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BWR Coolant Chemistry Loop (BCCL)

The BCCL was also designed as an approximately 1/3 scale model of a single flow channel in a BWR. In this case, the parameters that govern BWR coolant radiolysis and the associated parameters of electrochemical corrosion potential (ECP) and nitrogen chemistry were simulated as closely as possible in the in-core loop. The loop operated at the same temperature and pressure as BWR core with capability for outlet quality up to 15%. Operating in single phase mode the loop could also be used to simulate bypass region conditions.

For the BCCL, makeup and letdown systems were designed to provide heated feedwater at a variety of conditions. Feedwater gas content (H2 and O2) was independently controllable and other dissolved species could be added through a separate injection system. The core exit stream was separated into steam and water phases that were independently assayed for N16 content using on-line gamma monitors. ECP was monitored in the steam separator plenum and in the liquid phase letdown line. A cooled sampling system was installed on the loop to allow core exit hydrogen peroxide concentration to be measured. Hydrogen peroxide decomposes rapidly by thermal processes at BWR temperatures in the bulk coolant and on sample line walls. The possibility of close access to the loop during reactor operation and the use of the sample cooler combined to provide a unique capability for accurate hydrogen peroxide measurements.

Several sets of BCCL experiments were carried out. The first were aimed at providing well characterized datasets to be used for benchmarking radiolysis codes. Many codes were semi-empirical in nature and had been optimized to predict parameters measured in operating plants. The availability of a test bed that was better characterized and more controllable than a commercial plant was of significant value in the improvement of the codes. Another set of experiments studied the possibility of achieving the benefits of hydrogen water chemistry (HWC) in a BWR without the concomitant increase in carryover of radioactive nitrogen into the steam line. Alternate ways to produce reducing coolant environments were evaluated, as was the possibility of injecting other species together with hydrogen to achieve reductions.