Heat Transfer in Severe Accident Simulations*

Sandia National Laboratories (SNL) utilizes fire test facilities to subject military components and nuclear material shipping containers to postulated accident environments. There are two general approaches for specifying the thermal exposure. One is to specify a furnace temperature history, such as that used for building fires in the AS1M test method E-119; the other is to define the heat transfer rate to a surface in terms of the relative temperatures of the surface and the fire. The regulations concerned with the transport of radioactive materials (RAM) use the latter approach. To begin to define the actual thermal environment, measurements of temperature and heat flux are necessary. Temperatures in the furnace/fire are important because many material limits are directly related to temperature. Test item temperatures define the response of the item to the environment. The initial response of the test item is governed by the heat flux. The heat flux levels indicate how severely an item will be thermally stressed and the integrated flux helps define the total thermal insult.