Vol.9 No.3 2017

Research paper : Radioactive cesium decontamination technology for ash (T. Kawamoto et al.)−144−Synthesiology - English edition Vol.9 No.3 (2017) solid–liquid ratio at the dehydration of ash, and (3) reuse of water used for washing. Because ash often exhibits extreme hydrophobicity, water and ash cannot be mixed by simple stirring. The cesium extraction is difcult. Point (1) is effective to resolve the problem. A vibrating granulator is normally used at incineration plants as a device to create granules when transporting incinerated ash to the final disposal site. Water and ash are mixed to form granules by adding only a small amount of water. Using this device, it was possible to mix water and ash effectively. In addition, because block-like ash can be ground by the device, the washing was done smoothly. With point (2), the filter press method was used as an inexpensive solid–liquid separation device. By setting up a circulating route, the solid–liquid ratio in the dehydration area was increased to avoid clogging. For point (3), water reuse became possible by installing a coagulation–sedimentation basin to remove harmful substances other than radioactive cesium.For the recovery of radioactive cesium that is dissolved in water, the granular adsorbent or the nonwoven type with the PB nanoparticles was used. Results veried that the expected adsorption was generally achieved. Results claried that the adsorption behavior was estimated by the dosage monitor set on the column.Figure 8 presents the effect on volume reduction of waste using this technology. For example, when one ton of combustible waste contaminated by 1,800 Bq/kg of radioactive cesium was processed, the waste materials that can be treated as regular waste, those that must be disposed in managed disposal sites, and those that must be stored at interim storage facilities were 7.8 kg, 6.0 kg, and 4.4 g, respectively. Thereby, extremely high volume reduction was achieved.[6]Fig. 7 Schematic view of the ash washing and recovery plant[6]7!"#$%&!'#()%&!%&!%&!*&!+,&!-.&!/,'01()%&!-.&!-.&!0#$%&-.!0#$%&!"#$%%&&'()*(10)(9)(8)(7)(6)(6)(5)(5)(4)(3)(2)(1)Extracted waterPuried waterCs-removal waterRecycle(70 L/h)Coagulation Columns(Cs-uptake)Decontaminated ash(16‒27 kg/h)Extraction tankExtracted water(70 L/h)Extracted waterHigh V/m(36)Suspension liquidLow V/m(4)Suspension liquidDehydratorVibrating granulator Ash (20 kg/h)Water (80 L/h)Decontamination1,000kg–1800Bq/kgWoods etc.IncinerationManaged disposal site for high concentrationManaged disposal site for low concentrationNormal Disposal 4.4g(*)–360 MBq/kgAdsorbent6.0kg31 kBq/kgDecontaminated y ash–7.8kg4.1 kBq/kgDecontaminated bottom ash7.5kg226 kBq/kgFly ash5.8kg–18 kBq/kgBottom ash13.3kg134 kBq/kgAshFig. 8 Example of volume reduction when the incinerated ash processing technology is used[6]

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