Jun-ichi Saito

Velocity Profile Measurement of Lead-Lithium Flows by High-Temperature Ultrasonic Doppler Velocimetry

Abstract This paper describes a high-temperature ultrasonic Doppler Velocimetry (HT-UDV) technique that has been successfully applied to measure velocity profiles of the lead-lithium eutectic alloy (PbLi) flows. The impact of tracer particles is investigated to determine requirements for HT-UDV measurement of PbLi flows. The HT-UDV system is tested on a PbLi flow driven by a rotating-disk in an inert atmosphere. We find that a sufficient amount of particles contained in the molten PbLi are required to successfully measure PbLi velocity profiles by HT-UDV. An X-ray diffraction analysis is performed to identify those particles in PbLi, and indicates that those particles were made of the lead mono-oxide (PbO). Since the specific densities of PbLi and PbO are close to each other, the PbO particles are expected to be well-dispersed in the bulk of molten PbLi. We conclude that the excellent dispersion of PbO particles enables the HT-UDV to obtain reliable velocity profiles for operation times of around 12 hours.

High-Temperature Ultrasonic Doppler Velocimetry for Lead-Lithium Flows

Nuclear fusion reactors are a promising candidate of the future power source. Magnetic confinement fusion (MCF) blankets adopt high-temperature liquid metals (LM) such as the lead-lithium eutectic alloy (PbLi), as a coolant/tritium breeder. Developments of the LM-MCF blankets require comprehensive understanding of the high-temperature LM flows under the influence of the plasma-confining magnetic field. A high-temperature ultrasonic Doppler velocimetry (HT-UDV) has been developed as a flow diagnostic technique to acquire local velocity profiles of the opaque, high-temperature LM flow. This paper describes HT-UDV technique that has been successfully applied to measure velocity profiles of PbLi flows. The impact of tracer particles is investigated to determine requirements for HT-UDV measurement of PbLi flows. The HT-UDV system is tested on a PbLi flow driven by a rotating-disk in an inert atmosphere. We find that a sufficient amount of particles contained in the molten PbLi are required to successfully measure PbLi velocity profiles by HT-UDV. An X-ray diffraction analysis is performed to identify those particles in PbLi, and indicates that those particles were made of the lead mono-oxide (PbO). Since the specific densities of PbLi and PbO are close to each other, the PbO particles are expected to be well-dispersed in the bulk of molten PbLi. We conclude that the excellent dispersion of PbO particles enables the HT-UDV to obtain reliable velocity profiles for operation times of around 12 h.

Reaction, Transport and Settling Behavior of Lead-Bismuth Eutectic in Flowing Liquid Sodium

The experimental study has been carried out to investigate reaction, transport and settling behavior of lead-bismuth eutectic (LBE) in flowing liquid sodium. In the test, 168g of LBE were poured into flowing sodium from the top of a vertical-type sodium loop which contained 23.2 kg of sodium. The initial temperature of LBE and sodium was 673K. The flow rate and the maximum velocity of sodium in the loop were controlled and measured at 20 dm3 /min and 1 m/sec, respectively, using an electro-magnetic pump and an electro-magnetic flow meter. The sodium loop has a settling chamber at the lower part to investigate the concentration decrease behavior of solid particle reaction products in the sodium due to the settling effect. The concentration was measured by sodium sampling from the 11 positions of the loop during the experiment and its post-test chemical analysis. The temperature changes at the various parts of the loop were also measured during the experiment by thermo-couples attached on the outer surface of the loop. Ultrasonic detectors were attached on the outer surface of the loop below the position of a LBE pour nozzle to demonstrate the utility as a leak detector.Copyright

Effect of the Titanium Nanoparticle on the Quantum Chemical Characterization of the Liquid Sodium Nanofluid

Suspension state of a titanium nanoparticle in the liquid sodium was quantum chemically characterized by comparing physical characteristics, viz., electronic state, viscosity, and surface tension, with those of liquid sodium. The exterior titanium atoms on the topmost facet of the nanoparticle were found to constitute a stable Na-Ti layer, and the Brownian motion of a titanium nanoparticle could be seen in tandem with the surrounding sodium atoms. An electrochemical gradient due to the differences in electronegativity of both titanium and sodium causes electron flow from liquid sodium atoms to a titanium nanoparticle, Ti + Na → Ti(δ-) + Na(δ+), making the exothermic reaction possible. In other words, the titanium nanoparticle takes a role as electron-reservoir by withdrawing free electrons from sodium atoms and makes liquid sodium electropositive. The remaining electrons in the liquid sodium still make Na-Na bonds and become more stabilized. With increasing size of the titanium nanoparticle, the deeper electrostatic potential, the steeper electric field, and the larger Debye atmosphere are created in the electric double layer shell. Owing to electropositive sodium-to-sodium electrostatic repulsion between the external shells, naked titanium nanoparticles cannot approach each other, thus preventing the agglomeration.

Technical Development for IASCC Irradiation Experiments at the JMTR

Irradiation assisted stress corrosion cracking (IASCC) is considered to be one of the key issues from a viewpoint of the life management of core components in the aged Light Water Reactors (LWRs). To simulate IASCC behavior by the in-pile IASCC experiment or post-irradiation experiment (PIE), it is necessary to irradiate specimens up to a neutron fluence that is higher than the so-called IASCC threshold fluence in a test reactor. There are, however, some technical hurdles to overcome for the experiments. For the in-pile IASCC test, techniques assembling pre-irradiated specimens into an in-pile test capsule in a hot cell by remote handling are necessary, and the Japan Atomic Energy Agency (JAEA) developed the techniques for the in-pile test to be carried out in the Japan Material Testing Reactor (JMTR). To examine crack growth and crack initiation behaviors under neutron irradiation, pre-irradiated specimens were relocated from pre-irradiation capsules to an in-pile capsule. Hence, a remote welding machine has been newly developed and welding work for inner and outer tubes of capsule are carried out with rotating of the capsule. The other hurdle is the material integrity of the capsule of the capsule housing for a long term irradiation. Since the changes in microstructure, micro chemistry and mechanical properties of materials increase with neutron fluence, the integrity for capsules of long irradiation period was evaluated by tensile tests in the air and slow strain rate test (SSRT) in oxygenated water. Specimens were obtained from the outer tubes of capsule irradiated to 1.0–3.9 × 1026 n/m2 (E> 1 MeV) previously. Elongation more than 15% in tensile test at 423 K was confirmed and no IGSCC fraction was shown in SSRT at 423 K which was estimated as temperature at the outer tubes of the capsule under irradiation.Copyright