The Effectiveness of Hydrogen Water Chemistry on Corrosion Mitigation in an Advanced Boiling Water Reactor

For further improvements on thermal efficiency and operation safety, reactor internal pumps, instead of conventional recirculation systems, are adopted in an advanced boiling water reactor (ABWR). With the novel design of internal circulation, the traveling path and pattern of the recirculated liquid coolant in an ABWR is actually different from that of the coolant in a conventional boiling water reactor. To ensure operation safety, optimization of the coolant chemistry in the primary coolant circuit (PCC) of a nuclear reactor is essential no matter what type or generation the reactor belongs to. For a better understanding of the water chemistry in an ABWR, such as the one being constructed in the northern part of Taiwan, and for safer operation of this ABWR, in this study we conducted a proactive, thorough water chemistry analysis prior to the completion of this reactor. A well-developed computer code was used to investigate the effectiveness of hydrogen water chemistry (HWC) on the redox species concentrations and electrochemical corrosion potential (ECP) behavior of components in the PCC of the Lungmen ABWR in Taiwan. Our analyses indicated that the effective oxidant concentrations at the top of the downcomer location would be expected to be >100 ppb at 0.5 ppm [H₂]_FW at the original rated power. While an effective ECP reduction at 0.4 ppm [H₂]_FW was observed at the downcomer outlet, a 2.0 ppm [H₂]_FW was not enough to reduce the ECP below the E_crit at the upper plenum outlet. In summary, the effectiveness of HWC in the PCC of an ABWR is expected to vary from location to location and eventually from plant to plant due to different degrees of radiolysis and physical dimensions in different ABWRs.