Primary Inventor: Krishna P. Singh
Date of Filing: May 13, 2015
Equipment Type: HI-STAR
Docket Number: HOL-101
Abstract: Heavy casks containing hazardous materials such as High Level Nuclear Waste and fissile materials are typically handled by a set of “trunnions”. The trunnions are generally made of a cylindrical bar stock welded to a hard location near the top of the cask such as the top flange shown in Figure 1. The trunnion must project out sufficiently to provide the engagement shoulder for the lift yoke (Figure 2) to engage it. This projection, however, is a problem where the cask must be designed to withstand a free fall event such as that required for transport casks containing used nuclear fuel under the regulations of 10CFR71.73. The federal regulations (as well as the IAEA standards) require the cask to be qualified under a free fall event from a height of 30 feet onto an essentially unyielding surface under any orientation of impact. In such a case, the cask is equipped with an “impact limiter” at each extremity which absorbs the kinetic energy of impact by crushing. The projection of the trunnion, made of a high strength steel or other alloy material, however, interferes with the crushing action of the impact limiter if the impact orientation of the cask is aligned with the plane of the trunnion. The solution to this design problem thus far has been to tap the trunnions and thread them into the cask’s flange. The trunnion is removed when not in use to eliminate the threat of trunnion penetration during the above-mentioned design basis accident event. This approach has two major shortcomings:
- The threaded joint sometimes freezes under the bending moment from the lifted load making the trunnion’s subsequent removal problematic.
- It may not be possible to handle the cask without the trunnions in place (after all, their sole purpose is to enable cask’s handling).
- The trunnions restricted to be located in the neck of the cask so that its projection beyond the cask’s body is minimized.
The above limitations make the classical trunnion design a rather unsatisfactory embodiment.
While the shortcoming of conventional trunnion discussed above has been presented in the context of a cylindrical cask, it applies to other cask shapes as well such as a rectangular cask and casks that don’t necessarily utilize impact limiters.