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JAEA Reports

Hydraulic Experiment on Flow Optimization in Compact Reactor Vessel; Effects of double dipped plates and outer shell of UIS

Nakayama, Oukatsu; Kimura, Nobuyuki; Kamide, Hideki; Ito, Masami*; Sekine, Tadashi*

JNC TN9400 2005-032, 103 Pages, 2005/03

JNC-TN9400-2005-032.pdf:33.44MB

On the FBR feasibility study, an innovative sodium cooled fast reactor has been investigated in Japan Nuclear Cycle Development Institute. In order to reduce the construction cost of reactor, the compact reactor vessel is designed. Gas entrainment at the free surface is one of issues to be solved because of high velocity in the upper plenum vessel. We performed an 1/10th scaled model water experiment for the upper plenum of reactor vessel and investigated flow fields in the plenum in order to optimize flow. In the last experiment, we established flow optimization structures for reduction of flow toward to the free surface and restraint on the vortex cavitations near H/L inlet, i.e., plug into the dipped plate hole to install a fuel handling mechanism (FHM) and a flow splitter at vessel wall. In this report, effects of double dipped plates (D/Ps) and outer shell of upper inner structure (UIS) are investigated. In the result, we could confirm that the double D/P structure set below the free surface is effective to reduce flow toward the free surface between reactor vessel wall and guide tube of fuel transfer machine. An FHM plug, which has a step structure at mid height between double D/Ps, showed that it reduced flow velocity through the gap between the plug and the D/P. A perforated outer shell was set around the UIS to reduce vortex strength developed from the cold legs to the hot leg intake and also to restrain the vortex cavitation. It was shown that the onset condition of vortex cavitation at reactor vessel wall was reduced and the cavitation occurred easily. At the cold leg the onset condition of the caviation was not advanced. The flow distribution through the perforated outer shell should be optimized.

JAEA Reports

Water experiment on gas entrainment in reactor vessel using 1/1.8th scaled model, Gas entrainment in large scaled model

Kimura, Nobuyuki; Tobita, Akira; Kobayashi, Jun; Nakayama, Oukatsu; Ito, Masami*; Kamide, Hideki

JNC TN9400 2004-067, 48 Pages, 2004/05

JNC-TN9400-2004-067.pdf:19.55MB

An innovative sodium cooled fast reactor has been investigated in a frame work of the FBR feasibility study. A compact reactor vessel is designed to reduce the construction cost, where sodium flow velocity increases. One of the thermal hydraulic issues in this design is gas entrainment at free surface in the reactor vessel. Dipped plates (D/P) are set below the free surface in order to prevent the gas entrainment.We performed an 1/10th scaled model water experiment for the upper plenum of reactor vessel and flow optimization was done to reduce flow velocity near the free surface. However, previous studies showed that the gas entrainment depends on model scale. Then an 1/1.8th scaled model was also planned to confirm the phenomena in an enough large model. As a test section, 90 degree sector and region between the free surface and the D/P was modeled by 1/1.8th scale. Boundary conditions at D/P gaps and radial cross sections of sector ends were obtained by the 1/10th scaled full sector model. The gas entrainment was not observed in the model under the velocity condition of reactor full power operation at water levels higher than 4% of the normal height from the D/P. It is shown that the gas entrainment will be eliminated in the reactor vessel according to the current design approach.

JAEA Reports

Study on In-vessel ISI for JOYO - Core support plate inspection equipment under sodium -

Ariyoshi, Masahiko; Nakayama, Oukatsu

JNC TN9400 2004-015, 27 Pages, 2004/03

JNC-TN9400-2004-015.pdf:0.8MB

This report describes the feasibility study on the in-vessel inspection technique to be applied for the experimental fast reactor JOYO. Since JOYO is a sodium cooled fast reactor and the core structure components are in high temperature and fast neutron irradiation environment, material strength yields to decrease due to heat fatigue and irradiation induced embrittlement. The present surveillance method of testing structural material mechanical property, monitoring subassembly outlet temperature and sodium leak are not sufficient to detect a small crack. Therefore, the direct inspection method to confirm the core structure integrity needs to be developed considering the recent innovative technology. Since the core structure has a complicated form and components under sodium are not visible, the manipulator technology is essential which has various positioning functions. The core support plate was selected to be an important inspection item, and the method which combines ultrasonic non-destructive inspection technology and manipulator technology was examined. In this study, the core support plate inspection equipment concept was examined on the assumption that the inspection of the core support plate was executed under sodium. The sensor for the nondestructive testing is built into the inspection assembly which is loaded in most outer core area, and can be accessed to a low-pressure plenum sidewall by the manipulator. The linear array sensor which arranges several piezo-electric elements were applied to the sensor for the nondestructive testing, and for scanning the inspection object in non-contact. It was assumed for the concept of the manipulator that the sensor was positioned by moving of the arm and bending the joint. The technology of the Master Slave Manipulator for Laparoscopic Surgery was applied for the manipulator. A detailed examination is necessary for this concept in the future. And, the development of in-vessel inspection equipment is continued and prot

JAEA Reports

All under-water experiment on the acoustic characteristic of high temperature ultrasonic transducers

Nakayama, Oukatsu;

JNC TN9400 2000-087, 74 Pages, 2000/07

JNC-TN9400-2000-087.pdf:3.25MB

We have been developing an Ultrasound Doppler Velocimetry technique (UDV), in order to apply thermo-hydraulic measurement in sodium. A feasibility study had been conducted to identify development subjects of sensor and signal processing. Thus, high temperature ultrasonic transducers were manufactured to use in water and sodium tests, which will be scheduled to optimize an algorism of signal processing and to improve the characteristic of the transducer. ln this report, we described the results of an experiment on the acoustic characteristic of transducer in water. The results are as follows : (1)The ultrasound beam profile of the transducer relating to the characteristic of velocity profile measurement using scattering ultrasound wave was obtained. The estimation of ultrasound beam profile in liquid and an ultrasound near-field region were introduced from these experimental data, (2)lt was confirmed that the frequency's spectrum of transducers are adequate for the design requirement of flow velocity range. The specifications of a transmitter and receiver for a transducer were identified, such as the amplitude gain for scattered ultrasound signal and the frequency resolution for Doppler sift signal. (3)The spatial resolution of the ultrasound beam was estimated to evaluate the accuracy of now profile measurement on UDV system.

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