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Journal Articles

Ten years of Fukushima Dai-ichi post-accident research on the degradation phenomenology of the BWR core components

Pshenichnikov, A.; Shibata, Hiroki; Yamashita, Takuya; Nagae, Yuji; Kurata, Masaki

Journal of Nuclear Science and Technology, 59(3), p.267 - 291, 2022/03

https://doi.org/10.1080/00223131.2021.1985647

Times Cited Count：2 Percentile：31.78(Nuclear Science & Technology)

Journal Articles

Control blade degradation test under temperature gradient in steam atmosphere

Shibata, Hiroki; Tokushima, Kazuyuki; Sakamoto, Kan*; Kurata, Masaki

Proceedings of Annual Topical Meeting on LWR Fuels with Enhanced Safety and Performance (TopFuel 2016) (USB Flash Drive), p.1033 - 1042, 2016/09

To understand the degradation process of control blade channel, control blade degradation tests using sim-materials were performed under various atmospheres with the temperature increase and temperature gradient conditions. In the steam atmosphere with a flow rate of 0.0125 g/s/rod, control blade, channel box, and fuel rods were degraded, especially at the upper part of the test piece, which was similar to that observed in argon atmosphere test. However, the observed degradation was rather different at a flow rate of 0.0417 g/s/rod. At the upper part of the test piece, only the control blade was degraded preferentially and did not react with channel box wall. In contrast, the eutectic reaction of S.S./B $_{4}$ C-melt and Zry occurred at the lower part. These observations suggested the existence of a threshold condition for the control rod degradation between 0.0125 and 0.0417 g/s/rod which is significantly affected by the thickness of the oxide layer on Zry.

Journal Articles

Chlorination of UO $_{2}$ and (U,Zr)O $_{2}$ solid solution using MoCl $_{5}$

Sato, Takumi; Shibata, Hiroki; Hayashi, Hirokazu; Takano, Masahide; Kurata, Masaki

Journal of Nuclear Science and Technology, 52(10), p.1253 - 1258, 2015/10

https://doi.org/10.1080/00223131.2015.1070110

Times Cited Count：6 Percentile：45.92(Nuclear Science & Technology)

In order to explore the applicability of the chlorination by MoCl $_{5}$ as a potential pretreatment technique for waste treatment of fuel debris by pyrochemical methods, chlorination experiments of UO $_{2}$ and (U $_{0.5}$ Zr $_{0.5}$ )O $_{2}$ simulated fuel debris were carried out in two steps: the first one is a chlorination reaction by homogeneous heating, the second one is a volatilization of molybdenum by-product by heating under temperature gradient condition. Most of UO $_{2}$ and (U $_{0.5}$ Zr $_{0.5}$ )O $_{2}$ powder were converted to UCl $_{4}$ or UCl $_{4}$ and ZrCl $_{4}$ mixture at 573 K, respectively. In the case of (U $_{0.5}$ Zr $_{0.5}$ )O $_{2}$ sintered particle, most of sample was converted to the chlorides because the products evaporated and be separated from sample surface at 773 K, while only the surface of the sample disk was converted to the chlorides at 573 and 673 K. Most of molybdenum by-product and ZrCl $_{4}$ were separated from UCl $_{4}$ by volatilization at 573 K.

Journal Articles

Chemical interaction between granular B $_{4}$ C and 304L-type stainless steel materials used in BWRs in Japan

Shibata, Hiroki; Sakamoto, Kan*; Ouchi, Atsushi*; Kurata, Masaki

Journal of Nuclear Science and Technology, 52(10), p.1313 - 1317, 2015/10

https://doi.org/10.1080/00223131.2015.1011721

Times Cited Count：16 Percentile：79.46(Nuclear Science & Technology)

Chemical interactions between S.S. and B $_{4}$ C may lead to the melting of control rods and subsequent relocation of control rod materials in the early stage of severe accident. The liquid products interact with the surroundings such as control rod blades, Zircaloy channel boxes and fuel rods, which may accelerate the fuel bundle degradation. Previous studies on the chemical interactions between S.S. and B $_{4}$ C have been performed using the B $_{4}$ C powders or pellets. However, almost all of control rods of BWR in Japan consist of granular B $_{4}$ C filled in S.S. tubes. In the present study, the chemical reaction tests were carried out using the materials adopted in BWR in Japan, namely granular B $_{4}$ C and 304L type S.S. and it was concluded that the kinetics of chemical interaction between S.S. and granular B $_{4}$ C is clearly different from that between S.S. and pellet or powder B $_{4}$ C.

Journal Articles

Recent progress and future R&D plan of nitride fuel cycle technology for transmutation of minor actinides

Hayashi, Hirokazu; Nishi, Tsuyoshi; Takano, Masahide; Sato, Takumi; Shibata, Hiroki; Kurata, Masaki

NEA/NSC/R(2015)2 (Internet), p.360 - 367, 2015/06

https://www.oecd-nea.org/science/docs/2015/nsc-r2015-2.pdf#page=362

Uranium-free nitride fuel was chosen as the first candidate for transmutation of long-lived minor actinides (MA) using accelerator-driven system (ADS) under the double strata fuel cycle concept by Japan Atomic Energy Agency (JAEA). The advantages of nitride fuel are good thermal properties and large mutual solubility among actinide elements. A pyrochemical process is proposed as the first candidate for the reprocessing of the spent nitride fuel, because this technique has some advantages over aqueous process, such as the resistance to radiation damage, which is an important issue for the fuels containing large amounts of highly radioactive MA. This paper overviews the recent progress and future R&D plan of the study on the nitride fuel cycle technology in JAEA.

Journal Articles

Liquefaction interaction between oxidized Zircaloy and other fuel assembly components of BWR in the early stage of fuel assembly degradation

Tokushima, Kazuyuki; Shibata, Hiroki; Kurata, Masaki; Sawada, Akihiko*; Sakamoto, Kan*

Annual Topical Meeting on Reactor Fuel Performance (TopFuel 2015), Conference Proceedings, Poster (Internet), p.478 - 485, 2015/00

https://www.euronuclear.org/events/topfuel/topfuel2015/transactions/topfuel2015-transactions-poster.pdf#page=478

Two type tests were performed to examine the prevention effect of the oxide layers to liquefaction interaction between Zircaloy and core component materials. The oxide layer of Zircaloy was clearly confirmed to prevent the liquefaction interaction under the temperature of melting point of stainless steel even if the oxide layer on Zircaloy of approximately 30 micro meters, which is thinner than it is predicted to be formed under typical accident condition. The oxide layers were able to be formed even in the region where the gas flow is significantly limited by narrow arrangement. Although the oxide layers at the inner position of upper end plug was hard to form, the prevention effect of the oxide layers was sufficiently observed. The axial variation of the thickness of the oxide layers was observed. It suggested that variation of partial pressure of H $_{2}$ O should be considered to evaluate the growth rate of the oxide layers for detail.

Journal Articles

Pyrochemical treatment of spent nitride fuels for MA transmutation

Hayashi, Hirokazu; Sato, Takumi; Shibata, Hiroki; Kurata, Masaki; Iwai, Takashi; Arai, Yasuo

Science China; Chemistry, 57(11), p.1427 - 1431, 2014/11

https://doi.org/10.1007/s11426-014-5205-9

Times Cited Count：5 Percentile：5.84(Chemistry, Multidisciplinary)

Nitride fuels have several advantages, such as high thermal conductivity and high metal density like metallic fuels, and high melting point and isotropic crystal structure like oxide fuels. Since the late 1990s, the partitioning and transmutation of minor actinides (MA) has been studied to decrease the long term radio-toxicity of high level waste and mitigate the burden on the final disposal. Japan Atomic Energy Agency (JAEA) has been proposing dedicated transmutation cycle using the Accelerator-Driven System (ADS) with the nitride fuels containing MA. We have been developing the nitride fuel cycle including pyrochemical process. Our focus is on electrolysis of nitride fuels and refabrication of nitride fuel from the recovered actinides because other processes are similar to the technology for the metal fuel treatment and have been studied elsewhere. In this paper, we summarized our activity on developments of the pyrochemical treatment of the spent nitride fuels.

Journal Articles

Experimental study on control blade degradation and its modeling

Kurata, Masaki; Shibata, Hiroki; Sakamoto, Kan*; To, Takehiko*

Proceedings of 2014 Water Reactor Fuel Performance Meeting/ Top Fuel / LWR Fuel Performance Meeting (WRFPM 2014) (USB Flash Drive), 8 Pages, 2014/09

Control blade degradation is predicted to occur at the early stage of severe accident of boiling water reactor. Simulation tests and modeling are being performed by collaboration among JAEA, Hitachi-GE Nuclear Energy (Hitachi-GE), Nippon Nuclear Fuel Development (NFD), and Nippon Steel & Sumitomo Metal Corporation (NSSMC). Preliminary simulation tests under inert atmosphere indicated that complicated chemical reactions progressed and that finally the mixture of degraded control blade and the channel box separated into two parts. The first part rich in Zr had low melting temperature and flowed down from the high temperature region like candling. The second part rich in steel, B, and C mechanically collapsed down at temperatures higher than approximately 1673K. The interaction between the control blade and the channel box was highly exothermic. Preliminary model for control blade degradation is being developed using VOFFLUENT, which successfully simulates the early stage ofthe control blade degradation.

Journal Articles

Hydrogen absorption/desorption behavior through oxide layer of fuel claddings under accidental conditions

Sakamoto, Kan*; Shibata, Hiroki; Une, Katsumi*; Ouchi, Atsushi*; Aomi, Masaki*; Kurata, Masaki

Proceedings of 2014 Water Reactor Fuel Performance Meeting/ Top Fuel / LWR Fuel Performance Meeting (WRFPM 2014) (USB Flash Drive), 7 Pages, 2014/09

The depth profiles of hydrogen were measured at outer surface of fuel claddings corroded in high temperature steams at 1073-1473 K to examine the barrierness of surface oxide layer against the hydrogen absorption/desorption. The results indicated that the oxide layer would be no longer the barrier against the hydrogen under some conditions although it remained as the barrier against the oxidation.

Journal Articles

Evaluation of Gibbs free energies of formation of Ce-Cd intermetallic compounds using electrochemical techniques

Shibata, Hiroki; Hayashi, Hirokazu; Akabori, Mitsuo; Arai, Yasuo; Kurata, Masaki

Journal of Physics and Chemistry of Solids, 75(8), p.972 - 976, 2014/08

https://doi.org/10.1016/j.jpcs.2014.04.004

Times Cited Count：18 Percentile：59.26(Chemistry, Multidisciplinary)

Gibbs free energies of formation of six Ce-Cd intermetallic compounds, CeCd, CeCd $_{2}$ , CeCd $_{3}$ , CeCd $_{58/13}$ , CeCd $_{6}$ and CeCd $_{11}$ , were evaluated systematically using electrochemical techniques in the temperature range from 673 to 923 K in the LiCl-KCl-CeCl $_{3}$ -CdCl $_{2}$ molten salt bath. The linear dependence of the Gibbs free energies of formation on temperature yields to the enthalpies and entropies of formation of these intermetallic compounds. By extrapolating the molar Gibbs free energy of Ce-Cd intermetallic compounds to the Cd distillation temperature, it was clear that the molar Gibbs free energy of Ce in Ce-Cd intermetallic compounds decreases gradually from CeCd $_{11}$ to CeCd $_{2}$ and attains to the minimum value at CeCd $_{2}$ . This suggests on the Cd distillation from the U-Pu-Ce-Cd alloy that the dissolution of U or Pu into CeCd $_{2}$ should be mostly taken into consideration.

Journal Articles

Progress review of research and development on accelerator driven system in JAEA

Oigawa, Hiroyuki; Tsujimoto, Kazufumi; Sasa, Toshinobu; Kurata, Yuji; Takei, Hayanori; Saito, Shigeru; Nishihara, Kenji; Obayashi, Hironari; Sugawara, Takanori; Iwamoto, Hiroki

KURRI-KR(CD)-40 (CD-ROM), p.16 - 30, 2013/00

In JAEA, research and development on an Accelerator-Driven System (ADS) have been conducted in order to transmute minor actinides (MA) contained in high-level radioactive wastes. One unit of ADS with thermal power of 800 MW can transmute MA generated in 10 units of light water reactors with electric power of 1 GW. In JAEA, we are studying variety of technical areas such as a superconducting proton accelerator, a spallation target including a beam window and a subcritical core including neutronics design and safety assessment. Moreover, construction of the Transmutation Experimental Facility is being planned as a phase-2 program of the J-PARC project to perform basic experiments for transmutation technology.

Journal Articles

Formation of atomically flat -FeSi $_{2}$ /Si(100) interface using ion irradiated substrate

Sasase, Masato*; Yamamoto, Hiroyuki; Kurata, Hiroki*

Thin Solid Films, 520(9), p.3490 - 3492, 2012/02

https://doi.org/10.1016/j.tsf.2011.12.067

Times Cited Count：0 Percentile：0.02(Materials Science, Multidisciplinary)

Thin uniform -FeSi $_{2}$ films were fabricated on ion irradiated Si(100) substrates to achieve an atomically flat interface. Ion irradiation produces a surface with more defects than chemical etching, however, it is expected that the presence of defects can promote the formation of compound films such as -FeSi $_{2}$ that require interdiffusion and reaction processes. However, excess defects can also result in random nucleation, poor crystallinity and a rough interface. Cross-sectional transmission electron microscopy was used to determine the optimum conditions for ion irradiation of the substrate to obtain a clear -FeSi $_{2}$ /Si interface.

Journal Articles

Present status for research and development on accelerator driven system in JAEA

Tsujimoto, Kazufumi; Oigawa, Hiroyuki; Kurata, Yuji; Nishihara, Kenji; Sugawara, Takanori; Takei, Hayanori; Saito, Shigeru; Obayashi, Hironari; Iwamoto, Hiroki

Proceedings of International Conference on Toward and Over the Fukushima Daiichi Accident (GLOBAL 2011) (CD-ROM), 8 Pages, 2011/12

To continue the utilization of the nuclear fission energy, the management of the high-level radioactive waste (HLW) is one of the most important issues to be solved. Partitioning and Transmutation technology of HLW is expected to be effective to mitigate the burden of the HLW disposal by reducing the radiological toxicity and heat generation. The Japan Atomic Energy Agency (JAEA) has been conducting the research and development (R&D) on accelerator-driven subcritical system (ADS) as a dedicated system for the transmutation of long-lived radioactive nuclides. The ADS proposed by JAEA is a lead-bismuth eutectic (LBE) cooled fast subcritical reactor with thermal output of 800 MW. For ADS to play important roles in the nuclear fuel cycle, several critical issues have to be resolved. Items of R&D are divided into three technical areas peculiar to the ADS: (1) superconducting linear accelerator (SC-LINAC), (2) LBE as spallation target and core coolant, and (3) subcritical core design and technology. For these technical areas, various R&D activities are progressing in JAEA. In this paper, the present status of the R&D activities in JAEA is reported.

Journal Articles

A Phase-field simulation of uranium dendrite growth on the cathode in the electrorefining process

Shibuta, Yasushi*; Unoura, Seiji*; Sato, Takumi; Shibata, Hiroki; Kurata, Masaki*; Suzuki, Toshio*

Journal of Nuclear Materials, 414(2), p.114 - 119, 2011/07

https://doi.org/10.1016/j.jnucmat.2011.01.040

Times Cited Count：16 Percentile：73.97(Materials Science, Multidisciplinary)

The uranium dendrite growth on cathode during pyroprocessing of uranium is investigated using a novel phase-field model, in which electrodeposition of uranium and zirconium from molten-salt is taken into account. The threshold concentration of zirconium in molten salt demarcating the dendritic and planar growth is then estimated as a function of the current density. Moreover, growth process of both the dendritic and planar electrodeposits has been demonstrated by way of varying the mobility of the phase field, which consists of the effect of attachment kinetics and diffusion.

Journal Articles

Structure of beam tracks induced by swift heavy ions in Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8}$ superconductors

Sasase, Masato*; Okayasu, Satoru; Yamamoto, Hiroyuki; Kurata, Hiroki*; Hojo, Kiichi

Japanese Journal of Applied Physics, Part 1, 46(2), p.783 - 786, 2007/02

https://doi.org/10.1143/JJAP.46.783

Columnar defects are produced in semiconducting and insulating materials by swift heavy ion irradiation. In the present study, we investigate the columnar defects produced in the Bi $_{2}$ Sr $_{2}$ CaCu $_{2}$ O $_{8}$ superconductor by the heavy ion irradiation (Au $^{+}$ , I $^{+}$ , Br $^{+}$ , Ni $^{+}$ ) in the energy range of 60-600 MeV. On the basis of the transmission electron microscopy, it is shown that the diameters of columnar defects become smaller and their distributions become narrower with the ion velocity. These facts are explained as the effect of nuclear collision by calculating the mean free path for the irradiated ions. Present results imply the nuclear collisions strongly affect the columnar defect formations even for the swift heavy ion irradiation.

Journal Articles

Structure of beam tracks induced by swift heavy ions in BiSrCaCuO superconductors

Sasase, Masato*; Okayasu, Satoru; Yamamoto, Hiroyuki; Kurata, Hiroki*; Hojo, Kiichi

Japanese Journal of Applied Physics, Part 1, 46(2), p.783 - 786, 2007/02

https://doi.org/10.1143/JJAP.46.783

Times Cited Count：1 Percentile：5.42(Physics, Applied)

Columnar defects are produced in semiconductor and insulator materials by swift heavy ion irradiation. It has been considered that the electronic stopping power of irradiating ions is the dominant factor in the formation of defects. However, our recent results suggest that ion-velocity is also an important parameter for use in describing this phenomenon. We investigate the columnar defects produced in BiSrCaCuO (Bi-2212) superconductor by heavy ion irradiation (Au $^{8+,12+}$ , I $^{8+,29+}$ , Br $^{12+}$ , and Ni $^{11+}$ ) in the energy range of 60-600MeV. From tansmission electron microscopy, it is shown that the diameters of columnar defects become smaller and their distribution become narrower with an increase in ion velocity. This is explained as an effect of nuclear collision by calculation of the mean free path for the irradiated ions. The present results imply that nuclear collisions strongly affect the formation of columnar defects, even for swift heavy ion irradiation.