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Ito, Daisuke*; Ito, Kei*; Saito, Yasushi*; Aoyagi, Mitsuhiro; Matsuba, Kenichi; Kamiyama, Kenji
Nuclear Engineering and Design, 334, p.90 - 95, 2018/08
Times Cited Count：9 Percentile：62.99(Nuclear Science & Technology)Two-phase flow through porous media must be well understood to develop a severe accident analysis code not only for light water reactor but also sodium-cooled fast reactor. When a core disruptive accident occurs in sodium-cooled fast reactor, the fuel inside the core become melted and interacts with the coolant. As a result, gas-liquid two-phase flow will be formed in the debris bed, which may have porous nature depending on the cooling process. In such condition, the local porosity and its distribution are very important to characterize two-phase flow field in the porous media. In this study, X-ray radiography was applied to measure the local porosity in the packed bed of spheres. The radial profiles were estimated from the chordal profiles measured by the X-ray method and compared with the previous porosity model. In addition, the void fraction radial profiles were also obtained in air-water two-phase flow.
Muroi, Masayuki*
JNC TJ8400 2000-042, 142 Pages, 2000/02
JNC-TJ8400-2000-042.pdf:14.6MB
Hyperalkaline pore water of cementitious material used in TRU waste repository would react with bentonite and cause the increased porosity and the loss of the swelling and sorption ability. This work is a modelling study on bentonite-cement pore water. The possible extent of reaction between bentonite and cement pore water was simulated using the PRECIP reaction-transport code. Three cement pore fluid compositions (leachates 1,2 and 3) were reacted with a 1-D, 1m flowpath of bentonite (+ sand) at 25 and 70
C. Key minerals were allowed to dissolve and precipitate using kinetic reaction mechanism. Leachate 1 was the most aggressive fluid (highest pH, Na and K), and leachate 3 (1owest pH, Na and Ca) the least aggressive. Simulation with leachate 1 showed total removal of primary bentonite minerals up to 60 cm from the contact with cement after 
1000 years. The maximum porosity increase observed was in leachate 1(up to 80-90%) over a narrow zone 1-2 cm. Simulations with all fluids showed total filling of pore with CSH minerals in a zone very close to the interface with the cement, whereas zeolites and sheet silicates formed far away. For a given leachate composition, there was little difference in the profiles at the two temperatures studied. It was suggested that bentonite alteration was not sensitive to the kinetic parameters over the conditions studied. The conceptual model chosen for the modelling study assumed that there was an unlimited amount of cement pore fluid available for reaction with bentonite so that the results of the simulations represent a conservative (pessimistic) estimate. There were a number of uncertainties associated with the modelling which relate to assumptions concerning: the kinetic mechanisms for dissolution and growth of minerals at elevated pH; evolving surface areas of minerals with time; thermodynamic data for CSH minerals, zeolites and aqueous species at high pH; the synergy between changing porosity and fluid ...
Miki, Takahito*; Sasamoto, Hiroshi; Chiba, Tamotsu*; Inagaki, Manabu*; Yui, Mikazu
JNC TN8400 2000-007, 32 Pages, 2000/01
JNC-TN8400-2000-007.pdf:0.69MB
This report presents a summary of literature survey about geochemical reactions which are important to evaluate the redox conditions in the near field rock mass and buffer. The results of literature survey are summarized as follows; (1)Minerals including ferrous iron and organic materials in the rock mass are important reductants. Initial stage after closure of repository, oxygen will be consumed by pyrite, because the reaction rate between pyrite and oxygen is relatively fast. (2)It is possible to estimate the redox capacity for reductants by rock (mineral)-water iteraction experiment in a laboratory. And it is expected that the ferrous iron-rich rock and higher porosity rock may have bigger redox capacity. (3)It is possible to estimate the oxygen consumption rate by reductants such as minerals including ferrous iron. The rate law and rate constant for the oxidation reaction of ferrous iron in the solution are also determined. As a conclusion, it seems that we can evaluate kinetically the evolution of geochemical conditions in the near field rock mass and buffer by excavation of drifts, based on data derived from these existing literatures.
; ; Ishiguro, Katsuhiko; Nakajima, Kunihiko*;
JNC TN8400 99-087, 41 Pages, 1999/11
Corrosion of the carbon steel overpack leads to a volume expansion since the specific gravity of corrosion products is smaller than carbon steel. The buffer material is compressed due to the corrosive swelling, reducing its thickness and porosity. On the other hand, Buffer material may be extruded into fractures of the surrounding rock and this may lead to a deterioration of the planned functions of the buffer, including retardation of nuclides migration and colloid filtration. In this study, the sensitivity analyses for the effect of volume expansion and intrusion of the buffer material on nuclide migration in the engineering barrier system are carried out. The sensitivity analyses were performed on the decrease in the thickness of the buffer material in the radial direction caused by the corrosive swelling, and the change in the porosity and dry density of the buffer caused by both compaction due to corrosive swelling and intrusion of buffer material. As results, it was found the maximum release rates of relatively shorter half-life nuclides from the outside of the buffer material decreased for taking into account of a volume expansion due to overpack corrosion. On the other hand, the maximum release rates increased when the intrusion of buffer material was also taking into account. It was, however, the maximum release rates of longer half-life nuclides, such as Cs-137 and Np-237, were insensitive to the change of buffer material thickness, and porosity and dry density of buffer.
Yamaguchi, Tetsuji; Isobe, Hiroshi;
Hoshasei Haikibutsu Kenkyu, 3(2), p.99 - 108, 1997/00
no abstracts in English
; Iwamoto, K.
JAERI-M 5937, 30 Pages, 1974/12
no abstracts in English
Fukuda, Kenji; Ozaki, Yusuke; Murakami, Hiroaki; Itai, Kaori*; Ishibashi, Masayuki; Sasao, Eiji
no journal, ,
Matrix diffusion is one of the important for evaluating solute transport in crystalline rock. In this study, effective diffusion coefficient, porosity, and resistivity of crystalline rock were measured. There was a positive correlation between the formation factor calculated from the resistivity measurement and the effective diffusion coefficient calculated from the transmission diffusion test. Therefore, the effective diffusion coefficient can be estimated from the resistivity measurement of crystalline rock.
