FORMALDEHYDE TREATMENT OF PUREX RADIOACTIVE WASTES

Continuous denitration of Purex acid waste (PAW) with formaldehyde was successfully demonstrated in a fullscale plant prototype unit in the Hanford Purex plant. The reaction is smooth and is easily and safely controlled. Because severe foaming can occur in the reaction vessel, the use of an antifoam agent is required to attain acceptable plant processing rates. Extensive laboratory and pilot plant work, proper equipment design, and satisfactory oper ating procedures were the bases for developing adequate safeguards that assure complete control of the reaction at all times. During operation, the formaldehyde and the preheated PAW stream (with 50 to 100 parts antifoam per million parts PAW) are added continuously to the reactor which is maintained at 95 deg C. From an initial feed concentration of approximately 6.1M, the free acid is reduced to 0.5 to 1.0M in the treated waste. About 2.5 moles of free acid are destroyed per mole of formaldehyde added to the unit for a 60% reaction efficiency. A decontamination factor of 10/sup 4/ from feed to recovered acid is typical, which means that the ratio of radioactivity to HNO/sub 3/ in the recovered acid is reduced by a factor of 10,000 when compared to the same ratio in the high activity waste (PAW). Formaldehyde denitration of the Purex acid wastes reduces the chemical costs of waste treatment and storage. In addition, the process increases the storage capacity of underground tanks because of less salts in the waste, increases the flexibility of waste treatment equipment, and improves the quality of feed for fission product recovery. (auth