Über die bildung von U 2C 3 durch zerfall des urandicarbides

Abstract

The stability of the UC 2-phase is of great interest with regard to operating HTR's using dicarbide coated-particle fuel. In the literature the reaction 2 UC 2 a ́ g U 2C 3 + C is mentioned. There is, however, partial disagreement on the detailed description of the conditions at which U 2C 3 is formed. This paper presents experimental results of the reaction of decomposition with special emphasis on the presence of certain moderating or accelerating forces. The enhancement of the decomposition, occurring when additional mechanical energy is brought into the UC 2 matrix, was studied. A maximum in the U 2C 3 forming rate of reaction was observed in the temperature range 1300–1400 °C. With a material pre-heat treated at 1900 °C however no transformation was detected. U 2C 3 formation is reported after heat treatment of irradiated coated particles, and a stabilization of the dicarbide fuel therefore is advantageous. In this respect the contamination of the UC 2 by N 2, of about 1500 ppm, seems most effective, while oxygen contamination has little or no effect. Of great influence on the reaction is the shape and quantity of the primary graphite precipitation: a large amount of laminar graphite favours the transformation while globular graphite, preferably forming during rapid cooling, inhibits the reaction.