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

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

JNC TJ8400 2000-034, 212 Pages, 2000/02

JNC-TJ8400-2000-034.pdf:7.91MB

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 nitlate 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 2000-015, 46 Pages, 2000/02

JNC-TJ8400-2000-015.pdf:2.96MB

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.

EIS study on corrosion of overpack materials in bentonite

Ishikawa, Hiroki*; Tada, Eiji*; Nishikata, Atsushi*; Taniguchi, Naoki; Tachikawa, Hirokazu*

no journal, , 

In current concept of geological disposal of high-level radioactive waste, the vittrified wastes are stored in metallic container which is called overpack, and then disposed in deep underground. Similarly in direct disposal of spent nuclear fuel, the fuel assemblies are disposed in deep underground contained in metallic disposal container. In order to ensure the long term integrity and safety of overpack or disposal container, corrosion monitoring was performed using electrochemical impedance spectroscopy (EIS) technique.

Diffusion behavior of heavy water in magnetite film formed on iron in basic solution

Haruna, Takumi*; Miyataki, Yuki*; Hirohata, Yohei*; Taniguchi, Naoki; Tachikawa, Hirokazu*

no journal, , 

no abstracts in English

Polarization behavior of pure titanium, pure copper and nickel base alloy in alkaline simulated groundwater under irradiation

Yukawa, Takuji*; Inoue, Hiroyuki*; Kojima, Takao*; Tachikawa, Hirokazu*; Taniguchi, Naoki

no journal, , 

no abstracts in English

None

Kai, Itsuki*; Nakanishi, Yuki*; Taniguchi, Naoki; Dobashi, Ryuta*; Hirohata, Yohei*; Haruna, Takumi*

no journal, , 

no abstracts in English

Effect of bicarbonate ions on the cathodic reaction of copper electrodes in fresh groundwater environments

Miyoshi, Yuma*; Inoue, Hiroyuki*; Mitsui, Seiichiro; Dobashi, Ryuta*

no journal, , 

In Japan, research and studies on direct disposal of spent fuel as an alternative disposal option are underway in order to secure a wide range of options. For direct disposal, a copper-carbon steel composite vessel covered with pure copper, which is expected to provide longer confinement, has been considered in consideration of the time required for sufficient attenuation of C-14, one of the dominant radionuclides in the safety assessment. In this study, the effect of HCO on the cathodic reaction of pure copper in a fresh groundwater environment with a low oxygen atmosphere was investigated. From the results of polarization measurements using pure copper as a test electrode, it was inferred that HCO promotes the cathodic reaction, which is a hydrogen evolution reaction using H as an oxidant, by buffering the pH change at the electrode interface in the relatively low current density range, which is assumed to be the cathodic current of corrosion. It is unlikely that HCO acts directly as an oxidant in the cathodic reaction of corrosion. The hydrogen evolution reaction rate on the pure copper surface is relatively low in comparison with the polarization measurements on pure iron and platinum.