SCIENTIFIC AND TECHNICAL COMMUNICATIONS OPERATIONAL SAFETY OF TECHNOLOGICAL FACILITIES FOR CONDITIONING RADIOACTIVE WASTES

摘要

An accident is a particular set of system and component failures in which radionuclides can be emitted into the environment. Such a sequence of events is called a scenario. The collection of all scenarios forms an event tree. Let S_n (n = 1,2,..., N) be the probability that the nth system fails and S_n = 1 - S_n the probability that the same system operates without failure. Then the probability P_m of each scenario is a product of the corresponding probabilities of independent events either S_n or S_n depending on whether or not the system n is in a failure state. To formalize the procedure, we introduce for the nth system the indicator q_n, where q_n = 0 if the system is in a failure state and q_n = 1 if the system is in an operating state. Then the probability of the nth scenario can be calculated from the formula P_m = ∏ S_n~(1-q_n)S_n~(q_n), where ∏ is the product symbol. The next step in analyzing an object is to develop and construct a failure tree for individual systems. This is a structural relation between the system components from the standpoint of operational reliability and failure-free operation. The probability of failures of the systems S_n is calculated by constructing a failure tree. In other words, a failure tree is a logical chain of failures of components which are connected by the logical symbols AND or OR corresponding to multiplication or addition of random failure events.