Program Plan for Correction of U.S. Instrument Degradation or Failure in the Upper Plenum Test Facility (UPTF) in the Federal Republic of Germany

摘要

The report documents the investigation of the failure or degradation of some of the advanced two-phase flow instruments supplied by the USNRC to the Upper Plenum Test Facility (UPTF), including Tie-Plate Drag Bodies, Breakthrough Detectors, Loop Drag Disc paddles, Fluid Distribution Grid sensors, and Liquid Level Detector sensors. The exact causes for these instrument degradation or failures are not known, but several potential causes have been identified. For DBs and BTDs, the primary mechanism for the degradation seems to be a leakage in the Inconel 600 strain gage encapsulation and the subsequent burnout of the strain gage elements. For DDs the degradation or failure cause seems to be excessive loads. The degradation cause for most of the FDGs and LLDs seems to be either steam/water erosion or mechanical abrasion of sensor tips, which are made of sapphire. However, some of the FDG tips were found to be cracked also. The corrective actions are being directed toward finding out what are the primary causes for the instrument degradation or failure and what should be done to prevent these degradations or failures from continuing or recurring.