Water penetration and chemical degradation phenomena of long-term confinement concrete package to reduce the dose rate of C-14 released from hulls and end-pieces were discussed. Long-term confinement concrete package restrains the release of the radionuclides by using the high strength and ultra low permeability concrete (HSULPC) which blocks the contact between the wastes and groundwater. In the previous work, the authors had estimated the water-penetration depth to HSULPC as 14cm for 60000 years by the "water penetration and chemical degradation coupled calculation". This result shows the possibility of the reduction of the influences from C-14 by using HSULPC without placing joints and/or cracks. However, the verification by the long term experiment is necessary to show the conservativeness of the evaluated value.
  To obtain such long term data, the authors carried out the water penetration test in the 1MPa and 10MPa water and the leaching experiment to obtain the chemical degradation of HSULPC. The observed progress of the water penetration was lower than that evaluated by Murata's law and micro pore structure didn't change by the 3 years water penetration test. The depth of the Ca dissolution observed by EPMA after 6 months leaching was almost the same as the value calculated from the increase of weight. From these results, the authors reasoned that the evaluation by the "water penetration and chemical degradation coupled calculation" shows the conservative value of the water penetration depth, because the assumption of the calculation was relatively conservative than that of the calculation by Murata's law. presented.

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  The long-term integrity of TRU waste package, with a titanium alloy for the outer corrosion resistance layer and carbon steel for the inner structural vessel, has been evaluated.
  The target confinement period is settled at 60,000 years in this study (i.e., 10 times of half-life). So the outer corrosion resistance layer with titanium (Ti-Pd alloy) is developed through focus on the high corrosion resistance of Ti alloy as a technology that has long-term confinement.
  In investigation about integrity of its passive film, the thickness of corrosion layer of 60,000 years is calculated by building an empirical formula between temperature and corrosion current density, considering the results of constant voltage examination in the TRU waste repository assumed environment. About crevice corrosion, its occurrence conditions is investigated in the TRU waste repository assumed environment, then, Ti.Gr-17 is selected as candidate material of the corrosion resistance layer. In investigation about SCC in Ti alloy, using the models of growth of hydride-layer, the thickness of hydride-layer after 60,000 years is estimated by the results of constant currents tests. Then, the hydride-layer of this thickness is confirmed not to generate cracks, in consideration of destructive critical hydride cracking thickness and the models of crack propagation. The knowledge that the process of generation of hydrogenated layers changes with differences in acceleration conditions (i.e., current density) is obtained. So we must confirm the adequacy of this model by the examination with natural condition.

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  For the geological disposal of the high-level radioactive waste, it is important to develop the model to evaluate the long-term stability of the engineered barrier system. The increase in the reliability of the evaluation model may reduce the uncertainty of the safety assessment. In this study, the density distribution of the bentonite buffer extruded into the artificial fractures was measured by using a X-ray CT scanner to promote understanding of the extrusion phenomenon of the bentonite into fractures.

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