Investigation of high-temperature chemical interaction of calcium silicate insulation and cesium hydroxide

Rizaal, M.; Nakajima, Kunihisa; Saito, Takumi*; Osaka, Masahiko; Okamoto, Koji*

Journal of Nuclear Science and Technology, 57(9), p.1062 - 1073, 2020/09

https://doi.org/10.1080/00223131.2020.1755733

The interaction of cesium hydroxide and a calcium silicate insulation material was experimentally investigated at high temperature conditions. A thermogravimetry equipped with differential thermal analysis was used to analyze thermal events in the samples of mixed calcium silicate and cesium hydroxide under Ar-5%H and Ar-4%H-20%H0 with maximum temperature of 1100C. Prior being mixed with cesium hydroxide, a part of calcium silicate was pretreated at high temperature to evaluate the effect of possible structural changes of this material due to a preceding thermal history and also the sake of thermodynamic evaluation to those available ones. Based upon the initial condition (preliminary heat treatment) of calcium silicate, it was found that if the original material consisted of xonotlite (CaSi0(0H)), the endothermic reaction with cesium hydroxide occurred over the temperature range 575-730C meanwhile if the crystal phase of original material was changed to wollastonite (CaSi0), the interaction occurred over temperature range 700-1100C. Furthermore, the X-ray diffraction analyses have indicated on both type of pretreated calsils that regardless of Ar-5%H and Ar-4%H-20%H0 atmosphere, cesium aluminum silicate, CsAlSi0 was formed with aluminum in the samples as an impurity or adduct.

Development of experimental technology for simulated fuel-assembly heating to address core-material-relocation behavior during severe accident

Abe, Yuta; Yamashita, Takuya; Sato, Ikken; Nakagiri, Toshio; Ishimi, Akihiro

Journal of Nuclear Engineering and Radiation Science, 6(2), p.021113_1 - 021113_9, 2020/04

https://doi.org/10.1115/1.4045450

Observation of simulated fuel debris using synchrotron radiation

Yoneda, Yasuhiro; Harada, Makoto; Takano, Masahide

Transactions of the Materials Research Society of Japan, 44(2), p.61 - 64, 2019/04

https://doi.org/10.14723/tmrsj.44.57

We performed three-dimensional observation of simulated fuel debris using Synchrotron Computed Tomography (CT). CT was used to make the inside of fuel debris clear. The CT observation provides that a clear contrast in the zirconia rich part and concrete rich part. Zirconia heavier than concrete moved to the lower part when crystals precipitate and aggregates near the bottom surface. As a result, phase separation occurs. The phase separation is caused by the difference in the composition ratio of zirconia, and can also be observed difference in crystal growth mode by composition ratio.

Evolution of the excavation damaged zone around a modelled disposal pit; Case study at the Horonobe Underground Research Laboratory, Japan

Aoyagi, Kazuhei; Miyara, Nobukatsu; Ishii, Eiichi; Nakayama, Masashi; Kimura, Shun

Proceedings of 13th SEGJ International Symposium (USB Flash Drive), 5 Pages, 2018/11

The construction of underground facilities induces fractures in the rock mass around the underground voids due to the resultant stress redistribution. This has particular implications for high-level radioactive waste (HLW) disposal projects, where fracture development creates an excavation damaged zone (EDZ) that increases the hydraulic conductivity of the surrounding rock mass and can provide a pathway for the migration of radionuclides from the storage facilities. It is therefore important to understand the long-term evolution of the EDZ and perform a comprehensive HLW disposal risk assessment. An in situ engineered barrier system experiment was conducted in the 350 m gallery at the Horonobe Underground Research Laboratory, Japan, to observe the near-field coupled thermo-hydro-mechanical-chemical (THMC) process in situ and validate coupled THMC models. Here we investigate the evolution of the EDZ around the gallery and model a test pit that was excavated below the floor of the gallery using a series of seismic tomography surveys. There was a significant decrease in the seismic velocity field around the test pit due to its excavation, which became slightly more pronounced over time after the excavation. These seismic results, coupled with hydraulic tests and pore pressure measurements around the pit, indicate that fracture development and the decrease in saturation around the test pit resulted in a decrease in the seismic velocity field after the excavation of the test pit. Furthermore, the increase in saturation around the test pit is a key reason for the increase in the seismic velocity field after the heater test.

Development of non-transfer type plasma heating technology to address CMR behavior during severe accident with BWR design conditions

Abe, Yuta; Sato, Ikken; Nakagiri, Toshio; Ishimi, Akihiro; Nagae, Yuji

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 7 Pages, 2017/04

A Code MOGRA for predicting the migration of ground additions and its application

Amano, Hikaru

Shigen Kankyo Taisaku, 41(12), p.89 - 96, 2005/10

no abstracts in English

Electrochemical behaviors of PuN and (U, Pu)N in LiCl-KCl eutectic melts

Shirai, Osamu; Kato, Tetsuya*; Iwai, Takashi; Arai, Yasuo; Yamashita, Toshiyuki

Journal of Physics and Chemistry of Solids, 66(2-4), p.456 - 460, 2005/02

https://doi.org/10.1016/j.jpcs.2004.06.040

Electrochemical behaviors of PuN and (U, Pu)N in the LiCl-KCl eutectic melt containing UCl and PuCl at 773 K were investigated by cyclic voltammetry. The electrochemical dissolution of PuN and (U, Pu)N began nearly at -1.0 V vs. the Ag/AgCl reference electrode. The rest potentials of PuN and (U, Pu)N were observed at about 0.15 V more negative potential than that of UN since the equilibrium potential of UN is about 0.15 V more positive than that of PuN. In the cyclic voltammogram measured by using (U, Pu)N as the working electrode, a steep rise of the positive current was observed at more positive potential than -0.4 V in analogy with the cyclic voltammogram measured by using UN as the working electrode. In addition, there were two anodic current waves in the voltammogram with (U, Pu)N, though the wave form was not clear. This indicates that UN and PuN would be dissolved independently irrespective of formation of the solid solution, (U, Pu)N.

Interfacial properties of a direct bonded Nd-doped YVO and YVO single crystal

Sugiyama, Akira; Nara, Yasunaga; Wada, Kengo*; Fukuyama, Hiroyasu

Journal of Materials Science; Materials in Electronics, 15(9), p.607 - 612, 2004/09

Laser crystal bonding of a neodymium-doped yttrium orthovanadate (Nd: YVO) and a non-doped yttrium orthovanadate (YVO) crystal as a cold finger has been demonstrated. Instead of a traditional chemical treatment, a newly developed dry etching process was applied to the preparation for contact of mechanically polished surfaces. In the subsequent heat treatment process, stable heating at 873 K was required to prevent precipitation at the bonded interface. The bonded interface of 3 mm 3 mm was investigated by optical scattering and wavefront distortion measurements. The scattering density around the bonded interface was less than 4.610 /cm and the wavefront distortion caused by the bonded region was assumed to be around 0.04-wave at 633 nm. Additional magnified inspection showed that atoms in the bonded region were well arranged with the same regularity as the bulk crystal. The diffusion coefficient of Nd ions in the YVO crystal was estimated at 2.310 m/sec at 873 K.

Reproducibility of thermal neutron flux distribution on patient's brain surface with a realistic phantom

Yamamoto, Kazuyoshi; Kumada, Hiroaki; Yamamoto, Tetsuya*; Matsumura, Akira*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 3(2), p.193 - 199, 2004/06

https://doi.org/10.3327/taesj2002.3.193

To investigate the possibility of experimental approach for dose evaluation using a realistic phantom that faithfully reproduced the shape of a head, this research considered the manufacture of a patient's realistic phantom and the reappearance of actual medical irradiation conditions. We selected the rapid prototyping technology to produce the realistic phantom from the Computed Tomography (CT) imaging. This phantom was irradiated under the same clinical irradiation condition of this patient, and the thermal neutron distribution on the brain surface was measured in detail. Several subjects on material and data conversion in the production of realistic phantom were mentioned. As a result of reproducing medical irradiation using the realistic phantom, the maximum thermal neutron flux became a value about 22% lower than the surface of the actual brain. If the problems pointed out in this paper are solved, it may also be expected that it would become possible to check computational dosimetry system.

Development of a code MOGRA for predicting the migration of ground additions and its application to various land utilization areas

Amano, Hikaru; Takahashi, Tomoyuki*; Uchida, Shigeo*; Matsuoka, Shungo*; Ikeda, Hiroshi*; Hayashi, Hiroko*; Kurosawa, Naohiro*

Journal of Nuclear Science and Technology, 40(11), p.975 - 979, 2003/11

https://doi.org/10.3327/jnst.40.975

MOGRA is a migration prediction code for toxic ground additions including radioactive materials in a terrestrial environment. MOGRA consists of computational codes that are applicable to various evaluation target systems, and can be used on personal computers. The computational code has the dynamic compartment analysis block, GUI for computation parameter settings and results displays, data bases. The compartments are obtained by classifying various natural environments into groups that exhibit similar properties. A hypothetical combination of land usage was supposed to check the function of MOGRA. The land usage was consisted from cultivated lands, forests, uncultivated lands, urban area, river, and lake. Each land usage has its own inside model which is basic module. Also supposed was homogeneous contamination of the surface land from atmospheric deposition of Cs (1.0 Bq/m). The system analyzed the dynamic changes of Cs concentrations in each compartment, fluxes from one compartment to another compartment.