Kinetic study on eutectic melting process between boron carbide and stainless steel in sodium-cooled fast reactor

Kikuchi, Shin; Sakamoto, Kan*; Takai, Toshihide; Yamano, Hidemasa

Nihon Kikai Gakkai 2020-Nendo Nenji Taikai Koen Rombunshu (Internet), 4 Pages, 2020/09

In a postulated severe accidental condition of sodium-cooled fast reactor (SFR), eutectic melting between boron carbide (BC) as control rod element and stainless steel (SS) as control rod cladding or related structure may occur. Thus, behavior of BC-SS eutectic melting is one of the phenomena to evaluate the core disruptive accidents in SFR. In order to clarify the kinetic feature of BC-SS eutectic melting process in the interface, the thinning test for SS crucibles using the pellets of BC or SS with low BC concentration were performed to obtain the rate constant with dependence of BC concentration against SS. It was found that the rate constants of eutectic melting between SS and SS low BC concentration were smaller than that of BC-SS in the high temperature range. Besides, the rate constant of eutectic melting between SS and BC containing SS became small when decreasing the BC concentration against SS.

CHEMKEq; Evaluation code for chemical composition based on partial mixed model with Chemical Equilibrium and Reaction Kinetics (Contract research)

Ito, Hiroto*; Shiotsu, Hiroyuki; Tanaka, Yoichi*; Nishihara, Satomichi*; Sugiyama, Tomoyuki; Maruyama, Yu

JAEA-Data/Code 2018-012, 42 Pages, 2018/10

JAEA-Data-Code-2018-012.pdf:4.93MB

Chemical composition of fission products transported in nuclear facilities in severe accidents is controlled by slower chemical reaction rates, therefore, it could be different from that evaluated on the chemical equilibrium assumption. Hence, it is necessary to evaluate the chemical composition with reaction kinetics. On the other hand, databases applicable to the analysis of nuclear facilities have not been constructed because knowledge of reaction rates of complex chemical reactions in severe accidents is currently limited. Accordingly, we have developed the CHEMKEq code based on a partial mixed model with chemical equilibrium and reaction kinetics to decrease uncertainties of the chemical composition caused by the reaction rate. The CHEMKEq code, under mass conservation law, firstly evaluates chemical species obeying the chemical equilibrium model, and then, relatively slow reactions are solved by the reaction kinetics model. Moreover, the CHEMKEq code has a multiplicity of use in evaluations of chemical composition because general chemical equilibrium and reaction kinetics models are also available and databases required to calculation are external file formats. This report is the user's guide of the CHEMKEq code, showing models, solution methods, structure of the code and calculation examples. And information to run the CHEMKEq code is summarized in appendixes.

Homogeneous transesterification kinetics of triglyceride to biodiesel using grafted fibrous catalyst

Ueki, Yuji; Seko, Noriaki

JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 53, 2014/03

https://jopss.jaea.go.jp/pdfdata/JAEA-Review-2013-059.pdf

no abstracts in English

Study on evaluation method of colloidal migration of radionuclides; Models on colloid transport in porous media

Mukai, Masayuki; Tanaka, Tadao; Yukawa, Kazuhiko; Suryantoro*

Genshiryoku Bakkuendo Kenkyu, 12(1-2), p.41 - 51, 2006/03

https://doi.org/10.3327/jnuce.12.41

To evaluate radionuclides migration through geologic media coexistent with colloids in groundwater, a model has been coded. To evaluate an applicability of four models to colloid transport through porous media, breakthrough curves (BTCs) from column experiments using sand and reddish soil have been analyzed. Instantaneous equilibrium model could not explain both timings of breakthrough and reach to C/C=1 concurrenyly, however 1st order kinetic reaction model successfully simulate them well. BTCs from the reddish soil column have a particular feature that shows step-wise rising pattern in response to alternately inflow of colloid. Both the instantaneous equilibrium, the 1st order kinetic reaction and filtration models could not simulate this feature, however a 1st order kinetic reaction with filtration capacity model reasonably simulates the feature. The model for colloid transport, given an important role as a part of colloidal migration model of radionuclide, has been validated on the basis of the laboratory experiments.

Effect of solute atoms on swelling in Ni alloys and pure Ni under He ion irradiation

Wakai, Eiichi; Ezawa, Tadashi*; Imamura, Junko*; Takenaka, Tsuyoshi*; Tanabe, Tetsuo*; Oshima, Ryuichiro*

Journal of Nuclear Materials, 307-311(Part.1), p.367 - 373, 2002/12

https://doi.org/10.1016/S0022-3115(02)01192-3

no abstracts in English

Experimental study of pyrite oxidation in compacted sodium bentonite

JNC TN8400 2000-012, 33 Pages, 2000/04

JNC-TN8400-2000-012.pdf:1.04MB

The redox condition of near-field is expected to affect the performance of engineered barrier system. Especially, the oxygen initially existing in the pore space of compacted bentonites strongly affects the redox condition of the near-field. For assessing the influence of the oxygen, the transport parameters of it in the compacted bentonite and consumption process should be known. Therefore, following researches were conducted. In order to understand the diffusion of dissolved oxygen (DO) in compacted bentonite and to predict the effect of DO, the effective diffusion coefficients of DO in compacted sodium bentonite were measured by electrochemistry. As the results, the following relationship between the dry density of compacted sodium bentonite and the effective diffusion coefficient of DO in compacted sodium bentonite was derived: De=1.530.1310exp(-2.150.2410p) where De is the effective diffusion coefficient (ms) of DO in compacted sodium bentonite and is the dry density (kg m) of compacted sodium bentonite. The oxygen concentration in the bentonite is expected to be controlled by oxidation of pyrite as impurity in the bentonite. In order to investigate the above idea, the rates of pyrite oxidation by DO in compacted sodium bentonite were estimated from the experimental data on pyrite-bentonite systems usig the obtained effective diffusion coefficient of DO. The results show that the averages of the rate constants of pyrite oxidation by DO in the bentonite for dry densities of 0.8, 0.9, 1.0, 1.1 and 1.210kgm were 1.380.3210, 1.100.2410, 1.160.3510, 9.362.2310 and 7.481.9210ms, respectively. The relationship between the dry density () and the rate constant (k') was expressed as follows: k'=3.941.0610exp(-1.330.2810) ...

Modelling of the interaction of bentonite with hyperalkaline fluids

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 70C. 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 ...

The Study on degradation of engineered barrier in ratioactive waste repositories effect of nitrate and leaching solutions

Iriya, Keishiro*; *; Kubo, Hiroshi*; Fujita, Hideki*

JNC TJ8400 2000-033, 95 Pages, 2000/02

JNC-TJ8400-2000-033.pdf:11.11MB

Cementious materials and highly compacted bentnite are expectable candidates as materials of TRU waste repositories. It was pointed out that Bentonite might be changed to Zeolite and surrounding rock might be altered by high alkalinity water flow, since cement hydrate leached to pore water of cement and it was changed to alkaline. Transportation of radio-nuclides might be accelerated by organic materials, such as super plasticizer, and nitrate which is contained in nuclear wastes. It was concluded by previous studies that rock and bentonite is stable in alkaline water which pH is less than 10.5. The new type of low alkalinity cement with high silica fume and fly ash content which could keep pH below 11.0 was developed and its performance has been assessed. However since Zeolitation and ilitation were reported upon deterioration of bentonite bated in certain condition, it should be assessed by long term experiment. Since Capacity of keeping integrity of bentonite hasn't been directly checked by experiments upon the developed new type of low alkalinity cement it should be done. Although amount of leaching organic was quantitatively and experimentally assessed at an early age, effect of changing of amount and shape hasn't assessed in leaching of radio nuclides. Although it is pointed out that deterioration of cementitious materials isn't accelerated by condensed nitrate solution at early period after closure, it is considered that it might be accelerated corresponding to chemical composition in case of decrement of concentration of nitrate. In this study, deterioration of materials will be assessed in detail in order to feed back the results to assessment of transportation of radio nuclides. Long term deterioration of bentonite by leaching water of cement will be experimentally assessed, and deteriorating test of bentonite will be carried out by leaching water of low alkalinity cement. Amount of organic and component of it will be measured. Furthermore ...

Study on cathodic reaction control efficiency by low alloy steels

Akashi, Masatsune*; Fukaya, Yuichi*; Asano, Hidekazu*

JNC TJ8400 2000-014, 22 Pages, 2000/02

JNC-TJ8400-2000-014.pdf:0.75MB

Difference of hydrogen generation phenomena on the surface of the Steels were not observed between carbon steel, atmospheric corrosion resisting steel and 5%-Ni steel. Rust layer was formed on these three-type of steels by steam oxidation method. And the chemical composition of the rust for the steels were basically two(2) layers structure for the previous two steels as hematite(FeO) based for the outer layer and magnetite(FeO) based for the inner layer. And for the last steel, it had three(3) layer in the rust as hematite(FeO) based for the outer layer, magnetite(FeO) based for the intermediate layer and Ni based layer for the inner layer. These steels showed mostly same Tafel gradient in their cathodic polarization curves compare with that for no rust specimens. However, the exchange current density which reaction is assumed as a hydrogen generation reaction was largely increased. The cathodic reaction for each steels whose surface is covered by magnetite layer might be accelerated, then the corrosion rate was considered as accelerated, too.

Corrosion of iron buried in clay

Sumiyama, Morio*

JNC TJ8400 2000-009, 138 Pages, 2000/02

JNC-TJ8400-2000-009.pdf:3.0MB

To evaluate corrosion behavior of carbon steel, a candidate materials of overpack, buried in soil for a long time, the water pipes buried in freshwater clay for a long time we digged out and the soil environment and the corrosion weight loss of pipes have been researched. From the results, a corrosion model (an empirical equation), an oxygen reduction reaction rate-determing step type, of carbon steel buried in soil was introduced. The corrosion data of under ground pipe collected by the Japan Community Gas Associations was used to increase reliability of the corrosion model equation. These data are one of researches of corrosion behavior of carbon steel buried in soil for a long time studied by at home and abroad. 38 samples buried freshwater clay were selected in 171 samples. With estimating the corrosion velocities and the soil environment factors of the above data, the maximum depth of pit corrosion was calculated by the statistical method of the extreme values using the area of overpack as the recurrent time. The correlation between the soil environment factors and the corrosion weight loss was obtained by the correlation analysis. The corrosion model of the maximum depth of pit corrosion at 0.99 of cumulative probability was compared between the under ground pipe data and the above data. On the reference data and the above data, the corrosion model equation; H = aY was compared with the maximum depth of pit corrosion at 0.99 cumulative probability. The data of water pipes and community gas pipes at 0.99 cumulative probability showed the reasonable values when these data were compared with the reference data. So that the model was proved as a good corrosion model m the neutral low dissolved oxygen environment.