5. A METHOD OF RECOVERING RADIOACTIVE CAESIUM IN A HIGHLY PURIFIED CONDITION FROM AN AQUEOUS NITRIC ACID SOLUTION OF NUCLEAR FISSION PRODUCTS COMPRISING THE STEPS OF PRECIPITATING SAID RADIOACTIVE CAESIUM AS PHOSPHOTUNGSTATE FROM SAID SOLUTION BY THE ADDITION THERETO OF PHOTOSPHOTUNGSTIC ACID, SEPARATING THE PRECIPITATE OF SAID PHOSPHOTUNSTATE FROM SAID SOLUTION, ADDING TO SAID PRECIPITATE A SOLUTION OF AN ALKALINE EARTH METAL HYDROXIDE, SAID ALKALINE EARTH METAL BEING IN EXCESS OF THE CHEMICAL EQUIVALENT OF THE PHOSPHATE AND TUNGSTATE IN SAID PHOSPHOTUNGSTATE SO THAT A SOLUTION CONTAINING SAID RADIOACTIVE CAESIUM AS HYDROXIDE AND A PRECIPITATE OF THE PHOSPHATE AND TUNGSTATE OF SAID ALKALINE EARTH METAL ARE FORMED, PRECIPITATING THE EXCESS OF SAID ALKALINE EARTH METAL AS CARBONATE BY THE ADDITION OF AMMONIUM CARBONATE IN EXCESS AND BOILING THE SOLUTION, EVAPORATING THE SOLUTION NOW CONTAINING SAID RADIOACTIVE CAESIUM AS CARBONATE TO SMALL BULK WHEREBY AMMONIA IS DRIVEN OFF, AND SEPARATING THE SOLUTION CONTAINING SAID RADIOACTIVE CAESIUM AS CARBONATE FROM THE PRECIPITATE OF THE CARBONATE, PHOSPHATE AND TUNGSTATE OF SAID ALKALINE EARTH METAL.