received by the International Bureau on 11 July 2016 (11.07.2016)

A method for concentrating and/or entrapping radioisotopes from an aqueous solution comprising tritium, said method comprises mixing the aqueous solution with at least one inorganic salt under conditions in which said salt forms at least one stable hydrate, incorporating the tritium as water of crystallisation, wherein the at least one salt is a borate, such as tetraborate and/or metaborate.

The method according to claim 1, wherein the borate is an alkali-metal borate, such as sodium borate, preferably anhydrous borax or sodium borate pentahydrate; or an alkaline earth metal borate, such as calcium borate, calcium tetraborate and calcium metaborate.

The method according to claim 1 or 2, wherein the at least one salt is a metal or amphoteric salt selected from the group comprising salts of copper, cobalt, chromium, vanadium, iron, manganese, and nickel.

The method according any of the preceding claims, wherein said aqueous solution further comprises radioisotopes from group I and II of the Periodic System of Elements, such as ¹³⁷Cecium and/or ⁹°Strontium, and wherein said radioisotopes are immobilised in the stable hydrate.

The method according any of the preceding claims, wherein the aqueous solution is frozen to an ice snow before being mixed with the at least one inorganic salt.

The method according claim 5, wherein the ice snow is mixed with the one or more salts under cooling, preferably at a temperature between 60°C and 80°C. The method according any of the preceding claims, wherein the mixing of the aqueous solution and the at lest one salt will provide a preliminary slurry comprising a combination of the aqueous solution, the at least one salt and the stable hydrate, said preliminary slurry is transferred to a storage container, and wherein the hydration process is allowed to run to completion to form a solid stable hydrated salt in said storage container.

The method according any of the preceding claims, wherein the aqueous solution is treated with a heavy metals precipitations agent prior to mixing with the at least one salt, said precipitations agent is arranged for immobilising soluble and mobile heavy metal radio nucleotides from Group III and above of the Periodic System of Elements.

The method according any of the preceding claims, wherein the method further comprises providing a higher concentration of the tritium in the aqueous solution prior to mixing with the at least one salt.

The method according any of the preceding claims for proving an aqueous solution with a reduced concentration of tritium, said method comprises

a. providing a stable hydrate incorporating tritium as water of crystallisation

b. separating said stable hydrate from the remaining aqueous solution, and

c. repeating step a) and b) on the remaining aqueous solution until the tritium concentration reaches radioactive levels permissible for safe discharge of the aqueous solution to the environment.