| Abstract: | Approximate measurements were made on fuel fragmentation of stainless steel/sodium and copper/sodium systems: the surface area of stainless steel increased by a factor of 260 to 3.1 and that of copper by a factor of 300 to 2.7 m2/kg. The number of particles obtained was about 108 per kg fuel. The conditions were: stainless steel 1600°C, copper 1927°C, sodium 400°C at 1 bar ambient pressure (argon cover gas); no detectable pressures accompanied the interaction.A violent sodium boiling model is used for the explanation of the results. A specified number of sodium vapor bubbles grow and collapse with high frequency on the contact surface. The collapse effectively increases the fuel (=heating) surface, and an appropriate energy transfer coefficient is assumed. Contact temperatures, nucleation, bubble statistics, mechanical energy transfer, surface increase and heat transfer are coherently treated and describe the fragmentation transient. The copper surface area is calculated to increase by a factor of about 750 to 6.6 m2/kg within very short times of 1 ms or even less, the stainless steel surface by 200 to 2.4 m2/kg. |
