And probabilistic risk assessment

After determining what functions must be accomplished for each goal, it is necessary to determine how well each function must be accomplished to meet the top-level criteria and requirements. For this purpose, reliability evaluations and probabilistic risk assessment techniques (Ref. 3) have been used to supplement standard engineering techniques and to provide an integrated allocation of the top-level criteria and requirements to specific plant systems. PRA techniques have also been used to identify the relative importance of events and plant structures, systems, and components in responding to such events, as described in Section 3.2. 

The Safety Case produced for the Windscale Vitrification Plant in 1994 included a detailed and comprehensive assessment of fault conditions in the plant using HAZOP and Probabilistic Risk Assessment techniques. The Safety Case identified a number of major hazards. These major hazards, along with the protective measures, Operating Rules, and Safety Mechanisms designed to prevent these hazards or to mitigate them are briefly described below. 

After quantification decision must be made if obtained HEP is satisfying the safety requirements and probabilistic risk assessments. If they are not fulfilled necessary modifications in designing the control and alarm systems must be made taking into account following aspects ... 

Stewart, M.G. and Netherton, M.D. (2008), Security risks and probabilistic risk assessment of glazing subject to explosive blast loading. Reliability Engineering and System Safety, 93(4), pp. 627 38. 

Safety-related software is defined as those computer codes used in safety- related analyses done in support of the Technical Specifications, SAR, and Probabilistic Risk Assessment (PRA). This limited set of software is selected to provide reasonable quality assurance for the technical programs essential to the reactor operation safety. 

Research space industry use of fauit tree anaiysis and probabilistic risk assessments (PRAs) and evaluate their use for SNPP design. 

Core damage and containment performance was assessed for accident sequences, component failure, human error, and containment failure modes relative to the design and operational characteristics of the various reactor and containment types. The IPEs were compared to standards for quality probabilistic risk assessment. Methods, data, boundary conditions, and assumptions are considered to understand the differences and similarities observed. 

EPRI NP-5664 is a study based on interviews of personnel at 10 utilities and 15 NRC personnel regarding the usefulness of PSA (they use the term PRA - probabilistic risk assessment). The general utility motivation for using PSA is to demonstrate an acceptably low level of risk to the NRC. Some utilities applied PSA to individual systems, functions, or issues. These smaller [ir(>grams served to train a PSA cadre and introduce PSA to other utility personnel and management. 

Chu, T. L. et al., 1990, Quantification of the Probabilistic Risk Assessment of the High Flux Beam Reactoi (HFBR) at Brookhaven National Laboratory, ANS Topical Meeting, The Safety, Siauis and Future of Non-Commercial Reactors and Irradiation Facilities, Boise, ID, Sepiember Ol - October 4, 1990. 

Roger, C., J. L. Boccio, and M. A. Azarm, 1985, Evaluation of Current Methodology Employed in Probabilistic Risk Assessment of Fire Events at Nuclear Power Plants, BNL report A-3710, February. 

The last three decades have seen the development of a new science to help us better understand the risk of events about which there is often very little information. The reason there is interest in such a science is that there are a great many societal benefits from activities that involve risk risk that if properly managed through better understanding can greatly benefit the quality of all life on the planet earth, both plant and animal. That science is quantitative risk assessment, also known by such names as probabilistic risk assessment and probabilistic salety assessment, the latter being the preferred name for this text. Probabilistic safety assessment divides the risk question into three questions "What can go wrong " "How likely is it " and "What are the consequences "... 

I am a physicist who switched to nuclear engineering for my Ph D. My introduction to PSA was as an original participant in the Reactor Safety Study in 1972. Material for this book was first gathered in 1974 for a workshop on what to expect in WASH-1400 (the results of the Reactor Safety Study). Materials were gathered over the years for EPRI, Savannah River Laboratory, and other workshops. A culmination was in 1988 with "Probabilistic Risk Assessment in the Nuclear Power Industry" with Robert Hall as coauthor. This book updates these materials and adds material on PSA in the chemical process industry. I prepared the material for printing using a word processor... 

Banks, W., Wells, J. E. (1992). A Probabilistic Risk Assessment Using Human Reliability Analysis Methods. In Proceedings of the International Conference on Hazard Identification and Risk Analysis, Human Factors, and Human Reliability in Process Safety. New York American Institute of Chemical Engineers, CCPS. 

Leverenz, F. L. and D. C. Cox. Probabilistic Risk Assessment Course Documentation, Volume 6, NUREG/CR-4350, U. S. Nuclear Regulatory Commission, Washington, DC, 1985. 

Giddings, J.M., Solomon, K.R., and Maund, S.J. (2001). Probabilistic risk assessment of cotton pyrethroids.il Aquatic mesocosm and held studies. Environmental Toxicology and Chemistry 20, 660-668. 

Moore DRJ, Sample BE, Suter GW, Parkhurst BR, Teed RS. 1999. A probabilistic risk assessment of the effects of methyhnercury and PCBs on mink and kingfishers along East Fork Poplar Creek, Oak Ridge, Tennessee, USA. Environ Toxicol Chem 18 2941-2953. 

While these objectives for method sensitivity may seem ambitious, experience has shown that data from such studies are much more usable for supporting fate and transport models (development and/or validation efforts) that may have to be used when more precise and geographically detailed probabilistic risk assessments become necessary. 

Partly with the high stakes in mind, changes have been made in U.S. reactor equipment and operation since the TMI accident to reduce the chance of another accident. The results of these changes are reflected in the predictions of probabilistic risk assessments and by a variety of direct performance indicators. For example, in one measure for U.S. reactors, since the pre-TMI days there has been a reduction of more than a factor of 100 in the number of precursors to potential core damage accidents, as reported by the Nuclear Regulatory Commission (Muley, 1990 Belles et al., 1998). 

The terminology used varies considerably. Hazard identification and risk assessment are sometimes combined into a general category called hazard evaluation. Risk assessment is sometimes called hazard analysis. A risk assessment procedure that determines probabilities is frequently called probabilistic risk assessment (PRA), whereas a procedure that determines probability and consequences is called quantitative risk analysis (QRA). 

Giddings JM, Solomon KR, Maund SJ (2001) Probabilistic risk assessment of cotton pyrethroids in aquatic ecosystems 2. Aquatic mesocosm and field studies observed effects and their ecological significance. Environ Toxicol Chem 20 660-668... 

Probabilistic methods can be applied in dose-response assessment when there is an understanding of the important parameters and their relationships, such as identification of the key determinants of human variation (e.g., metabolic polymorphisms, hormone levels, and cell replication rates), observation of the distributions of these variables, and valid models for combining these variables. With appropriate data and expert judgment, formal approaches to probabilistic risk assessment can be applied to provide insight into the overall extent and dominant sources of human variation and uncertainty. 

Variability and uncertainty affect every element of every risk assessment. For example, participants in the European Workshop on Probabilistic Risk Assessment for the Environmental Impacts of Plant Protection Products (EUPR A) were asked to list sources of uncertainty affecting current procedures for assessing pesticide risks to aquatic... 

Extensive general guidance for problem formulation exists already (e.g., USEPA 1998). This chapter reviews the main steps in problem formulation and discusses issues that require special consideration because of the use of uncertainty analysis in probabilistic risk assessment. 

Burmaster and Anderson (1994) have proposed 14 principles of good practice for using Monte Carlo techniques. They suggest that before an analyst undertakes a Monte Carlo risk assessment, the growing literature on probabilistic risk assessment should be thoroughly examined. Principles for a properly conducted Monte Carlo analysis have also been proposed by the USEPA (1997). 

There are many reasons why communicating risk and uncertainty to stakeholders and participants is critical to an informed assessment but 3 are, perhaps, most fundamental. First, participants (especially stakeholders with expertise in topics germane to probabilistic risk assessment or a particular assessment), if given opportunities to interact with practitioners, can contribute information and perspectives that could help focus and... 

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