## 5 In-Line Application of LIBS in Industrial Production
### Nuclear Material  
In the nuclear industry the analysis of nuclear and other materials before, during, and after production and utilization is required for safe and economic operation. This includes different processes in the nuclear fuel cycle such as mining of ore, fabrication of fuel, power plant operation, fuel reprocessing, and spent fuel storage (Figure 13a) [259]. Laser spectroscopy techniques such as LIBS, laser-induced fluorescence (LIF), and cavity-ring down spectroscopy (CRDS) are employed for analysis due to their elemental and molecular selectivity and high sensitivity. The inherent advantages of LIBS make it an efficient method for the analysis of hazardous samples in harsh environments. The nuclear industry is one of the fast-growing fields of LIBS application [248]. The development of stand-off LIBS systems enables for remote and in situ inspection of samples that are at large distance from the LIBS sensor (i.e., many meters). Figure 12: LIBS in-line measurement of steel scrap. (**a**) Schematic of LIBS sensor installed above a conveyor belt in a steel plant. (**b**) Variation of the silicon mass in the scrap on the conveyor as derived from the in-line LIBS measurements. Adapted from [102]. Figure 13: LIBS in nuclear materials analysis. (**a**) Potential applications of LIBS in nuclear fuel cycle. Adapted from [259]. (**b**) Schematic of a stand-off LIBS analyzer installed at the THORP nuclear plant in UK. Adapted from [263]. Figure 13b shows a stand-off LIBS system using an optical telescope for the characterization of high-level radioactive waste at the THORP nuclear reprocessing plant in UK [263]. Optical access to the material was possible via a 1 m thick lead-glass radiation shield window. The LIBS system was used for remote identification of an unknown solid material that accumulated on the basket surface. The perforated basket was used in the processing of spent fuel. Remote analysis of this surface contamination was necessary due to the difficulties in taking a sample from behind the radiation shield and the subsequent difficulties with laboratory analysis. The LIBS analysis showed that the contaminant material was rich in zirconium and molybdenum (mainly zirconium molybdate which forms during the reprocessing of spent fuel). Remote analysis of materials in nuclear fusion reactors is another important application for stand-off LIBS [249; 257]. During operation of a tokamak fusion reactor, the inner walls of fusion chambers and divertors (plasma-facing components, PFC) are severely interacting with the plasma. As a consequence, the PFCs are subject to erosion, re-deposition of eroded material, and retention of fuel. The performance of fusion tokamaks such as ITER [459] can be influenced by such processes. Figure 14a shows the schematic of a stand-off LIBS system installed at the Experimental Advanced Superconducting Tokamak (EAST) [257; 460]. The Nd:YAG laser beam (1064 nm, 5 ns, 180 mJ) was focused on the wall surface on the high-magnetic-field side using a quartz lens (f = 3 m) mounted at port H of the EAST device. The emission of LIBS plasma was collected in a backward direction using an optical telescope. The LIBS spectra measured in situ showed spectral signals of multiple elements (D, H, Li, Mo, W, Ti, La, Fe, and Si). The signals of Mo, W, C, and La were from the substrate materials of tiles, the signals of D and H came from the fuel (H was used for isotope experiments). The Li signal was caused by Li wall conditioning and Ti, Fe, and Si were due to impurities in the Li co-deposited layer. Figure 14b shows LIBS spectra with the H\(\alpha\) and D\(\alpha\) lines measured in situ at EAST on different days. From such measurements, the H/H + D ratio in the plasma phase can be determined. These results demonstrate the potential of LIBS for in situ characterization of D/H retention and Li co-deposition on the walls of the fusion reactor. Figure 14: LIBS in fusion materials analysis. (a) Schematic of a stand-off LIBS system installed at the EAST tokamak in China.