where te and ts are the thickness for cylindrical and spherical shells, respec-

tively (in.); P is the design pressure (psig); S’is the maximum allowable stress (psi); E is the joint efficiency; and R is the internal radius of the building (in.). Assuming a joint efficiency of unity and neglecting the small pressure effect, then, for cylindrical and spherical shells, the wall thickness (neglecting the corrosion allowance) should be t = PRjS and t = PR/2S, respectively.

The relevant code (13) waives stress relief for wall thicknesses of less than one and one-eighth inches. For this thickness, the above equations show that the containment building would stand 20-30 psig. It therefore appears to be very fortunate that in each case the design basis accident gave rise to design pressures within the limit for which expensive stress relief of the containment outer shell was not required.

In practice, it is possible to include design features, such as an inner containment barrier of reinforced concrete, which would avoid subjecting the outer steel shell to high pressures even in the remote event of a core disruptive accident.