Stress of containment steel shell under blowdown loading

Since 1977 about 35 steam and water blow downs have been performed as part of the HDR Safety Program. Certain of them were conducted with an automatically-closing valve to simulate pipe rupture upstream of the valve. Approximately 10 tests simulated rupture located between the reactor pressure vessel and an isolation valve, resulting in a total blow down (unlimited in time) of the primary system. The size of ruptured gap was varied during these tests, as well as the distance between the theoretical break location (rupture disk) and the RPV nozzle, the latter under nominal boiling water reactor operating conditions (typically 80 bar and 2800C initial pressure and temperature.) One of the many test objectives was the behaviour of the containment steel shell, which was subjected to an increase in inner pressure and local as well as global temperature gradients while the primary coolant flowed from the simulated pipe break. The containment shell was instrumented outside and inside, axially and circumferentially, with thermocouples and strain gauges. (orig./WL)