高盐份条件下低放废水深度净化机理与方法研究

High-salt low-level waste liquids are ubiquitous in the nuclear fuel cycle and nuclear facilities decommissioning in our country. They are characterized by high salinity and various but very low content radionuclides. Enrichment of radionuclides into concentrated liquid or solid waste is usually used to achieve the purpose of reducing waste.. High-salt low-level waste liquid treatment technologies require a high selectivity and decontamination factor to the radionuclides under the influence of high concentration of salt. Currently, the commonly used evaporation technology is difficult to achieve the required efficiency. To solve the problem restricting the management of radioactive waste in our country, it is urgent to carry out research on new methods and mechanisms of advanced purification of high-salt and low-level waste liquid.. Targeting the treatment object of the spent fuel off processing waste liquid, this project set up the combined process of "flocculation and sedimentation microfiltration pretreatment + membrane distillation concentration + selective adsorption and ion exchange", to achieve the purpose of "high concentration and advanced purification".. The project will intensively study the occurrence forms of typical radionuclides such as Sr, Tc, Cs, U, Np, Pu and Am in the chemical environment of the off processing high salinity low-level waste liquid; the surface and interface chemical behavior and removal mechanisms of nuclides of very low concentrations; optimization of the convergence mechanism between the various treatment units in the combined process to achieve stable operation.. By obtaining new processes and new materials, this research will provide new idea and basis for the management of high salt low level radioactive waste in our country.

高盐低放废液在我国核燃料循环与核设施退役中普遍存在，其特点是盐度高、核素种类多但含量极低，通常采用将放射性核素富集至浓缩液或固相废物中以实现废物减量化目的。高盐低放废液处理技术要求在承受高浓度盐影响条件下对核素具有较高选择性和去污因子，目前普遍采用的蒸发技术难以达到所需精度，亟待开展高盐低放废液深度净化新方法及机理研究，解决制约我国放射性废物管理的难题。本课题以乏燃料后处理废液为研究对象，建立“絮凝沉淀微滤预处理+膜蒸馏浓缩+选择性吸附与离子交换”相结合的组合工艺，达到“高度浓缩和深度净化”目的。课题将深入研究后处理高盐低放废液水化学环境中Sr、Tc、Cs、U、Np、Pu和Am等典型核素的赋存形态；极低浓度下核素在不同处理过程中的表界面化学行为与去除机理；优化组合工艺中各技术单元之间的衔接机制，实现工艺的稳定运行。通过研究，获得新工艺与新材料，为我国高盐低放放射性废物管理提供新的思路和依据

高盐低放废液处理一直是制约核工业放射性废物管理的难题，相应的处理技术需在高盐背景影响下对极痕量的核素具有高选择性和去污因子，使最终产生的放射性浓缩液或固相废物的体积最小。本课题全面研究了废液中主要核素的赋存形态，以及核素在吸附、膜分离、沉淀、絮凝等过程中的界面行为与去除机理。研究中，选择典型核电厂、乏燃料后处理、核设施退役以及铀燃料回收工艺产生的高盐低放废液，获得了典型核设施源项中Sr、Tc、Cs、Ag、Co、U、Np、Pu、Am等形态分布规律。研究了疏水膜对核素的去污效果，完成了基膜优化及扩大规模制造，采用等离子体对基膜进行表面疏水改性，利用压驱膜与疏水膜结合，优化了膜蒸馏运行条件。研制出对典型核素具有高选择性的无机吸附材料，优选出与无机吸附材料具有互补性的树脂，剖析了核素的吸附类型与吸附机理。通过本项目的研究，形成高盐低放废液处理的技术路线：a）吸附组合工艺，根据源项优化吸附剂与树脂的匹配，适于处理非连续产生、分散式废液；b）膜技术组合工艺，适于处理核素种类复杂、连续产生的废液，并通过核心膜材料配置，分别适合于处理强电解质含量高、弱电解质含量高以及放射性核素均为二价/高价的废液。通过研究，获得了核心关键材料，包括2款铯吸附剂、1款多核素吸附剂、2款银吸附剂、1款碘吸附剂、1款疏水性膜材料，4种压驱膜改性方法。疏水基膜完成半工业规模制备，多核素吸附剂和铯吸附剂完成工业规模制备，铯吸附剂产品已经为我国核设施供货。随着研究工作的持续深入，有望形成系列化的选择性核素吸附材料与膜分离材料，全面走向产业化应用，服务于核电厂、核设施退役等重大技术需求。