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Journal Articles

Basic concept on structural design criteria for zirconia ceramics applying to nuclear components

Shibata, Taiju; Sumita, Junya; Baba, Shinichi; Yamaji, Masatoshi*; Ishihara, Masahiro; Iyoku, Tatsuo; Tsuji, Nobumasa*

Key Engineering Materials, 297-300, p.728 - 733, 2005/11

no abstracts in English

JAEA Reports

Coarse break-up of a stream of oxide and steel melt in a water pool (Contract research)

Moriyama, Kiyofumi; Maruyama, Yu; Usami, Tsutomu*; Nakamura, Hideo

JAERI-Research 2005-017, 173 Pages, 2005/08

JAERI-Research-2005-017.pdf:11.17MB

A series of experiments on the break-up of high temperature oxide and steel melt jets in a water pool was conducted. The objective was to obtain data for the jet break-up length and size distribution of the droplets produced by the jet break-up, and information on the influence of material properties. Also, we tried to obtain additional information giving a clue to the mechanism governing the melt jet break-up, such as flow intensity of the steam column surrounding the melt jet, and its relation with the droplet size. In the experiments, zirconia-alumina mixture and stainless steel melt jets with diameter 17mm and velocity 7.8m/s at the water surface were dropped into a deep (2.1m) or shallow (0.6m) water pool with various subcool. From the results of the present experiments and also by referring other experimental data from literature, we obtained empirical correlation equations for the jet break-up length, the fraction of jet broken-up in a shallow pool where the jet was not completely broken-up, and the droplet size.

Journal Articles

Oxygen potential and defect structure of oxygen-excess pyrochlore Ce $_{2}$ Zr $_{2}$ O $_{7+x}$

Otobe, Haruyoshi; Nakamura, Akio; Yamashita, Toshiyuki; Minato, Kazuo

Journal of Physics and Chemistry of Solids, 66(2-4), p.329 - 334, 2005/02

https://doi.org/10.1016/j.jpcs.2004.07.015

Times Cited Count：23 Percentile：65.92(Chemistry, Multidisciplinary)

Pyrochlore-type (P-type) zirconias have been attracting significant research interest as disposable forms of high-level radioactive waste. In this work, we have clarified the oxygen potentials (g(O $_{2}$ )) vs. oxygen nonstoichiometry (x) and temperature relations of P-type Ce $_{2}$ Zr $_{2}$ O $_{7+x}$ by the emf method and determined the lattice parameters (a0) with respect to x by XRD method.

Journal Articles

Variations in mechanical properties of zirconia-base ceramics due to superplastic deformations

Kikuchi, Makoto*; Motohashi, Yoshinobu*; Ito, Tsutomu*; Sakuma, Takaaki*; Shibata, Taiju; Baba, Shinichi; Ishihara, Masahiro; Sawa, Kazuhiro; Hojo, Tomohiro*; Tsuji, Nobumasa*

Nihon Kikai Gakkai Kanto Shibu Ibaraki Koenkai (2004) Koen Rombunshu (No.040-3), p.57 - 58, 2004/09

no abstracts in English

Journal Articles

Effects of neutron irradiation on some superplastic characteristics of tetragonal zirconia polycrystals containing 3 mol% yttria

Shibata, Taiju; Ishihara, Masahiro; Motohashi, Yoshinobu*; Ito, Tsutomu*; Baba, Shinichi; Kikuchi, Makoto*

Materials Transactions, 45(8), p.2580 - 2583, 2004/08

https://doi.org/10.2320/matertrans.45.2580

Times Cited Count：3 Percentile：26.88(Materials Science, Multidisciplinary)

Fast neutrons (energy 1.610 $^{23}$ J) were irradiated to tetragonal zirconia polycrystals containing 3 mol% yttria (3Y-TZP) at the fluence levels of 2.510 $^{24}$ (Light irradiation) and 4.310 $^{24}$ (Heavy irradiation) m $^{-2}$ . The irradiation caused no significant swelling in the 3Y-TZP specimens. After the neutron irradiation, superplastic characteristics were examined by tensile tests at a temperature range from 1623 to 1773 K with initial strain rates ranging from 5.010 $^{-4}$ to 1.6710 $^{-2}$ s $^{-1}$ . It was found that the elongation to fracture of the irradiated specimens was quite small in comparison with the unirradiated ones. The apparent activation energy for the superplastic flow of the irradiated 3Y-TZP was fairly high, i.e., 781 and 693 kJ・mol $^{-1}$ for Light and Heavy irradiations, respectively. Atomic displacement damages and defects in the 3Y-TZP caused by the irradiation were thought to be main causes of these property changes.

Journal Articles

Irradiation behavior of rock-like oxide fuels

Yamashita, Toshiyuki; Kuramoto, Kenichi; Shirasu, Noriko; Nakano, Yoshihiro; Akie, Hiroshi; Nagashima, Hisao; Kimura, Yasuhiko; Omichi, Toshihiko*

Journal of Nuclear Materials, 320(1-2), p.126 - 132, 2003/07

https://doi.org/10.1016/S0022-3115(03)00178-8

Times Cited Count：10 Percentile：56.43(Materials Science, Multidisciplinary)

Two irradiation tests on the rock-like oxide (ROX) fuels, small disk-shape fuel targets and pellet-type fuels, were performed in order to clarify in-pile irradiation stabilities. Swelling, fractional fission gas release (FGR) and phase change were examined by puncture test, profilometry and ceramography. YSZ single-phase fuel showed an excellent irradiation behavior, ie. low fission gas release (less than 3%), negligible swelling and no appreciable restructuring. The particle dispersed fuels showed lower swelling and higher fission gas release than those of mechanically blended fuels. Spinel decomposition and subsequence restructuring in the spinel matrix fuels was observed for the first time in the present investigation. It would be possible to reduce the FGR of the spinel matrix fuels, if the maximum fuels temperature is limited below 1700 K where neither spinel decomposition nor restructuring was observed. Damaged area of spinel matrix due to fission fragment irradiation seemed to be confined to thin layers around the surface of YSZ particles.

Journal Articles

Radiation damage effects in superplastic 3Y-TZP irradiated with Zr ions

Motohashi, Yoshinobu*; Kobayashi, Tomokazu*; Harjo, S.*; Sakuma, Takaaki*; Shibata, Taiju; Ishihara, Masahiro; Baba, Shinichi; Hoshiya, Taiji

Nuclear Instruments and Methods in Physics Research B, 206, p.144 - 147, 2003/05

https://doi.org/10.1016/S0168-583X(03)00702-X

Times Cited Count：4 Percentile：33.69(Instruments & Instrumentation)

The 3mol% yttria containing tetragonal zirconia polycrystals(3Y-TZP) were irradiated using 130MeV Zr $^{11+}$ ions in the TANDEM accelerator facility at Tokai Research Establishment, JAERI. Irradiation was performed with the fluence of 3.510 $^{16}$ and 2.110 $^{17}$ ions/m $^{2}$ . Residual stress and changes in mechanical properties caused by the ion irradiation and the effects of the subsequent annealing are studied. The occurrence of compressive residual stresses and increases in hardness and fracture toughness were found at the surface regions of as-irradiated specimens. It was found from the subsequent annealing that these quantities decreased gradually with raising the annealing temperature and returned to that of un-irradiated state at around 1173K. A most probable cause of the increases in the hardness and fracture toughness after the irradiation may, therefore, be the residual compressive stresses left in the irradiated surface region.

Journal Articles

Superplastic deformation characteristics of 3Y-TZP after Zr ion irradiation

Shibata, Taiju; Ishihara, Masahiro; Motohashi, Yoshinobu*; Baba, Shinichi; Hoshiya, Taiji; Kobayashi, Tomokazu*; Harjo, S.*; Sakuma, Takaaki*

Nuclear Instruments and Methods in Physics Research B, 206, p.139 - 143, 2003/05

https://doi.org/10.1016/S0168-583X(03)00701-8

Times Cited Count：4 Percentile：33.69(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Oxygen potential measurements of pyrochlore-type Zr $_{2}$ M $_{2}$ O $_{7+x}$ 7(M=Pu, Ce) by EMF method

Otobe, Haruyoshi; Nakamura, Akio; Yamashita, Toshiyuki; Ogawa, Toru

Journal of Nuclear Science and Technology, 39(Suppl.3), p.652 - 655, 2002/11

http://www.tandfonline.com/doi/abs/10.1080/00223131.2002.10875553

Pyrochlore-type (P-type) zirconia has been widely studied as a disposable form of the high-level radioactive nuclear waste. We have developed the EMF (electromotive force) measurement system using the cubic zirconia sensor, in order to investigate the oxygen potential (g(O $_{2}$ )) of P-type Zr $_{2}$ Pu(Ce) $_{2}$ O $_{7+x}$ . For P-type Zr $_{2}$ Ce $_{2}$ O $_{7+x}$ at 1078 K, we have found that g(O $_{2}$ ) vs. oxygen composition (x) relationship has different behavior between x more than 0.34 and x less than 0.34. This may suggest that the degree and way of the ordering of oxide ions (O $^{2-}$ ) and oxygen vacancies (V0) should change around x =0.34. We have also measured the g(O $_{2}$ ) vs. temperature (T) relationship between 763 and 1078 K at various x, and derived the partial molar enthalpy (h(O $_{2}$ )) and entropy (s(O $_{2}$ )) of oxygen. It was found that h(O $_{2}$ ) and s(O $_{2}$ ) of P-type Zr $_{2}$ Ce $_{2}$ O $_{7+x}$ exhibit significantly different behavior from those of fluorite-type CeO $_{2-x}$ . The similar experiments are in progress for P-type Zr $_{2}$ Pu $_{2}$ O $_{7+x}$ , and the results are discussed in comparison with those of P-type Zr $_{2}$ Ce $_{2}$ O $_{7+x}$ mentioned above.

Journal Articles

Rock-like oxide fuels and their burning in LWRs

Yamashita, Toshiyuki; Kuramoto, Kenichi; Akie, Hiroshi; Nakano, Yoshihiro; Shirasu, Noriko; Nakamura, Takehiko; Kusagaya, Kazuyuki*; Omichi, Toshihiko*

Journal of Nuclear Science and Technology, 39(8), p.865 - 871, 2002/08

https://doi.org/10.3327/jnst.39.865

Times Cited Count：25 Percentile：81.52(Nuclear Science & Technology)

Research on the plutonium rock-like oxide (ROX) fuels and their once-through burning in light water reactors has been performed to establish an option for utilizing and disposing effectively the excess plutonium. The ROX fuel is a sort of the inert matrix fuels and consists of mineral-like compounds such as yttria stabilized zirconia, spinel and corundum. A particle-dispersed fuel was devised to reduce damage by heavy fission fragments. Some preliminary results on swelling, fractional gas release and microstructure change for five ROX fuels were obtained from the irradiation test and successive post-irradiation examinations. Inherent disadvantages of the Pu-ROX fuel cores could be improved by adding 238U or 232Th as resonant materials, and all improved cores showed a nearly the same characteristics as the conventional UO2 core during transient conditions. The threshold enthalpy of the ROX fuel rod failure was found to be comparable to the fresh UO2 rod by pulse-irradiation tests simulating reactivity initiated accident conditions.

Journal Articles

Experimental investigation on the effect of superplastic deformation on the specific heat of a zirconia-based ceramic

Wan, C.*; Shibata, Taiju; Baba, Shinichi; Ishihara, Masahiro; Hoshiya, Taiji; Motohashi, Yoshinobu*

Netsu Bussei, 16(2), p.58 - 63, 2002/06

https://doi.org/10.2963/jjtp.16.58

no abstracts in English

Journal Articles

Effect of neutron irradiation on electromotive force of oxygen sensor using zirconia solid electrolyte

Hiura, Nobuo*; Yamaura, Takayuki; Motohashi, Yoshinobu*; Kobiyama, Mamoru*

Nihon Genshiryoku Gakkai Wabun Rombunshi, 1(2), p.202 - 208, 2002/06

https://doi.org/10.3327/taesj2002.1.202

The purpose of this study is to develop oxygen sensor which can measure the oxygen potential of the fuel in a nuclear reactor. The oxygen sensor with CaO stabilized zirconia solid electrolyte has been specially designed in order to prolong its life time. Electromotive force (EMF) of solid galvanic cell Ni/NiO|ZrO $_{2}$ -CaO|Fe/FeO was measured in both the out-pile tests and the in-situ tests using Japan Material Testing Reactor (JMTR), and the characteristics of EMF was discussed. In the out-pile test, it was found that the EMF was almost equal to the theoretical values at temperatures ranging from 700 to 1,000 $^{circ}C$ , and the life span of the sensor was very long up to 980h at 800 $^{circ}C$ . In the in-situ test, it was found that the EMF showed almost the reliable values up to 300 h (neutron fluence (E 1 MeV) 1.510 $^{23}$ m $^{-2}$ ), at temperatures from 700 to 900 $^{circ}C$ . The imprecision of the EMF was found to be within 6% of the theoretical values up to 1,650 h irradiation time (neutron fluence (E 1 MeV) 8.010 $^{23}$ m $^{-2}$ ) at 800 $^{circ}C$ . The oxygen sensors were found to be applicable for the oxygen potential measurement of the fuels in a reactor.