Chemistry Reference
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found to be comparable to those of ICP-OES after wet-chemical digestion of
the ceramics. The average relative standard deviation for all elements was
below 10%, the correlation coefficient was 0.997—similar to ICP-OES values.
5.4.5ImpuritiesinNuclearMaterials
Nuclear materials used for power production in a reactor have to be analyzed
with the special condition of small sample size. The analysis has to be
consumption-free so that a loss of radioactive and precious materials is avoided.
Consequently, XRF and especially TXRF is the method of choice. TXRF is
simple and fast, needs only a minute sample amount, and is accurate even if it
needs only one single internal standard for quantification. Apparently, there is
no alternative.
Traces of several elements at ppb levels in UO
2
, ThO
2
, and zircalloy as well as
chlorine traces in U
3
O
8
, and PuO
2
and In traces in heavy water were determined
by Misra and coworkers [133,134]. The determination of chlorine traces in nuclear
fuel materials is very important because chlorine is extremely corrosive. It can
be incorporated into nuclear materials during the various stages of fabrication
and processing. Even in low concentrations, chlorine can lead to a depassiva-
tion of the oxide layer and corrosion of cladding materials. Consequently,
the specification limits for chlorine in nuclear materials are very low. Depending
on the different materials, these limits are between 5 and 50
μ
g/ml (ppm).
Chlorine was determined by TXRF after its separation from the solid
matrices by pyrohydrolysis [133]. For that purpose, 500 mg of a solid sample
was put into quartz glass boats, and heated at 900
°
C. Volatile impurities, such as
B, F, S, and Cl, were set free, and led into a cooled condenser by a stream of Ar/
O
2
and steam. Chlorine was collected as HCl in an aqueous solution of 5 mM
NaOH. Afterward, cobalt was added as an internal standard to the distillate and
aliquots of 30
μ
l were analyzed by TXRF with a W tube used for excitation.
Several materials were investigated, such as U
3
O
8
, (U,Pu)C, PuO
2
, and Pu
alloys. Concentrations down to about 0.1
μ
g/ml (ppm) were determined. The
precision could be improved from about 27 to 8% by a continuous helium flow
of 800 cm
3
/min instead of atmospheric air. The results were compared with
those obtained from ion chromatography and found to deviate by about 14% in
the range of 1 to 70
μ
g/ml (ppm).
Total reflection XRF was shown to be simple, fast, and accurate. It requires
only a small sample volume of some 10
μ
l and consequently produces less
analytical liquid waste. A complete and cumbersome dissolution of the nuclear
material is avoided by pyrohydrolysis at 900
°
C. Matrix matched standards are
not required for quantification but only one single internal standard is needed.
5.4.6HydrocarbonsandTheirPolymers
In addition to inorganic materials, aliphatic, cyclic, and aromatic compounds of
the organic chemistry can also be analyzed and distinguished by TXRF. About
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