Vol.:(0123456789) 1 3 Journal of Radioanalytical and Nuclear Chemistry https://doi.org/10.1007/s10967-019-06736-x Denitration of simulated radioactive liquid waste Mira Ristić 1  · Svetozar Musić 1,2  · Marijan Marciuš 1  · Stjepko Krehula 1  · Ernő Kuzmann 3  · Zoltán Homonnay 3 Received: 31 July 2019 © Akadémiai Kiadó, Budapest, Hungary 2019 Abstract Radioactive liquid wastes containing large amounts of nitric acid (approx. 4–7 M) generated in the nuclear fuel cycle are very undesirable by-products. Denitration of highly acidic radioactive liquid wastes with organic reducing agents has sev- eral advantages, such as a signifcant pH increase, possibility of separation of radioisotopes which can be utilized in other technologies, reduction of volatility of radioisotopes and fxation of certain mono- and divalent radioisotopes with zeolite. In the present work some aspects of denitration of simulated radioactive liquid wastes at laboratory level were investigated. Denitration of HNO 3 with formic acid was investigated for diferent [HCOOH]/[HNO 3 ] ratios. The changes in the induction time, pH increase and volume reduction were determined. It was shown that by the denitration of simulated radioactive liquid waste high pH values could be achieved which in real systems would create more possibilities in radioactive waste manage- ment. Analysis of solid phases formed after the oxidation of excess HCOOH with H 2 O 2 showed the presence of amorphous fraction as well as goethite and hematite phases, which could remove diferent radioactive cations from the liquid phase. The immobilization of simulated solid radioactive waste with borosilicate glass matrix was also shown. Keywords Radioactive liquid waste · Denitration · Formic acid · Borosilicate glass Introduction Radioactive liquid waste containing a large amount of nitric acid as generated in the nuclear fuel cycle is a very undesir- able by-product. For example, high-level radioactive liquid waste and medium-level radioactive liquid waste originating from the reprocessing of irradiated nuclear fuel are strongly acidic due to the presence of nitric acid. There are several strong reasons for the application of chemical denitration in the treatment of radioactive liquid wastes. Partial denitration with organic reducing agents of high- level radioactive liquid wastes stored in steel tanks for many years has been utilized to reduce the corrosion of steel tanks and to minimize the volume of radioactive liquids. The pH increase of these liquid wastes using neutralization with sodium hydroxide (NaOH) is not convenient because of the increased Na + content. Since acidity decreases during chemical denitration, this is the main reason for a decrease in the corrosion rate. Gaseous reaction products formed in this process can be safely removed. Another very important reason for the application of chemical denitration of high-level radioactive liquid waste is a drastic reduction of radioactive ruthenium volatiliza- tion into the of-gas system. It is known that the initial content of nitrates afects the volatilization of radioactive ruthenium in the process of radioactive waste vitrifcation. Radioactive ruthenium in the chemical form of RuO 4 is primarily responsible for its volatility. Under the chemical conditions created by the organic reducing agents the vola- tile RuO 4 is reduced to non volatile RuO 2 . Ito and Kanno [1] investigated the efect of denitration on coprecipitation and volatilization of ruthenium and technetium. Formic acid (HCOOH) was used as a reducing agent. An almost quantitative coprecipitation for RuNO 3+ was obtained at the molar ratio [HCOOH]∕[NO − 3 ] from 1.2 to 1.3. The copre- cipitation of RuNO 3+ decreased drastically with an increase of the molar ratio [HCOOH]∕[NO − 3 ] above 1.5, which was attributed to the formation of RuNO 3+ formate complexes. The quantitative coprecipitation was also obtained upon the * Svetozar Musić music@irb.hr 1 Ruđer Bošković Institute, Bijenička cesta 54, P.O. Box 180, 10002 Zagreb, Croatia 2 Croatian Academy of Sciences and Arts, Trg Nikole Šubića Zrinskog 11, 10000 Zagreb, Croatia 3 Institute of Chemistry, Eötvös Loránd University, Budapest, Hungary