Zinc addition experience in BWRs under normal and hydrogen addition chemistry

Experience at GE BWRs has shown that DZO (Depleted zinc oxide) addition is a viable method for reactor water activity reduction, piping dose rate reduction and radiation worker exposure control, even for plants injecting moderate HWC (Hydrogen water chemistry) for IGSCC (Intergranular stress corrosion crack) mitigation. It is recommended that zinc addition be practiced only with DZO and that reactor water concentrations of 5-10 ppb zinc be maintained during plant operation. Other methods for dose control such as source term reduction and decontamination are also viable but should be evaluated on a cost benefit basis. Plant data supplied from the GE BWRs in this report have been acquired from plants with varying levels of feedwater iron and cobalt input, different decontamination histories and varied operating experience, yet all have observed significant benefits from zinc addition. It is also recommended that HWC be practiced with minimal cycling and that the required level of hydrogen injection for IGSCC control be performed. (J.P.N.)