Patent ID: 7323613

Claim:
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 2 and KBO 2 , until reaching a concentration wherein the alkali metaborates contained therein have a mol ratio of Na/B equal to 1, and the boron salts reach a concentration from 35 to 200 grams/liter; (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.