Fundamental study on thermo-hydraulic behaviors of a fuel channel during a severe power transient

Thermo-hydraulic behavior during a severe power transient is studied experimentally. A stainless rod of 4mm in diameter and 120mm in length, simulating a fuel rod is transiently heated by Joule heating using discharge of a power condenser charged up to 50KJ. Expansion of transiently developed thermal boundary layer, transient nucleate and film boiling around the heater rod generate a high pressure pulse which is converted to mechanical energy of the fluid. When the power input becomes large enough, the heated rod is melted and dispersed into the liquid. The peak pressure and the mechanical energy due to the transient power input are investigated for various power input and coolant conditions. The main results are; 1. When the heated rod do not melted, there is a combination of power input and subcooling that generates peak pressure and maximum mechanical energy where nucleate boiling is the dominant mechanism through the transient. However, they are suppressed in the high power input region. 2. When the rod melts, the peak pressure and the mechanical energy increase to about 10 times larger than those of the non-melting case. (author)