“Imagination is more important than knowledge. For knowledge is limited to all we now know and understand, while imagination embraces the entire world, and all there ever will be to know and understand.”
—Albert Einstein
We have learned about some aspects of the primary radiation damage in Chapter 3 and covered on the evaluation of damage in terms of displacements per atom (dpa). Radiation effects generally refer to the behavior (or properties) of materials in the aftermath of the radiation damage. As this book is on nuclear reactor materials, we will focus on the radiation effects caused by neutron irradiation. However, most of the radiation effects are universal in nature regardless of the type of radiation (i. e., proton, heavy ions, electrons) with specific different features. Let us make some general observations on the radiation effects: (i) defect concentration increases with fluence, (ii) nuclear transmutation occurs, (iii) chemical reactivity changes, (iv) diffusion increases, (v) new phases, both equilibrium and nonequilibrium, can take place, and (vi) impurities are produced. The changes of properties are, in general, proportional to neutron flux, irradiation time, and temperature. From the previous chapters, it has been very clear that the essence of materials science as applied to nuclear field is in structure-property performance. Figure 6.1 illustrates this very aspect. Defects formed during primary radiation damage evolve to form clusters and subsequently extended defects and change the microstructural features in various ways. These microstructural changes, in turn, alter the materials properties. That is why materials undergo extensive irradiation testing before they could qualify to be fit for use in nuclear reactors. In this chapter, while we will discuss general aspects of radiation effects, we will give examples from nonfuel (i. e., structural/fuel cladding, etc.) reactor materials. Some specific examples of radiation effects in fuels will be discussed in Chapter 7.
6.1
