Barrier Analysis Approach

The Barrier Analysis method aims at assessing the safety margin of the plant, given occurrences of a specific events. It is a systematic engineering approach designed to indicate the strengths of barriers which are available for a variety of events analysed. For the analysis of a shutdown operating mode, the Barrier Analysis was used by a utility in Sweden. 

The objective of the Barrier Analysis approach is to identify the most important active and passive safety barriers available to cope with initiators during an outage. Overall, the Barrier Analysis is used to assess the safety margin of a plant in presence of specific conditions or against undesirable events. 

The information generated in Barrier Analysis is presented in a diagram illustrating the barriers available and their strength. The Barrier Analysis approach does not include quantification. The results are based on a qualitative judgement on the number of barriers and their strength, where strengths are assessed separately for specific barriers. 

The Barrier Analysis method can be characterised as an analysis of available barriers and their specific strength against a chosen number of undesired events. The concept of undesirable events also includes actions which may not lead to an accident, but reduce available Technical Specifications below adequate safety margins. As an example, the performance of a critical test with a safety system inoperable is an undesirable event. 

The Barrier Analysis is carried out in three phases and they are as follows  

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Chapter 2 summarises the international experience on the use of different approaches to the assessment of risk during shutdown operating mode. It focuses on three main approaches 1) Full-Scope SEP PSA models, 2) Barrier Analysis Approach and 3) Configuration control tools. 

The Barrier Analysis approach aims at providing a fast alternative to determine safety related deficiencies of an outage in a systematic and transparent way. In addition to providing the results on its own, the Barrier approach could also be used for prioritisation of sequences to be evaluated within a fiill-scope SEP PSA. Due to its transparency, the Barrier analysis approach could also be useful for presentation of the SLP PSA results to plant personnel. 

The Barrier Analysis is claimed to be successfully used in Sweden. It is now known if the application of the barrier analysis approach has been applied for the analysis of outage operations elsewhere. 

Original Swedish Barrier Analysis approach was used on two NPPs, Ringhals 4 and Forsmark 2. These were limited scope studies evaluated selected predefined events such as main circulation pump overhaul, cold over-pressurisation, refuelling, control rod drive overhaul, testing and inspections. 

The kinetic analysis approach for the determination of the barriers of the dibenzofuranyl system consisted of reducing a species to ist smallest active unity to allow the calculation of the transition state structures. Further improvements were achieved by using literature data, calculated data of Mebel et al. on the vinyl + O2 system and those of Hadad et al. on the phenyl + O2 system. This approche confirmed the satisfactory accuracy of DFT with isodesmic reactions method. 

A Brief Overview of Selected System Safety Analytical Approaches Working with the Risk Assessment Matrix Preliminary Hazard Analysis Energy Flow/Barrier Analysis Failure Modes and Effects Analysis Fault Tree Analysis... 

A general approach to common cause failure analysis is to identify critical systems or components and then use energy trace and barrier analysis (ETBA) to evaluate vulnerability to common environmental hazards, unwanted energy flows, and barrier failures (see Chapter 13). 

The causes of the specific types of accidents/incidents that have occurred within your workplace must be assessed. The approach you wish to use in the assessment and analysis process depends greatly on your familiarity with and the types of occurrences that have transpired in your workplace. Analyses covered in this book are root cause, causal factor, change, and barrier analysis. 

Each accident/incident should be methodically analyzed using an accident investigation/root cause analysis approach. Because many root cause analysis methods exist, it will be the investigator s responsibility to select the appropriate analysis approach (e.g., barrier analysis). Use of proper accident/incident investigation methods and tracking will lead to intervention, which will successfully prevent further occurrence of these occupational accidents and incidents. 

Barrier analysis Use to identify barrier and equipment failures and procedural or administrative problems Provides systematic approach Requires familiarity with process to be effective This process is based on the MORT Hazard/ Target Concept... 

PSA models are a highly useful tool for assessing the risk in the SLP operating modes. Many plants, especially in Europe, use detailed Shutdown PSA models, which address different operational states and initiators. Other approaches used include very simple (practically look-up tables) models called Barrier Analysis. Other, especially in the USA, use simplified train level models coupled with a presentation system called ORAM (Outage Risk Assessment and Management). 

To calculate N (E-Eq), the non-torsional transitional modes have been treated as vibrations as well as rotations [26]. The fomier approach is invalid when the transitional mode s barrier for rotation is low, while the latter is inappropriate when the transitional mode is a vibration. Hamionic frequencies for the transitional modes may be obtained from a semi-empirical model [23] or by perfomiing an appropriate nomial mode analysis as a fiinction of the reaction path for the reaction s potential energy surface [26]. Semiclassical quantization may be used to detemiine anliamionic energy levels for die transitional modes [27]. 

Because the technical barriers previously outhned increase uncertainty in the data, plant-performance analysts must approach the data analysis with an unprejudiced eye. Significant technical judgment is required to evaluate each measurement and its uncertainty with respec t to the intended purpose, the model development, and the conclusions. If there is any bias on the analysts part, it is likely that this bias will be built into the subsequent model and parameter estimates. Since engineers rely upon the model to extrapolate from current operation, the bias can be amplified and lead to decisions that are inaccurate, unwarranted, and potentially dangerous. 

In this section, we present a unified picture of the different electronic effects that combine to determine methyl rotor potentials in the S0, Sp and D0 electronic states of different substituted toluenes. Our approach is based on analysis of ab initio wavefunctions using the natural bond orbitals (NBOs)33 of Weinhold and cowork-ers. We will attempt to decompose the methyl torsional potential into two dominant contributions. The first is repulsive steric interactions, which are important only when an ortho substituent is present. The second is attractive donor-acceptor interactions between CH bond pairs and empty antibonding orbitals vicinal to the CH bonds. In the NBO basis, these attractive interactions dominate the barrier in ethane (1025 cm-1) and in 2-methylpropene (1010 cm-1) see Figure 3. By analogy, donor-acceptor attractions are important in toluenes whenever there is a substantial difference in bond order between the two ring CC bonds adjacent to the C-CH3 bond. Viewed the other way around, we can use the measured methyl rotor potential as a sensitive probe of local ring geometry. 

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