Crushing behaviour of high temperature reactor coated fuel particles

This paper examines in detail the crushing behaviour of high-temperature reactor fuel particles with pyrolytic carbon or silicon carbide outer coatings and discusses their failure mechanisms, in an attempt to relate crushing failure loads to coating strengths, and provide a simple, quick testing technique for quality control or performance assessment. Failure occurs by a series of mechanisms, in varying sequence, initiated by Hertzian cracking. Because the first event detected in a crushing test load/deflection curve is not the formation but the propagation of the Hertzian crack, the crushing load cannot be related to the coating strength; instead, it is governed by the fracture surface energy of the outer coating. A crushing test is therefore not a suitable technique for measurement of the strength of particle coatings. However, through measurement of the size of the contact surface, reliable estimates of the Young's modulus of the outer coating can be made by application of the Hertz theory of contact.