Particles For High-temperature Reactors Research Articles

Peridynamic modelling of cracking in TRISO particles for high temperature reactors

A linear-elastic computer simulation (model) for a single particle of TRISO fuel has been built using a bond-based peridynamic technique implemented in the finite element code ‘Abaqus’. The model is able to consider the elastic and thermal strains in each layer of the particle and to simulate potential fracture both within and between layers. The 2D cylindrical model makes use of a plane stress approximation perpendicular to the plane modelled. The choice of plane stress was made by comparison of 2D and 3D finite element models. During an idealised ramp to normal operating power for a kernel of 0.267 W and a bulk fuel temperature of 1305 K, cracks initiate in the buffer near to the kernel-buffer interface and propagate towards the buffer-iPyC coating interface, but do not penetrate the iPyC and containment of the fission products is maintained. In extreme accident conditions, at around 600% (1.60 W) power during a power ramp at 100% power (0.267 W) per second, cracks were predicted to form on the kernel side of the kernel-buffer interface, opposite existing cracks in the buffer. These were predicted to then only grow further with further increases in power. The SiC coating was predicted to subsequently fail at a power of 940% (2.51 W), with cracks formed rapidly at the iPyC-SiC interface and propagating in both directions. These would overcome the containment to fission gas release offered by the SiC ‘pressure vessel’. The extremely high power at which failure was predicted indicates the potential safety benefits of the proposed high temperature reactor design based on TRISO fuel.

The development of TRIAC-BATAN: a triso fuel performance analysis code

A computer code for analyzing the safety feature of triso coated particles for high temperature reactor has been developed based on PANAMA code. This python based code were separated into several modules to perform the main TRIAC-BATAN and linear interpolation calculation, to read the input data file, and to control the sequence of all TRIAC-BATAN calculation. In this initial development phase, TRIAC-BATAN can produce similar pattern as PANAMA calculation in the case of failure fraction of triso particles, either for Depressurized Loss Of Forced Cooling (DLOFC), 100°C higher than DLOFC temperature and constant accident temperature at 1600°C. By using the euclidean distance, TRIAC-BATAN calculation and PANAMA for DLOFC condition are separated in around 3.23 ⋅ 10−7.

A direct measurement of Bacon anisotropy factors on pyrocarbon coatings deposited on fuel particles for the high temperature reactor

An X-ray diffraction technique for measuring the Bacon anisotropy factor of pyrocarbon coatings deposited on spherical fuel particles for high temperature reactors has been developed. Using an X-ray microbeam measurements can be made directly on single particles and, after correction for X-ray absorption by the specimen, the BAF can be calculated for individual coatings. Results on initially isotropic coatings deposited on dummy particles irradiated at 1400°C to a fluence of 4.8 × 10 21 n.cm −2 (EDN) show that the BAF increases with increasing creep strain. The largest increase in BAF from 1.01 to 1.26 was observed for the pyrocarbon coating with the lowest initial density of 1.66 g.cm −3.

Transmission electron microscopy of isotropic pyrocarbon deposited on spherical particles for high temperature reactor

Thin films of isotropic pyrocarbons deposited onto nuclear fuel kernels in a fluidized bed were studied by transmission electron micrography. The pyrocarbons were found to be made of stacked growth units exhibiting a more or less spherical shape. The existence of two distinct structural arrangements of carbon atoms could be evidenced by electron diffraction: a first one, identical with the structure of turbostratic graphite, and a second one, poorly organized, similar to vacuum evaporated “amorphous” carbon. Micrographs of the material clearly show the distribution of the two pyrocarbon varieties. It is concluded from all these observations that there is a close relationship between the microstructure of the spherical growth units and that of carbon blacks.

Mesure par diffraction de rayons X de l'anisotropie du pyrocarbone dans les particules combustibles d'un reacteur a haute temperature

An X-ray diffraction technique for measuring the anisotropy factors of pyrocarbon coatings on fuel particles for high temperature reactors has been developed. The measurements yield directly absolute values of BAF averaged over about 100 particles, with an accuracy of ± 0.01. A modified procedure for measuring a single irradiated particle is considered. BAF-values obtained from discs and from particles coated in the same run do not exhibit any simple correlation.