Quantitative Determination of Crystalline Phases in Nuclear Waste Glasses
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QUANTITATIVE DETERMINATION OF CRYSTALLINE PHASES IN NUCLEAR WASTE GLASSES R. H. FELD AND M. STAMMLER Battelle-Institut e.V., Am R6merhof 35,
D-6000 Frankfurt am Main
INTRODUCTION In order to assess the longterm chemical and physical stability of high level waste glasses it is important to know the amounts of crystalline phases present. In principal all information about the crystalline state can be derived from its X-ray powder diffraction pattern,provided the spectral resolution is sufficiently high. Powderdiffraction techniques are the only means available to determine the concentration of crystalline phases in the presence of equivalent amorphous components. In addition it permits the determination of specific crystalline phases in a multicomponent system. To test the merits of the quantitative X-ray powder diffraction analysis for the characterization of nuclear waste glasses, measurements were carried out to - determine relatively small weight fractions of crystalline phases next to high concentrations of amorphous materials - test whether components remain stable in their crystalline state, yield new crystalline compounds or dissolve in the glassmatrix - determine the total crystallinity of nuclear waste products. The "matrix flushing" method (1) was chosen since it was considered to be accurate, fast, and relatively easy to apply (2). MATRIX-FLUSHING The original matrix flushing procedure required a binary reference mixture of each phase i to be determined and exactly the same amount of the flushing agent c which may be any well crystallized compound not present in the sample. After addition of a known weight fraction of flushing agent to the sample, it should "flush out"mass absorption, diffracting power and instrument geometry. The method was simplified, according to (3) yielding the following equation: I x K = c . I x.1 Ic
(1)
Ki = relative intensity ratio x = wt.fraction c c x. = wt.fraction phase i I c = intensity of c Ii = intensity of phase i
Thus n relative intensity ratios Ki could in fact be determined using only one reference mixture with n + 1 phases, where one of them is the flushing agent.
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After known weight fractions x. and x have been mixed,only the strongest intensity I. 1 'foreach phase and the strongest of the flushlng agent are being measured. To intensity I determine t~e weight fraction x! of the sample according to 1 Ii
X! = x'c 1
(2) Ki
Ic
a known wt. percentage x' of flushing agent is added and the intensities I! and 19 are measured. 1 c Integral intensities are used rather than peak height intensities, as the latter are extremely sensitive to differences in line width arising from lattice distortions and crystallite size. SAMPLES AND MEASUREMENTS Although the simulated radwaste-glass mixtures were made for different purposes, they were found to be ideally suited as test substances. The simulated waste contained 34.2 wt% ruthenium, a substance which does not change during processing; 17.3 wt% Zr which was expected to partly oxidise and dissolve i
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