Fusion or thermonuclear power is a promising, literally endless source of energy. Development of fusion power is still in investigation and experimentation phases and a number of fusion facilities are under construction in Europe. Since fusion energy is innovative and fusion facilities contain unique and expensive equipment an issue of their reliability is very important from their efficiency perspective.A Reliability, Availability, Maintainability, Inspectability (RAMI) Analysis is being performed or is going to be performed in the nearest future for such fusion facili ties as ITER and DEMO in order to ensure reliable and efficient operation for experi ments (e. g. in ITER) or for energy production purposes (e. g. in DEMO). On the other hand, rich experience of the Reliability and Probabilistic Safety Analysis (PSA) exists in nuclear industry for fission power plants and other nuclear installations.In this article, the Wendelstein 7-X (W7-X) facility is mainly considered. It is a stel larator type fusion facility under construction in the Max-Planck-Institut für Plasmaphysik, Greifswald, Germany (IPP). In the frame of cooperation between the IPP and the Lithuanian Energy Institute (LEI) under the European Fusion Development Agreement a pilot project of a reliability analysis of the W7-X systems was performed with a purpose to adopt NPP PSA experience for fusion facility systems. During the project a reliability analysis of a divertor target cooling circuit, which is an important system for permanent and reliable operation of in-vessel components of the W7-X, was performed.
The procedure used at the Ignalina nuclear power plant for probabilistic analysis of the actions taken using the ASEP and THERP methods by operators during accidents is described. The method makes it possible to evaluate the probability of operator error at different stages of the action taken -identification, making a decision, and taking action -as well as correctly taking account of different factors influencing human actions -emergency signaling, instrument indications, presence of instructions, preparation and experience, stress, time, and others. The procedure used in the qualitative and quantitative analysis is briefly reviewed and examples of the evaluation of real actions taken by operators are given. It is shown that it is important to take account of the specific nature of the development of an accident when evaluating the probabilities of operator error.An integral part of probabilistic safety analysis of nuclear power plants is the evaluation of operator error probabilities. The objective of such an analysis is to determine the operator actions, the factors having the greatest effect on the operators, and the operator error probabilities for each action which are most important for nuclear power plant safety. Human actions depend on many factors, such as training and experience, stress, and the availability of information. In turn, these factors can differ for different initial events and development scenarios of accidents. In this connection, one and the same operator action will have different error probabilities under the conditions of different accident scenarios.Operator Actions in an Emergency Situation. In an emergency situation, the operators of a nuclear power plant take actions to stop and cool down the reactor. These actions include monitoring the automatic actuation of the safety systems (or similar manual actions), monitoring the parameters of the power-generating unit, and controlling the operation of the safety systems. Operator actions are an integral part of the general course of liquidating an emergency situation; they are clearly defined and described in the emergency instructions. The importance of operator actions increases enormously if the accident develops in a manner different from the expected scenario, for example, safety systems are not actuated or additional failures occur. In such cases, the operators must duplicate the actuation of systems, use back-up systems or equipment instead of the failed equipment, and take additional measures to maintain the safety parameters of a plant within prescribes limits. Such actions include the evaluation of the situation, making decisions, acting on the decisions, and monitoring the results based on which subsequent decisions are made. The factors influencing operator actions are specific to different scenarios, i.e., their effect and correspondingly the error probability will be different for one and the same actions taken under different circumstances depending on the initial event and the course of the accident.Main Stages of an Acc...
Some safety systems of the Ignalina Nuclear Power Plant (NPP) operate in standby mode. An equipment of such systems is periodically tested and that allows timely detect and repair equipment failures. The periodic testing is an important measure of ensuring systems’ operability and reliability. However, during the test and repair the equipment cannot perform it’s safety function, therefore too often testing decreases the availability of the system. This paper describes the mathematical model that represents how availability and reliability of the systems and their components depend on testing interval, taking into account different failure modes of the equipment. This model allows to find the optimal testing interval for the safety. As an example, the auxiliary feedwater pumps, that are a part of the Ignalina NPP Reactor Emergency Core Cooling System, are analysed. The model parameters calculation is based on Ignalina NPP data regarding pumps operation and failure as well as on general Nordic NPPs reliability data (T-Book) appling Bayesian approach for parameters updating. The analysed safety system is a redundant system that consists of six pumps and other equipment. Therefore a model for multiple components failure was developed. The model accounts for actual operational requirements of the system. The results of this model are compared with usually used binominal model.
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