On the pressure buckling of rectangular bellows for fusion reactors

Bellows are planned for use in the torus vacuum vessel of ITER to absorb the relative displacements resulting from thermal expansion. Though both sides of the bellows are in vacuum during normal conditions, these bellows would be subjected to external or internal pressures of several MPa during accidents. Since the vacuum vessel forms the tritium boundary during postulated accidents, the prevention of bellow failure in these events is very important in the ITER design. For equipping the internal components, rectangular bellows are preferable to circular bellows in the ITER design. However, investigations concerning pressure buckling of rectangular bellows are few. Therefore, we investigated the buckling behavior of rectangular bellows and proposed a simplified evaluation method based on the half pitch model for bellows with a relatively high length-to-diameter ratio, where elastic column squirm is dominant. For bellows with a lower number of convolutions, however, inplane squirm buckling should be considered, therefore, we have investigated inplane squirm of rectangular bellows and compared it with that of circular bellows in this paper.