An Estimation of the chemical evolution of nitrate due to the metal corrosion and microbiological reaction.

Masuda, Kaoru*; Kato, Takashi; Honda, Akira

Uranium and Plutonium are planed to be recovered from spent fuel by the reprocessing in Japan. PUREX method is internationally dominant among the commercial reprocessing plants. PUREX method has been also employed in Japan. The low level liquid waste from PUREX process would contain NO as forms of soluble salts, if the special process for decomposing NO were not adopted. The nitrate is possibly brought within the repository for TRU waste. The generation of H gas and the reduction of NO due to metal corrosion and the generation of N gas due to the microbiological reactions in repository for group3 waste were estimated. The uncertainty on the hydraulic conductivity of cementitious materials, corrosion rates, and microbiological reactions are reflected to the analyses through setting the multiple cases. The analysis results suggested followings. (1) The maximum concentrations of both NO and NH were given in the case where the hydraulic conductivity of cementitious material was assumed to be low ( 5.010 m/s) and the corrosion rate was constant at the initial value (0.1 um/y). (2) The maximum concentration of NH was estimated to be 0.8 mol/dm. (3) The impact of microbiological reaction (denitrifying reaction) was negligible in terms of yield of NO and NH because the proportion of denitrified NO was low. (4) The existence of NO was strongly reduced the evolution of H gas because the nitrate reduction and nitrite reduction dominate the cathodic reactions. (5) The N gas evolution rate due to the denitrifying reaction by microorganisms dominated the total gas evolution rate, if time dependent reduction of corrosion rate was employed. However, the H gas evolution rate in the case is similar to those of N gas due to the denitrifying reaction mentioned above, if time dependent reduction of corrosion rate was neglected