# Resurgence of a Nation's Radiation Science Driven by Its Nuclear Industry Needs
## 3 Exemplar Results
### Materials Chemistry for Nuclear Waste Immobilisation  
High-level waste (HLW) generated by the nuclear industry is incorporated into a glass and the effect of radiation on this glass must be understood for the industry to have confidence in this waste immobilization method. Glass samples of relevance to the nuclear industry were produced at Sheffield Hallam University and the compositions are provided in Table 1. MWsection and Ca/Zn are similar to the base glasses used in the UK [36] while ISG refers to the International Simple Glass [37]. Vitreous silica samples were purchased from Galvoptics Ltd. To prepare all four glasses for ion irradiations, one 25 by 25 mm face was hand polished using diamond lapping films to produce surfaces with <100 nm roughness. Four samples were loaded into a custom build sample holder for 14 MeV Ni ion beam irradiation (fluence of 4.56 \(\times\) 10\({}^{14}\) ions/cm\({}^{2}\)). The holder masked part of each sample from the ion beam so only a 5 mm by 5 mm area of each sample was irradiated. Profilometry (Bruker Contour Elite K with Multimode 8 AFM System at the University of Sheffield) provided optically gathered 3D surface maps of the border between the irradiated and unirradiated sample areas. Step heights were calculated as a percentage of the penetration depth of the incoming ion beam, as reported by SRIM-2013 [38] (Table 1), using the mean step height from seven measurements at different points along the border. Figure 7 shows that vitreous silica compacted under ion beam irradiation, whereas all other glasses expanded. The change in volume of the silica corresponds to values recorded in other literature [39; 40; 41]. For both the MW and Ca/Zn glass, a fourfold increase in ion beam flux leads to a twofold increase in the degree of swelling. A much smaller volume change was observed in ISG such that the effect of altering the flux is not clear. The structure of these glasses comprises a network of tetrahedral units (SiO\({}_{4}\), AlO\({}_{4}\), BO\({}_{4}\)) and trigonal (BO\({}_{3}\)) units. Network modifiers (Na, Li, Ca, and Zn) exist in the glass as somewhat free-floating ions that charge compensate non-bridging O atoms, and in the case of ISG, also charge compensate for Al in the glass network. The different responses suggest that glass chemistry plays a part in their radiation response. The expansion of the UK base glasses suggests that the network is depolymerizing and so producing more dangling bonds, which may be influenced by the reorganization of the mobile network modifiers in response to the ion beam. The trend with flux suggests that the chemical changes that lead \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Component** & **MW** & **Ca/Zn** & **ISG** \\ \hline SiO\({}_{2}\) & 61.75 & 56.10 & 56.18 \\ B\({}_{2}\)O\({}_{3}\) & 21.88 & 21.51 & 17.34 \\ Na\({}_{2}\)O & 11.05 & 11.48 & 12.17 \\ Li\({}_{2}\)O & 5.33 & 2.92 & - \\ ZnO & - & 6.03 & - \\ CaO & - & 1.94 & 4.98 \\ ZrO\({}_{2}\) & - & - & 3.27 \\
**Penetration Depth (\(\upmu\)m)** & 5.68 & 6.40 & 6.75 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Three glass compositions, in wt%, of relevance to the nuclear industry were exposed to a 14 MeV ion beam. Vitreous silica was also used. The penetration depth of the ion beam, as calculated by SRIM-2013 [38], and used in the step height calculations, is also provided. to the volume change are dose rate dependent. Further work will probe these chemical changes using, for example, Raman and NMR spectroscopies. Work is also underway at DCF, focusing on understanding the interplay between radiation and the crystalline phases that are present in waste form [36]. Complementary work will probe how radiation affects leaching in anoxic groundwater, in a disposal scenario where the canister housing the glass has begun to corrode. Similar work has previously been carried out under oxic conditions [42].