[en] Performance assessment has many applications in the field of radioactive waste management, none more important than demonstrating the suitability of a particular repository system for waste disposal. The role of performance assessment in radioactive waste disposal is discussed with reference to assessments performed in civilian waste management programmes. The process is, however, relevant, and may be applied directly to the disposal of defence-related wastes. When used in an open and transparent manner, performance assessment is a powerful methodology not only for convincing the authorities of the safety of a disposal concept, but also for gaining the wider acceptance of the general public for repository siting. 26 refs

[en] The management of radioactive wastes has become a major concern particularly with regard to the release of radioactive material to the environment and possible risks of contamination. The development of rational and acceptable options for radioactive waste disposal requires a clear understanding of radiators protection objectives and their application in planning, regulation and licensing. Considerable progress has been made over the past three decades within many countries utilising nuclear power to develop strategies for the management of nuclear wastes. All wastes should be managed in such a way that high standards of conditioning are maintained and that potential hazards originating from their disposal are reduced to levels that are as low as reasonable and well below admissible levels. However, deficiencies are evident in some areas of nuclear weapon fabrication. The nuclear fuel cycle is associated in the military weapon fabrication sector as well as in the civilian energy production field with two rather similar types of risk: 1. the risk due to the operation of the nuclear reactors and the appertaining fuel facilities, and 2. the risk contribution originating from the generation of radioactive wastes. The difference between these two categories of risk is that the first one has only a short time factor associated with it, since the lifetime of the plants is relatively short and drops to zero after plant shutdown. The second category is, more or less, a permanent kind of risk which will be inherited by future generations. Actual health effects of waste on people and populations, particularly over long periods of time, are not necessarily related to the level of radioactivity. If intensely radioactive waste is effectively isolated, then the radiation dose it causes can be much less than that accumulating from widely-dispersed but low-activity waste, particularly if this includes long-lived radioisotopes. By far the most important producers of nuclear wastes are nuclear power plants and their supporting fuel cycle facilities. Compared to nuclear power and reprocessing plants, only very small waste contributions come from research establishments, industry and medical applications. An additional source of radioactive waste arises from nuclear weapons production and related testing activities. The problems associated with disarmament requirements, however, are not dealt with in this paper. 10 refs

[en] The application of natural materials to the isolation of radioactive waste and spent nuclear fuel is being assessed, together with possible isolation technologies. The operational requirements for such materials are identified and a proposal for an inter-regional ecological and technological project is discussed. 39 refs

[en] The total volume of vitrified high-level waste (HLW) and of intermediate-level wastes containing significant amounts of long-lived alpha emitters, generated over the lifetime of Kozloduy Nuclear Power Plant (NPP), is estimated to be about 2,100 m³. Selection of a suitable formation to host a deep HLW repository in Bulgaria presents serious difficulties owing to the small area of the country, its complex geology, and the expected negative reaction of the local population. After a preliminary categorization of the Bulgarian territory, more than 40 areas were identified initially as potential disposal sites. This number was reduced to 20 using a screening method. A large portion of the selected regions comprises thick (up to 1,000 m) Lower Cretaceous marls, some at a distance of 60-80 km to the south of Kozloduy NPP. There are no active faults in the vicinity of the chosen areas and the seismicity is of degree VII on the MSK scale. Several regions in south-east Bulgaria containing magmatic and metamorphic rocks, have been suggested as prospective sites for deep HLW disposal: the Byala Reka structure of Precambrian highly metamorphic gneisses, the Avren and Zalti Chal areas in meta-ultrabasites, the Sakar Palaeozoic granite pluton, and two areas in volcanogenic-sedimentary rocks. The possibility of subsea geological disposal has also been discussed. At present, a programme is being developed for more detailed investigations of the suitable geological formations. 20 refs

[en] This paper is devoted to the treatment of pre-stack migration of seismic data for hi-fi stationary systems created by 2D arrays of sources and geophones, via diffraction and focusing transformations. Such an approach is based on a diffraction model that treats a real geological medium as the sum of two components: a smooth velocity model with ordered travel times, with diffraction objects placed within it, generating strong scattered waves. 7 refs

[en] The migration and subsequent release of radionuclides from a repository to the accessible environment is an important part of the assessment of natural barrier systems. The speciation of key radionuclides in natural waters as well as the solubility limits for the principal solid phases are prime problems for physico-chemical modelling. A simple and effective method for calculating equilibrium actinide concentrations at the interface between solid phases and solution was achieved using the dissolution Of PuO₂ as an example. Complex formation processes were taken into account using the Froneaus function, which reflects the extent of complexing and depends on ligand concentrations. Possible increases in Pu concentrations of 6 to 8 orders of magnitude were predicted for groundwaters of Boettstein granites and Hanford basalts, respectively, owing to plutonium-fluoride complexing. The increasing influence of oxalate complexes on the dissolution of Pu-containing solid phases can be expected at oxalate concentrations > 10⁶ M. 24 refs

[en] Commercial electric power generation, nuclear weapons production, the operation of naval reactors, and research and development activities produce spent nuclear fuel and high-level radioactive waste. Spent nuclear fuel and high-level radioactive waste have been accumulating at commercial reactor sites and storage facilities across the country since 1957. Spent nuclear fuel and high-level radioactive waste have been accumulating at sites now managed by U.S. Department of Energy (DOE) since the mid-1940s. The DOE has the statutory obligation to dispose of these wastes. The U.S. has studied methods for the safe storage and disposal of radioactive waste for more than 40 years. Many organizations and government agencies have participated in these studies. In the 1950s, the U.S. Atomic Energy Commission requested the National Academy of Sciences to evaluate options for land disposal of radioactive waste. The U.S. Atomic Energy Commission and its successor agencies, the Energy Research and Development Administration and the DOE, continued to analyze radioactive waste management options throughout the 1960s and 1970s. In 1979, an Interagency Review Group that included representatives of 14 federal government entities provided findings and recommendations to the President. After analyzing a range of options, disposal in a geologic repository emerged as the preferred long-term environmental solution. This consensus is reflected in the Nuclear Waste Policy Act of 1982 (NWPA). The NWPA and related statutes established the framework for addressing the issues of radioactive waste disposal and designated the roles and responsibilities of the federal government and the owners and generators of the waste

[en] At the Hanford Site in Richland, Washington, the path to site cleanup involves vitrification of the majority of the wastes that currently reside in large underground tanks. A Joule-heated glass melter is the equipment of choice for vitrifying the high-level fraction of these wastes. Even though this technology has general national and international acceptance, opportunities may exist to improve or change the technology to reduce the enormous cost of accomplishing the mission of site cleanup. Consequently, the U.S. Department of Energy requested the staff of the Tanks Focus Area to review immobilization technologies, waste forms, and modifications to requirements for solidification of the high-level waste fraction at Hanford to determine what aspects could affect cost reductions with reasonable long-term risk. The results of this study are summarized in this report

[en] This paper describes the program to stabilize nuclear materials, consistent with the Department of Energy Office of Environmental Management (EM) plan, Accelerating Cleanup: Paths to Closure. The program is managed by the Plutonium Stabilization and Disposition Focus Area, which defines and manages technology development programs to stabilize nuclear materials and assure their subsequent safe storage and final disposition. The scope of the Plutonium Stabilization and Disposition Focus Area (PFA) activities includes non-weapons plutonium materials, special isotopes, and other fissile materials. The PFA provides solutions to site-specific and complex wide technology issues associated with plutonium remediation, stabilization, and preparation for disposition. Our paper describes an important programmatic function of the Department of Energy nuclear materials stabilization program, including the tie-in of policy to research needs and funding for the nuclear materials disposition area. The PFA uses a rigorous systems engineering determination of technology needs and gaps, under the guidance of a Technical Advisory Panel, consisting of complex-wide experts. The Research and Development planning provides an example for other waste areas and should be of interest to Research and Development managers. The materials disposition maps developed by the PFA and described in this paper provide an evaluation of research needs, data gaps and subsequent guidance for the development of technologies for nuclear materials disposition. This paper also addresses the PFA prioritization methodology and its ability to forecast actual time to implementation

[en] The Mixed Waste Focus Area (MWFA) in conjunction with the Characterization Monitoring and Sensor Technology (CMST) crosscut program identified the need to objectively evaluate the capability of nondestructive waste assay (NDA) technologies. This was done because of a general lack of NDA technology performance data with respect to a representative cross section of waste form configurations comprising the Department of Energy (DOE) contact-handled alpha contaminated [e.g., transuranic (TRU) waste]. The overall objective of the Capability Evaluation Project (CEP) was to establish a known and unbiased NDA data and information base that can be used to support end-user decisions with regards to technology system selection and to support technology development organizations in identifying technology system deficiencies. The primary performance parameters evaluated in the CEP were measurement bias and relative precision. The performance of a given NDA technology is a direct function of the attributes represented by the waste matrix configuration. Such attributes include matrix density, matrix elemental composition, radionuclidic composition, radionuclide mass loading, and the spatial variation of these components. Analyzing the manner in which bias and precision vary as a function of test sample attribute and NDA technology provides a foundation for deriving performance capability and limitation statements and determines which waste matrix attributes, or combinations of attributes, are compatible or incompatible with existing technologies. The CEP achieved the stated end-user objective. The data indicate that the nondestructive waste assay systems evaluated have a definite capability to perform assay of contact-handled TRU waste packaged in 55-gallon drums. There is, however, a performance envelope where this capability exists, an area near the envelope boundaries where it is questionable, and a realm outside the envelope where the technologies do not perform. Therefore, the end user must be aware of this envelope and ensure the appropriate technology is selected. This program provides the end user with waste type specific performance data to assist in the assessment and selection of a given waste NDA technology. Additionally, the CEP afforded the private sector participants the opportunity to evaluate system performance using National Institute of Standards and Technology traceable radioactive significant enhancements to their respective systems and supported all participants in attaining DOE-CAO certification. Ultimately, the DOE end users will benefit from these enhancements