【作者】 石拥军；

【导师】 杨长辉；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2007， 硕士

【摘要】 能源是人类赖以生存和发展的物质基础。随着全球可用石油、天然气和煤炭等资源的日益短缺以及“京都协议”的贯彻执行,核能已被认为是未来最重要、最有潜力的新型能源之一。核能生产过程中必然产生一定的核废料,尤其是核电站及其它核利用在运行中产生大量的高、中、低放射性废物。在这些废物中,中、低放射性废物(ILW、LLW)超过95%。因此,如何安全处置核废物已成为制约核能发展的重要障碍之一。研究和应用表明,采用水泥基材料固结核废物是经济、有效的处置方式。使用的胶结材可以是硅酸盐水泥(OPC)、复合硅酸盐水泥等。比较而言,采用复合水泥系统固结核废物具有高效、低水化热、低成本等优点,是目前的主要应用方式。但这种固化体系碱度很高(pH可超过13.0),即使矿渣(Blast Furnace Slag, BFS)取代水泥达到90%,体系碱度仍然维持在12.5左右。高碱度液相易与中、低放射性废物中的活泼金属如镁和铝等发生腐蚀发应,产生大量氢气并导致体系过度膨胀甚至破坏,为放射性废物的处置带来安全隐患。因此,选择碱度更低的固结系统十分必要。熟料矿物的水化是硅酸盐水泥系统和复合硅酸盐水泥系统碱度的主要来源。取消熟料的使用是降低系统碱度的有效技术措施。本文采用碱矿渣水泥体系作为固结核废物的固化基体,并使用中性盐Na2SO4和CaSO4激发矿渣(Ground Granulated Blastfurnace Slag, GGBS)的活性以期降低体系的碱度。试验主要研究了该体系(中性盐-矿渣-粉煤灰胶结材体系)的凝结时间及标准稠度用水量、抗压强度、碱度、自由水含量、对金属Al的腐蚀状况及Cs+的浸出率,并对该体系的微观结构进行了分析。试验结果表明:①矿渣-硅酸盐水泥胶结材体系(BFS/OPC)凝结时间短(3～5.5h)。虽然早期强度较高,但后期发展缓慢,60天强度仍低于25.0MPa。该体系对Cs+的滞留能力差,养护至28天龄期时,Cs+浸出率仍高达60%以上。并且体系各龄期碱度高,尤其是新拌浆体,其碱度超过13.0,使得该体系内金属发生显著的腐蚀现象。因此,该体系不宜直接用于固结放射性废物。②中性盐-矿渣-粉煤灰胶结材体系初凝时间可控制在4h以上,终凝时间可控制在48h以内。早期强度发展缓慢,但28天强度可达到20～35.0MPa且后期强度持续增长。各龄期碱度均可控制在12.0以内,并随着PFA掺量的增加,碱度进一步降低,一定条件下可降至11.0以下;体系自由水含量低,可控制在10～15.0%之间,较低的碱度及自由水含量为避免金属发生腐蚀提供了有利条件。③激发剂掺量适当时,中性盐-矿渣-粉煤灰胶结材体系内未发生明显的金属腐蚀现象,且Cs+浸出率低,本研究条件下28天浸出率低于32.0%。因此,该体系能够满足固结核废物的基本要求。④中性盐-矿渣-粉煤灰胶结材的主要水化产物为低碱度水化硅酸钙、钙矾石型水化硫铝酸钙和杆沸石型水化硅铝酸钙钠。三者相互结合,形成致密的结构,提高了固化体的强度及对核素离子的滞留能力。另外,在水化后期,仍残留一定量未参与水化反应的粉煤灰。⑤BFS/OPC胶结材体系在水化期间无明显的钙矾石类和杆沸石类水化产物的生成,水化后期仍有未反应的矿渣残留,结构较疏松,对核素离子滞留能力差。更多还原

【Abstract】 The energy sources is substantial basic on which human depend to survive and develop. With reduced oil, gas and coal production and the obligation for implementing the Kyoto Protocol, nuclear power is regarded as a kind of most new important potential source. Production of nuclear power must bring some nuclear wastes, especially a mass of high, intermediate and low level radioactive wastes come from nuclear power plants and other nuclear power use. More than 95% of the bulk of the wastes is intermediate and low level radioactive wastes (ILW and LLW). So, how to deal with nuclear wastes safely is one of the importent barriers for promoting nuclear power.Research and application indicate that it is economical and effective to immobilise nuclear wastes by using cementitious materials, which can be Porland cement or composite Porland cement. Using composite cement system to immobilise nuclear wastes is a primary manner now, which has several advantages of higher efficiency, lower heat of hydration and inexpensive price comparatively. Nonetheless, the high internal pH (typically above 13) will bring security hidden trouble, because it can cause the corrosion of metals such as aluminium and magnesium in ILW and LLW, excess generation of hydrogen and leading to expansion. Although replacement of OPC with up to 90% blast furnace slag (BFS) is used, the pH still remains about 12.5. So, it’s very important to choose an immobility system have lower internal alkalinity.The hydration of cinker minerals is primary alkalinity source of Porland cement system and composite cement system, so it’s an effectual technique measure to reduce alkalinity by avoiding cinker use. The alkali-activated slag cement (AASC) system being immobility concretion have been used in this paper, and reduce system’s alkalinity by using neutral salt Na2SO4 and CaSO4 to activate ground granulated blastfurnace slag (GGBS). In this paper, the setting time and Water for standard consistency,compressive strength, alkalinity, free water content, Al corrosion and Cs+ leaching rate of neutral salt-slag-fly ash cementitious materials were studied, and microcosmic structure of this system was analysed. The result of testing shows:①The setting time of BFS/OPC is short (3～5.5h). Although this system could get to a higher early strength, evening strength increased slowly and the strength at 60 days is lower than 25.0MPa. The system’s ability to immobilising Cs+ was weak, which at 28 days curing age, the Cs+ leaching rate was more than 60% all the same. On the other hand, because the alkalinity were high of this system at every age, which alkalinity of fresh paste was more than 13.0 especially, marked metal corrosion happened in system. So, this system didn’t adapt to immobilise nuclear wastes directly.②The initial setting time of neutral salt-slag-fly ash binding materials could be controlled more than 4h and the final setting time could be controlled within 48h. Early strength developed slowly, but compressive strength could get to 20~35.0 MPa at 28 days ages and evening strength increased continuously. The alkalinity could be controlled within 12.0 at every age, and with an increase of the PFA content, the alkalinity decreased much more, less than 11.0 indeed under certain condition. The free water content of this system was low and could controled between 10.0 and 15.0 percent. The lower alkalinity and free water content became to an advantage to avoid metal corrosion.③In the neutral salt-slag-fly ash binding materials, there didn’t happen metal corrosion evidently under proper activator content and Cs+ leaching rate was low, which is less than 32.0% at 28 days under this researching condition. So this system can satisfy the basic demand of immobilising nuclear wastes.④The main hydration products of the neutral salt-slag-fly ash binding materials are low-alkali hydrous calcium silicate, ettringite and calcium sodium sillo-aluminate hydrate similar to thomsonite, and due to these products combining one another to form compact structure, the strength and immovable ability for nuclear ion of concretions increases. In addition, some quantity of PFA are remained in concretions at hydration evening however.⑤During hydration, there didn’t have ettringite and thomaonite products in BFS/OPC binding material and BFS are remained in concretions at hydration evening however. The immobilising ability for nuclear ion was weak due to looser structure.更多还原