CONFINEMENT ANALYSIS OF DUAL PURPOSE METAL CASK SUBJECTED TO IMPULSIVE LOADS DURING HANDLING ACCIDENTS

Necessity of the interim dry storage of nuclear spent fuel using metal casks has risen year by year. The metal gaskets are used to keep the leak-tightness of the metal cask for long-term storage. The metal cask storage system should be designed to withstand man-made events such as handling accidents, and external natural events, such as earthquakes, tornadoes, floods, etc. without impairing its capability to perform its intended design functions. The purpose of the investigation in this paper is to assess the structural and confinement integrity of the transport and storage metal cask for spent fuel without impact limiters in case of severe impact loads and to estimate a conservative leakage rate for calculating the amount of radioactive release. Behavior of the structural integrity of the metal cask was examined using a finite-element method of analysis in a computer program, LS-DYNA. A detailed 3-D finite element model of the floor structure and the metal cask was developed for the explicit method of dynamic analysis, and confirmed by comparing with the impact test results with a full-scale metal cask (horizontal drop and rotational impact onto concrete floor from 1m height). The analyses of the several nonmechanistic tip-over (on the concrete floor and transport rack) and drop events from 1m height in the storage building have been executed. The leakage rates were calculated in connection with the determination of the accumulated relative displacements between the metallic gaskets and the flange. After the lid behaviors in each case have been evaluated, it is found that the leakage rate from the primary lid might be less than 1.0×10-5 Pa?m3 /s and the loss of the inner pressure in the cask might be excluded in the accidental events considered in the storage building.