12.178. Over the course of nuclear reactor development, some accidents have occurred, which is not entirely unexpected for a new technology. In all cases, the effects were managed and the general public was not affected [21]. Commercial reactors earned an excellent record until the Three Mile Island accident in 1979, in which there was a negligible release of radiation to the public but major economic losses occurred. The accident also led to important changes in plant design, management, and regulation. In 1986, the Chernobyl accident, as a result of which there were 32 direct fatalities, had worldwide consequences on public acceptance of nuclear power and has had an effect on the design of future reactors. We will examine the effects of each of these two accidents on nuclear reactor engineering practice.