Vol.9 No.3 2017
Research paper : Radioactive cesium decontamination technology for ash (T. Kawamoto et al.)−145−Synthesiology - English edition Vol.9 No.3 (2017) 2.2.4 Storage and disposal of post-treatment wasteRegarding the practical application of our technology, the remaining issue is storage of the waste materials generated by the treatment. The main waste materials are washed incinerated ash, wastewater used for washing, and the adsorbents after adsorption. With regard to washed ash, waste standards are 8,000 Bq/kg and 100,000 Bq/kg of radioactive cesium concentration, the criteria for the storage level by regulation of the Japanese government. The washed ash could be stored or disposed of to maintain the standards. Regarding wastewater, because radioactive cesium can be removed sufciently by the adsorbent, the water can be released after conducting regular wastewater processing. Even in cases where release is difficult because of the concerns of local governments, treatment is possible by minimization of the amount of water use by reuse, followed by evaporation.The used adsorbent would pose no problem for regular storage because it is sufciently stable. However, in this case, extremely long-term storage might be necessary because it includes radioactive materials. In this case, safer storage methods will be requested. To convert the used adsorbents into oxides is an approach for storage in a stable condition. However, oxidation reaction of PB entails large amounts of oxidative heat, implying the evaporation of the adsorbed radioactive cesium at temperatures higher than 600 °C. For stable oxidation at temperatures lower than 500 °C, we established an oxidation method under mild conditions using superheated steam. Using this method, we converted the adsorbents into oxides while maintaining evaporation of cesium at an extremely low level.3 Team formation for the ash decontamination technology developmentAs described above, we proceeded with the integration of technologies using the incineration method, the extraction of radioactive cesium from ash, recovery by adsorbents, and the safe storage of waste products. We also conducted tests at a pilot plant on site after laboratory tests. Using these approaches, it was possible to establish technologies for practical use in a short period. At the initial stage of this research, the researchers in materials science played a central role, followed by participation of chemical engineering and geo-engineering researchers at AIST. However, it was impossible for the AIST researchers to construct everything. For example, incineration technology, plant design, operation, and the design of adsorbents that could be set for mass production in a short time could not be accomplished by AIST, a research institute, alone. For these missions, corporate collaboration is necessary.We rst produced a ground design for commercialization, extracted elemental technologies to achieve such commercialization from the design, and formulated a strategy for the realization of the elemental technologies. What is important is that the strategy must include “who” will conduct the process, “when” the R&D for each technology will be done, “who” will do it, and “when” the commercialization will be done. As described above, because AIST is a research institute that cannot engage in commercial projects, commercialization is conducted by companies. Therefore, it is necessary to produce an R&D plan with consideration of the technology transfer to companies at a certain time. For the specic R&D contents, the theme in the pilot plant must be determined with tests to realize the technology transfer strategy. Moreover, the theme at the laboratory must be determined to nd a means of deciding the parameters used in the pilot plant test. The strategy established in this manner is presented in Table 2, which shows the experiment contents and the R&D method, which are presented in a bottom-up fashion from the initial stage or a small-scale stage. It Method developmentOriginal+With companiesAdsorbentLaw-compliance－○○○○Conventional technologyAsh/liquidWaste managementLocal agreement/on-site management－○With companies + support by AISTPlant-site managementScale upElution management○Original + with companiesAdsorbent managementMass productionGranule/non-woven○With companiesGranulation/immobilizationMass-productionOptimization of PB-NP composition○Original + universitiesMaterialCs-uptakeAsh crushing/decrease of water amountConventional/condition optimization○○Internal collaboration ＋Invited researchersCs-extraction20kg/h biomass boilerConvectional technology○○PurchaseIncineration(4)(3)(2)(1)Pilot plantLaboratoryTechnology transferMethod for R&DExperimentsR&D methodComponents of technologyTable 2. Research for the development of ash decontamination technology and the policies for technological developmentThe transferring strategies are: (1) patent + technological transfer, (2) technology disclosure, (3) research by companies, and (4) utilization of conventional technology.