202-RWD : Use of concrete in radioactive waste disposal facilities
Technical Committee 202-RWD
The design and construction of many of the facilities and structures for long-term storage of radioactive waste materials employ reinforced concrete. The reinforced concrete is used for many purposes including support, containment, and environmental protection. Facilities that rely on concrete range from surface structures, to shallow subsurface vaults, to deep underground repositories. The concrete structures in these facilities have increased requirements relative to conventional civil engineering applications in that the deteriorating influences, in addition to potentially being more severe, can also result from the materials they contain (e.g., elevated temperature, irradiation, and radionuclides from waste forms) as well as external influences (e.g., chemical and physical attack). Also, the desired service life of these structures, depending on the application, may range from tens to hundreds or even thousands of years. During this time the reinforced concrete is to provide both physical and chemical barriers to isolate the waste from man's environment. Although a number of deteriorating influences can affect these structures, corrosion of embedded steel, leaching, elevated temperature, and irradiation (depending of the application) probably represent the greatest initial threats. Over the long term, leaching and cracking have increased importance as water will provide the transport medium for radionuclides should the other engineered barriers fail. In nearly all chemical and physical processes influencing the durability of concrete structures, dominant factors involved include transport mechanisms within the pores and cracks, and the presence of a fluid. Concrete permeability therefore is of significant importance relative to the long-term durability of radioactive waste facilities. Concrete permeability will vary according to such things as the proportions of constituents, degree of cement hydration, cement fineness, aggregate gradation, and moisture content. One of the most important factors affecting ionic transport through concrete is the presence of cracks. Cracking not only controls the quantity of ions transported, but can also control whether there will be any convective transport. Factors that contribute to increases in concrete permeability or cracking therefore are of importance to the durability of the radioactive waste management facilities.
Terms of reference
Activities will be conducted over a four to five year period. Input will be from various international researchers working in the field (e.g., academia, industry, practice, and international organizations). Committee members will be recruited from contacts that the acting TC Chairman and Secretary (to be determined) have developed as a result of their participation in activities that directly address the subject matter as well as programs related to aging management of concrete structures in nuclear power plants.
Detailed working programme
Detection and assessment of the magnitude and rate of occurrence of any environmental factor-related degradation are key factors in maintaining the capability of these structures to meet their operational requirements. As the knowledge base for modern concretes, such as would be used in fabrication of radioactive waste disposal facilities, is relatively short compared to the desired minimum service life (e.g., 100 versus 500 or more years), additional input is required in several areas to help provide the continued assurance that these structures will continue to meet their operational requirements throughout their service life. A status report on use of concrete structures in nuclear power plant fuel-cycle facilities has been prepared by the Nuclear Energy Agency of the Organization for Economic Cooperation and Development (NEA/OECD), "Report of the Task Group Reviewing Activities in the Area of Ageing of Concrete Structures Used to Construct Nuclear Power Plant Fuel Cycle Facilities [NEA/CSNI/R(2002)14, July 2002]. Several areas were identified in this report where additional information is required: * Functional and performance requirements for concrete structures used in radioactive waste disposal facilities; * Degradation mechanisms and their effects, particularly where the mechanisms can operate over extended periods of time, or synergistic effects are present, and improved characterization of service environments; * Instrumentation and monitoring methods for use in performance assessments; * Condition assessment approaches and criteria for acceptance; * Service life models, development and validation, that take into account reliability methods and updating as additional data become available (Bayesian); * Repair techniques to extend the performance period should premature degradation occur; * Decommissioning, procedures and assessment criteria for "safestor" and entombment approaches; and * Codes and standards specific to radioactive and hazardous waste facilities. An international workshop is proposed for 2004. Subcommittees will be established to adresse the above topics with the results utilized to prépare a state-of-the-art report. Finally an international conference will be sponsored in 2007 and results presented in a final report to be finalized in 2008.
The technical committee would build on prior related work conducted under RILEM committees, TC-104-DDC, "Damage Classification of Concrete Structures," and TC 160-MLN, "Life Prediction of Concrete Structures in Nuclear Power Plants;" would involve interdisciplinary fields that are linked with the "core business" of RILEM ; and would utilize developments of several existing RILEM committees. Work under this committee would also be a logical follow-on to activities sponsored by international organizations such as the Nuclear Energy Agency of the Organization for Economic Cooperation and Development, International Atomic Energy Agency, and American Concrete Institute Committee 349, "Nuclear Concrete Structures." Key input will be provided by researchers selected from countries that are major participants in the design, construction, operation, and regulation of facilities associated with storage of radioactive waste.
Products of this TC are expected to be: recommendations on testing procedures, guidelines and standards for helping assure continued safe operation of concrete structures used in radioactive waste disposal facilities; a state-of-the-art report on current practices associated with use of concrete in radioactive waste disposal facilities; an international workshop on experience and practices associated with use of concrete in radioactive waste disposal facilities; an international conference; and a final report presenting TC recommendations
Group of users
This TC will address a broad spectrum of activities related to concrete technology (e.g., material development, performance and degradation, monitoring, condition assessment, service life prediction, repair, and decommissioning). As a result, products developed under this TC will be of interest to academia, testing laboratories, architectural/engineering firms, as well as regulatory agencies.
Specific use of the results
Results of this TC will have application in the management of aging of concrete and concrete structures contained as a part of a radioactive waste disposal facility. Application of the results of this TC can potentially result in reduced costs through use of improved materials and design methods, increased understanding of degradation parameters, and guidance on performance monitoring, while effecting improved safety and reliability.