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 (alpha) 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 alpha-nuclides (plutonium [Pu], americium [Am], and curium [Cm]) were detected by alpha track detection and the morphology of particles with alpha-nuclides were analyzed by SEM-energy dispersive X-Ray (EDX) analysis. Several uranium-bearing particles ranging from sub-mu m to several mu m in size were identified by SEM observation. These particles contained zirconium (Zr) and other elements which constituted fuel cladding and structural materials. The U-235/U-238 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 alpha-nuclide-containing particles identified by alpha track analysis were several tens to several hundred mu m in size. The EDX spectra showed that these particles mainly comprised iron (Fe). Since the amount of alpha-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 alpha-nuclides in the sediment of stagnant water in the torus room of FDiNPS's Unit 2 reactor differed.

Automated summary

This study identified particles containing alpha nuclides from the sediment in stagnant water in the torus room of the Fukushima Dai-ichi Nuclear Power Station's Unit 2 reactor. The particles consisted of uranium and other elements, with different morphologies and composition for uranium and other alpha nuclides. The uranium particles were smaller in size and contained fuel cladding elements, while the alpha nuclide particles were mainly composed of iron.