Three Mile Island accident event

The Three Mile Island accident, rated as one of the top media events of the century, was a crowning blow in the battle. The media consistently portrayed the accident as a close call on a public health disaster, and continue to do so to this day, although none of the studies done after the accident gives any reason to believe that to be the case. As demonstrated in those studies, the containment building would have prevented release of large amounts of the radioactivity regardless of what might have hap-... 

As it can be seen, both the risk objectives and the risk analyses on existing plants are reassuring, but, it is frequently asked, how reliable these analyses are How much the inevitable uncertainties on data and methods can influence the results Is it possible that some accident sequence has been forgotten in performing a probabilistic analysis All the available information, including the analyses made before the Three Mile Island accident and the sequence of events in the accident itself, indicate that a corrective... 

You don t need to be reminded of the most recent nuclear accidents, principally Fukushima Daiichi in Japan in 2011. After the Three Mile Island accident in the late 1970s, the U.S. Atomic Energy Commission developed WASH 1400, The Reactor Safety Study. The WASH 1400 report laid the foundation for the use of probabilistic risk assessments (called probabilistic safety assessments in Europe). According to Henley and Kumamoto (1991), probabilistic risk assessment involves studying accident scenarios and numerically rank[ing] them in order of their probability of occurrence, and then assess[ing] their potential consequence to the public. Event trees, fault trees, and other risk-consequence tools are applied in developing and studying these scenarios. These techniques are extremely useful for the engineer but very expensive. The nuclear industry has been the leader in probabilistic safety analyses. 

The occurrence which has generated more public concern than any other is the well-known Three Mile Island accident. The reactor involved was the second unit of two located on an island in the Susquehanna River, near Harrisburg, Pennsylvania. The layout of the reactor circuit and ancillary systems is shown in Fig. 12.14. The sequence of events leading to the accident is given below. 

Since the Three Mile Island accident, considerable effort has been devoted to the development of "symptom-based" procedures to replace (or at least significantly augment) the event-specific procedures. The basic premise underlying these symptom-based procedures is that there is a limited set of critical safety functions (CSFs), which, if successfully performed by either automatic plant response or manual action, result in a "safe" condition for the plant. The basic goal of the plant safety systems and the ultimate goal of operator actions is to ensure the performance of these critical safety functions. Symptom-based operating procedures relate critical safety function performance to specific plant/control room instruments. 

The 1970s were hard times for the nuclear industiy. The decade opened with the first Earth Day (April 22), which featured thousands of teaching events, many of them aimed at halting further nuclear power development, and ended with the accident at the Three-Mile Island nuclear plant in Pennsylvania. In... 

The hardest part of engineering risk assessment has turned out to be the prediction of the modes of failure. Serious accidents at nuclear installations, such as those at Three Mile Island or at Chernobyl, have been caused by modes of failure that had not been analysed at all. For example, the report of the Presidents Commission on the Accident at Three Mile Island (Presidents Commission, 1979, p9) highlighted that the concentration of the assessment process on more obvious large break scenarios meant that the eventual mode of failure, which was a result of a chain of a number of more minor events, was not even considered. Despite the use of significant resources in the design process, the risk assessment had been unable to characterize the complex system adequately, a system that was totally human-made and defined. In particular, the risk assessment process had not been able to identify modes of failure caused by humans involved in the operations of the reactor behaving in unexpected ways. 

LWR tests-to-failure had been performed to evaluate accident scenarios involving loss of coolant accident (LOCA) events such as occurred in the Three Mile Island incident. The power burst tests in a 20 MWt PWR have created fuel failures and defined the initiating conditions. The LOCA tests with a 50 MWt... 

Three historical events have been recognized as significant radiological accidents. These events include the meltdown at Chernobyl, the partial meltdown at Three Mile Island, and an incident of radioactive waste mishandling in Brazil. Elaborate on the events that occurred in Brazil. What were the impacts on the public health of the local community ... 

The worst nuclear power accident in the U.S. occurred at the Three Mile Island plant in Pennsylvania. In this accident no one was killed and no one was directly injured. The event at Three Mile Island occurred from faulty instrumentation that gave erroneous readings for the reactor vessel environment. A series of equipment failures and human errors along with inadequate instrumentation allowed the reactor core to be compromised and go into a partial melt. The radioactive water that was released from the core was confined within the containment building and very little radiation was released. In the Three Mile Island incident, the safety devices worked as planned and prevented any serious injury. This accident resulted in improved procedures, instrumentation, and safety systems being implemented. 

At the start, the research was mainly concentrated on reactivity accidents (SPERT and BORAX experiments in the USA). Subsequently, in the 1960s, the most studied issue was a large LOCA. After Three Mile Island, the attention moved to small LOCAs because that event, together with the results of the Rasmussen Report, highlighted their danger, and to severe accidents. 

ABSTRACT The analysis of events during the accident at Three Mile Island concluded that the accident was due to confused control room operators with inadequate instrumentation and inaccurate procedures. Therefore, the United States Nuclear Regulatory Commission (USNRC) called for improved nuclear reactor operator training and Emergency Operating Procedures (EOPs). 

As a result of the analysis of events during the accident at the Three Mile Island nuclear plant (TMI, March 1979), the importance of human error in nuclear plants was better understood. The accident resulted from the confusion of the control room operators with inadequate instrumentation and inaccurate procedures. The most important factor was that they had to act in spite of the weaknesses in the training to respond to unexpected events. Therefore, the United States Nuclear Regulatory Commission (USNRC) called for the improvement of Emergency Operating Procedures (EOPs) and in nuclear reactor operator training. The philosophy of incident response implemented in the improved procedures was to take a symptom-based approach (operators foUow a series of yes - no questions to ensure that the reactor core remains covered and only then determine what was the cause of the problem) (USNRC, 2009). 

March 28, 1979, Three Mile Island, PA. One of the nuclear power plants on this island in the Susquehanna River near Harrisburg, PA, experienced a loss-of-coolant accident. The event involved many complex issues. One class of problems involved the design of displays and controls in the plant control room. 

Even when the safety risk of accidents is limited, the financial burden posed by events such as at Three Mile Island may cany unacceptable risk for investors. Financial exposure would be greatly reduced for utilities operating multiple small units. 

After the Three Mile Island Unit 2 accident, the NRC reviewed auxiliary feedwater system designs with respect to timely initiation, as described in 10 CFR 50, Appendix A, (GDC 20), (Reference 3). Upon completion of the review, the NRC determined that new guidance identified in NUREG-0737, (Reference 4) was necessary in order to assure a timely start of the AFW system after a design basis event (e.g., loss of main feedwater). Among this new guidance was automatic system initiation, environmental and seismic equipment qualification, and single failure criterion. 

Scenario independent procedures do not handle any specific event or group of events. The need for such procedures follows from realistic anticipation of situations in which the operator is not able to identify the event or misdiagnoses the event (as occurred during the Three Mile Island (TMI) accident) and, consequently, a scenario dependent type of procedure is not suitable. While the objective of scenario dependent procedures is to provide the operator with instructions to recover from a certain event or accident, the primary objective of scenario independent procedures is to make sure that all the safety barriers remain intact. This objective is achieved by taking actions that ensure continuous monitoring/diagnosis of the status of all plant barriers... 

This book is very unusual in the field of organization studies because it is a collaborative effort to dissect a decision-making situation from many perspectives. The nearest forerunners are probably Allison and Zelikow s (1999) book on the Cuban missile crisis and Moss and Sills et al. s (1981) book about the accident at Three Mile Island, which also used multiple lenses to interpret single chronologies of events. Overall, there are almost no examples of organizational research that bring... 

An incident or near miss is an almost accident. Three Mile Island was a radioactive near miss. No massive quantities of radioactivity were released to the environs, but they almost were. Figure 2.1 shows the events that lead to an accident. 

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