Oxidation caused by oxidants such as oxygen and hydrogen peroxide in the cooling water of BWRs can cause stress corrosion cracking (SCC) on reactor components, and cause corrosion of the zirconium alloy cladding of the fuel pins. Known SCC reduction strategies for reactor components such a reactor pressure vessel (RPV) internals of BWRs include noble metals chemistry addition (NMCA) and hydrogen water chemistry (HWC). These SCC reduction strategies can reduce SCC of internals, but may increase corrosion of the fuel pin cladding.
NMCA methods are described for example in U.S. Pat. Nos. 5,818,893, 5,904,991 and 6,793,883, and as defined herein NMCA may include both off-line or on-line addition of noble metals.
HWC used with NMCA is described in the background section of U.S. Patent Application Publication No. 2005/0018805, which then also describes application of a reductive nitrogen compound such as hydrazine in combination with hydrogen. Application of an alcohol such as methanol with hydrazine is also disclosed. DE 100 30 726 describes application of photocatalytic substances for depositing on reactor internals, and mentions the injection of hydrogen or methanol.
Application of methanol to reduce oxidizing effects is described in U.S. Patent Application Publication No. 2005/0135542, as well as in the publication entitled “Study of the Methanol Injection in Reactor Water in Reactor Water of BWR Plants” by Saneshige et al. presented at the Proc. Symp. on Water Chemistry and Corrosion of Nuclear Power Plants in Asia, Oct. 11-13, 2005, Gyeongju, Korea.
Shut down and then start-up of BWRs can occur at regular intervals, for example, every one to three years, and present very different water chemistries than during normal operation. As discussed, for example, in the publication “The First Application of Hydrogen Water Chemistry during Start-up for Mitigation of SCC initiation in Tokai-2 BWR” by Takiguchi and Otoha, oxidant concentration in reactor water is high during start-up. The publication describes the addition of HWC during start-up via an additional hydrogen injection system.
U.S. Patent Publication No. 2005/0018805 also describes adding hydrogen and a reductive nitrogen compound during start-up and shut-down.
USPTO Backgrounds
USPTO Backgrounds