Nuclear fission materials

RPV steels

Both The National Nuclear Laboratory (NNL) and Rolls-Royce have long standing and very productive working relationships with the Department of Materials at Oxford. Collaborative research has included the study of the effects of thermal ageing and irradiation on reactor pressure vessel (RPV) steels.  During service, these materials degrade and this can result in embrittlement. In high-Cu RPV steels, the degradation of mechanical properties is primarily caused by formation of small Cu-enriched clusters during irradiation.  With the local electrode atom probe (LEAP) it is possible to measure their composition, size and number density and correlate the results to changes in mechanical properties. An example of LEAP data showing the atomic-scale structure of an irradiated RPV steel is presented in Figure 1, below.  The microstructural features are even more obvious when the data are rotated (see adobe shockwave flash movie file).

Figure 1: LEAP analysis of an irradiated RPV steel. During the analysis 50 million ions were detected, corresponding to a volume of ~90x90x380nm3, and their original position within the material determined. Each dot represents an individual atom. A grain boundary, a large Cu precipitate, two carbides, several dislocations and several hundred small Cu-enriched clusters can be identified.

Figure 2 shows a highly magnified view of a single irradiation-induced cluster containing Cu, Mn, Ni and Si atoms. The P atoms tend to be found at peripheries of the clusters. The research has led to an improved mechanistic understanding of RPV embrittlement and contributes to the safety cases for commercial RPVs.

Figure 2: Enlarged view of an irradiation-induced cluster (extents of outline box 8x8x8nm3).

For more details on this project, please contact Dr Jonathan Hyde or Prof. George Smith.

304 steels

Stress corrosion cracking (SCC) in austenitic stainless steels has been identified as limiting the long-term reliability of structural components in many critical applications, such as pressurized water reactors. However, to correctly understand the mechanisms underlying this behaviour, atomic-scale mapping of the grain boundary chemistry is required.

For more details on this project, please contact Sergio Lozano-Perez from the Nanoanalysis Group or Prof. George Smith.

Zr-based alloys

Zirconium alloys are used in the nuclear industry as fuel rod cladding. A specific page dedicated to Zr-based alloys can be found here .