Waste Package System Research Articles

Nuclear waste viewed in a new light; a synchrotron study of uranium encapsulated in grout.

How do you characterise the contents of a sealed nuclear waste package without breaking it open? This question is important when the contained corrosion products are potentially reactive with air and radioactive. Synchrotron X-rays have been used to perform micro-scale in-situ observation and characterisation of uranium encapsulated in grout; a simulation for a typical intermediate level waste storage packet. X-ray tomography and X-ray powder diffraction generated both qualitative and quantitative data from a grout-encapsulated uranium sample before, and after, deliberately constrained H2 corrosion. Tomographic reconstructions provided a means of assessing the extent, rates and character of the corrosion reactions by comparing the relative densities between the materials and the volume of reaction products. The oxidation of uranium in grout was found to follow the anoxic U+H2O oxidation regime, and the pore network within the grout was observed to influence the growth of uranium hydride sites across the metal surface. Powder diffraction analysis identified the corrosion products as UO2 and UH3, and permitted measurement of corrosion-induced strain. Together, X-ray tomography and diffraction provide means of accurately determining the types and extent of uranium corrosion occurring, thereby offering a future tool for isolating and studying the reactions occurring in real full-scale waste package systems.

緩衝材付き廃棄物パッケージの特性試験

A high level waste (HLW) package system with buffer material was designed considering a long-term storage system of the packaged waste in a repository.For the γ-ray shielding, the buffer material of high density was prepared using bentonite powder and heavy sand of zircon. The density of the dry buffer material was about 3g/cm3.Heater test was carried out to study thermal characteristics of this buffer material and the waste package system. The buffer material was heated by an electric heater which was set at the center of the package to simulate the decay heat generation of HLW. The thermal conductivity of the buffer material was calculated from temperature distribution in the package. It was found that the measured thermal conductivity of the buffer material vary with the electric power of the heater and the radial distance from the heater surface. The thermal conductivity was in the range of 0.720-1.070W/m·K at the electric power of the heater of 0.3kW, and it was in the range of 0.685-1.410W/m·K at 0.7kW. This is attributed to the water migration in the buffer material, caused by the heat flux.The changes of the swelling pressure and the water uptake rate in the buffer material was measured to study swelling pressure, water uptake rate and water diffusion coefficient of the buffer material by immersing double distilled water from the outside of the package. Consequently the water diffusion coefficient in the buffer material was calculated to be 2.5×10-10mm2/s.

The Role of Laboratory Analog Experiments in Assessing the Performance of Waste Package Materials

ABSTRACTThere is an immediate need to begin to validate models that can be used for assessing the performance of waste package materials in an unsaturated repository environment. This paper examines available testing information and testing approaches that could support validation of models for engineering barrier system (EBS) radionuclide release. The content is presented in the context of the general methodology that has been proposed for validating performance assessment models [1], Available experimental observations are used to test some of the EBS release rate modeling premises. These observations include evidence of fluid film formation on waste glass surfaces in isothermal humid environments, accelerated waste glass reaction rates under repository service conditions of large glass surface area to water volume ratio, and mobilization of radionuclides as solutes and colloids. It is concluded that some important modeling premises may not be consistent with available experimental Information. However, it is also concluded that future laboratory testing, which simulates the Integrated waste package system (i.e., laboratory analog testing), is needed to evaluate the significance of these Inconsistencies and to test the system level models. A small-scale apparatus which was developed and tested to examine the feasibility of laboratory analog testing for the unsaturated Yucca Mountain repository environment is described.