Uranium Powder Ignition Studies

Because ignition temperature is not an intrinsic property of a substance, the investigation reported in this paper was undertaken to measure the ignition behavior of uranium powder under well-defined boundary conditions such that quantitative predictions are possible. The ignition behavior of uranium powder has been found to be dependent on specific area of powder fraction, rate of heating, and geometry of sample. For a given mesh size powder and heating rate, constant limiting ignition temperature values are obtained practically independent of container size, when the powder bed exceeds a critical height. Critical height values are found to increase with particle size of powder; for a given particle size powder, critical height values decrease with heating rate. On the basis of the Frank-Kamenetskii theory of thermal explosions, when used in a restricted manner, limiting ignition temperature values for uranium powder can be estimated using critical height values as the significant geometrical dimension of the container. These calculated ignition temperatures are in reasonable agreement with those obtained with our experimental apparatus. The ignition behavior of uranium powder can be adequately described by converting isothermal expressions to a rising temperature basis according to the treatment of Murray, Buddery, and Taylor.