Temperature Conditioning of Large Packages for Impact Testing

Regulations governing the transport of radioactive materials require that most hypothetical accident condition tests and analyses consider the effects of the environmental temperature that most challenges package performance. For many packages and/or package features, the most challenging temperature environment is the cold condition temperature of -29ºC. This is especially true for packages with wood or foam-based energy absorbers because the low temperature causes the highest free drop impact forces due to the higher strength of these materials at cold temperatures. Other package designs and/or package features may be more challenged by the high temperature extreme. More frequently than in the past, competent authorities are requiring direct evidence of performance at temperature extremes, and, consequently, temperature-conditioned testing is being conducted more frequently. For small packages and scale-model test units, the temperature conditioning requirements are relatively easy to meet. However, for large packages it can be difficult to achieve the required temperature extremes. Strictly speaking, it is only necessary that the temperature-critical parts of the package have the required temperature prior to the drop. Usually, there will be temperature gradients through the package, either during the temperature conditioning or while the package is returning to ambient temperature during the period between removal from the conditioning chamber and impact. A critical issue is balancing these temperature gradients with the need to have critical components within a specified temperature range. This paper will discuss these issues and show how they were addressed for example drop test programs.