An overview of research activities on cementitious materials for radioactive waste management

Abstract

An overview is given on research activities on cementitious materials for radioactive waste management systems based on the IAEA Coordinated Research Project (CRP) held in 2007-2010. It has been joined by 26 research organizations from 22 countries which shared their research and practical activities on use of cementitious materials for various barrier purposes. The CRP has initially formulated the research topics considered within four specific streams: A) Conventional cementitious systems; B) Novel cementitious materials and technologies; C) Testing and waste acceptance criteria; and D) Modelling long term behaviour.The CRP has analysed both barrier functions and interactions envisaged between various components with focus on predisposal stage of waste management. Cementation processes have achieved a high degree of acceptance and many processes are now regarded as technically mature. A large body of information is currently available on proven waste conditioning technologies although novel approaches are continuing to be devised.Most of the existing technologies have been developed for conditioning of large amounts of operational radioactive waste from nuclear power plants and other nuclear fuel cycle facilities. However new waste streams including those resulting from legacy and decommissioning activities required improved material performance and technologies.The most important outcome of CRP was the exchange of information and research co-operation between different institutions and has contributed towards general enhancement of safety by improving waste management practices and their efficiency. The paper presents the most important results and trends revealed by CRP participants. The research contributions of participating organizations will be published as country contributions in a forthcoming IAEA technical publication.

An Assessment of Initial Leaching Characteristics of Alkali-Borosilicate Glasses for Nuclear Waste Immobilization

“…Glass leaching mechanisms were evaluated based on the analysis of the experimental data to a collective model that represents the cumulative leach fraction (CLF i ) of the structural elements, modifiers, and waste oxides as superimposed leaching processes that include a first-order reaction exchange between the leaching solution and bounded element on the matrix or the formed colloides, bulk diffusion of elements throughout the matrix, congruent dissolution, and instantaneous release of loosely bounded element from the surface [6,7,9,10,11,12,13,14,36]:CLFi=QOi(1−e−Kinormalt)+(SV)(2Dinormaltπ+Uinormalt)+normalC, where Q oi is the initial exchangeable fraction of element on the surface of the waste form, K i is the rate constant for the exchange reaction (h −1 ), U i is the glass network dissolution rate (m·h −1 ), and D i is the effective diffusion coefficient of the element (m 2 ·h −1 ) .This equation is used in conditions when saturation effects are not important, such as the initial stage of glass dissolution.…”

Introductory Chapter: Development of Assessment Models to Support Pollution Preventive and Control Decisions

“…Figure 2 illustrates the iterative nature of the modeling process and its relation with the system-specific data, in which the developed model complexity or simplicity is determined based on the stage of development of the studied system and the availability of system-specific data [11,12]. The developed model, in each iterative stage, is produced from multi-step process that includes the development of conceptual and computational models (mathematical model and the tool that solves the mathematical model) [5][6][7][8][9].…”

“…Generally, the modeling efforts are divided into research and assessment models. Research (process) models use laboratory and field experiments to identify FEPs that affect a subsystem or more, whereas assessment models link important processes (determined from research model) to predict the overall system performance [5,6]. Figure 1 illustrates the integration of research and assessment models, in which the studied subsystems are characterized and the factors that affect their behavior are identified experimentally.…”

“…Then models are used within the research efforts to interpret, extrapolate/interpolate, and optimize the collected data; the modeling results will be used to evaluate and rank the FEPs that affect the system. In assessment models, important FEPs are linked to identify the problem formulation and basic system description, and then conceptual and computational models are constructed, verified, and used [5][6][7][8][9][10][11]. For instance, the quantification of the effect of time on the pollutants migration in terrestrial, aquatic, and/or atmospheric subsystems is usually conducted by measuring the concentration of major pollutants at incremental time at different distances from the source.…”

Introductory Chapter: Introduction to Current Trends in Nuclear material Research and Technology

“…Nuclear Energy Agency (NEA) developed reports that summarize current and anticipated trends in NFC development within 20 years [5,6]. Tables 2 and 3 list these trends for front-and back-end NFC processes, respectively [3,[5][6][7][8][9][10][11][12][13][14][15]. Table 1.…”