[en] This report provides the results of accident simulation tests of three typical light water reactor containment penetration systems to provide a technical basis for the support and development of equipment qualification procedures at design basis load levels and to determine safety margins at severe accident load levels. The three systems tested were (a) an 8-in. gate valve system modeling containment spray system; (b) an 8-in. butterfly valve system modeling a purge and vent system; and (c) a 2-in. globe valve system modeling the numerous small-bore piping systems. The valve types, valve sizes, piping configurations, penetrations, and supports used for the tests are typical of those found in commercial US nuclear power plants for containment isolation applications. The three systems tested were mounted in a fixture and exposed to simulated severe accident mechanical loads by displacing the penetrations relative to the piping. Thermal and pressure loads were also applied. The test results indicate that valve, penetration, or piping system failure during hypothesized accident even is unlikely due to accident-induced loads. 14 refs., 44 figs., 11 tabs