Natural versus artificial aging of nuclear power plant components

This program seeks to understand the aging of polymeric materials, in cables and other components in nuclear reactor containment, by comparing aging processes for a variety of materials under natural conditions with those under the accelerated laboratory conditions used in qualification. The first five-year phase has been completed in what is planned as a long-term study of up to 40 years. Data from the program can be used as a basis of forecasting more realistic lifetimes in reactor service. The program is of critical importance for utilities both for the safe operation of plants and for minimizing the cost of periodic replacements upon expiration of originally predicted qualified life. The first five-year period has involved the selection and acquisition of test specimens, their preparation for placement in the containment, the selection of plants and locations for the specimens, the establishment of methods for monitoring radiation and temperature levels at each site, development of plans for scheduled removals, test method development, and testing of the specimens by physical and mechanical methods. Specimens have been subjected to short-term accelerated aging, as well as to reactor containment aging for up to five years. They consist of many types of polymers in products of several different manufacturers. Environmental conditions cover a wide range of temperature and radiation levels at 17 locations in 9 reactors of participating utilities. Initial results, which include tests of special cases subject to 8 years of reactor aging at Northeast Utilities, indicate several instances of changes having statistical significance in density or tensile properties due to containment service, but none of these changes are large enough to be of any concern. 12 refs., 19 figs., 21 tabs