Furuya, Osamu*; Fujita, Satoshi*; Muta, Hitoshi*; Otori, Yasuki*; Itoi, Tatsuya*; Okamura, Shigeki*; Minagawa, Keisuke*; Nakamura, Izumi*; Fujimoto, Shigeru*; Otani, Akihito*; et al.
Proceedings of ASME 2021 Pressure Vessels and Piping Conference (PVP 2021) (Internet), 6 Pages, 2021/07
Since the Fukushima accident, with the higher safety requirements of nuclear facilities in Japan, suppliers, manufacturers and academic societies have been actively considering the reconstruction of the safety of nuclear facilities from various perspectives. The Nuclear Regulation Authority has formulated new regulatory standards and is in operation. The new regulatory standards are based on defense in depth, and have significantly raised the levels of natural hazards and have requested to strengthen the countermeasures from the perspective of preventing the simultaneous loss of safety functions due to common factors. Facilities for dealing with specific serious accidents are required to have robustness to ensure functions against earthquakes that exceed the design standards to a certain extent. In addition, since the probabilistic risk assessment (PRA) and the safety margin evaluation are performed to include the range beyond the design assumption in the safety improvement evaluation, it is very important to extent the special knowledge in the strength of important equipment for seismic safety. This paper summarizes the research and examination results of specialized knowledge on the concept of maintaining the functions of important seismic facilities and the damage index to be considered by severe earthquakes. In the other paper, the study on reliability of seismic capacity analysis for important equipment in nuclear facilities will be reported.
Morita, Takami*; Niwa, Kentaro*; Fujimoto, Ken*; Kasai, Hiromi*; Yamada, Haruya*; Nishiuchi, Ko*; Sakamoto, Tatsuya*; Godo, Waichiro*; Taino, Seiya*; Hayashi, Yoshihiro*; et al.
Science of the Total Environment, 408(16), p.3443 - 3447, 2010/06
Iodine-131 (I) was detected in brown algae collected off the Japanese coast. The maximum measured specific activity of I in brown algae was 0.370.010 Bq/kg-wet. Cesium-137 (Cs) was also detected in all brown algal samples used in this study. There was no correlation between specific activities of I and Cs in these seaweeds. Low specific activity and minimal variability of Cs in brown algae indicated that past nuclear weapon tests were the source of Cs. Although nuclear power facilities are known to be pollution sources of I, there was no relationship between the sites where I was detected and the locations of nuclear power facilities. Most of the sites where I was detected were near big cities with large populations. On the basis of the results, we suggest that the likely pollution source of I, detected in brown seaweeds, is not nuclear power facilities, but nuclear medicine procedures.
Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.
Journal of Physics and Chemistry of Solids, 68(11), p.2103 - 2106, 2007/11
A lot of attention is currently focused on Pu-based superconductors. These systems have relatively high superconducting (SC) transition temperatures, 18 K for PuCoGa and 9 K for PuRhGa. Both compounds crystallize in the tetragonal HoCoGa (115) structure, which is well known for the heavy-fermion SC systems CeIn (=Co, Rh, Ir)with 2 K at most. Recently, NMR and NQR experiments have been reported for PuCoGa by Curro et al. and for PuRhGa by our group. In both cases, measurements of using NQR have revealed that the Pu115 superconductors show unconventional superconductivity with an anisotropic gap. Now we have measured the more detailed data of for NQR lines in PuRhGa, especially focusing on the low-lying magnetic excitation in the normal state. From the viewpoint of spin-fluctuations, we will discuss the difference between PuRhGa and PuCoGa and between superconducting Pu115 and non-superconducting An115 series.
Tokunaga, Yo; Walstedt, R. E.*; Homma, Yoshiya*; Aoki, Dai*; Kambe, Shinsaku; Sakai, Hironori; Fujimoto, Tatsuya; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; et al.
Journal of Physics and Chemistry of Solids, 68(11), p.2016 - 2019, 2007/11
In this paper, we report a comprehensive study of O nuclear spin-lattice relaxation in NpO for a wide range of fields and temperatures. In both the paramagnetic and ordered-state regions, a strong, field-dependent Np -O nuclei cross-relaxation process is observed in addition to the expected background rate. The cross relaxation process, driven by the Np spins, is conveyed to the O via a greatly enhanced indirect nuclear spin-spin coupling which is described and reported here for the first time. The magnitude and temperature dependence of the indirect coupling are in reasonable accord with a simple theoretical model. The magnitude and temperature dependence of the Np process are also deduced from the data obtained.
Tokunaga, Yo; Sakai, Hironori; Fujimoto, Tatsuya; Kambe, Shinsaku; Walstedt, R. E.*; Ikushima, Kenji*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Haga, Yoshinori; et al.
Journal of Alloys and Compounds, 444-445, p.241 - 245, 2007/10
In this paper, we present our recent NMR works on Neptunium and Plutonium compounds. In order to elucidate the nature of the exotic multipolar ordered phase of NpO, we have initiated the first NMR measurements on this system. We have shown that direct observation of multipole order parameters is possible by means of NMR. Our NMR results provide further insight into the microscopic nature of multipole phase transitions in f-electron systems. We have also performed Ga NMR/NQR studies on a single crystal of PuRhGa. From the temperature dependence of the spin-lattice relaxation rate (), we have found that PuRhGa is an unconventional superconductor having an anisotropic superconducting (SC) gap 2=5. Furthermore, we have confirmed the Knight shift to be decreased below . This gives strong evidence for spin singlet SC pairing.
Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya*; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.
Physical Review B, 76(2), p.024410_1 - 024410_14, 2007/07
Nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR)experiments have been performed on a single crystal of NpCoGa with a Nel temperature =47 K. Knight shift, electric field gradient (EFG), frequency, and asymmetry parameter of the EFG are deduced for each site. These parameters are confirmed by NQR measurements in zero field. Hyperfine tensors for each site are deduced. Antiferromagnetic NMR spectra in zero field were also observed. A sharp anisotropy for spin fluctuations in NpCoGa has also been demonstrated.
Kambe, Shinsaku; Sakai, Hironori; Kato, Harukazu*; Tokunaga, Yo; Fujimoto, Tatsuya*; Walstedt, R. E.*; Ikeda, Shugo; Maehira, Takahiro*; Haga, Yoshinori; Onuki, Yoshichika
Physical Review B, 76(2), p.024411_1 - 024411_6, 2007/07
We report NMR studies on a single crystal of UCoGa, which has the same tetragonal HoCoGa (115) structure as the-wave high- superconductor PuCoGa. The spin-lattice relaxation rate () in UCoGa issmall comparing with those of other actinide 115 compounds. This fact is consistent with a semi-metallic nature of UCoGa suggested by de Haas-van Alphen effect measurements and band calculations. From comparison of at crystallografically different Ga and Co sites and the static susceptibility, an existence of two bands with rather different characters is revealed.
Ito, Takashi; Higemoto, Wataru; Oishi, Kazuki; Fujimoto, Tatsuya*; Heffner, R. H.; Nishida, Nobuhiko*; Sato, Kazuhiko*; Sugawara, Hitoshi*; Aoki, Yuji*; Kikuchi, Daisuke*; et al.
Journal of the Physical Society of Japan, 76(5), p.053707_1 - 053707_4, 2007/05
A filled skutterudite compound SmRuP shows metal-insulatortransition at =16.5K with magnetic anomaly. A possibility of magnetic octupole ordering has been discussed on the basis of multipole degrees of freedom belonging to thecrystalline-electric-field ground state. We investigated local magnetic states in the ordered state by using the muon spin relaxation method. An increase of muon spin relaxation rate was detected in zeroapplied field just below , indicating time-reversal-symmetry breaking in the ordered state. This result suggests that the order parameter includes magnetic octupole and/ordipole. Magnitude of the internal field at the muon site monotonically increases with decreasing temperature, growing steeply below =3K. The longitudinal relaxation rate has a maximum at around , suggesting suppression of magnetic fluctuations. We discussed these experimental facts on the basis of the multipoledegrees of freedom.
Tokunaga, Yo; Kambe, Shinsaku; Sakai, Hironori; Fujimoto, Tatsuya*; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; Walstedt, R. E.*; Yasuoka, Hiroshi; Homma, Yoshiya*; et al.
Kotai Butsuri, 42(4), p.241 - 252, 2007/04
We have initiated the first NMR measurements in the ordered state of NpO. From the angular dependence of hyperfine fields at O nuclei, we have obtained clear evidence for the appearance of field-induced antiferro-octupolar as well as field-induced antiferro-dipolar moments below T=26 K. The NMR studies provide definitive support for the proposed longitudinal triple-q antiferro-octupolar ordering model for NpO.
Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Fujimoto, Tatsuya*; Walstedt, R. E.*; Ikeda, Shugo; Aoki, Dai*; Homma, Yoshiya*; Haga, Yoshinori; Shiokawa, Yoshinobu*; et al.
Physical Review B, 75(14), p.140509_1 - 140509_4, 2007/04
We report spin-lattice relaxation time measurements in isostructural (HoCoGa type) actinide compounds withdifferent ground states (paramagnet, antiferromagnet and superconductor) using single-crystal samples. The anisotropy oflocal magnetic fluctuation due to coupling on the actinide (magnetic) site is evaluated. In the superconductor PuRhGa, the type magnetic anisotropy is strong compared with non-superconducting compounds. Favorable magnetic anisotropy for -wave superconductivity in -electron systems is discussed.
Tokunaga, Yo; Aoki, Dai*; Homma, Yoshiya*; Kambe, Shinsaku; Sakai, Hironori; Ikeda, Shugo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Shiokawa, Yoshinobu*; et al.
Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.735 - 737, 2007/03
In this paper, we present recent and detailed O-NMR results obtained in a single crystal. From the analysis of the field-angle dependence of the NMR spectrum, the appearance of a hyperfine interaction with field-induced antiferro-octupole (AFO) moment has been confirmed. This field-induced AFO moment appears as a result of the longitudinal triple- antiferro-quadrupole (AFQ) structure in the ordered state. We have also observed spin echo modulations caused by quadrupole interactions between the O nuclei and the Np-5f quadrupole moments. This reveals that the AFQ structure is directly observable by NMR. Our NMR results provide further insight into the microscopic nature of multipole phase transitions in f-electron systems.
Fujimoto, Tatsuya; Haga, Yoshinori; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Onuki, Yoshichika*
Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.746 - 747, 2007/03
UPd shows the successive quadrupole orders at K, K and K. The phase transition at comes from the (1/2,0,1/2)-type quadrupole orders on quasi-cubic uranium-sublattice. On the other hand, the quadrupole states below are still controversial; while the Polarized Neutron Diffraction suggested the triple- structure, the Resonant X-ray Scattering assumed the canted quadrupole order. In addition, below , an antiferromagnetic order has been suggested, but the magnetic structure and so on are not still identified. To investigate the local symmetry of the quadruple order in UPd, we tried the nuclear quadrupole resonance, and we succeeded to find the first spin-echo signals from the UPd probed by Pd nuclei. In this paper, we report the nuclear properties of Pd isotope and discuss the characteristics of the quadrupole orders emerging in each temperature phases.
Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Kato, Harukazu; Fujimoto, Tatsuya; Walstedt, R. E.*; Ikeda, Shugo; Matsuda, Tatsuma; Haga, Yoshinori; Aoki, Dai*; et al.
Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.176 - 181, 2007/03
performed NMR measurements in 5f-115 compounds with various ground states [UFeGa (Paramagnet), UPtGa, NpCoGa, NpFeGa (Antiferromagnet) and PuRhGa (Superconductor)], and evaluated the T-dependence of the local (actinide site) magnetic fluctuation energies (//c and c) in the paramagnetic states. An anisotropy in the magnetic fluctuations is observed in all compounds due to the strong LS coupling, in contrast to 3d-high Tc cuprates which have isotropic magnetic fluctuations at Cu sites. It is remarkable that the XY-type magnetic anisotropy is strong in PuRhGa comparing with the non-superconducting 5f-115 compounds. The fluctuation energy in PuRhGa is of the order of 10meV which is between of heavy fermion superconductors (1meV for 1K) and high cuprates (102meV for 100K). The relation between the magnetic fluctuation properties and the ground states will be discussed.
Sakai, Hironori; Kambe, Shinsaku; Tokunaga, Yo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.
Journal of Magnetism and Magnetic Materials, 310(2, Part1), p.e118 - e119, 2007/03
The spin-lattice relaxation rates () have been measured under zero fieldusing nuclear quadrupole resonance (NQR) linesin superconductor PuRhGa and Pauli-paramagnet LuCoGa. In the reference LuCoGa with fully-occupied shell, the shows the constant behavior of (secK). On the other hand, in PuRhGa, is much larger than in LuCoGaand the behavior below 30 K is seen, where its value is 3.27 0.005 (secK). These results suggest a development of coherent Fermi liquid stateincorporated with electronsbelow 30 K in PuRhGa.
Tokunaga, Yo; Aoki, Dai*; Homma, Yoshiya*; Kambe, Shinsaku; Sakai, Hironori; Ikeda, Shugo; Fujimoto, Tatsuya; Walstedt, R. E.*; Yasuoka, Hiroshi; Yamamoto, Etsuji; et al.
Physical Review Letters, 97(25), p.257601_1 - 257601_4, 2006/12
We report a microscopic investigation of multipolar order parameters in the ordered state of NpO conducted via O NMR on a single crystal. From the angular dependence of hyperfine fields at O nuclei, we have obtained clear evidence for the appearance of field-induced antiferro-octupolar as well as field-induced antiferro-dipolar moments below K. We have also observed oscillatory spin-echo decay, which is well understood in terms of small electric field gradients created by antiferro-quadrupolar ordering. This reveals that the quadrupolar order parameter is directly observable by means of NMR. The present NMR studies provide definitive support for a proposed longitudinal triple- type octupolar-quadrupolar ordering model for NpO.
Sakai, Hironori; Tokunaga, Yo; Fujimoto, Tatsuya; Kambe, Shinsaku; Walstedt, R. E.; Yasuoka, Hiroshi; Aoki, Dai*; Homma, Yoshiya*; Yamamoto, Etsuji; Nakamura, Akio; et al.
Journal of the Physical Society of Japan, 75(Suppl.), p.50 - 52, 2006/08
Very recently, we have succeeded in NMR/NQR measurements for PuRhGa. PuRhGa is a superconductor with 9 K, which is isomorphic to PuCoGa with the higher =18 K. We have reported that PuRhGa is an unconventional superconductor with an anisotropic gap, through the measurement of NQR spin-lattice relaxation rate , while PuCoGa is also reported to be such an anisotropic superconductor. The Knight shift and of NMR under applied field for the normal state of PuRhGa suggest an anisotropic feature of hyperfine and/or spin fluctuation in this system. We will outline the superconducting state and report the nature of the normal state based on the basis of and results. The difference between PuRhGa and PuCoGa will be also discussed.
Tokunaga, Yo; Homma, Yoshiya*; Kambe, Shinsaku; Aoki, Dai*; Ikushima, Kenji; Sakai, Hironori; Ikeda, Shugo; Yamamoto, Etsuji; Nakamura, Akio; Shiokawa, Yoshinobu; et al.
Journal of the Physical Society of Japan, 75(Suppl.), p.33 - 35, 2006/08
The low-temperature phase transition in NpO has attracted much attention as a promising candidate for a new class of phase transitions associated with octupolar degrees of freedom. In order to elucidate the nature of this exotic phase transition in NpO, we have initiated the first O-NMR measurements on this system using a powder sample. From the O-NMR spectrum, the occurrence of two inequivalent oxygen sites has been confirmed below = 26 K. It has also been shown that the temperature and field dependence of the O NMR spectrum can be understood by considering an unconventional hyperfine interaction between the O nuclear spins and field-induced antiferromagnetic moments arising from the longitudinal triple- antiferro-quadrupolar order. These NMR results give strong evidence for the occurrence of the longitudinal triple- multipole structure in NpO. We will also discuss our recent O-NMR results in a single crystal.
Fujimoto, Tatsuya; Sakai, Hironori; Tokunaga, Yo; Kambe, Shinsaku; Walstedt, R. E.; Ikeda, Shugo; Matsuda, Tatsuma; Haga, Yoshinori; Onuki, Yoshichika
Journal of the Physical Society of Japan, 75(Suppl.), p.113 - 115, 2006/08
The low-dimensional systems exhibit wide-variety of physical properties. In the antiferromagnetic triangular lattice, for instance, resonating valence bond state is expected, furthermore, in one-dimensional (1D) systems, metal-insulator transition (Peierls transition) occurs due to charge-lattice couplings. Up to now, the study of low-dimensional systems has been mostly performed in oxides and organic compounds, but it is rare in the rare-earth and actinide intermetallics. To looking for the novel low-dimensionality in -electron systems, we focused on the UIrB, and NMR measurement was carried out. From Knight shift and nuclear spin-lattice relaxation rates, ferromagnetic correlations develop above 50 K, but below 50 K, the emergence of antiferromagnetic correlations was clarified along with the saturation of ferromagnetic correlations. The possible model to explain the obtained result is nesting effect on the 1D Fermi surface, and it is expected that UIrB will be the typical compound to investigate the physical properties of 1D -electrons systems.
Kambe, Shinsaku; Sakai, Hironori; Tokunaga, Yo; Fujimoto, Tatsuya; Kato, Harukazu; Walstedt, R. E.; Ikeda, Shugo; Matsuda, Tatsuma; Haga, Yoshinori; Onuki, Yoshichika
Journal of the Physical Society of Japan, 75(Suppl.), p.127 - 129, 2006/08
Recently, new superconductors have been discovered in Pu-based HoCoGa(115) structure compounds: PuCoGa () and PuRhGa (). The discovery has stimulated a lot of interest in actinide compounds. We report NMR measurements on a high-quality single crystal sample of the non-superconducting U- and Np-based 115 compounds. In order to elucidate universal magnetic properties and the origin of superconductivity in the 115 families, spin-lattice relaxation and Knight shift measurements have been performed systematically in the non-superconducting 115 compounds. Comparison of dynamical properties with the superconducting Pu115 compounds will be presented.
Walstedt, R. E.*; Tokunaga, Yo; Kato, Harukazu*; Sakai, Hironori; Fujimoto, Tatsuya; Kambe, Shinsaku; Yasuoka, Hiroshi
Journal of the Physical Society of Japan, 75(Suppl.), p.77 - 81, 2006/08
In a brief recap of recent work on actinide NMR studies at JAERI, we review the direct observation of U NMR which has been carried out for both UO and USb, as well as the estimate of (T) for U which has been obtained from indirect (i.e., of Rh) NMR studies of the Pauli paramagnet URh. New data for 1/ vs. T for O in NpO are presented and analyzed. A sizeable fraction of the observed relaxation rate is strongly field-dependent, an effect attributed to a cross-relaxation process from the 100%-abundant, I = 5/2 Np nuclear spins. Analysis of this relaxation component leads to quantitative estimates of (40ns) and of anomalously enhanced values of the O-Np nuclear spin-spin coupling. These effects as well as future prospects for actinide NMR studies are discussed.