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Extending the Half-Life Computer modeling may make it possible to lengthen the life of nuclear reactors.
For the past 40 years, researchers at Oak Ridge National Laboratory have been testing reactor vessels, the critical part of nuclear power plants where nuclear reactions take place under extraordinary pressure. Specifically, they study the various steels the reactors are made of to assist the Nuclear Regulatory Commission in developing safety regulations for the plants. In the 1970s, ORNL researcher Richard Bass and his team employed large steel specimens weighing more than one ton to simulate the response of components to the pressure and temperatures caused by nuclear reactions inside commercial power plants. Today, the labs once housing ORNL's heavy-section steel technology program are closed. Bass and his colleagues now carry out large-scale simulations on high-performance computers. The results of this transformation have had a significant impact on the nuclear power industry. A computational tool developed at ORNL, known as the Fracture Analysis of Vessels of Oak Ridge, or FAVOR, is proving to be a key factor in a proposed change in regulation that could double the operational life expectancy of nuclear power plants in the United States. Most of the nation's 104 nuclear power facilities, which provide approximately 20% of the U.S. electricity supply, face expiration of their 40-year Nuclear Regulatory Commission licenses within the next 10 to 20 years. Using ORNL's research, the NRC recently issued a revised regulatory rule central to the agency's efforts to approve 20-year license renewals for many of those plants. Analysis and reliability tools developed at Oak Ridge indicate that an additional 20-year renewal will be feasible for many plants, extending their total lifetime to 80 years and making a significant contribution to the nation's energy demands. The economic impact of this extension is estimated in the hundreds of billions of dollars. "All of the nuclear plants in operation today were approved by the NRC to be built in the 1960s and 1970s," Bass says. "While some were constructed in the 1980s, most plants have licenses due to expire within the next decade. We are looking at a replacement cost of billions of dollars for each plant, in addition to the time required to build and license a new facility and the associated reduction in power capacity when an existing plant is closed. With a projected renaissance in the nuclear power business, the extension to current licenses should provide enough time to build new plants that will replace aging ones and meet the growth in electricity demand." Since the 1960s, ORNL has, with NRC funding, tested a variety of reactor vessels and their materials to help the agency create guidelines for operation and safety of the vessels. Results from that research contributed heavily to the first rulemakings in the 1980s and 1990s for assessing pressurized thermal-shock scenarios. Those rules, however, were conservative, partly because detailed information about the vessels and their response to a variety of stresses was not fully understood. As more information about the equipment has become available and modeling and computational tools have become more sophisticated, ORNL researchers have been able to reevaluate with much greater accuracy the probability of these events. The result is the ability to determine which vessels can operate longer than allowed by their current regulations with no compromise of safety. ORNL is working with other national laboratories and research institutions to create a similarly comprehensive analysis tool that will encompass all pressure-bearing components of a nuclear plant, providing detailed findings about the condition of the plant as a whole. Bass says the capabilities developed at ORNL will be available for developing regulations for an anticipated increase in the number of new plants planned for construction in years to come. —Larisa Brass Contact: Bennett Richard Bass
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