The aerosol release factor for Pu as a consequence of an ion exchange resin fire in the process cell of a fuel reprocessing plant

Abstract

One of the upper limit accidents usually considered in the safety analysis of a fuel reprocessing plant is an accidental explosion, followed by a fire, of an ion exchange column containing resin loaded with large quantities of plutonium. In such accidents, a certain fraction (release factor) of Pu is released in the form of an aerosol into the ventilation system, and finally to the environment through HEPA filters and the stack. The present study was undertaken to determine the aerosol release factor for Pu in the process cell of a typical fuel reprocessing plant. Geometrically similar scaled-down models of three different sizes were built, and suitably scaled-down quantities of resin loaded with thorium in nitric acid medium were burnt in these model cells. Thorium was used in place of Pu because of its physical and chemical similarities with Pu. The release factor was obtained by comparing the amount of Th in air with the total. The study also dealt with aerosol characteristics and kinematics of process of fire. The aerosol release factors for the three models were found to lie in the range 0.01–0.07%, and varied non-monotonically with model size. The analysis of scaled down results in conjunction with simplified aerosol modelling yielded the release factor for the actual cell conditions as 0.012% with an upper limit value of 0.1%. The particle size analysis based on Th-radioactivity and particle-mass indicated nonuniform tagging of Th to aerosol particles. These particles were irregularly shaped, but not as long chain-like aggregates. The study proposes, with a reasonable degree of conservatism, the release factor of 0.1% for such fires, and aerosol parameters, AMAD and σ g , as 2 μm and 2 respectively. However, for situations significantly different from the present one, the release factor of 1% recommended by the American National Standards Institute may be used with a greater degree of confidence in the light of the present work.