Probabilistic Risk Assessment in Nuclear Reactors: Engineering Success, Public Relations Failure

Abstract

Probabilistic Risk Assessment in Nuclear Reactors: Engineering Success, Public Relations Failure RODNEY P. CARLISLE From its beginnings in the Manhattan Project, the nuclear indus­ try in the United States faced two interrelated safety issues: how to design and operate reactors safely, and how to persuade the public that in fact these facilities posed no danger. While engineers eventu­ ally grew convinced that they had mastered the first, they virtually abandoned efforts to address the public relations issue after the late 1970s. At the core of the problem was the difficulty of explaining to nonspecialists evolving methods of estimating and designing safety. Procedures for the safe design and operation of nuclear reactors evolved during World War II, when the first reactors were built not to generate electric power but to produce plutonium for nuclear weapons. The Manhattan Project was secret, and the public rela­ tions issue did not arise. The new profession of nuclear engineer­ ing emerged from the designers and operators of these produc­ tion reactors. This article traces how nuclear engineers, designing both production reactors and, later, power reactors, developed new methods of assessing reactor risk and how the public reaction to those methods shaped the debate over the safety of these facili­ ties. From the beginning, reactor designers could lean on civil and me­ chanical engineers’ long-established methods of designing struc­ tures and machines so as to prevent accidents or mitigate their ef­ fects. Standard engineering practice included identifying risks and estimating the consequences of various types of failure, and design­ ing around them. Even before the first reactor operated, such potenDr . Carlisle is professor of history at Rutgers University in Camden, NewJersey, and a senior associate at History Associates Incorporated of Rockville, Maryland. He is the author of several works in the history of technology, including Supplying the Nuclear Arsenal (Baltimore, 1996), and is at present completing a history of the United States Navy’s David Taylor Research Center in Carderock, Maryland.© 1997 by the Society for the History of Technology. All rights reserved. 0040-165X/97/3804-0004$02.00 920 Probabilistic Risk Assessment in Nuclear Reactors 921 tial problems as radiation exposure and meltdown were identified and addressed in the initial designs. In the years following World War II, as reactor design grew more sophisticated, a new method of assessing risk began to emerge. The emerging technique sought to estimate the likelihood of accident, us­ ing mathematical calculations of the probability that systems and subsystems would fail. More fully developed in the 1970s, the new method of risk evaluation came to be called probabilistic risk assess­ ment (PRA).1 Probabilistic risk assessment could be used to compare the degree of risk between two reactors, using estimates for the probability of failure of various components. Multiplying those probabilities to generate an overall calculation, or PRA number, the risk of core damage could be represented as a number with a negative expo­ nent—in other words, the level of risk could be represented as one chance in some number (presumably a high number) of reactoryears . PRA gained increasing acceptance within the nuclear engi­ neering community as more and more reactors were built for the purpose ofgenerating electricity (as opposed to producing weapons plutonium). The technique came to be used regularly to evaluate these power reactors, to identify potential high-risk components and, eventually, to evaluate competing reactor designs. Among some operators of production reactors and among the general public, however, the methods of PRA encountered opposition and skepti­ cism. * * * The Manhattan Project brought together a diverse collection of talents from academia, the military, and industry. Different cultural styles among the various groups from which the profession of nu­ clear engineering emerged helped to fuel debates over PRA in the 1940s. The first reactor designers came from three existing professional cultures. Physics provided one source. Through the 1930s, experi­ mental physicists often coupled academic and scientific education with experience as mechanical laborers in physics laboratories such as the Lawrence Radiation Laboratory in Berkeley, California.2 The ‘In Europe, the same techniques came to be called probabilistic safety analysis, or PSA. 2On Lawrence’s use of physics graduate students as technicians seeJ. L. Heilbron and Robert W. Seidel...