Longitudinal Hydraulic Wave Phenomena in Fuel Assemblies Consisting of Concentric Fuel Elements

Water-hammer theory is extended to the fuel assembly configuration of concentric annular fuel elements and flow passages. The analysis shows that due to the coupling of the hydraulic effects in adjacent coolant passages to each other through an elastic structure separating them, several modes of pressure wave propagation are possible. These compression (and rarefaction) waves travel at velocities less than the velocity of sound in the fluid depending on the dimensions of the fuel elements and flow passages. The existence of these compression and rarefaction waves traveling at different velocities leads to complex pressure disturbance patterns as a function of time, which may be of importance in fatigue analysis of the structure or possibly in determining whether or not voids could form as a result of the rarefaction waves. The analysis is general enough that it can be extended to include a wide variety of configurations when it is desirous to evaluate the effect of hydraulic pressure waves on fuel element performance.