Patent ID: 7323613
Filing Date: 2008-01-29
Classification: G21F

Abstract:
1. A method for the treatment of acid- and alkali-containing liquid radioactive wastes resulting from the operation of a nuclear power plant utilizing a pressurized water reactor with boron reactivity regulation, comprising the steps of: (A) separately collecting the liquid radioactive wastes as (i) acidic wastes having a pH of less than 5.5 and free of boron acid, and (ii) as alkali wastes having a pH greater than 5.5 and containing boron salts; (B) thereafter separately concentrating the liquid acidic radioactive wastes until it reaches a total salt content of 400 to 500 grams/liter; (C) separately concentrating the liquid alkali radioactive wastes, which comprise boron salts inclusive of the alkali metaborates of NaBO (D) mixing the concentrated radio active waste solutions of steps (B) and (C) in a reactor vessel and treating the reaction mixture at a temperature range of 10 to 35° C. with a correction additive of nitric acid for providing a pH of the mixture in the range of 8.0-10.1, and optionally adding a mineral salt for adjusting, if necessary, and maintaining the pH of the reaction mixture at 8.0-10.1; until crystallized sodium tetraborate and a sodium tetraborate solution is obtained having a mol ratio of Na/B from 0.5 to 0.6 and whose concentration is 20-25 grams/liter; (E) separating crystallized sodium tetraborate having a particle size greater than 0.5 mm from the remaining radioactive 20-25 grams/liter of sodium tetraborate solution of step D which comprises sodium tetraborate crystals having a particle size less than 0.5 mm; (F) transferring the radioactive solution of step (E) to a mixing-settling vessel wherein the radioactive sodium tetraborate solution is treated with alkali metal salts of calcium and manganese to produce an environmentally acceptable radioactive reaction solution of calcium-manganese hexaborate and calcium-manganese tetraborate crystals having a mol ratio of Ca/Mg to B in the range of 0.25 to 0.35; (G) separating the calcium-magnesium hexaborate and calcium-magnesium tetraborate crystals from the environmentally acceptable radioactive reaction solution of step (F) by filtering, subsequent washing, and drying for eventual packaging, whereby the remaining boron salt solution has a concentration of 2-4 grams/liter thereby rendering it suitable for immobilization by cementation; (H) subjecting the sodium tetraborate crystals having a particle size greater than 0.5 mm obtained in step (E) to aqueous washing and filtration, and subsequent re-crystallization to produce a non-radioactive, re-crystallized sodium tetraborate product; and (I) subjecting all or a portion of the re-crystallized sodium tetraborate product of step (H) to aqueous dissolution and thereafter submitting the borate solution to electrodialysis for producing a boron acid solution and a sodium hydroxide solution.