Experimental Investigation of Combined Axial Flow and Jet Cross-Flow on PWR Mock-Up Array

Abstract

Abstract Some pressurized water reactors (PWRs) are designed to relieve the pressure increase in the barrel-baffle region associated with a loss of coolant accident (LOCA). Flow holes, called LOCA holes, are introduced in the baffle plates to equalize the pressure difference between the core side and the barrel-baffle region. However, it has been found that jet flow emanating from LOCA holes induces fretting wear of the fuel rods at the spacer grid position during normal operation. The effect of jet in transverse flow (JITF) on a PWR mock-up array should be investigated in order to determine the rod array response and, as a result, to set safe operating conditions for these reactors. This research looks at the effect of axial flow velocity on the stability of a single-span 6 × 5 square rod bundle having a prototypical fuel assembly dimensions in some designs of pressurized water reactor cores. The axisymmetrically flexible rods in the highly compact array are instrumented with four strain gauges to measure the two-dimensional rod displacements. Then, the response of the rod bundle under combined flows (i.e. JITF) is measured for three test axial flow velocities, VAxial = 1.0 m/s, 1.5 m/s, and 2.0 m/s. The experimental results show that the critical jet cross-flow velocity increases with the axial flow velocity. This is attributed to the bending effect of axial flow on the jet flow (i.e. jet trajectory). The critical flow velocities are collected to provide a stability map of the arrays subjected to the jet in transverse flow.