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

Area of Science:

• Nuclear Engineering
• Materials Science

Background:

• Carburization of nuclear cladding materials is a long-standing concern, impacting fuel choices.
• Small modular reactors (SMRs) with graphite core-blocks reintroduce carburization risks for reactor components.

Purpose of the Study:

• To investigate the carburization kinetics of Zircaloy-4 (Zry-4) cladding.
• To determine the Arrhenius relationship for Zirconium Carbide (ZrC) growth.
• To assess the impact of carburization on Zry-4 mechanical properties.

Main Methods:

• Experimental carburization of Zry-4 across a temperature range of 1073–1673 K.
• Analysis of Zirconium Carbide (ZrC) growth kinetics using an Arrhenius relationship.
• X-ray diffraction (XRD) for phase identification.
• Mechanical testing (hardness and elastic modulus) of carburized samples.

Main Results:

• An Arrhenius relationship for parabolic rate constant of ZrC growth was derived: Kp (in μm²/s) = 609.35 exp(-1.505 × 10⁵/RT).
• ZrC growth is sluggish below 1473 K, within the typical SMR operational temperature range.
• Hypo-stoichiometric ZrC formed via solid-state reaction.
• Carburization did not negatively affect the mechanical response of Zry-4 at 1073 K and 1473 K after 96 hours.

Conclusions:

• Zircaloy-4 exhibits acceptable carburization resistance for SMR applications.
• The established kinetics and mechanical data support the use of Zry-4 in SMRs.
• Further research may explore longer-term effects and different SMR operating conditions.