[en] A nuclear spent fuel cask that employs air or an inert gas such as helium as the cooling medium in the fuel cavity is commonly known as a ''dry'' cask. The thermal characteristics of a dry cask differ considerably from a wet cask. A gas is a poorer heat transfer medium than water. As a result, the fuel and cask basket temperatures will be higher for a given fuel heat level. The response characteristics during operating transients will also differ. Detailed thermal tests on a dry cask were performed to verify design parameters and to obtain operational data for shipping and unloading. Results of a number of thermal tests performed on the NL1 ¹/₂ legal weight truck cask are presented. The uniqueness of these tests are that they were performed using a full-scale geometric and thermal mockup of a nuclear fuel assembly. This results in more realistic fuel and basket temperatures being measured than those obtained using a simpler, single heater assembly