For mitigating intergranular stress corrosion cracking in operating boiling water reactors (BWRs), hydrogen water chemistry, a common technique for producing a reducing coolant environment, has been adopted worldwide. However, the issue of accompanied buildup of radiation field at feedwater hydrogen concentrations >0.5 ppm has been a concern of the utilities. In particular, the increase in shutdown dose rate would pose a serious health threat to maintenance workers during outages.

To maintain low shutdown dose rates in drywells, the operators of Kuosheng Nuclear Power Plant adopted effective techniques to improve the coolant chemistry in their two BWRs, leading to a reduction in iron concentration in the feedwater and in 60Co activity in the primary coolant. The radiation buildup in the recirculation system was lowered through an optimized management of hydrogen injection during regular operations and an enhanced operation mode of the reactor cleanup system at the early stage of an outage. In the meantime, the shutdown dose rates in the entire primary coolant circuit, especially in the drywell, were also significantly reduced. This paper describes the adopted techniques and results of water chemistry improvement at the Kuosheng nuclear power reactor.