The aqueous reprocessing is the current widespread method used in the nuclear fuel cycle and is evaluated as the main concept for the fast reactor (FR) MOX fuel reprocessing in FaCT (Fast Reactor Cycle Technology Development) Project, designated as one of the national critical technologies of Japan. On the other hand, the pyroprocess as a non-aqueous reprocessing, is oriented as a complementary concept for the FR metal fuel cycle.
In this paper, the author has introduced the pyroprocess development, highlighting the spent electrolyte treatment from the viewpoint of economical and environmental load reduction.
The pyroprocess possesses some inherent problems that have yet to be solved. The purification and recycling of the spent electrolyte as a regenerated medium by removing its fission products (FP) must be further investigated to reduce the volume of high-level radioactive waste (HLW) . Some FP elements dissolved in the medium are apt to remain in the spent electrolyte after recovering actinoid elements. To remove such FP, the zeolite sorption is applied as it is considered the most suitable method, but its concept should be modified in order to reduce the generating waste volume.
There are some alternative methods which use phosphates, among them three are presented here, i.e., the phosphates precipitation method developed by RIAR, Russia, the GRSS method using SAP by KAERI, Korea, and the phosphate conversion method by JAEA. In the phosphate conversion method, the iron phosphate glass (IPG) , which shows unique properties, is employed for FP separation and FP immobilization. From preliminary experiments, it found that the IPG could separate insoluble FP in the spent electrolyte when used as a filtration medium. In addition to that, when used as a sorbent, it could remove the soluble FP. The IPG is regarded as a potential effective material to treat FP.
It is necessary to further develop the spent electrolyte treatment method successively as this could contribute to the realization of the pyroprocess.

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The practical application of the rock cavern storage of liquefied fuels (such as natural gas, liquid hydrogen or dimethyl ether) requires stability analysis of the cavern in question with regard to thermal stress, and an understanding of thermophysical properties and mechanical properties of rock mass is essential for such analysis.
In our research, a linear expansion strain measurement test up to —170°C was first conducted using Kimachi sandstone (24.0% porosity) to study the relationship between the freezing of pore water and its expansion strain. Then a uniaxial compression test and indirect tensile test were conducted with wet sandstone cooled down below freezing point to ultralow temperatures to review the influence of the formation of pore ice on the strength of wet sandstone. The following findings were obtained.
When Kimachi sandstone is cooled down, frost swelling occurs twice, and therefore the linear expansion coefficient fluctuates over range of temperatures between 0 to —70°C. This may be because pores of two different sizes exist in Kimachi sandstone and the freezing temperature of the pore water differs depending on the pore size. The compressive strength and indirect tensile strength of the wet sandstone increase with the decrease in the specimen temperature. Two causes of this phenomenon may be identified. One is that an increase in pore ice that shares the load is the main cause of the phenomenon in temperatures down to —50°C where freezing of the pore water is almost completed. The other is that an increase in strength by volumetric shrinkage of the rock forming minerals and pore ice is the main cause in temperatures below —50°C.

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The purpose of this study is to clarify the mechanical properties of hydrothermally altered rocks found in northeastern Hokkaido, Japan, based on point load strength test results.
Rock specimens are hydrothermally altered soft and semi-hard rocks, including volcaniclastic rocks of the Upper Miocene Series. The modes of occurrence of these hydrothermally altered rocks were examined in the field, and the hydrothermal alteration minerals in the rocks were identified primarily by X-ray powder diffraction. The hydrothermal alteration zone can be divided into nine more specific zones on the basis of mineral assemblages of hydrothermally altered rocks. 1,523 rock specimens were collected for the axial point load strength test, whereas 1,869 rock samples for the irregular lump point load strength test. These came primarily from the earth's surface in ancient hydrothermal fields.
For rock specimens, the axial and irregular lump point load strength tests were performed using a laboratory testing machine with specimens under forced dry- and forced wet-states.
K-feldspar zone rocks had the largest axial and irregular lump point load strengths, followed by alunite-quartz zone rocks. Mixed-layer mineral zone and smectite zone rocks had the smallest. Illite zone and clinoptilolite zone rocks tend to be small.
Alunite-quartz zone rocks had the smallest point load strength decrease ratio. Mixed-layer mineral zone rocks, on the other hand, had the largest. Excess of 50 % at low point load strength decrease ratio of hydrothermal alteration zone rocks is related with surface water and ground water, suggesting possibility of landslides.
The point load strength test is very convenient and effective, because it can be done promptly using on-site and laboratory testing equipment for small rock specimens having various shapes taken from outcrops or floats.

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Knowledge of rock stress, such as initial stress, induced stress and stress change, is one of fundamental importance for designing and constructing rock structure, since the mechanical behavior of rock mass around it is affected by these stresses. In order to measure initial stress and induced stress, many methods have been suggested. On the other hand, there are a few methods for stress change around an opening under construction. Only stress in one direction in a plane perpendicular to a borehole axis is measured in most measurements of stress change. Furthermore, the instrument for the measurement has a rigidity which affects on measured results.
In this paper, a method for measurement of stress change is developed to monitor rock stress using a borehole. Two dimensional state of stress change within rock mass in a plane perpendicular to a borehole axis can be measured by this method. This method was named the Cross-sectional Borehole Deformation Method (CBDM) . Firstly, the theory of the CBDM is described, and the required specification of instrument for measurement is clarified by the theory of elasticity. Secondly, the prototype instrument with the laser displacement sensor is developed, based on the analysis of the required specification. Furthermore, the influence factors on measurement result are analyzed theoretically. As a result, it made clear that the rock stress change in a plane perpendicular to the borehole axis can be measured by the CBDM.

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Comparison of removal characteristics between coprecipitation and adsorption method of aluminum hydroxide for wastewater containing F (-I) was attempted by sorption isotherms, X-ray diffraction (XRD) patterns, and zeta potential analysis.
When F (-I) was coprecipitated with aluminum hydroxide, the sorption density was higher at pH 7 than at pH 5. The sorption density at both pH values followed a BET-type isotherm. High sorption density was obtained when the initial F/Al molar ratio was high, and some of the aluminum hydroxide dissolved. The sorption density in adsorption treatment was slightly lower than that in coprecipitation treatment. These results suggest that the mechanism of F^— coprecipitation was not simply surface complexation of F^—.
At pH 7, the XRD patterns for F (-I) coprecipitates and aluminum hydroxide were identical. The slope between zeta potential and sorption density changed when the initial molar ratio was F/Al=3 in both coprecipitation and adsorption experiments. This F/Al=3 transition point corresponded to the point where the sorption density increased abruptly in the sorption isotherm. These results reveal that F (-I) was primarily adsorbed as a surface complex to aluminum hydroxide when the initial molar ratio was F/Al‹3. In contrast, when the initial molar ratio was F/Al›3, amorphous compounds of F^— and Al (III) formed or F-Al complexes such as AlF^2-, AlF₂⁺, AlF₃⁰ and AlF₄^- were adsorbed.

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The control of the growth or the corrosion creep of a Pb-based alloy grid is very important for extending the life of a lead-acid battery. In this study, the creep behavior of various Pb-Ca alloys was investigated in air, in a highly concentrated H₂SO₄ solution, and in a highly concentrated H₂SO₄ solution with the intermittent electrifying to the specimen electrode. For Pb-Ca alloys with Ca content ranging from 0 to 0.08 mass%, the steady state creep rate decreased exponentially with increasing of Ca content. The decrease of the creep rate is deeply related to the improvement of the material strength by refining of the grain size. On the other hand, the fracture time of Pb-0.08mass%Ca-Sn alloys was extended with increasing Sn content in the range of 0 to 1.60 mass%. The alloying of Sn may be effective in controlling the third creep or the accelerating creep by means of solution hardening. The steady creep rates of Pb-0.08mass%Ca and Pb-0.08mass%Ca-1.20mass%Sn alloys followed Norton's formula and the material coefficients were 9.1 and 9.2 respectively. The coefficients also reveal that the creep of these Pb-Ca base alloys proceeds according to the dislocation creep mechanism. Therefore, it can be explained that the refining of grain size by Ca and the solution hardening by Sn are very efficient in controlling the dislocation movement, to improve the creep resistance of the Pb-base alloys.

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Strain measurements are conducted on drill rods to investigate the rock drillability for percussion drilling. When the length of drill rod with a uniform cross section is short, the method of two-point strain measurement must be employed to separate an incident wave and a reflective wave.
Strain measurements on two types of short drill rod (rod 1 and rod 2) using the two-point method are described. Results from experimental measurements using rod 1 include the following:
(1) An accurate analysis of strain at the evaluation point could not be obtained when the 4-gage method was applied. On the other hand, accurate strain measurements were obtained using the 2-gage method (opposite side) .
(2) Measurements using strain gages of length 5 mm were more suitable for the analysis of strain at the evaluation point than measurements using 2-mm strain gages.
Results from tests to measure strain in two parts of rod 2 (part S and part F) include the following:
(3) A complete measurement of a strain wave could not be obtained at part S, even using the 2-gage method. However, approximately two-thirds of the wave could be analyzed correctly.
(4) For part F, an almost complete measurement of the strain wave was obtained using the 2-gage method. In addition, the similarity of the strain waves of part S and part F was confirmed.
Finally, based on the results for rod 2, the complete percussion energy per hammer blow for part S was estimated.

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This study was carried out to examine the properties and the durability of light-weight concrete which used lapilli. As a result, it was made clear that stable compressive strength of 24N/mm2 was provided by making 50% of lapilli by volume ratio. However, Lapilli are materials of the high absorption that is many apertures quality. As for the concrete using lapilli, progress of hardening of concrete and drying shrinkage are thought about enough. Therefore I decided to mix steel fiber as an improvement method here. The steel fiber mixture stabilizes the strength and durability property, and furthermore it seemed that I can expect it for expression of flexural toughness and restraint of drying shrinkage. As for the result, drying shrinkage and water loss are relatively similar to lightweight concrete II at 50% of lapilli by volume, steel fiber mixture ratio 1.5%, it may be said that the use of 50% of lapilli by volume is possible enough from a strength property.

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