Detection of Gadolinium in Surrogate Nuclear Fuel Debris Using Fiber-Optic Laser-Induced Breakdown Spectroscopy under Gamma Irradiation

Ryuzo Nakanishi,Morihisa Saeki,Hironori Ohba,Ikuo Wakaida

doi:10.3390/app10248985

Abstract

Fiber-optic laser-induced breakdown spectroscopy (FO-LIBS) was applied to a qualitative and quantitative analysis of gadolinium (Gd) in mixed oxide samples, simulating nuclear fuel debris in the damaged reactors of the Fukushima Daiichi Nuclear Power Station. The surrogate debris was prepared from mixed oxide materials containing Gd2O3, with varying Gd concentrations. The emission spectra of the surrogate debris show that the optical emission lines at 501.5 nm and 510.3 nm are suitable for Gd detection in the nuclear fuel debris. LIBS measurements were further performed under gamma irradiation (0–10 kGy/h), resulting in a decrease in spectral intensities due to radiation-induced damage to the optical fiber. For quantification of Gd, robust calibration curves against gamma irradiation were established from the intensity ratio of Gd (501.5 nm)/Ce (474.5 nm) emission lines, yielding the limits of detection for Gd in the range of 0.03–0.08 wt%. These results demonstrate that FO-LIBS is a potential tool for in situ and remote analysis of nuclear fuel debris.

Highlights

Since the accident at the Fukushima Daiichi Nuclear Power Station (F1-NPS) in 2011, a great deal of effort has been devoted to the decommissioning of F1-NPS
This paper reports on the application of our Fiber-optic laser-induced breakdown spectroscopy (FO-Laser-induced breakdown spectroscopy (LIBS)) system for the identification and quantification of Gd in surrogate nuclear fuel debris under gamma irradiation
This study aims to reveal Gd emission lines applicable to Gd identification in the nuclear fuel debris and obtain calibration curves that will prove robust against gamma irradiation

Summary

Introduction

Since the accident at the Fukushima Daiichi Nuclear Power Station (F1-NPS) in 2011, a great deal of effort has been devoted to the decommissioning of F1-NPS. The biggest challenge facing this process is the retrieval of the nuclear fuel debris, which was formed in the reactor vessels during the meltdown accident [1]. The fuel debris is presumed to contain uranium oxide (UO2 ) from the fuel itself, zirconium (Zr) from the cladding, and stainless steel (Fe, Ni, Cr) from the surrounding structural material, while the actual composition ratio may vary depending on where the debris was formed [2,3]. Besides those elements, another key element is gadolinium (Gd). There is a compelling need for methods to remotely analyze the debris and detect the above elements in a high-radiation field

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