Impact of Power Uprate on the Water Chemistry in the Primary Coolant Circuit of a Boiling Water Reactor Operating under a Fixed Core Flow Rate

Abstract

The approach of power uprate has been adopted by the utilities of light water reactors over the past few decades in order to increase the power generation efficiency of a nuclear reactor. Upon a power uprate, the power density of a nuclear reactor would change immediately, followed by water chemistry variations due to the enhanced radiolysis of water in the core and near-core regions. For commercial boiling water reactors (BWRs), it is currently a common practice to adopt hydrogen water chemistry (HWC) for corrosion mitigation. The optimal hydrogen injection rate may require a proper adjustment after a power uprate is practiced in a BWR. A DEMACE computer code was used in the current study to investigate the impact of various power uprate levels on major radiolytic species concentrations and the electrochemical corrosion potential (ECP) behavior of components in the primary coolant circuit of a domestic BWR operating under either normal water chemistry or HWC. The results of our analysis indicated that the chemical species concentrations and ECP did not vary monotonically with increases in reactor power level at a fixed feedwater hydrogen concentration. In particular, the upper plenum and upper downcomer regions exhibited uniquely higher ECPs at a 102% power level than at the other evaluated power levels. The impact of power uprate on the water chemistry in the primary coolant circuit of a BWR is expected to vary from location to location and eventually from plant to plant due to different degrees of radiolysis and physical dimensions.