系统管理优化”,“附加柴油机接入方式优化”两项重要的管理与设计优化,研究表明,实施变更后机组功率运行内部事件一级PSA堆芯损伤频率降低约10%。本方法对于核电机组的PSA见解应用与运行安全提升,具有重要现实意义与推广价值。

Handling Uncertainty in Human Cognitive Reliability Method for Safety Assessment Based on DSET

Human Reliability Analysis(HRA)is an important part in safety assessment of a large complex system.Human Cognitive Reliability(HCR)model is a method of evaluating the probability that operators fail to complete during diagnostic decision making within a limited time,which is widely used in HRA.In the application of this method,cognitive patterns of humans are required to be considered and classified,and this process often relies on the evaluation opinions of experts which is highly subjective and uncertain.How to effectively express and process this uncertain and subjective information plays a critical role in improving the accuracy and applicability of HCR.In this paper,a new model was proposed to deal with the uncertain information which exists in the processes of cognitive pattern classification in HCR.First,an evaluation panel was constructed based on expert opinions and processing including setting corresponding anchor points and qualitative indicators of different cognitive patterns,and mapping them to fuzzy numbers and unit intervals.Second,based on the evaluation panel,different analysts judge the cognitive pattern types of actual specific events and provide the level of confidence he or she has in the judgments.Finally,the evaluation opinions of multiple analysts were expressed and fused based on the Dempster-Shafer Evidence Theory(DSET),and the fused results were applied to the HCR model to obtain the Human Error Probability(HEP).A case study was used to demonstrate the procedure and effectiveness of the proposed method.

百万千瓦级压水堆核电厂停堆PSA研究

对百万千瓦级核电厂的停堆运行事故风险进行内部事件1级概率安全评价(PSA),并根据不同的停堆进程分别建立停堆PSA模型,分析经历LOI-RRA水位对电厂风险水平构成的影响。分析结果表明停堆工况下的电厂风险不可忽视,在冷停堆工况下经历LOI-RRA水位导致堆芯损坏频率明显增加。

故障树和模糊贝叶斯网络在管廊运维风险评估中的应用研究

地下综合管廊是城市的生命线,一旦出现问题就会对人们生命财产安全造成巨大损害。为了系统地分析管廊运维风险,建立了基于模糊贝叶斯网络的风险评估框架。首先,通过分析管廊运维风险源与风险形成的原因以确定风险事件和风险类别;其次,建立管廊运维风险故障树来梳理风险因素之间的逻辑关系,将故障树映射为贝叶斯网络;最后,结合专家模糊评价,构建地下综合管廊运维风险评估模型。案例分析结果显示:中间事件“火灾、爆炸”与“危害气体浓度过高”的发生概率较高。敏感性分析结果显示:“运维人员操作和维护不当”是导致管廊运维风险发生的根本事件,因此需要制定严格管理措施及规范,加强对运维人员的素质培训,以降低管廊运维过程中各种风险的发生概率。

核电厂外部水淹PSA分析

在福岛核事故后,国内对超设计基准的灾害尤为关注,核电厂应具备足够的裕量应对超设计基准灾害。而外部水淹是重要的外部灾害之一。目前关于超设计基准外部水淹的风险评价仍在研究中,国内外尚无成熟统一的风险评价方法。本文基于国内外调研和工程实践,开发了一套适用于核电厂外部水淹概率安全分析(PSA)的方法,并基于某核电厂开展外部水淹PSA的风险分析,以识别核电厂外部水淹防护设计的薄弱项,优化核电厂外部水淹的防护设计。

基于概率分析的铁路安全风险传递网络模型研究

传统的风险评价大多是在定性分析的基础上展开的,给风险评价带来了一定的局限性。为深化风险评价水平,拓展风险定量评价方法,提出一种基于概率分析的铁路安全风险传递网络模型。首先,面向铁路局集团公司层面,识别出35项安全风险;然后,通过关联关系分析明确风险间的传递关系,并依托风险传递关系构建安全风险传递网络模型;之后,基于贝叶斯网络对风险传递网络进行传递概率分析;最后,选取异物侵限类风险事件作为案例对模型进行应用验证。结果表明:模型基于铁路运营历史数据,对风险传递网络进行定量分析,能识别出安全风险传递网络中的关键安全风险和风险传递关键路径。模型为有效利用铁路安全相关数据,开展定量的风险评价提供基础。

高放废液分离系统安全分析方法浅析

高放废液集中了乏燃料中95%以上的放射性,其如何妥善处理处置是影响核燃料循环可持续发展的关键因素之一。中国提出的TRPO流程能够有效分离高放废液中的锕系元素和裂片元素,经过40余年的发展,目前已经具备了较好的工程化应用基础。然而,作为新型的核化工系统,对其安全分析方面的研究还较为欠缺。文章将基于对高放废液分离系统特点的分析,结合其他系统相关安全分析的实践和研究情况,对高放废液分离系统安全分析可以采取的方法路径进行了分析,并进一步对概率安全分析(PSA)的方法在高放废液分离系统应用的前景进行了展望。

基于最小割集故障树分析的安全风险发生概率评估

针对武器装备安全风险发生概率评估的实际需求,详细介绍了最小割集的确定方法、重要度计算分析和安全风险发生概率计算等内容。采用了一种基于最小割集故障树分析的安全风险发生概率评估方法,完成对拔销器意外动作危险事件发生概率的评估,得到了拔销器意外动作安全风险发生的概率值,并结合重要度分析确定了引发拔销器意外动作的关键因素,采取相关设计措施降低安全风险发生的概率。

考虑共因失效的列控系统定量安全分析研究

列车运行控制系统(简称“列控系统”)作为保障列车安全运营的安全相关系统,因采用多通道冗余设计而较易引发共因失效,因此对列控系统进行共因失效分析和防护是很有必要的。文章根据系统安全理论,结合β因子和独立性分析方法对系统可能出现的共因失效情况进行分析评估,通过共因失效检查表识别分析系统设计过程中的薄弱环节,并提出相应的安全防御措施;同时结合β因子模型对共因失效进行定量评估,判定系统危险侧失效率是否在可接受的范围并达到规定的安全目标。文章以计算机联锁系统作为研究对象,定量计算结果表明,β因子越小,共因失效影响越小。因此为了最大限度地减少共因失效发生的概率,在系统设计中应采用适当的安全防御措施,减小在估算因为共因失效而引发系统失效时使用的β因子数值,进而提升系统的安全性。