Non-isothermal kinetics of the thermal decomposition of gadolinium nitrate

High-level liquid waste (HLLW) contains more than 30 kinds of nitrates which consist of fission products. A series of such phenomena as evaporation, melting and thermal decomposition of HLLW takes place within the 'cold cap', which is floating on top of the molten glass pool. An understanding of the varied thermal decomposition behavior of various nitrates constituting HLLW is necessary to elucidate a series of phenomena occurring within the cold cap. In this study, gadolinium nitrate, which is one of main compositions of HLLW, was chosen as an example of the nitrate salt and its thermal decomposition was investigated using non-isothermal thermogravitmetry-differential thermal analysis-mass spectrometry and X-ray powder diffraction. Ozawa method was applied for gaining kinetic parameters for the consecutive reaction of gadolinium nitrate. Reaction rate equation of the decomposition under non-isothermal condition was described. (author)