Nuclear Materials

Nuclear power plants present the most demanding of environments for structural materials. Many nuclear materials must operate under stress at elevated temperatures and in corrosive environments, while simultaneously being exposed to neutron irradiation. The design requirements for many nuclear components will also include the need to withstand thermal shocks, such as those that might arise if there were to be a loss-of-coolant accident. Indeed, the challenges associated with developing materials for Generation IV reactors and, in particular, fusion reactors, are particularly acute since these applications invariably involve much higher neutron fluxes and higher operating temperatures than those that are seen in Generation III fission reactors. While the prospect of developing materials for such environments is daunting, the challenges for materials engineers and scientists are fascinating.

The issue commences with two articles focusing on composite materials. While a particle-reinforced aluminium matrix composite may not seem at home in a nuclear environment, the article by Chen et al. [1] examines boron carbide as a reinforcing phase, and this is known to be effective as an absorber of neutrons. The article by Tan et al. [2] reports on the successful fabrication by spark-plasma sintering of 316L–30W composites, which offer potential as plasma-facing materials in fusion reactors. In fission reactors, it is important from a structural integrity standpoint to mitigate tensile residual stresses, and Moat et al. [3] report on the importance of selecting an appropriate weld interpass temperature when using novel low-transformation-temperature filler materials for this purpose. Fission power plants typically contain safety-critical joints in which the weld metal is nickel-based, and the potential for texture in these welds has important implications in terms of anisotropy. For this reason, the article by Kumara et al. [4] should be of great interest to readers. The article by Wang et al. [5] will be of significant interest to those in the modelling community involved in the prediction of residual stresses in steel welds since, in order to account for the effects of solid-state phase transformations, it is important to obtain reliable estimates for the prior-austenite grain size. Multipass welding of the primary components in a pressurised water reactor subjects the material to significant thermomechanical cycling. The article by Peng et al. [6] is particularly relevant to the primary piping in a fission power plant, and indeed to stainless steel overlays that are deposited on to the internal surfaces of steel pressure vessels, since work hardening in austenitic stainless steels is dramatic. Finally, the article by Liu et al. [7] touches on the field of grain boundary engineering, which serves an important role in mitigating the corrosion of nuclear components.

The remaining articles in this issue do not have a direct focus on nuclear applications, but they have been selected for inclusion because they are likely to be of interest to those working with nuclear materials. Of course, there are many aspects of nuclear materials that are not addressed here, but it is hoped that readers will appreciate the ideas and research that are presented.