THE INFLUENCE OF THERMAL EXPANSION ON PACKAGE TIGHTNESS DURING FIRE

Packages for the transport of radioactive materials are subjected to a fire test of thirty minutes at 800°C according to TS-R-1. As a result of the fire test, significant temperature gradients usually occur within the package. This is supported by thick walled designs of those packages, in particular. Temperature gradients lead to different thermal expansion, which results in displacements as well as stresses. This has an impact on the package wall but also on the leak tightness because of different influences of thermal expansion on the package wall and the lid. The paper provides approaches based on analyses. Starting with well known analytical correlations for thin and thick walled pipes, a finite element model will be developed to analyse the problem on a numerical basis also. After the verification of the numerical model with respect to the results of the analytical approaches, the finite element model will be adjusted to be nearer to real package designs. In particular, the link to the lid system and the evaluation of leak tightness will be made. Finally, design aspects will be included in the finite element model. Results of the analyses are presented and conclusions are drawn. As a result, shock absorber design and the design of the lid system are important aspects to improve the safety of the package with respect to leak tightness. The effects of thermal expansion during fire test can be analysed numerically. Analytical approaches are suitable for basic estimations and to support first design steps. Experimental verification is a difficult task because the event will occur during the fire test and the leak tightness could be rebuilt after the fire test is done and the measurements take place. Nevertheless, the opening of the package can last a significant time. Therefore, analyses are important to explore this effect and to demonstrate safety.