Vibroacoustical Diagnostics of the Fuel Assemblies of a Nuclear Power Plant with RBMK

This paper deals with the results of studies on hydroelastic oscillations of a fuel assembly (FA) in the annular gap of a fuel channel (FC), induced by an axial coolant flow. Nuclear reactor operation is accompanied by quasistatic variations in the assembly and channel parameters, i.e. stiffness relaxation, swelling of fuel cladding, FC diameter changes due to radial creep. As a result, the annular gap between the fuel assembly and the inner wall of the fuel channel grows. Analytical and numerical solutions are provided for the non-linear problem on fuel assembly oscillations under its vibroimpact interaction with the inner walls of the annulus for three gap values of 1, 2 and 3 mm. It is shown that under vibroimpact conditions the shock pulse intensity grows with the increase in the gap.