[en] X-ray and neutron powder diffraction were employed to study the crystal and magnetic structures of pseudo-binary Laves-phase compounds (Zr_1-xMn_x)Co₂ and (Zr_1-xMn_x)Co_2.45. It is found that the Zr_0.8Mn_0.2Co₂ compound has the MgCu₂-type cubic structure (space group Fd3m), while Zr_0.64Mn_0.36Co_2.45 and Zr_0.64Mn_0.36Co₂ have the AuBe₅-type (space group F-43m) cubic structure. All compounds are ferromagnets

[en] We measured the resistivity and magnetization of La_0.2Pr_0.5Ca_0.3MnO₃ polycrystals under hydrostatic pressure and magnetic fields. With increasing pressure and fields, overall resistivity values drop sharply and the metal-insulator transition temperature increases monotonically. At the same time, the resistivity data show an anomaly developing at lower temperature than T_C with increasing fields and pressure. Based on the susceptibility measurements, we suggest that this new anomaly should not be due to a thermodynamic transition but that it should be related to percolation phenomena of the metallic phase coexisting with the insulating phase

[en] The Safety Depressurization System (SDS) of KNGR prevents RCS from overpressurization by discharging high pressure and temperature coolant through the I-sparger into the IRWST during an accident. If IRWST water temperature rise locally, around the sparger, beyond 200 .deg. F by the discharged coolant, unstable steam condensation can cause large pressure load on the IRWST wall. To investigate whether this condition can be avoided for the design basis event IOPOSRV (Inadvertent Opening of one Pilot Operated Safety Relief Valve), the flow and temperature distribution of water in the IRWST is calculated by using CFX 4.2 computational fluid dynamic code. According to the results, since pool water temperature does not exceeds temperature limit within 5 seconds after the opening of one POSRV, it can be assured that the integrity of IRWST wall is maintained

[en] Studies of (Ce, U)Al₂ alloys have been made by means of resistivity and susceptibility measurements. We have found that the antiferromagnetic transition temperature (T_N) (3.87 K for CeAl₂) increases continuously with U substitutions and reaches around 6 K for a 20% U-doped sample, while the Kondo temperature (T_K) also seems to increase with U doping up to 30%. We have seen a strong suppression of spin fluctuations in UAl₂ with Ce doping. (author)

[en] We report a low-temperature resistivity-minimum anomaly along with the Cr-like one in Y- and Sc-doped systems, as previously seen for heavy rare-earth and Th-doped systems. In the Y alloys, it is found that this low-temperature-minimum anomaly exists even up to 50% Y. However it is easily destroyed by alloying Ir on the Ru site of already Sc-doped samples. For Sc, the Cr-like anomaly moves towards lower temperature before disappearing at 15% Sc, while we observe that the itinerant antiferromagnetic transition becomes a spin-glass type at 50% Y. The concentration dependence of the various effects varies for Sc, Y, La, and Ce substitutions. (Author)

[en] The magnetic structures of the intermetallic compound La_0.75Sm_0.25Mn₂Si₂ were determined over the temperature region 4.2-500 K by magnetic methods and neutron diffraction. Four different magnetically ordered states are found with critical temperatures of the magnetic phase transitions at T_Sm=14 K, T_AF=150 K, T_C=305 K, and T_N∼500 K. The peculiarities and possible reasons for the existence of these phase transitions are discussed

[en] A detailed X-ray scattering study of the phase transitions in GdB₆ has been performed. For photon energies away from resonance, peaks are observed with two distinct wave vectors of q₁=(0 0 ((1)/(2))) and q₂=(((1)/(2)) ((1)/(2)) 0) at low temperatures. These are shown to arise from distortions of the lattice, although an earlier study had attributed them to competing magnetic-order parameters [J. Appl. Phys. 63 (1998) 3580]. With the photon energy tuned to the Gd L₂ edge, a third set of peaks with q₃=(((1)/(4)) ((1)/(4)) ((1)/(2))) was discovered. This is shown to be the true magnetic-order parameter. Our results reveal a surprisingly rich interaction between the lattice and spin degrees of freedom in this compound

[en] We have observed in recent inelastic neutron scattering experiments that CeTe₂ exhibits two well-defined crystal-field excitations centered at 8 and 18.5 meV above the ground crystal-field level, respectively, and another one at 280 meV which is attributed to the ²F_5/2 → ²F_7/2 intermultiplet transition. These experimental findings clearly demonstrate that the Ce 4f electrons in CeTe₂ are localized. Using crystal-field parameters obtained from the analysis of the crystal-field excitations, we have used a single-ion crystal-field model with mean-field approximation to calculate magnetization and heat capacity both with and without external fields, and have obtained results that are in good agreement with the experimental data

[en] We report on the thermopower of (Ce_xPr_1-x)Cu₆ for 0≤x≤1 from 2 K up to room temperature. Over the studied temperature range, it is found that the thermopower is positive and show a maximum except for pure PrCu₆. Besides the maximum, we notice a shoulder at low temperature. With increasing Pr concentrations, the shoulder becomes more apparent and almost comparable in size to the main maximum. Using the Nordheim-Gorter rule, we have been able to estimate the magnetic contribution of Ce to the thermopower, which is found to be 50 μ V K^-1 at the maximum. We also report the thermopower of PrCu₆ for the first time. It is positive over the studied temperature range. PrCu₆ also shows a modest maximum at higher temperature. This maximum, however, is much broader and smaller than that for the Ce-rich side of CeCu₆. (author)

[en] There are various problems in applying the digital equipment including software to the safety-related system of a nuclear power plant because no standard on quantitative safety assessment is well- accepted. Especially, the fault-tolerant features which is one of the most beneficial aspects of a microprocessor-based system should be evaluated quantitatively in order to assess the safety of a digital system. This paper describes the fault-tolerant features of digital systems which can be applied to software, hardware or system. For the case of watchdog timer which is expected to be the most competitive fault-tolerant mechanism for nuclear power plant's safety systems, this paper show an example of the process of probabilistic safety assessment. The estimation of the coverage factor value of applied lerant mechanism is found to be very important