Method for detecting and characterising actinide-bearing micro-particles in soils and sediment of the Fukushima Prefecture, Japan

Research progress on the analysis and application of radioactive hot particle

Radioactive hot particle is the particulate form of nuclear material that exists in the environment. The U, Pu, Am, Cs, and other radionuclides isotope in the hot particle contain abundant and accurate fingerprint information, such as the origin and age of the nuclear material. The acquisition and analysis of the key information in the hot particle can be equivalent to the analysis of bulk nuclear material, which could directly reflect the real situation of nuclear activities. Therefore, the single particle analysis of hot particles has become an irreplaceable key technology in nuclear safeguards inspection. The rapid identification, screening, locating, and accurate isotope analysis of hot particles from a large number of particles dispersed in environmental media or on the surface of other materials are one of the most important research field in nuclear emergency. In this review, the research process of the analytical methods for hot particles in the last decade was summarized, including the physical character of hot particles, and the techniques of localization, screening, and extraction of hot particles. Furthermore, we also focused on the mass spectrometry technology for the analysis of hot particle. The advantages and disadvantages of the most used mass spectrometry were summarized. Finally, the research trend for hot particle analysis methods was proposed.

Identification, isolation, and characterization of a novel type of Fukushima-derived microparticle

In the course of the Fukushima nuclear accident, radionuclides were released in various forms, including so-called radiocesium-bearing microparticles (CsMP). So far, four types of CsMP were described: Type A is smaller in size (< 10 μm), Types B, C, and D are larger (> 100 μm). In this work, we present a novel type of CsMP (proclaimed Type E). Three particles of Type E were extracted from a contaminated blade of grass that was sampled 1.5 km from the Fukushima Daiichi nuclear power plant in late 2011. They were located using autoradiography, isolated using an optical microscope and micromanipulator, and characterized using scanning electron microscopy, energy dispersive x-ray spectroscopy, and low-level gamma-ray spectrometry. Type E CsMPs are 10–20 μm in size and exhibit an unusually low and barely detectable 137Cs activity of only ≤ 10 mBq per particle. Their brittle and fragile character may indicate a high surface tension.

Analysis of particles containing alpha-emitters in stagnant water at torus room of Fukushima Dai-ichi Nuclear Power Station’s Unit 2 reactor

Particles containing alpha (α) nuclides were identified from sediment in stagnant water in the torus room of the Fukushima Dai-ichi Nuclear Power Station(FDiNPS)’s Unit 2 reactor. We analyzed uranium (U), which is the main component of nuclear fuel, using scanning electron microscopy (SEM). Other α-nuclides (plutonium [Pu], americium [Am], and curium [Cm]) were detected by alpha track detection and the morphology of particles with α-nuclides were analyzed by SEM-energy dispersive X-Ray (EDX) analysis. Several uranium-bearing particles ranging from sub-µm to several µm in size were identified by SEM observation. These particles contained zirconium (Zr) and other elements which constituted fuel cladding and structural materials. The 235U/238U isotope ratio in the solid fractions that included U particles was consistent with what was found for the nuclear fuel in the Unit 2 reactor. This indicated that the U of similar fuel composition had made finer. The α-nuclide-containing particles identified by alpha track analysis were several tens to several hundred µm in size. The EDX spectra showed that these particles mainly comprised iron (Fe). Since the amount of α-nuclide material was very small, Pu, Am, and Cm were adsorbed on the Fe particles. This study clarifies that the major morphologies of U and other α-nuclides in the sediment of stagnant water in the torus room of FDiNPS’s Unit 2 reactor differed.