Vol.9 No.3 2017

Research paper : Radioactive cesium decontamination technology for ash (T. Kawamoto et al.)−140−Synthesiology - English edition Vol.9 No.3 (2017) consists of metal hexacyanoferrate (MHCF or Prussian blue type complex) nanoparticles. Actually, MHCF is a porous coordination polymer with chemical composition of AyM[Fe(CN)6]1−x • zH2O, where A stands for a cation such as an alkali metal, and M denotes a transition metal cation. When M = Fe, it is Prussian blue (PB), an articial pigment synthesized in the early 18th century, used by van Gogh and Hokusai in their paintings, and even used in present days. The metal species (A, M) and composition (x, y, z) can be controlled over a wide range. The crystal structure, presented in Fig. 1, has a jungle-gym structure in which the cyano group crosslinks the metal atoms. The crystal includes a hollow network in which cation A adsorbs and desorbs. It is known for its highly selective adsorption of cesium ions.[13]Fig. 1 The crystal structure of hexacyanoferrate AyM[Fe(CN)6]1−x • zH2O, where A and M indicate the cations and the transition metal ions of Fe, Cu, Co, or othersThe red atoms around the vacancy show the oxygen in the H2O molecule.The rst report of the radioactive cesium adsorption capacity of PB was published around 1950.[14] Since then, radioactive cesium adsorption by various MHCFs, not only PB, has been investigated and used.[13][15]–[17] For example, various MHCFs were used for removing radioactive cesium from contaminated water at Hanford, where nuclear development was conducted in the United States in the 1960s.[18] Recently, nickel hexacyanoferrate (NiHCF) was used in the Areva device for decontamination of contaminated water from the nuclear plant accident in 2011.[19][20]An outline of PB research at AIST is presented in Fig. 2. At AIST, the development of a PB type complex has been conducted jointly with Yamagata University from 2005,[21][22] with particular emphasis on the development of electrochromic devices.[23]–[26] Before the accident at Fukushima, we had been involved in R&D of a system for electrochemically adsorbing/desorbing and concentrating radioactive cesium.[27]–[29] The accident at Fukushima occurred as we were accumulating related technological knowledge. In its aftermath, we immediately shifted the main focus of our R&D to decontamination. We conducted R&D of two main areas: the development of an adsorbent based on PB nanoparticles,[30]–[34] and the development of decontamination technology using this adsorbent.[35]–[38]2.2 Outline of incinerated ash decontamination technologyOne specically examined technological development topic is the volume reduction of vegetal contaminants.[3][5][6] Actually, incinerated ash decontamination includes this technology. An Fig. 2 History of the development of radioactive cesium decontamination technology using PB nanoparticles at AIST, where PB and PB-NP represent Prussian blue and PB nanoparticles, respectivelyM-NC-Fe-CN-MCs+‒0.5 nmCs+Flow systemPB-NP(Kanto Chem.)Non-wovenadsorbent(Japan Vilene)Cs concentrating robotVerication plantR&D Cs-decontamination with companiesCs-uptake robot (Octscience)• Composites with PB-NP• Granules/non-woven etc. MonitoringDcontamination AdsorbentMaterialRobot for Cs-uptake with PB-NP0.01Bq/L AvailableCs-uptake from ash by PB-NPPilot plant test in Fukushima areaIn marketCs-monitoringPilot plant test completedR&D for ash decontaminationIn market for evaluation• Nanostructure optimization for Cs-decontamination• 67 performance than commercial pigmentsAdsorbent R&DIn market20113.11PB-NP mass-production (2012)Accident at Fukushima Daiichi NPP5 mm

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