Carburization Kinetics of Zircalloy-4 and Its Implication for Small Modular Reactor Performance

• Published in: Materials Vol. 15; no. 22; p. 8008
• Main Authors: Kardoulaki, Erofili, Abdul-Jabbar, Najeb, Byler, Darrin, Hassan, Md Mehadi, Mann, Shane, Coons, Tim, White, Josh
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 12.11.2022; MDPI
• Subjects: Building materials; carburization; Carburization (corrosion); Carburizing; Cladding; Corrosion; Failure mechanisms; Graphite; Heat conductivity; Hydrogen as fuel; indentation; Kinetics; Mechanical analysis; Modulus of elasticity; Nuclear reactors; Operating temperature; Reactors; small modular reactors; Steel alloys; Temperature; Thermal conductivity; Uranium; zircaloy; Zircaloys (trademark); Zirconium base alloys; Zirconium carbide; United States > US; indentation; zircaloy; kinetics; carburization; small modular reactors
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma15228008

Carburization of cladding materials has long been a concern for the nuclear industry and has led to the restricted use of high-thermal conductivity fuels such as uranium carbides. With the rise of small modular reactors (SMRs) that frequently implement a graphite core-block, carburization of reactor components is once more in the foreground as a potential failure mechanism. To ensure commercial viability for SMRs, neutron-friendly cladding materials such as Zr-based alloys are required. In this work, the carburization kinetics of Zircaloy-4 (Zry-4), for the temperature range 1073-1673 K (covering typical operating temperatures and off-normal scenarios) are established. The following Arrhenius relationship for the parabolic constant describing ZrC growth is derived: K (in μm /s) = 609.35 exp(-1.505 × 10 /RT)). Overall, the ZrC growth is sluggish below 1473 K which is within the operational temperature range of SMRs. In all cases the ZrC that forms from solid state reaction is hypo-stoichiometric, as confirmed through XRD. The hardness and elastic modulus of carburized Zry-4 are also examined and it is shown that despite the formation of a ZrC layer, C ingress in the Zry-4 bulk does not impact the mechanical response after carburization at 1073 K and 1473 K for 96 h.