Effect of calcium on niobium solubility in alkaline solutions

Ohira, Saki; Abe, Takeyasu; Iida, Yoshihisa

Radiochimica Acta, 111(7), p.525 - 531, 2023/07

https://doi.org/10.1515/ract-2022-0115

The solubility of Nb in calcium alkaline solutions is one of the important parameters in safety assessment of intermediate-depth disposal which are assumed to use cementitious materials. Nb solubility and solubility-limiting solid phases of Nb in these systems remain unclear. The oversaturation solubility experiments were performed systematically in the 0.001-0.1 M CaCl solutions under alkali conditions, and the characterization of precipitated solid phase controlling Nb solubility was conducted. The negative dependence of Nb solubilities on pH and Ca concentration was observed in solubility experiments, the molar ratio of Nb to Ca of precipitated solid phase was 0.66. The pH and Ca dependence of Nb solubilities was reproduced by the reaction with Nb aqueous species Nb(OH) and Ca-Nb oxide with the molar ratio of Nb to Ca 0.66, e.g., CaNbO(am).

Sodium-cooled Fast Reactors

Ohshima, Hiroyuki; Morishita, Masaki*; Aizawa, Kosuke; Ando, Masanori; Ashida, Takashi; Chikazawa, Yoshitaka; Doda, Norihiro; Enuma, Yasuhiro; Ezure, Toshiki; Fukano, Yoshitaka; et al.

Sodium-cooled Fast Reactors; JSME Series in Thermal and Nuclear Power Generation, Vol.3, 631 Pages, 2022/07

https://shop.elsevier.com/books/sodium-cooled-fast-reactors/morishita/978-0-12-824076-2

This book is a collection of the past experience of design, construction, and operation of two reactors, the latest knowledge and technology for SFR designs, and the future prospects of SFR development in Japan. It is intended to provide the perspective and the relevant knowledge to enable readers to become more familiar with SFR technology.

Consideration on modeling of Nb sorption onto clay minerals

Yamaguchi, Tetsuji; Ohira, Saki; Hemmi, Ko; Barr, L.; Shimada, Asako; Maeda, Toshikatsu; Iida, Yoshihisa

Radiochimica Acta, 108(11), p.873 - 877, 2020/11

https://doi.org/10.1515/ract-2020-0006

Study on plutonium burner high temperature gas-cooled reactor in Japan; Introduction scenario, reactor safety and fabrication tests of the 3S-TRISO fuel

Ueta, Shohei; Mizuta, Naoki; Fukaya, Yuji; Goto, Minoru; Tachibana, Yukio; Honda, Masaki*; Saiki, Yohei*; Takahashi, Masashi*; Ohira, Koichi*; Nakano, Masaaki*; et al.

Nuclear Engineering and Design, 357, p.110419_1 - 110419_10, 2020/02

https://doi.org/10.1016/j.nucengdes.2019.110419

The concept of a plutonium (Pu) burner HTGR is proposed to incarnate highly-effective Pu utilization by its inherent safety features. The security and safety fuel (3S-TRISO fuel) employs the coated fuel particle with a fuel kernel made of plutonium dioxide (PuO) and yttria stabilized zirconia (YSZ) as an inert matrix. This paper presents feasibility study of Pu burner HTGR and R&D on the 3S-TRISO fuel.

Development of fabrication technology for oxidation-resistant fuel elements for high-temperature gas-cooled reactors

Aihara, Jun; Honda, Masaki*; Ueta, Shohei; Ogawa, Hiroaki; Ohira, Koichi*; Tachibana, Yukio

Nihon Genshiryoku Gakkai Wabun Rombunshi, 18(1), p.29 - 36, 2019/03

https://doi.org/10.3327/taesj.J17.027

Japan Atomic Energy Agency carried out development of fabrication technology of oxidation resistant fuel element for improvement of safety of high temperature gas-cooled reactors in serious oxidation accident, based on precursor research in former JAEA. Dummy coated fuel particles (alumina particles) were over-coated with mixed powder of Si, C and small amount of resin to form over-coated particles, and over-coated particles were molded and hot-pressed to sinter dummy oxidation resistant fuel elements with SiC/C mixed matrix. We fabricated dummy oxidation resistant fuel elements with matrix whose Si/C mole ratio (about 0.551) is three times as large as that in precursor research. Si peak was not detected by X-ray diffraction of matrix. Better oxidation resistant was confirmed with oxidation test in 20% O at 1673 K than that of ordinal fuel compact with ordinal graphite/carbon matrix. All dummy coated fuel particles were held in specimen after 10 h oxidation.

Validation of plant dynamics analysis code using shutdown heat removal test-17 performed at the EBR-II

Ohira, Hiroaki; Doda, Norihiro; Kamide, Hideki; Iwasaki, Takashi*; Minami, Masaki*

Proceedings of 2015 International Congress on Advances in Nuclear Power Plants (ICAPP 2015) (CD-ROM), p.2585 - 2592, 2015/05

IAEA's Coordinated Research Project on Benchmark Analyses of Shutdown Heat Removal Test (SHRT) performed at the Experimental Breeder Reactor-II (EBR-II) has been carried out since 2012. The benchmark specifications were provided by the Argonne National Laboratory (ANL) and the model development for thermal-hydraulics codes and/or plant dynamics codes has been conducted by participating organizations. The experimental data were also provided by the ANL after the calculations have been performed as the blind simulation. JAEA participated in this benchmark analyses, and the plant dynamics analysis code; Super-COPD was applied to the SHRT-17 simulation. The calculated inlet temperature of the high pressure plenum agreed well with the test data in all simulation time. Although the Z-pipe inlet temperature and the IHX intermediate outlet temperature had some discrepancy in the first 400 sec. caused by larger mass flow rate of the primary pump and the perfect mixing model of upper plenum, these temperatures and the flow rate agreed well with the measured data after 400 sec. Hence it was concluded the present analytical model could predict the natural circulation in good accuracy.

Research on advanced fuel element for upgrading safety of high temperature gas-cooled reactors, 3; Development on inspection of oxidation resistant fuel element

Honda, Masaki*; Yasuda, Atsushi*; Ohira, Koichi*; Tachibana, Yukio

no journal, , 

For the purpose of upgrading safety of High Temperature Gas-cooled Reactor (HTGR), research on inspection technology for advanced fuel element was conducted with cooperation of JAEA from FY2014 to 2016. The advanced fuel element contains SiC as the matrix material and oxidation resistance is highly improved so that shape and integrity of the fuel element should be maintained even when large unexpected amount of air enters into the core in the air ingress (pipe rupture) accident which is a typical event for the HTGR. For the inspection technology, evaluation and inspection methods on homogeneity of SiC/C matrix and distribution of coated fuel particles as well as dissolution methods of coated fuel particles and SiC/C matrix for evaluation of failure fraction were developed and established.

Analysis of water collected at a drain sump of common stack for units 1 and 2 of Fukushima Daiichi NPS

Shimada, Asako; Taniguchi, Yoshinori; Ohira, Saki; Iida, Yoshihisa

no journal, , 

no abstracts in English

Solubility of Niobium under high Calcium concentration and alkaline conditions

Ohira, Saki; Abe, Takeyasu; Iida, Yoshihisa

no journal, , 

Niobium-94 is an important radionuclide in the safety assessment of intermediate depth disposal. Solubility-limiting solid and solution species of Nb under high Ca concentration and alkaline conditions, estimated as cement-equilibrated solutions, remain unclear. The solubility of Nb under high Ca concentration and alkaline conditions was measured, and solid phase was analyzed by scanning electron microscope energy disperse spectrometry and powder X-ray diffraction. The obtained results show that Nb solubility is negatively correlated with Nb and pH or Ca concentration. The results of Nb solubility experiments and solid phase analysis in this study suggest that the Nb solubility would be limited by solubility-limiting solid CaNbO(am) and solution species Nb(OH).

Nb solubility and sorption onto clay minerals in the presence of calcium

Ohira, Saki

no journal, , 

The solubility and sorption distribution coefficient of niobium-94 (Nb-94) are one of the important parameters in safety assessment of radioactive waste disposal. However, the solubility and sorption distribution coefficient of Nb under calcium and alkaline conditions are still unknown. In this study, Nb oversaturation solubility experiments in 0.001-0.1 M calcium chloride solutions were systematically carried out and the Nb solubility-limiting solid phase was evaluated: the Nb concentration showed a negative dependence on pH and Ca concentration and the Ca/Nb molar ratio of the precipitated solid phase was 0.66. The pH and Ca concentration dependence was confirmed to be reproducible in the dissolution reaction between the dissolved species of Nb hydroxide ions and the Ca-Nb solid phase showing a Ca/Nb ratio of 0.66. Sorption tests below solubility showed similar values for the Nb sorption distribution coefficient in the presence and absence of Ca, confirming that Nb sorption can be reproduced by the surface complexation model of Nb hydroxide complexes.