The SiC layers in experimental tristructural-isotropic (TRISO) coated particles with zirconia kernels were evaluated for their phase composition, impurity levels, crystal perfection, and twinning of the crystallites in the layers. This evaluation was necessary to compare the different SiC layers and relate these properties to various quality tests and ultimately to manufacturing parameters in the chemical vapor deposition (CVD) coater. Identification of the various polytypes was done using electron diffraction methods. This is the only method for the unequivocal identification of the different polytypes. The 3C and 6H polytypes were positively identified. The SiC in some samples is disordered. This is characterized by planar defects, of different widths and periodicities, giving rise to streaking in the diffraction pattern along the [111] direction of the 3C polytype. Polarized light microscopy in transmission easily distinguishes between the cubic (beta) and noncubic (alpha) SiC in the layers and provides valuable information about the distribution of these phases in the layers. Raman spectroscopy was used to examine the distribution of Si in the SiC layers of the different samples. Two samples contain elevated levels of Si $(∼50%)$, with the highest levels on the inside of the layers. The elevated Si levels also occur in most of the other samples, albeit at lower Si levels. This was also confirmed by the use of scanning electron microscope (SEM) electron backscatter analysis. Rietveld analysis using X-ray diffraction is presently the only reliable method to quantify the polytypes in the SiC layer. It was found that the SiC layer consists predominantly (82–94%) of the 3C polytype, with minor amounts of the 6H and 8H polytypes. Impurities in the SiC and PyC could be measured with sufficient sensitivity using laser ablation inductively coupled mass spectrometry (LA-ICP-MS). The SiC and PyC layers are easily located from the intensity of the $C13$ and $Si29$ signals. In most cases the absolute values are less important than the variation of impurities in the samples. Elevated levels of the transition elements Cu, Ni, Co, Cr, and Zn are present erratically in some samples. These elements, together with $Ag107$ and $Ag109$, correlate positively, indicating impurities, even metallic particles. Elevated levels of these transition elements are also present at the SiC/outer pyrolytic carbon (OPyC) interface. The reasons for this are unknown at this stage. NIST standards were used to calibrate the impurity levels in the coated particles. These average from 1 ppm to 18 ppm for some isotopes.

1.
,
L. L.
,
Nozawa
,
T.
,
Katoh
,
Y.
,
Byun
,
T. -S.
,
Kondo
,
S.
, and
Petti
,
D. A.
, 2007, “
Handbook of SiC Properties for Fuel Performance Modelling
,”
J. Nucl. Mater.
0022-3115,
371
, pp.
329
377
.
2.
Sawa
,
K.
,
Suzuki
,
S.
, and
Shiozawa
,
S.
, 2001, “
Safety Criteria and Quality Control of HTTR Fuel
,”
Nucl. Eng. Des.
,
208
, pp.
305
313
. 0029-5493
3.
Petti
,
D. A.
,
Buongiorno
,
J.
,
Maki
,
J. T.
, and
Miller
,
G. K.
, 2003, “
Key Differences in the Fabrication of US and German TRISO-Coated Particle Fuel, and Their Implications on Fuel Performance
,”
Nucl. Eng. Des.
,
222
, pp.
281
297
. 0029-5493
4.
Katoh
,
Y.
,
Hashimoto
,
N.
,
Kondo
,
S.
,
,
L. L.
, and
Kohyama
,
A.
, 2006, “
Microstructural Development in Cubic Silicon Carbide During Irradiation at Elevated Temperatures
,”
J. Nucl. Mater.
0022-3115,
351
, pp.
228
240
.
5.
Hélary
,
D.
,
Bourrat
,
X.
,
Dugne
,
O.
,
Maveyraud
,
G.
,
Perez
,
M.
, and
Guillermier
,
P.
, 2004, “
Microstructures of Silicon Carbide and Pyrocarbon Coatings for Fuel Particles for High Temperature Reactors (HTR)
,”
Second International Topical Meeting on High Temperature Technology
, Beijing, China, Paper No. B07.
6.
Krautwasser
,
P.
,
Begun
,
G. M.
, and
Angelini
,
P.
, 1983, “
Raman Spectral Characterization of Silicon Carbide Nuclear Fuel Coatings
,”
J. Am. Ceram. Soc.
0002-7820,
66
(
6
), pp.
424
434
.
7.
Nakashima
,
S.
, and
Harima
,
H.
, 1997, “
Raman Investigation of SiC Polytypes
,”
Phys. Status Solidi A
0031-8965,
162
, pp.
39
64
.
8.
Nakashima
,
S.
,
Higashihira
,
M.
, and
Maeda
,
K.
, 2003, “
Raman Scattering Characterization of Polytype in Silicon Carbide Ceramics: Comparison With X-Ray Diffraction
,”
J. Am. Ceram. Soc.
,
86
(
5
), pp.
823
829
. 0002-7820
9.
Naghedolfeizi
,
M.
,
Chung
,
J. -S.
,
Morris
,
R.
,
Ice
,
G. E.
,
Yun
,
W. B.
,
Cai
,
Z.
, and
Lai
,
B.
, 2003, “
X-Ray Fluorescence Microtomography Study of Trace Elements in a SiC Nuclear Fuel Shell
,”
J. Nucl. Mater.
,
312
, pp.
146
155
. 0022-3115
10.
van Rooyen
,
I. J.
, 2006, private communication.
11.
van der Berg
,
N.
, 2007, private communication.
12.
,
P.
, JEMS, I2M-EPFL, Lausanne, Switzerland.
13.
Kleeberg
,
R.
, and
Bergmann
,
J.
, 1998, “
Quantitative Röntgenphasenanalyse mit den Rietveldprogrammen BGMN und AUTOQUANT in der täglichen Laborpraxis
,”
Ber. DTTG Greifswald
,
6
, pp.
237
250
.
14.
Shaffer
,
P. T.
, 1969, “
A Review of the Structure of Silicon Carbide
,”
Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem.
0567-7408,
25
, pp.
477
488
.
15.
Ramsdell
,
L. S.
, and
Kohn
,
J. A.
, 1952, “
Developments in Silicon Carbide Research
,”
Acta Crystallogr.
,
5
, pp.
215
224
. 0365-110X
16.
Pecharsky
,
V. K.
, and
Zavalij
,
P. Y.
, 2005,
Fundamentals of Powder Diffraction and Structural Characterization of Materials
,
Springer
,
New York
.
17.
Coursey
,
J. S.
,
Schwab
,
D. J.
, and
Dragoset
,
R. A.
, 2005, “
Atomic Weights and Isotopic Compositions (Version 2.4.1)
,” http://physics.nist.gov/Comphttp://physics.nist.gov/Comp.