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High-strength and ultra low-permeability concrete (HSULPC) is a strong candidate for a radioactive waste package containing transuranic radionuclides (TRU waste) for geological disposal. Knowledge of the time-dependent fracturing of HSULPC and surrounding rock mass is essential to assess the long-term stability of such underground repositories. We have measured crack velocity in andesite and HSULPC both in air and water to examine subcritical crack growth by the Double-Torsion method. In air, the crack velocity in andesite increased when the temperature and relative humidity increased. On the other hand, the temperature and relative humidity had little effect on the crack velocity in HSULPC in air. In water, the crack velocity increased when the temperature was higher for both andesite and HSULPC. Using these experimental results, the longterm strength was estimated. It was shown that the long-term strength of HSULPC was higher than that of andesite. In air, the long-term strength for andesite was affected by the temperature and relative humidity. The long-term strength for andesite decreased when the temperature or relative humidity increased. For HSULPC, the change of the long-term strength with varying temperature or relative humidity was smaller than andesite in air. In water, the long-term strength for both materials decreased with increasing the temperature. Comparing the longterm strength of andesite and HSULPC at the same environmental conditions, it was recognized that the decrease of the long-term strength of HSULPC is smaller than that of andesite. The long-term strength in water was smaller than that in air for both materials.

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Synthesis of stable oxy-and oxyhydroxyapatites [(Ca,M)-Ap]was attempted by substitution of Caz+ with M3+ (M = Al, Y) assuming the composition Ca10--xMx(P04)6 (OH),-,O,. Yttrium-calcium oxyhydroxyapatite was successfully obtained. Its structure was analyzed and confirmed by X-ray diffraction and infrared spectroscopy. Dielectric dispersion and absorption were not so distinct in (Ca,Y)-Ap as in hydroxyapatite (Ca-Ap). The ac electrical conductivity of (Ca,o-,,Y,)-Ap was found to decrease with increasing x. These results are discussed in terms of a proposed charge transport mechanism.

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