Denitration of reprocessing concentrates by means of HCHO

The denitration of highly radioactive liquid waste and intermediate level liquid waste with formaldehyde have been investigated. A number of different simulated solutions as well as real waste from fuel reprocessing have been used in cold laboratory experiments and in hot experiments performed with the FIPS II denitrator. Partial or exhaustive reduction of nitric acid can be achieved in a simple and safe way feeding formaldehyde into the boiling acidic batch or by simultaneous feeding of acidic waste and formaldehyde generating mainly NO.Denitration in a formaldehyde batch with intent to increase N₂O generation is not straight away recommendable for the following reason. Aqueous formaldehyde usually contains 10 – 14 % methanol which will react with NO₂ and HNOp producing methylnitrite. The concentration of methylnitrite in the off gas during the first periode of denitration following the above mentioned procedure might reach ignition range.Experiments at ambiant temperature supplied the investigations of the reaction mechanism during the induction periode.