[en] In the liquid waste disposal system in Monju, the concentrated liquid waste was alkaline. This phenomenon was remarkable when we treated the sodium deposit and aerosol, which were produced during the sodium leak accident. We took a close look at our treatment process and concluded that the decrease in the pH of the liquid waste was due to reaction with sodium hydroxide solution. Consequently we changed the chemical control value and improved the system processing in order to avoid producing the concentrated alkaline liquid waste. (author)