Crack propagation in high strain regions of Sequoyah containment

The rate of release of radioactive materials from a containment during a severe accident has a significant impact on the consequences of the accident. One hypothesis for a containment leakage model states that the containment will develop a controlled, relatively small leak before the pressure reaches the point where a general rupture of the shell occurs. Another states that overall failure will occur with total release of the vessel contents almost instantaneously. The Sequoyah ice condenser containment vessel has been studied for some time to predict the possible location and extent of leakage which could occur during a severe accident. In this work, three critical high strain locations were studied to predict crack propagation from an initially small defect. The 1/2-inch plate near the Sequoyah springline was selected for further study. A detailed finite element model of the region was prepared and a virtual crack extension method for calculating the J integral was developed for use with the general purpose finite element program. The pressure in the model was increased to 78 psi which produced a maximum membrane strain of 6.5 percent. At this point the surface crack was assumed to propagate through the plate and leakage began. Using the virtual crack extension method, two through cracks with different lengths were found to be unstable at this pressure which would allow almost instantaneous release of the vessel contents