Circulating Crud Characterization in Condensate System of Boiling Water Reactors at NWC/HWC Environments

摘要

The coolant-borne corrosion products cause a lot of problems regarding removal efficiency of condensate polisher, crud deposition on cladding surface and radiation build-up on system piping and components. The single dominate corrosion product in reactor coolant is iron, approximately higher than 95% in our plants. For diagnostic reasons, the corrosion/erosion iron products should be measured weekly and be controlled within a good practice limit followed EPRI guidelines, depended upon the type of condensate demineralizer of BWR. The characteristics of the crud particles appearing in coolant sometimes varies between units and their different operational conditions. The main objective of the studies is to identify the phase composition of iron-bearing circulating particles in condensates by using appropriate methods. A variety of different techniques, including chemical dissolving measurements and auxiliary tools were also applied in characterization evolved from normal water chemistry to hydrogen water chemistry operational environment. The results of characterization indicate that the oxide particles have slightly different properties. The insoluble corrosion product in condensate pump discharge shows a trend of containing more amount of crystalline form, strong dominated by lepidocrocite at normal water chemistry conditions. In hydrogen water chemistry environment, amorphous particles have been observed to increase 15-20 % by weight and both magnetite and hematite crystalline appear to be more important in condensates. Crud in unit with more crystalline structure in condensate seems to have high removal efficiency, compared with unit containing less crystalline form. The result from the crud investigations can be used in the subsequent discussion to explain the discrepancy of crud removal efficiency of the individual plant unit with the same design that containing no pre-filter in the upstream of condensate demineralizer.