2012 Volume 54 Issue 168 Pages 92-109
Because of an accidental event of sodium spillage, occurred in a nuclear facility, Japan, sodium combustion has attracted special attention since 1995. In this lecture, relevant to the sodium combustion, the spontaneous ignition for a droplet and/or a pool has been discussed with putting focus on the ignition delay and ignitability which have been elucidated through coorparative works after the accident. For elucidating ignition phenomea of sodium, a theoretical work has been conducted, under consideration that the surface reaction can mainly exert influences. Through conducting the asymptotics, it has been found that the governing equation for the energy has the same form as that used in 1930s for constructing “Thermal Explosion Theory”, and that both the ignition delay time and the limit of ignitability are closely related to the oxygen concentration and the representative size of droplet and/or pool, as well as the initial sodium temperature. It has also been derived a set of comprehensive parameters for the ignition delay time and the limit of ignitability, by which it has succeeded in fairly correlating dominant parameters that can exert influences on the ignition. In addition, a fair degree of agreement between the experimental and analytical results has been demonstrated, as far as the trend and approximate magnitude are concerned. Because of the simple forms of the comprehensive parameters, they are expected to be useful in evaluating ignition delay and ignitability. Related subjects are also explained although they are on the way.
