Isotope replenishment in halocarbons of use in laser separation process

The replenishment of deuterium or tritium concentration in a laser isotope separation process for the production of D2O, or for the recovery of tritium from contaminated D2O or H2O is effected by selectively photodissociating a working compound which is preferably a deuterated or tritiated analogue of a dihalomethane, trihalomethane, 1,2-dihaloethylene, trihaloethylene, tetrahaloethane or pentahaloethane, by a laser beam and replenishing by contacting an exchange liquid in a countercurrent fashion in a first contacting column. The exchange liquid is replenished with isotope in turn by being contacted with a feed stream in a second contacting apparatus. This second contacting apparatus may be a gas/liquid contacting apparatus and the countercurrent flows therein may be about equal or unequal. (author)