Dynamic analysis of wetwell-to-drywell vacuum breakers in BWR Mark I containments

During steam condensation tests on BWR Mark I Containments, the wetwell-to-drywell vacuum breakers cycled repeatedly during the transient phase of steam blowdown. Since they were not originally designed for the loads resulting from this cycling, further investigation was warranted. A finite element analysis, and tests to confirm the analysis, showed that the valve was overstressed. An acceleration or velocity limiting mechanical snubber in conjunction with a suitable linkage was used to control the operation of the valve and, thus, maintain its functional and structural integrity. (orig.)