MODELLING THE THERMAL PERFORMANCE OF CORK AND WOOD IN THE THERMAL TEST

Cork and wood are materials which are frequently used in the design of transport packages, both inside transport flasks and in impact limiters or heat shields which are placed on the flasks during transport. Cork and wood are used in transport packages because they readily compress, absorbing energy during an impact, and also have a low thermal conductivity, protecting the flask from the heat of a fire. It is challenging to demonstrate, by testing alone, that a package meets all the thermal requirements of the IAEA Regulations. Nearly all thermal assessments therefore include some modelling. Cork and wood are natural materials and at high temperature their thermal behaviour is complex. A thermal assessment of heat transfer across a cork or wood heat shield, based just on reference values of density, specific heat and thermal conductivity may therefore be subject to considerable error. This paper addresses the challenge of modelling heat transfer through cork and wood, in a demonstrably pessimistic way, such that the effects such as charring, evaporation and condensation of water and oils, shrinkage and burning can be shown to have been considered and included. It is concluded that the modelling of heat transfer through cork and wood must be based on experimental data. Examples of thermal tests which include heat transfer through cork and wood are given and the calculation of the corresponding effective thermal conductivities described. In some situations it is known that the wood inside a transport package or shock absorber may burn, releasing heat. Ways in which any heat generation from burning can be included in the thermal model are described.