| As a major low and intermediate level radioactive solid waste,the prospect of the nuclear energy relies on the safe and efficient disposal of radioactive waste ion exchange resins.The cement solidification of radioactive resins is faced with two problems:1)Under high resin load,the impact resistance of cemented wasteform is poor.2)The leaching of radionuclides in cemented wasteform is higher than other solidification techniques.In this study,the simulated radioactive Cs-containing ion exchange resins were solidified by Ordinary Portland cement combined with zeolites,silica fume and polyvinyl alcohol(PVA)fiber,and the effects of additives on the properties of the cemented wasteform was investigated according to National Standard GB 14569.1-2011.The effects of additives on the propersities of wasteform were investigated,and the formula of wasteform was determined as cement:water:resins:zeolite:silica fume:PVA fiber=1000:520:400:150:50:3(wt%).After cured with 99%relative humidity at 25±5℃ for 28 d,the properties of the cemented wasteform were able to meet the requirements of GB 14569.1-2011.There was no free liquid on the surface or inside the wasteform.The 28 d compressive of the wasteform was 11.34 MPa,and the wasteform can still remain complete after fall down from 9 m high to the concrete ground.The 42 d leaching rate and cumulative leaching fraction of Cs in deionized water were 2.35×10-4 cm/d and 3.66×10-2 cm,much lower than the maximum limit specified in GB 14569.1-2011.Also,the compressive strength loss after irradiation resistance,freezing test and water test was less than 25%.PVA fiber can enhance the impact resistance of wasteform.Under 40%resins load,the impact resistance of the wasteform with 3‰ PVA fiber incorporation can met the requirements of GB 14569.1-2011,and the wasteform without PVA fiber was broken after impact test.Zeolite and silica fume can enhance the leaching security of wasteform,and reduce the leaching out of Cs,the wasteform with 15%zeolite and 5%silica fume has the best leaching security.The PVA fiber can also enhance the leaching security of the wasteform.The results of the experiments also showed that zeolite,silica fume and PVA fiber can enhance the compressive strength of wasteform,and the silica fume and PVA fiber can reduce the total porosity of the wasteform,while the zeolite cause an increasement on the total porosity.The leaching model of Cs in deionized water showed that the leaching behavior of Cs was controlled by different mechanism.The leaching behavior was controlled by surface wash-off and fast dissolution over the first 10 days,the leaching out of Cs was fast during the period,and the 10 d cumulative leaching fraction of Cs was more than 70%of the 42 d cumulative leaching fraction.After 21 days,the leaching out of Cs was controlled by diffusion through pores,and the reaching rate of Cs become much lower compared to the first 10 days.To explore the effects of γ-ray irradiation on the properties of the wasteform,a 890 Gy/h irradiation dose rate and 100 kGy cumulative irradiatiol dose 60Co γ-ray source was used.Because the resins was damaged by the γ-ray irradiation,the leaching out of Cs was increased significantly,and the 42 d cumulative leaching fraction of Cs became 3.88 times bigger after γ-ray irradiation.By comparing the properties of wasteform before and after γ-ray irradiation,it was found out that although the wasteform was damaged by γ-ray irradiation,but the properties of wasteform can still meet the requirements of GB 14569.1-2011. |
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