Michael Law, David G. Carr and Sven C. Vogel

Abstract Current and future nuclear-technologies such as fission and fusion reactor-systems depend on well-characterized structural materials, underpinned by reliable material-models. The response of the material must be understood with science-based models, under operating and accident conditions which include irradiation, high temperature and stress, corrosive environments, and magnetic fields. Neutron beams offer methods of characterizing and understanding the effects of radiation on material behaviour such as yield and tensile strength, toughness, embrittlement, fatigue and corrosion resistance. Neutron-analysis techniques improve our understanding of radiation damage, which is essential in guiding the development of new materials.

4.1 Introduction

Radiation damage changes structural materials; the role of microstructure, stress, and radiation flux on swelling, creep, embrittlement, and phase transformations must all be understood. This knowledge will allow development of materials with superior resistance to fast-neutron fluence and high temperatures.

The ability to model and predict the performance and life of materials in nuclear power plants is essential for the reliability and safety of these technologies. These systems may include new environments such as high-pressure water, molten salt, molten metal, and helium which all increase the potential for material degradation

M. Law (H) • D. G. Carr

Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW, Australia e-mail: michael. law@ansto. gov. au

D. G. Carr

e-mail: david. carr@ansto. gov. au S. C. Vogel

Los Alamos National Laboratories, Los Alamos, MN, United States e-mail: sven@lanl. gov

© Springer International Publishing Switzerland 2015 61

G. J. Kearley and V. K. Peterson (eds.), Neutron Applications in Materials for Energy, Neutron Scattering Applications and Techniques,

DOI 10.1007/978-3-319-06656-1_4

and corrosion. Significant material-development challenges must be met as com­ponents of Generation IV reactor systems will experience higher fluxes, tempera­tures, and sometimes stresses, than conventional light-water reactor systems. The same applies for fusion reactors which in the current developmental phase pose significant challenges to available structural materials. Only by improved charac­terization can we move to science-based models of material behaviour. Under­standing material behaviour from the atomic level up to the full-component scale is essential in developing new materials for these applications.

Creep and creep-fatigue of reactor materials is poorly understood. When the effects of irradiation are added, it is obvious that a better understanding is required. These same effects are intensified in welds due to texture, material inhomogeneity, residual stress, and thermal-expansion mismatch.

Irradiation can cause significant microstructural changes including atomic dis­placement, helium bubble formation, irradiation-induced swelling and irradiation — induced creep, crystalline-to-amorphous phase transitions, and the generation of point defects or solute aggregates in crystalline lattices. Irradiation also creates defects resulting from atomic displacement or from transmutation products. These defects increase the yield and tensile strengths while reducing ductility and causing embrittlement.

The neutron-beam techniques relevant to the nuclear-energy sector are residual stress and texture measurements, crystallographic phase analysis to establish phase diagrams and reaction kinetics, neutron radiography and tomography, prompt — gamma activation analysis, and small-angle neutron scattering. As exposure to neutron beams activates many materials, neutron facilities generally have the infrastructure to accommodate radioactive materials which allows post-irradiation examination of samples.

The ability to characterize materials in situ is essential, at the appropriate tem­perature and environment, rather than bringing the sample back to ambient con­ditions. This also allows the evolution of material behaviour to be studied rather than just the properties at the start and endpoint.