Study of thermal and radiation stability of the extractant based on CMPO in fluorinated sulfones
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Study of thermal and radiation stability of the extractant based on CMPO in fluorinated sulfones S.V. Stefanovsky,1 I.V. Skvortsov,1 E.V. Belova,1 A.V. Rodin1,2 1
A.N. Frumkin Institute of Physical Chemistry and Electrochemistry RAS, Moscow 119071, Russia 2 Scientific and Engineering Centre for Nuclear and Radiation Safety, Moscow 107140, Russia ABSTRACT The two-phase systems of pure diluent FS-13 – aqueous solution of 14 mol/L nitric acid and 0.02 mol/L solution of CMPO in diluent FS-13 – aqueous solution of 14 mol/L HNO3 were studied at autoclave temperatures 170 °C and 200 °C. The effect of pre-irradiation on the kinetics of thermolysis was determined. All samples were irradiated using an electron accelerator at a dose rate of 10 kGy/h up to absorbed doses of 0.1, 0.5 and 1 MGy. The parameters of heat and gas emissions were determined during thermolysis of the studied extraction system in a closed apparatus. It has been shown that the conditions required for the growth of autocatalytic oxidation are not created during heating of the two-phase systems in closed vessels even for the extraction systems contacted with 14 mol/l HNO3 for two weeks. INTRODUCTION One of the possible ways to dramatically reduce the environmental hazard of liquid high level radioactive waste (HLW) after reprocessing of spent nuclear fuel (SNF) is the extraction of longlived radionuclides (cesium, strontium and minor actinides) that will allow to decrease the amount of waste for further geological disposal. Extraction of chemically similar nuclides into separate fractions provides higher safety of their disposal in the form of stable matrices. One of the first industrial processes of the extraction of 137Cs and 90Sr was developed in Russia. This process is based on the systems of chlorinated cobalt dicarbollide (CCD)/polyethylene glycol (PEG) or Slovafol-909 in the meta-nitrobenzotrifluoride (F-3). This is a so-called DCC-process that has been tested [1] and has been started in 1996 at the "Mayak" plant in Ozersk ([2] section 4.2). By 2001, the total HLW volume of 1200 m3 was reprocessed and 50.106 Ci of 137Cs and 90 Sr were extracted [3]. However, the main goal still was the extraction of 137Cs, 90Sr and the bulk of the long-lived radionuclides (fraction of rare earth elements (REE)/transplutonium elements (TPE)) in a single cycle. A number of interesting processes and extractants were proposed, including diphosphorylated glycols, but the significant disadvantage was the presence of toxic diluent F-3 in extraction systems. The search for the optimal solution of this task was postponed till the beginning of the XXI-th century, when carbamoylmethyl phosphine oxide (CMPO) was added to the system based on CCD/PEG for the extraction of REE and TPE [4]. CMPO is the well-known complexing agent for TPE extraction that was studied long time before first works on development of the universal extraction process or the UNEX-process [5-7]. The intensive collaboration of V.G. Khlopin Radium Institute and the Idaho National laboratory have resulted in t
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