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Known for its use in photographic flashbulbs and surgical instruments, zirconium is a tough and ductile silver-gray metal. Atomic number 40 on the periodic table, it is not corroded by acids or alkalis and it resists heat. It is extracted from the mineral zircon, which is widespread in beach sands and coastal waters and has also been found in meteorites and in the Moon.
In nuclear power plants, zirconium alloys are used for cladding uranium oxide fuel rods. However, these alloys are vulnerable to oxidation at high temperature and hydrogen absorption, resulting in loss of ductility. This phenomenon is called pellet-clad interaction (PCI) and has been a concern for nuclear safety. Current mitigation measures have constrained operational limits and require large capital expenditures.
We report on the experimental study of the densification of zirconium pellets by supercritical pressure sintering (SPS). This method is demonstrated to produce denser and more homogeneous pellets than cold pressing and high temperature sintering techniques. The densification process also results in a higher resistance to cracking and corrosion. X-ray tomography is used to investigate the distribution of porosity and density gradients in SPS-produced pellets.
Using the Monte Carlo N-Particle eXtended code, the neutronic performance of SiC (silicon carbide), FeCrAl and SS-310 as alternative cladding materials for Zr in advanced PWR assemblies was evaluated through burnup calculations on unit cell and assembly level. Isotope depletion analysis, capture cross sections, spectral and spatial self-shielding analyses, peaking factor, thermal neutron fraction, delayed neutron fraction and reactivity coefficients are studied. The results show that SiC needs less enrichment compared to SS-310 due to its lower capture cross section.