Browsing by Subject "PRA"
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Item Algorithms for Incorporation of Dynamic Recovery in Estimating Frequency of Critical Station Blackout(2012-07-16) Rodi, Paul J.This thesis involves exploring enhancement of estimating the probability of a critical station blackout in nuclear power plant operations by the use of direct numerical evaluation of multidimensional nonrecovery integrals. This requires development of computational methods with data provided from South Texas Project Nuclear Operating Company (STPNOC). Several methods that are currently used in the industry to estimate such probabilities often overestimate the value substantially. The computational integral method developed in the thesis will reduce excess conservatism while maintaining plant safety standards. This computational integral is calculated using a MATLAB research code referred to generally as "STP-TAMIL" which is for South Texas Project --Texas A&M Improved LOOP. The code itself (along with the user manual) was developed in conjunction with this Thesis. STP-TAMIL is successful in reducing the estimated probability of critical station blackout by a significant amount (about 88.47 percent ) with the incorporation of recovery of offsite and onsite power for South Texas Project? s nuclear plants, and results were verified. This thesis also describes an asymptotic justification for to the non-recovery integral used. Applications to the industry, or STPNOC, which will use the "TAMIL" code are addressed. Some assumptions used throughout the problem suggest that if more dynamic rates or distributions are used then more recovery can be obtained, which will decrease the probability of critical station blackout. Methodology developed in this thesis will be used in future work to develop this STP-TAMIL research code into a model used industry wide in commercial nuclear power plants.Item Evaluation of the use of engineering judgements applied to analytical human reliablity analysis methods (HRA)(Texas A&M University, 2006-04-12) Kohlhepp, Katherine D.Due to the scarcity of Human Reliability Analysis (HRA) data, one of the key elements of any HRA analysis is use of engineering judgment. The Electric Power Research Institute (EPRI) HRA Calculator guides the user through the steps of any HRA analysis and allows the user to choose among analytical HRA methods. It applies Accident Sequence Evaluation Program (ASEP), Technique for Human Error Rate Prediction (THERP), the HCR/ORE Correlation, and the Caused Based Decision Tree Method (CBDTM). This program is intended to produce consistent results among different analysts provided that the initial information is similar. Even with this analytical approach, an HRA analyst must still render several judgments. The objective of this study was to evaluate the use of engineering judgment applied to the quantification of post-initiator actions using the HRA Calculator. The Comanche Peak Steam Electric Station (CPSES) Level 1 Probabilistic Risk Assessment (PRA) HRA was used as a database for examples and numerical comparison. Engineering judgments were evaluated in the following ways: 1) Survey of HRA experts. Two surveys were completed, and the participants provided a range of different perspectives on how they individually apply engineering judgment. 2) Numerical comparison among the three methods. 3) Review of CPSES HRA and identification of judgments and the effects on the overall results of the database. The results of this study identified thirteen areas in which an HRA analyst must interpret and render judgments on how to quantify a Human Error Probability (HEP) and recommendations are provided on how current industry practitioners render these same judgments. The areas are: identification and definition of actions to be modeled, identification and definition of actions to be modeled, definition of critical actions, definition of cognitive portion of the action, choice of methodology, stress level, rule-, skill- or knowledge-based designation, timing information, training, procedures, human interactions with hardware, recoveries and dependencies within an action, and review of final HEP.Item A new framework for African smallholder agriculture : harnessing innovation and the private sector to drive sustainable development(2010-05) Kosoris, Justin Michael; Wilson, Robert Hines; Wilson, Patricia A.; Evans, Angela M.This report will outline a new framework for improved yields and increased sustainability in Sub-Saharan African smallholder agriculture. Given the failures of agricultural development aid and policy in the past, cross-sector collaboration among local farmer networks, national governments, and private corporations could represent a new model to foster sustainable agricultural production and growth, as each has had past successes but have not traditionally come together to work as a collaborative unit. This paper will examine each sector to look at best practices and then develop a framework for such collaboration. After a normative case with a positive outlook as to the potential for implementing the framework to Senegal‘s groundnut sector, the paper concludes that the framework can work in a variety of settings as long as one is aware of and respects local conditions.Item Uncertainty quantification for risk assessment of loss-of-coolant accident frequencies in nuclear power plants(2013-08) Pan, Ying-An; Morton, David P.This research presents the methodologies used to resolve the Nuclear Regulatory Commission Generic Safety Issue 191. The presented results are specific to South Texas Project Nuclear Operating Company (STPNOC). However, the proposed methodologies may be applicable to other nuclear power plants given the appropriate plant-specific frequencies. This research provides important inputs to CASA Grande, a computer program used to model physical phenomena and quantify uncertainties to obtain estimates of failure probabilities for post-loss-of-coolant accident events at the STPNOC containment. We provide modeling and sampling methods for loss-of-coolant accident (LOCA) frequencies and break sizes. We focus on a study known as NUREG-1829 (Tregoning et al., 2008), which includes an expert elicitation of quantiles governing the (annual) frequency of a LOCA in boiling water reactors and pressurized water reactors. We propose to model LOCA frequencies with bounded Johnson distributions and to sample break sizes using uniform distributions. We then develop a new method to distribute LOCA frequencies to different locations within a plant to account for the location-dependent differences while preserving the NUREG-1829 frequencies. We also propose to linearly interpolate the NUREG-1829 LOCA frequencies to obtain the frequencies for any break sizes other than those from NUREG-1829. In addition, we present a method to obtain the distribution of LOCA frequency within a break-size interval providing important inputs to the probabilistic risk assessment quantification for STPNOC. We review methods of combining the probability distributions of multiple experts to obtain a single probability distribution. More specifically, we describe the relative merits of the arithmetic mean (AM) and geometric mean (GM) as ways of performing this aggregation in the context of probabilities associated with rare events. Examining a set of pressurized water reactor results from NUREG-1829, we conclude that the GM represents a consistently sensible notion of the middle of the opinions expressed by nine experts. We further conclude that the AM is inappropriate for representing the center of the group's opinion for large effective break sizes. Instead, as the break size grows large a single expert's opinion dominates the combination produced by the AM.