4.05.4.1 Introduction

The previous section included a description of how the effect of radiation damage on the bulk properties of ferritic steels was established from the 1950s and how critical insight into the important role of Cu arose in the late 1960s and early 1970s. Equivalent advances in mechanistic understanding did not occur for another 10 or 15 years.

The improved mechanistic understanding in the 1980s had its origin in the identification of the con­trolling variables that emerged from the experiments discussed in Section 4.05.3. This stimulated consider­able interest on the possible role of elements such as Cu in the embrittlement process. The other, possibly more important, reason was that in the 1970s there were only a few microstructural techniques available for characterizing irradiation damage. Transmission electron microscopy (TEM), the dominant technique, could not resolve the irradiation-induced damage in steels that resulted in a significant change in mechani­cal properties.14 However, in the mid-1980s there was an explosion of information resulting from the appli­cation of a range of different and improved micro­structural techniques. These techniques have now been applied to PWR, BWR, and Magnox steels irra­diated in surveillance locations of power reactors and to representative materials irradiated in materials test­ing reactors.

A more recent advance that is highly relevant to developing detailed mechanistic insight is the advent of ‘multiscale’ modeling. Here, the power of modern computing tools is such that microstruc­tural development (and the resultant change in mechanical properties) can be modeled across the various length and timescales involved in RPV embrittlement. Such models are subject to intense R&D and the current capability can be seen in Wirth et a/.,42 Soneda et al.,43 Becquart,44 and Domain et a/.45 However, these models have not, as yet, made a direct impact on the development of DDRs and so the current state of multiscale model­ing is not reviewed here.