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Samples of butanal oxime in aqueous nitric acid solutions have been irradiated with the helium ion (4He2+) beam of the CEMHTI (Orléans, France) cyclotron. The consumption yield of butanal oxime has been measured by gas chromatography coupled with mass spectrometry. Gaseous products (mainly H2 and N2O) have also been monitored by micro-gas chromatography. Yields of liquid phase products (hydrogen peroxide and nitrous acid) have been determined by colorimetric methods. The influence of nitric acid on the radiation chemical behavior of butanal oxime depends on the nitric acid concentration. For a low concentration (≤0.5 mol L-1) butanal oxime is protected by the nitrate ions, which can efficiently scavenge the water radiolysis radicals. For higher concentrations, nitrous acid can accumulate in the medium, therefore leading to a strong increase of the butanal oxime degradation. The associated mechanism is an autocatalytic oxidation of butanal oxime by HNO2. [ABSTRACT FROM AUTHOR]

A study of aqueous nitric acid solution alpha radiolysis was performed through experiments carried out at a cyclotron facility, where a helion beam with an energy of 13.5 MeV could be delivered into the solution. The effects of nitrate and hydronium ions on the formation yields of hydrogen peroxide and nitrous acid, G (H 2 O 2 ) and G (HNO 2 ), were studied. The results showed that G (H 2 O 2 ) decreases linearly with increasing nitrate ion concentration. On the other hand, G (HNO 2 ) increases with the nitrate ion concentration until it reaches a plateau for nitric acid concentrations higher than 2 mol L –1 . It was also found that an increase of hydronium ion concentration has a favorable effect on G (H 2 O 2 ) and G (HNO 2 ). Furthermore, it appears that these effects are additive and that the variations of G (H 2 O 2 ) and G (HNO 2 ) can be described by two parametric expressions, as a function of the nitrate and hydronium ion concentrations. [ABSTRACT FROM AUTHOR]

Abstract: The industrial treatment of spent nuclear fuel is based upon a hydrometallurgical process in nitric acid medium. In order to minimize the volume of radioactive waste it seems interesting to generate the reactive species in situ in such solutions using ultrasonic irradiation without addition of salt-forming reagents. This review summarizes for the first time the versatile sonochemical processes with uranium, neptunium and plutonium in homogeneous nitric acid solutions and heterogeneous systems. The dissolution of refractory solids, ultrasonically driven liquid–liquid extraction and the sonochemical degradation of the volatile products of organic solvent radiolysis issued from PUREX process are considered. Also the guidelines for required further work to ensure successful application of the studied processes at industrial scale are discussed. [Copyright &y& Elsevier]

The scavenging of OH⋅ radicals formed during H2O sonolysis with nitrate-ions was studied in HNO3/NaNO3 mixture at the constant NO3− ions concentration ([HNO3] + [NaNO3])=1 M in Ar atmosphere. Small amounts of N2H5NO3 was added to solutions to avoid HNO2 accumulation due to HNO3 sonolysis. It was shown that the increase of [H+] causes the increase of H2O2 formation rate (WH2O2). WH2O2 values reach the plateau at [HNO3] ∼ 1 M. The WH2O2 ratio in solution with [H+]=1 M and pure water was found to be equal to 2.4 ± 0.4. It was assumed that WH2O2 increase in nitric acid medium is related to the changing of H2O2 formation mechanism. In pure water H2O2 is formed due to the OH⋅ radicals recombination. In HNO3 + NaNO3 mixture the mechanism of H2O2 formation consists in conversion of OH⋅ radicals to NO3⋅ radicals followed by NO3⋅ radicals hydrolysis. Results obtained show that OH⋅ radicals recombination mainly occurs in the liquid phase surrounding the cavitating bubble. [Copyright &y& Elsevier]