Colloids are positively or negatively charged, and colloid suspensions are polydispersed in natural systems. In this work, we analytically investigated the diffusion in the binary suspension system of charged spherical colloidal particles. The ratio of the diffusion coefficient of a charged colloidal particle in the binary system calculated by Langevin equation to that of a non-charged colloidal particle in the free medium calculated by Stokes-Einstein relation was evaluated. The dependency of the ratio on the charge, diameter and molar fractionation of the colloidal particle was discussed. The ratio was found to be less than unity. This means that the diffusion of a charged colloidal particle is slowed down through the friction induced on the colloidal particle by the electrostatic interaction. It was found that the ratio does not depend on the charge and diamter when the molar fractionation of the charged colloidal particle is large, but that the ratio decreases as the charge and diamter of the charged colloidal particle decreases when the molar fractionation is small.

View full abstract

  Measurements of Raman spectra of U(VI) ions loaded silver and silver oxide colloidal particles have been carried out for wide range of pH of the aqueous suspension. It was observed that Raman active symmetric stretching frequency of UO₂²⁺ ion shifts to smaller wavenumber when adsorbed onto silver colloidal particle, and that the shift depends on pH of the suspension. This observation discounts the case that all U(VI) ligands are liberated following the adsorption onto silver colloidal particle.
  The spectra of U(VI) ions loaded silver and silver oxide colloidal particles have been compared, and the difference between the two spectra was explained as the difference of the forms of their adsorption.

View full abstract

  The DUPIC (Direct Use of spent PWR fuel In CANDU) fuel cycle is an advanced nuclear fuel cycle option, an alternative to the once-through fuel cycle, proposed in the early 1990's by Korea. It has the benefits of not only saving natural uranium but also substantially reducing the amount of spent fuel because of its synergetic effect expectable from burning PWR spent fuel again in CANDU reactor by direct fuel refabrication without separation of pure plutonium. In the present study, evaluations were made for the DUPIC fuel cycle, compared to the once-through cycle, about several issues such as a fabrication process of the DUPIC fuel, secondary radioactive wastes generated, mass flows, decay characteristics of the DUPIC spent fuel, and resource savings and environmental benefits. Impacts of three scenarios of DUPIC fuel cycle were evaluated when these are applied to Korea, compared to the once-through cycle, in reducing the amount of required natural uranium and spent fuel waste produced in Korea, based on the nuclear power capacity projected until 2030. Then, the optimized fuel cycle strategy in Korea was proposed from the view point of the optimization for the mass balance of DUPIC fuel cycle.

View full abstract

  In order to establish the method of assessment for barrier function for cementitious materials in radio-active wastes disposal, in this report, barrier function should be separated into physical barrier function and chemical barrier function. This report presents long term permeability at concrete structure and low level pH cement constructed by author.

View full abstract

  The adsorption behavior of Cs⁺ onto granite was investigated. The distribution coefficient (K_d) of Cs⁺ onto granite was determined in the solution of which pH was ranged from 2.3 to 10.9 and ionic strength was set at 10^-2 and 10^-1. It is found that the K_d values for granite were larger than those for quartz, and the K_d values were found to increase with increasing pH and with decreasing ionic strength. The obtained data were successfully analyzed by an electrical double layer model and the optimum parameter values of the double layer electrostatics and adsorption reactions were obtained. The selective adsorption behavior of Cs⁺ onto the mineral components was discussed, and Cs⁺ were considered to be mainly adsorbed onto feldspars in the granite.

View full abstract

  It is important to evaluate sorption ability of cementitious materials to enclose radionuclides therein in waste repository. The cementitious material will be neutralized by interaction with CO₂ in air and HCO₃ in groundwater and this neutralization is supposed to have an effect on the sorption ability of the materials. Therefore, it is necessary to clarify this effect of degraded cement by neutralization.
  The behaviors of ²³⁹Pu(IV) and ²³⁷Np(V) in a highly alkaline groundwater solution contacting with cement and also their sorption on degraded neutralized cement paste were studied by batch method.
  It was found that K_d values of ²³⁷Np(V) or ²³⁹Pu(IV) on non-neutralized cement were as large as over 10⁵ ml/g. The values gradually decreased with decreasing pH of the solution following neutralization of the cement paste. At pH 10, the K_d values of ²³⁹Pu(IV) and ²³⁷Np(V) remained in the order of 10⁴ and 10³ ml/g, respectively, and chemical barrier ability was still large. Chemical behaviors of ²³⁷Np(V) were also studied by spectroscopic method and particle size measurement. A shift of absorption peak was found and colloidal ²³⁷Np(V) was observed to be formed in solution contacting with cement. Colloidal ²³⁷Np(V) would be filtrated by cementitious materials in a repository.
  For the performance assessment of artificial barriers, it is necessary to take into account that chemical atmosphere in near field is affected by neutralization of cementitious materials, which will occur over a very long period.

View full abstract

  The US DOE'sHanford Site is the central facilities where the development of nuclear weapons had been made during the World War II and throughout the Cold War years thereafter.
  There are 177 tanks to store the wastes produced from the Pu production facilities after extracting Pu from the irradiated U fuels. The constituents of the wastes are very complicated and there still remain highly radioactive nuclides. Not only liquid, but also sludges and solid wastes are remained within the tanks.
  This is a brief summary on history and experiences at the Hanford Pu production facilities in general. In order to proceed the Hanford Tank Cleanup Operations, DOE has made the decision to privatize the Project Hanford Management Contract to Fluor Daniel and Tank Waste Remediation System to BNFL Inc. and Lockheed Martin in autumn 1996.

View full abstract

  An operational phase of Äspö Hard Rock Laboratory international project was started in 1995. Two different types of in situ experiments, i.e., experiments for description of the barrier function of host rock and for demonstration of the function of important parts of a repository system, are being carried out and/or planned. The former consists of groundwater flow and tracer migration experiments in a single fracture called TRUE, redox experiment in the detailed scale called REX, arid in situ column experiment by CHEMLAB called RNR. The latter consists of backfill and plug test, long term performance tests of bentonite as buffer material, and construction of prototype repository. This paper describes the status and the research plans of the Äspö HRL project during the operational phase and CRIEPI's contribution to the project as well.

View full abstract