An Investigation of cementitious materials for radioactive waste repository; Mechanical properties of law alkalinity cementitious materials

Owada, Hitoshi*; Mihara, Morihiro; Iriya, Keishiro*; *

JNC TN8400 99-057, 43 Pages, 2000/03

JNC-TN8400-99-057.pdf:5.13MB

Cementitious materials are considered as candidate materials for the geological disposal of high-level radioactive waste and TRU waste. As the pH and the Ca content of leachate from the cementitious materials are high, the host rock and the buffer-material would be degraded by the leachate in the long-term. Therefore, transport properties and parameters such as solubilities and distribution coefficients of radionuclides would be changed and affect the performance of the repository. In order to dissolve this "High pH plobrem", the use of a low alkalinity cement is considered for the disposal. In this study, we summarized the necessity of the low alkalinity cement, and developed the approach of the low alkalinization of cement. And, the following were carried out in this study : A leaching test of cement paste, a fluid test of the mortar and a installation test of the concrete to the trial structure. From the leaching test using the cement paste, we confirmed that we were able to obtain the low alkalinity cement (HFSC) by addition of pozzolanic materials such as silica-fume and flyash. From the result of the fluid test of the mortar, we chose the cement for the practicability evaluation. The practicability of low alkalinity concrete was evaluated by installation test to the trial structure.As a result of these examinations, we proved that the pH value of the leachate from the cementitious material was reduced by adding SF and FA to Portland cement. Simultaneously, SF and FA had to be added in order to obtain the good workability. In addition, workability and mechanical strength of the cement which SF and FA were added are almost equivalent to the ordinary Portland cement. The results shows that the HFSC has high practicability.

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; ; Fujisaku, Kazuhiko*; Ishibashi, Yuzo; Takeda, Seiichiro

PNC TN8410 98-060, 74 Pages, 1998/03

PNC-TN8410-98-060.pdf:4.25MB

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Design and evaluation of super-heat-resisting Nb-based and Mo-based alloys

Morinaga, Masahiko*; *; *; *; Inoue, Satoshi*

PNC TJ9603 96-001, 79 Pages, 1996/03

PNC-TJ9603-96-001.pdf:3.48MB

[PURPOSE] In order to develop the frontier domain of technique for the high temperature liquid alkali metal, candidate Nb-based and Mo-based alloys are needed. They are needed to have excellent compatibility with liquid Li (max. 1200C) and super-heat-resistance. In this study, alloy design using a d-electrons alloy theory and estimation of designed alloy were performed. [EXPERIMENTAL METHODS] (1)Workability : A bend test was carried out with the provisionally designed Mo-based alloys, but by modifying the compositions by adding intergranular strengthening elements, Ti, B, C, Hf, into them to improve the ductility. (2)Corrosion resistance to liquid Li : The provisionally desingned Nb-based alloys were immersed in liquid Li at 1200C for three hundred hours, and the weight change due to the corrosion was measured. The corrosion surface was also analyzed using SEM and EPMA. In addition, a similar corrosion test was carried out with binary Nb-based and Mo-based alloys. (3)Embrittlement at 800C : A series of experiments such as the hardness test, X-ray analysis and microstructure observation was perfomed with the Nb-1Zr alloy which was creep-tested at 800C or 1200C. Also, a Nb-1Zr alloy specimen which was not creep-tested, was used as a reference specimen. [RESULTS AND DISCUSSIONS] (1)Workability : The Ti addition into the Mo-based alloys was effective in improving workability. The brittleness of Mo may be caused by the existence of oxygen in the grain boundaries, so that the formation of Ti oxides probably weakened the oxygen effect, resulting in the better workability of the alloy. However, B, C and Hf additions into Mo-based alloys never improved the workability. (2)Corrosion resistance to liquid Li : Many cracks were observed on the corroded surface of the provisionally designed Nb-based alloys despite the addition of a corrosion resistant element, Hf, into them. In paticular, such cracks were developed ...

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PNC TN1410 92-030, 40 Pages, 1992/04

PNC-TN1410-92-030.pdf:1.44MB

no abstracts in English