Pressurized Water Reactor Core Crud Mapping

Abstract

Knowledge of the quantity and distribution of core deposits (crud) can be useful in many ways. Trending the amount of crud can show the effects of coolant chemistry changes and crud remediation efforts. The crud distribution reflects the locations of sub-cooled boiling, and indirectly, core performance. Both the quantity and distribution of crud can be useful in assessing the risk of Crud Induced Power Shifts (CIPS) and Crud Induced Local Corrosion (CILC). Measuring core crud is also essential in increasing the fundamental understanding of crud transport and the build-up of ex-core radiation fields. Several techniques have been used to measure core crud levels. Crud scraping is frequently applied to sample crud, but it cannot be applied economically over broad areas. Crud has been mapped over broad core areas by analyzing the waste stream from an ultrasonic fuel cleaner, but uncertainties in the cleaning efficiency limit the accuracy of this technique. Video crud mapping, the determination of crud coverage from video images of fuel assemblies, is an economical method that can be readily applied to peripheral rods on every fuel assembly. The mapping can be performed by computer image analysis, or by visual comparisons to standards. The two techniques are compared and the advantages and disadvantages of each are discussed. The effectiveness of video crud mapping in assessing fuel performance issues is shown in the results of several field applications.