Results 1 - 10 of 146
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[en] This publication is the outcome of an IAEA coordinated research project (CRP) on understanding and prediction of thermohydraulic phenomena relevant to supercritical water cooled reactors (SCWRs). The publication illustrates the state of the art in SCWR research and development. It is a key supporting publication to researchers and engineers pursuing the development of SCWRs or equipment/components operating at supercritical pressures. Scientific investigators from participating institutes identified specific research objectives to improve predictive capability of key technology areas (such as heat transfer and pressure drop for SCWR fuel related geometries, parallel channel stability boundary, natural circulation flow, critical heat flux at near critical pressures, critical flow, and subchannel and plenum mixing). The publication presents the background and objectives and descriptions of the revised Canadian SCWR design concept and a new SCWR design concept being developed at the Nuclear Power Institute of China. It also presents updated information on key areas of technology, such as supercritical heat transfer in simple geometries, stability and critical flow, which have been obtained after the completion of the previous CRP. New experiments and data on supercritical heat transfer in bundles and on critical heat flux, and the application of direct numerical simulation approach for supercritical heat transfer are also detailed.
[en] The paper presents the statistical analysis of experimental results of radiation-induced critical brittle temperature ∆TF shifts and reference temperatures ∆T0 obtained respectively from the impact bend and fracture toughness tests of the reactor vessel metal surveillance specimens to define the possibility of their mutual application for the irradiation embrittlement coefficient to be determined more accurately. The correlation between these parameters is shown to remain up to the accumulation of over-design fast neutron fluence. (author)
[en] The hoop conjecture, introduced by Thorne almost five decades ago, asserts that black holes are characterized by the mass-to-circumference relation 4πM/C≥1, whereas horizonless compact objects are characterized by the opposite inequality 4πM/C<1 (here C is the circumference of the smallest ring that can engulf the self-gravitating compact object in all azimuthal directions). It has recently been proved that a necessary condition for the validity of this conjecture in horizonless spacetimes of spatially regular charged compact objects is that the mass M be interpreted as the mass contained within the engulfing sphere (and not as the asymptotically measured total ADM mass). In the present paper we raise the following physically intriguing question: is it possible to formulate a unified version of the hoop conjecture which is valid for both black holes and horizonless compact objects? In order to address this important question, we analyze the behavior of the mass-to-circumference ratio of Kerr–Newman black holes. We explicitly prove that if the mass M in the hoop relation is interpreted as the quasilocal Einstein–Landau–Lifshitz–Papapetrou and Weinberg mass contained within the black-hole horizon, then these charged and spinning black holes are characterized by the sub-critical mass-to-circumference ratio 4πM/C<1. Our results provide evidence for the non-existence of a unified version of the hoop conjecture which is valid for both black-hole spacetimes and spatially regular horizonless compact objects.
[en] The Brazilian Multipurpose Reactor - RMB is a 30 MW pool type research reactor, that uses Materials Testing Reactor - MTR type fuel assemblies. It has a 5x5 square array core with 23 fuel assemblies and two in-core irradiation positions, operating with upward flow and average velocities nearly 10 m/s in the fuel plates channels. The IEA-R1 is a 5 MW pool type research reactor, which also has a 5x5 square array core with 19 standard fuel assemblies, four control fuel assemblies and a central beryllium irradiation device. It operates with downward flow nearly 1.8 m/s in the channels. In order to verify and provide data and information about the dynamical behavior of fuel assemblies under nominal and critical conditions, the experimental circuit ORQUIDEA is being designed. This circuit will permit upward and downward flow and dynamical behavior of the fuel assemblies and its parts will be tested and verified. Flow rate, temperature, pressure and differential pressure transducers are the instruments of the circuit. Endurance and critical flow velocity tests will be performed. The COLIBRI experimental circuit is being designed to make tests that allow the studies of the fluid-structure phenomenology of fuel plates similar to those of the RMB fuel assemblies when subjected to high flow velocities, which can induce pressure differences between the channels formed by the fuel plates. This work presents a preliminary design for the ORQUIDEA and COLIBRI experimental circuits to be built at the Instituto de Pesquisas Energéticas e Nucleares - IPEN of the Comissão Nacional de Energia Nuclear - CNEN. (author)
[en] We have measured the temperature dependence of resistivity in single-crystalline CeNiGe3 under hydrostatic pressure in order to establish the characteristic pressure–temperature phase diagram. The transition temperature to AFM-I phase TN1 = 5.5 K at ambient pressure initially increases with increasing pressure and has a maximum at ∼3.0 GPa. Above 2.3 GPa, a clear zero-resistivity is observed (SC-I phase) and this superconducting (SC) state coexists with AFM-I phase. The SC-I phase suddenly disappears at 3.7 GPa simultaneously with the appearance of an additional kink anomaly corresponding to the phase transition to AFM-II phase. The AFM-II phase is continuously suppressed with further increasing pressure and disappears at ∼6.5 GPa. In the narrow range near the critical pressure, an SC phase reappears (SC-II phase). A large initial slope of upper critical field μ0Hc2 and non-Fermi liquid behavior indicate that the SC-II phase is mediated by antiferromagnetic fluctuations. On the other hand, the robust coexistence of the SC-I phase and AFM-I phase is unusual on the contrary to superconductivity near a quantum critical point on most of heavy-fermion compounds. (author)
[en] Practical superconducting wires and tapes have been developed after a discovery of superconductivity in 1911. Nowadays, many“ practical” superconducting wires and tapes are available commercially and used for various applications. Most of them are multifilamentary wires with stabilizer. The present status of practical superconducting wires and tapes are introduced with short histories. (author)
[en] The superconducting joint is utilized for superconducting magnets operated using persistent current mode. MRI, NMR, and MCZ, which are commercial products in the superconducting market, are also operated using persistent current mode, and are constructed with low-temperature superconducting wires. Since these magnets need a constant and stable magnet field for long period of time, the superconducting joints must have extremely low resistivity, lower than 10-11 Ω to avoid rapid degradation of the magnetic field. Commercial low-temperature superconducting wires have NbTi or Nb3Sn filaments embedded in stabilizing materials such as copper or aluminum matrixes. To realize a low-resistance joint, the stabilizing materials are removed and the mutual filaments are directly jointed. This manuscript introduces superconducting joint methods for low-temperature superconducting wires, which has been developed by the superconducting magnet manufactures and related R&D institutions. (author)
[en] We studied the anisotropy of the superconducting upper critical field Hc2 in the heavy-fermion superconductor UTe2 under hydrostatic pressure by magnetoresistivity measurements. In agreement with previous experiments we confirm that superconductivity disappears near a critical pressure pc ≈ 1.5 GPa, and a magnetically ordered state appears. The unusual Hc2(T) at low temperatures for H∥ a suggests that the multiple superconducting phases which appear under pressure have quite different Hc2. For a field applied along the hard magnetization b axis Hc2(0) is glued to the metamagnetic transition Hm, which is suppressed near pc. The suppression of Hm with pressure follows the decrease of temperature Tχmax, at the maximum in the susceptibility along b. The strong reinforcement of Hc2 at ambient pressure for H∥b above 16 T is rapidly suppressed under pressure due to the increase of Tsc and the decrease of Hm. The change in the hierarchy of the anisotropy of Hc2(0) on approaching pc points out that the c axis becomes the hard magnetization axis. (author)
[en] The present study makes efforts to simulate the behavior of fully developed stationary shocks, caused by the incidence of supercritical flow with a cross-barrier in an open channel. The numerical solution of nonlinear governing shallow flow equations has been implemented by the application of a second-order Roe TVD scheme. The obtained results from numerical experiment are compared with some measured in a laboratory setup. It can be deduced by comparison of the flow depths in numerical and measured experiments in three different cases of cross-barrier width of 6, 12 and 16 cm that the numerical scheme of Roe is a robust and capable method for simulation of complicated stationary shocks in shallow water flow.
[en] We investigate the uniaxial strain effects on the quantum spin liquid κ-(ET)2Ag2(CN)3 which is an organic Mott insulator with a nearly regular S = 1/2 triangular lattice. The uniaxial compressive strains along the in-plane b- and c-axes suppress the semiconducting behavior and induce a Mott transition, followed by a superconducting transition at low temperatures. The simulations of band structure under the in-plane uniaxial strains suggest a significant distortion of triangular lattice. The critical temperature TC of the superconducting transition appeared above the critical pressure of Mott transition under uniaxial strain is higher than that under hydrostatic pressure as observed in the sister compound κ-(ET)2Cu2(CN)3. The enhancement of TC by the distortion of triangular lattice is a common feature of superconductivity neighboring to spin liquid. (author)