Plasma characteristics and element analysis of steels from a nuclear power plant based on fiber-optic laser-induced breakdown spectroscopy

Abstract

The laser-produced plasma and laser-induced breakdown spectroscopy (LIBS) of two steels from a nuclear power plant, including the Z3CN20-09M steel used for the main reactor coolant pipes, and the 16MND5 steel used for nuclear reactor pressure vessels. These were investigated based on a fiber-optic LIBS system. Under the same input laser energy, the laserproduced plasma from the Z3CN20-09M steel had a weaker emission intensity compared to the 16MND5 steel, probably due to a greater content of Cr. Thus, plasma from the Z3CN20-09M steel had a larger kinetic energy and induced a faster expansion shockwave in air. Calibrations of the fiber-optic LIBS system by the means of internal standardization, support vector regression and random forest regression were set up. For the Cr element, as a major element in Z3CN20-09M (19.33wt.%), it was determined with the relative error controlled under 3.5%; as a trace element (0.11wt.%) in 16MND5 it was measured with the best rootmean-square error of prediction as 0.032wt.%, and the Mn content (1.19-1.51wt.%) in both steels was measured with the relative error around 10%.

Progress of laser-induced breakdown spectroscopy in nuclear industry applications

“…As for the above three conventional calibration methods, LTE is an important prerequisite in order to make Boltzmann-Maxwell and Saha-Eggert theoretical expressions meaningful. To certify the LTE condition, the McWhirter criterion is the most popular criterion and also a necessary condition, as it defines the minimum electron number density [131], while the Cristoforetti criterion requires greater strictness on the temporal variation and spatial variation [139]. Moreover, the assumptions of optically thin plasma and stoichiometric equilibrium should also be satisfied.…”

“…The transmission fiber of FO-LIBS systems used in the nuclear industry should have a high damage threshold, with no interference due to ionizing radiation in a certain wave band. The length of the fiber could be in the short range (3 m length, 0.8 mm core diameter, 0.37 numerical aperture (NA) [131]), the medium range (10 m length, 1 mm core diameter, NA = 0.39, Thorlabs FT100EMT [15]), or the very longrange (75 m length, 550 µm core diameter, all-silica, M0550T, SpecTran, USA [23]). It is worth mentioning that Saeki et al [132] designed a transportable FO-LIBS instrument (3-20 m length, 0.55-1.0 mm core diameter, NA = 0.12-0.2) to analyze underwater samples in a high-radiation field, and investigated the influence on the optical transmittance of the laser delivery fiber.…”

Laser Ablation Plasmas and Spectroscopy for Nuclear Applications

“…272,273 FO-LIBS for nuclear research has also been employed by several research groups with systems ranging up to 100 m in length. 271,272,[274][275][276][277] Other elements that are commonly measured in-core as indicators of potential structural failures or material damage include Cr, Mn, Mo, Ni, Si, and V, where limits of detection range from around 100 to 200 parts per million (ppm). 271,274,[277][278][279] Crucial research efforts also include developing instrumentation to provide more affordable alternatives to Nd:YAG lasers that are typically implemented with the current detection systems.…”

“…271,272,[274][275][276][277] Other elements that are commonly measured in-core as indicators of potential structural failures or material damage include Cr, Mn, Mo, Ni, Si, and V, where limits of detection range from around 100 to 200 parts per million (ppm). 271,274,[277][278][279] Crucial research efforts also include developing instrumentation to provide more affordable alternatives to Nd:YAG lasers that are typically implemented with the current detection systems. For example, Tamura et al 275,276 developed a microchip laser FO-LIBS system that could potentially offer a cheaper alternative to the typical Nd:YAG lasers used.…”

“…272,273 FO–LIBS for nuclear research has also been employed by several research groups with systems ranging up to 100 m in length. 271,272,274–277…”