Electrochemical reductions of Hg(II), [RuNO(NO2)(4)OH](2-), CrO42-, and NO3- in 1.33 NaOH solution were studied at packed bed electrodes with a view to application of the electrochemical technique to treat nuclear waste solution. The reductions of Hg(II), [RuNO(NO2)(4)OH](2-), and CrO42- were mass-transfer controlled while nitrate reduction was activation controlled. Based on the data obtained, scale-up for each reduction is proposed and discussed. The experimental data obtained have been used in the design of a plant and detailed calculations have been made. An economic analysis has been made to point out the advantages of the electrochemical treatment.