ESTIMATION OF CASK DECELERATION AND IMPACT LIMITER DEFORMATION UNDER 9M DROP TEST CONDITIONS USING THE CALCULATION TOOL “IMPACTCALC”

The design safety assessment of transport casks for radioactive material in Germany is carried out by the Federal Institute for Materials Research and Testing (BAM). Both experimental and computational (analytical, numerical) methods combined with additional material and/or component tests are the basis for the safety evaluation and assessment concept at BAM according to the state of the art. The required mechanical tests according to IAEA regulations include, among others, a 9m drop test onto an unyielding target. In particular, the energy absorption capacity of the impact limiting components has a significant influence on package integrity and tightness. The comprehension and physical evaluation of the behavior of impact limiting components under dynamic loading are essential for the safety assessment. Mode of construction, temperature range and used materials are crucial aspects in regard to the behavior of the package. This paper presents considerations about wood-filled impact limiters. Special features and constructive conditions of impact limiters are shown. The paper focuses on the simulation of cask deceleration and wood-filled impact limiter deformation as they occur during a 9m drop test. For this purpose, the calculation tool “ImpactCalc” was developed. “ImpactCalc” can be used to plan drop tests, simulate the effect of variable special features and constructive conditions of impact limiters, and carry out parametric studies of impact limiting components. The basis for “ImpactCalc” is the reduction of a complex impact phenomenon to the dynamics of a plain mass-spring-system. The corresponding differential equation of motion describes the time dependent impact process including force-time-, deceleration-time- and deformation-timedependencies. The governing equations are solved by the computer-algebra-software ,,MathCAD” [1]. The programmed algorithm was verified by comparison with different current drop tests conducted at BAM. Restrictions concerning the application of “ImpactCalc” arise from its analytical approach. However, if applied correctly, the tool can give an acceptable estimation of the deceleration of the package and deformation of the impact limiter.