Reactor tree analysis

The QRA was conducted by risk sts and design innel to determine the probability of explosive releases of the chemical. Fault tree analysis identified several combinations of equipment failures and operator errors that could cause the top event (reactor explosion), Failure data were obtained from plant ex ice and industry da%.ui,/uoes to quantify the fault trees to estimate the frequency of reactor explosions. The fault trees suggested several safety improv-... 

Crosetti, P. A., 1971, Fault Tree Analysis for Reactor Systems, Inst. Power Ind. 14 p 54. 

Wyss, G. D. et al., 1990, Accident Progression Event Tree Analysis for Postulated Severe Accidents at N-Reactor, SNL, SAND89-2100. 

This event tree analysis shows that a dangerous runaway reaction will occur on average 0.025 time per year, or once every 40 years. This is considered too high for this installation. A possible solution is the inclusion of a high-temperature reactor shutdown system. This control... 

Another widely-used predictive method is the use of Fault Tree Analysis. This is a reversethinking method. The analyst assumes an accident or specific undesirable event—the so-called TOP Event. This could be the release of a toxic gas from a reactor safety relief valve. 

Toward the end of the Second World War, systems techniques such as fault tree analysis were introduced in order to predict the reliability and performance of military airplanes and missiles. The use of such techniques led to the formalization of the concept of probabilistic risk assessment (PRA). The publication of the Reactor Safety Study (NRC, 1975)—often referred to as the Rasmussen Report after the name of principal author, or by its subtitle WASH 1400—demonstrated the use of such techniques in the fledgling nuclear power business. Although WASH 1400 has since been supplanted by more advanced analysis techniques, the report was groundbreaking in its approach to system safety. 

Obtain a copy of a fault tree analysis for a system and review the analysis and results. You might wish to look at one of the classic reports on nuclear power plant safety Reactor Safety Study An Assessment of Accident Risks in U.S. Commercial Nuclear Power Plants, Report WASH-1400, U.S. Nuclear Regulatory Commission, October 1975. (This report is also known as the Rasmussen report.)... 

The predominant method of evaluation in these studies has been fault tree analysis. The Reactor Safety Study also utilized event tree analysis to conveniently document accident sequences and to link the subsystem fault trees into a plant analysis. Failure Mode and Effects Analysis, used extensively in fast reactor safety, is the recommended method for preliminary analysis. All of these methods have application to the analysis of the fuel cycle Including the problems of safe arding special nuclear material. ... 

Example The following is a demonstration of the fault tree analysis method using the example of an emergency cooling system of a water-boiler nuclear reactor. For the sake of clarity, only the mechanical components will be considered. 

Historically the FMEA technique has been used extensively used in the aerospace, automotive, electronics, and defense industries because they all require analysis of complex mechanical systems and because the failure of an equipment item can have such catastrophic consequences. The FMEA method has not been used a great deal in the process industries partly because of a perception that its use is very time consuming. The same criticism is sometimes made of the Fault Tree Analysis. In fact, neither the FMEA or FTA methods need to take a lot of time it is just that the level of detail that is necessary for the analysis of, for instance, a nuclear reactor or airplane wing is much greater than that needed for a... 

For fault tree analysis, the starting point is to specify an undesirable serious situation, called the top effect, and then to consider all possible causes that could produce it. For example, the specified top effect could be the over-pressurization of a chemical reactor. Possible causes could include a reduction or loss of coolant, excess catalyst, an ineffective pressure control loop, etc. Each possible cause is analyzed further to determine why it occurred. For example, the pressure control loop problem could be to the result of a sensor or control valve malfunction. Thus, FTA is a top-down approach that generates a tree of causal relations, starting with the specified top event and working backward. Standard logic concepts, such as AND and OR, are used in the logic diagrams. 

Subject Application of a fault tree analysis to a chemical reactor ... 

Within process industries characterized by large production units and high levels of automation, risk and accident analysis is focused on the avoidance of low-probability events entailing serious consequences for the plant and its environment. Safety analysis is based here on causal or probabilistic models of the accidental chain of events that can serve to identify deficiencies in the design of the plant and its protective system as well as to predict the level of risk involved in an operation. Methods developed are fault tree analysis, MORT (Johnson 1975) and INRS (Leplat Rasmussen 1984). A detailed analysis of the actual, individual incident or failure is performed to identify these possible weak spots in the plant and its operation. It is a common experience that human acts play an important role in such industrial mishaps so, especially after the reactor incident at Three Miles Island in 1979, much effort has been spent on developing suitable predictive tools for the... 

Fullwood, R. and R. C. Erdman, 1974, On the Use of Leak Path Analysis in Fault Tree Construction for Fast Reactor Safety, CONF-74040I-P3. 

As can be noted in Figure 21.7.2, steam and ediane are mi.xed before entering die reactor tubes where pyrolysis reacdons take place. All feed and product lines must be equipped with appropriate control devices to ensure safe operation. The FTA flow chart breaks down a TOP event (see descripdon of fault tree in Unit II) into all possible basic causes. Aldiough, diis mediod is more structured than a PHA, it addresses only one individual event at a dine. To use an FTA for a complete liazard analysis, all possible TOP events must be identified and investigated this would be extremely time consuming and perhaps urmecessary in a preliminary design. 

The SCB distribution (SCBD) has been extensively studied by fractionation based on compositional difference as well as molecular size. The analysis by cross fractionation, which involves stepwise separation of the molecules on the basis of composition and molecular size, has provided information of inter- and intramolecular SCBD in much detail. The temperature-rising elution fractionation (TREE) method, which separates polymer molecules according to their composition, has been used for HP LDPE it has been found that SCB composition is more or less uniform [24,25]. It can be observed from the appearance of only one melt endotherm peak in the analysis by differential scanning calorimetry (DSC) (Fig. 1) [26]. Wild et al. [27] reported that HP LDPE prepared by tubular reactor exhibits broader SCBD than that prepared by an autoclave reactor. The SCBD can also be varied by changing the polymerization conditions. From the cross fractionation of commercial HP LDPE samples, it has been found that low-MW species generally have more SCBs [13,24]. 

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