The influence of urea on initiation and termination of the reaction between nitric and formic acids was experimentally examined.
The urea injection can terminate the denitration reaction in 2 to 10M salt-free nitric acid solutions and the simulated high
level liquid wastes (HLLWs) with a nitric acid concentration of 2 to 6M. An excess of urea can interrupt the initiation of
denitration in both simulated HLLW and salt-free nitric acid solutions. The initiation and termination of denitration are
in relation with nitrous acid formation and decomposition. Urea reacts with nitrous acid easily in the denitrating solution
and decomposes nitrous acid. As the urea concentration increases in the solution, the continuance of denitration become impossible
because the decomposition rate of nitrous acid exceeds the generation rate. In addition, the nitrous acid concentration can
not be high enough to initiate the denitration in the solution with an excess of urea because nitrous acid is decomposed by