Repository geologic design

The final design of a geologic repository will employ multi-... 

Risk Assessment. The overall compilation and assessment of the factors that must be considered in designing and siting geologic repositories is pulled together in a general discipline of risk assessment. Risk assessment calculations develop both generic and site specific models and calculate the potential transport times as a result of various phenomena. Calculations are being... 

The classical Purex process was designed to produce nearly pure uranium and plutonium. The Chemical Engineering Division of Argonne National Laboratory has demonstrated UREX+, an advanced aqueous process with five extraction trains that split commercial reactor spent fuel into five streams 1) a nearly pure uranium stream (95.5% of the heavy metal in the spent fuel) 2) technetium sent to transmutation (0.08 /o) 3) Pu/Np converted to MOX fuel for LWR fuel and Am/Cm for transmutation or fast-flux reactor fuel (0.962 /o) 4) Cs/Sb decay heat producers sent to interim decay storage (0.017 /o) and 5) a mixed fission product stream (3.44 /o) composed of gases and solids incorporated into a waste form for geological repository disposal.f The percentages shown are computed from Table 1. 

Use of geologic media for waste isolation involves an action phase and a prediction phase. The action phase is concerned with site selection, waste repository design, waste form selection, etc. i.e., all activities related to selecting a repository site and putting it into use. 

Engineered barriers constitute a basic element in the conceptual design of repositories for radioactive waste in deep geological media. For the safety performance of a repository, it is very important to understand, on the one hand, individual processes in the barrier and the host medium in the near-field zone and the coupled mechanism, on the other hand, to parameterise all physical variables for the long-term modelling. 

Japan Nuclear Cycle Development Institute (JNC) has already developed the coupled thermo -hydro and mechanical (T-H-M) model and has initiated a research on the coupled T-H-M-C processes to predict the chemical evolution of buffer material and porewater chemistry, and the chemical effects on other (thermal, hydraulic and mechanical) processes. In this research, numerical experiment system for the coupled T-H-M-C processes is developed in order to predict the longterm evolution of the near-field (engineered barriers and surrounding host rock) for various repository designs and geological environments. 

JNC 2000. Second progress report on research and development for the geological disposal of HLW in Japan, Supporting Report 2, Repository Design and Engineering Technology. JNC TN1410 2000-003. 

The data from field studies is largely confirmed by the performance assessments of proposed nuclear waste r sitories. The intrusion scenario is calculated to have a lower risk than the undisturbed natural leach and migration scenario. The latter qualitatively agrees with the Oklo data and indicates no unacceptable risks result from a carefully chosen and designed geologic repository in which the nuclear wastes are enq>laced with appropriate packaging. 

The disposal of actinides requires effective containment of waste generated by the nuclear fuel cycle. Because actinides (e.g., Pu and Np) are long lived, they have a major impact on risk assessments of geologic repositories [46, 47]. Current research concerns new specific matrices designed for the immobilization of these long-lived radio nuclides. 

An active heat transfer system is another vital system in a nuclear reactor even though natural circulation has in some circumstances very important effect in safety. In a nuclear waste repository the heat production is fairly low and decreasing slowly with time. No active heat transfer systems are installed in waste repositories. Waste matrixes must be designed and located with respect to geological enviroiunent so that the temperature of waste and environment stays within specified limits. 

Another veiy essential design constraint is that repositories must be tailored to the local environment. Geological formations cannot be standardized This does not, however, mean that all the necessary research and development work must be done at each planned repository site. The site specific data is anyway only available from site-specific studies. 

The adequacy of the design parameters of repositories cannot be tested in real operational conditions and as far as tests are carried out close to operational conditions they are timely limited. The verification analyses for checking the compliance are based on limited confirmation of the validity of calculation models as well as physical, chemical, geological, and other parameters. 

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