ИСТИНА

EXAFS and NMR are being developed with respect to study and speciation of technetium- 99 in course of pyrometallurgical reprocessing of spent nuclear fuel. Based on the set of standards including technetium metal, different technetium halogenides, oxohalogenides, oxides and pyrometallurgically formed sediments, Tc chemical forms responsible for Tc accumulation in fused salts, deposits or gas-off depending on the applied reprocessing conditions are studying by means of NMR and EXAFS. NMR spectrum of Tc metal powder obtained by FT of a free induction decay accumulated after excitation of the spin system by a sequence of high frequency pulses (0.8 ìs) with a dead time of 5.4 ìs and a repetition time of 1 ìs, provided with Knight shift K(ppm) = 7305 - 1.52 x T; νQ(99Tc) = 230 kHz at 293 K , CQ(99Tc) = 5.52 MHz. EXAF spectra provided with excellent evidence for Tc(IV) halogenides, but need further development for lower oxidation states of technetium. EXAFS and NMR are promising methods to enable us with speciation of radioactive nuclides. It is important to use them for Tc speciation in pyrometallurgy which is now considered as the most probable alternative approach to reprocessing of spent nuclear fuel. Pyrometallurgy of uranium and plutonium in chloride and fluoride fused salts are now intensively studied while little attention is given to long lived fission product technetium which is one of the hazardous nuclear wastes. During pyrometallurgical spent fuel reprocessing, technetium can remain in the fused salt or enter (depending on the applied temperatures, reagents and potentials) either the sedimented phase contaminating Pu enriched phase, or electrodeposited U phase (Scheme 1). Neither in sediment nor in deposit Tc phase could be detected by means of X-ray diffraction, Tc phase being finely dispersed and X-ray amorphous. It is therefore very important to develop some other methods of analyses like EXAFS and NMR applicable to Tc speciation in such samples. Our preliminary results show that under such conditions Tc can also form several oxydes, oxychlorides and chlorides of different but rather high volatility, turning on an important polluting risk allied to gas-off.