New Technologies for Acceleration and Vibration Measurements Inside Operating Nuclear Power Reactors

A miniature biaxial in-core accelerometer has been inserted temporarily inside the Travelling In-core Probe (TIP) systems of operating 1300 MWel Boiling Water Reactors (BWR) during full power operation. In-core acceleration measurements can be performed in any position of the TIP-system. This provides new features of control technologies to preserve the integrity of reactor internals. The radial and axial position where fretting or impacting of instrumentation string tubes or other structures might occur can be localised inside the reactor pressure vessel. The efficiency and long-term performance of subsequent improvements of the mechanical or operating conditions can be controlled with high local resolution and sensitivity. Low frequency vibrations of the instrumentation tubes were measured inside the core. Neutron-mechanical scale factors were determined from neutron noise, measured by the standard in core neutron instrumentation and from displacements of the TIP-tubes, calculated by integration of the measured in core acceleration signals. The scale factors contribute to qualitative and quantitative monitoring of BWR internal’s vibrations by the only use of neutron signals.