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Torikawa, Tomoaki*; Odaira, Naoya*; Ito, Daisuke*; Ito, Kei*; Saito, Yasushi*; Matsushita, Kentaro; Ezure, Toshiki; Tanaka, Masaaki
Konsoryu, 36(1), p.63 - 69, 2022/03
On free surface of a sodium cooled fast reactor, gas entrainment can be caused by free surface vortices, which may result in disturbance in core power. It is important to develop an evaluation model to predict accurately entrained gas flow rate. In this study, entrained gas flow rate a simple gas entrainment experiment is conducted with focusing on effect of pressure difference between upper and lower tanks. Pressure difference between upper and lower tanks are controlled by changing gas pressure in lower tank. As a result, it is confirmed that the entrained gas flow rate increases with increasing pressure difference between upper and lower tanks. By visualization of swirling annular flow in suction pipe, it is also observed that pressure drop in suction pipe increases with increase in entrained gas flow rate, which implies that entrained gas flow rate can be predicted by evaluation model based on pressure drop in swirling annular flow region.
Ozaki, Yusuke; Ishibashi, Masayuki; Matsushita, Tomoaki*; Masumoto, Kazuhiko*; Imasato, Takehiko*
Proceedings of 13th SEGJ International Symposium (USB Flash Drive), 4 Pages, 2018/11
In the Mizunami Underground Research Laboratory, Groundwater REcoverty Experiment in Tunnel (GREET) is performed to understanding the recovery process of geological environment after the closure of drift. In this experiment, we performed 2D electrical resistivity surveys three times. First survey was performed before the closure of test drift. Second and third surveys were performed after the closure test. The first survey detected two layers conformation that consists of conductive and resistive zones at shallower and deeper part from the drift surface, respectively. These layers correspond to the shotcrete and host rock, respectively. Second and third measurements show that the conductive zone expanded to deeper resistive part while the shallower conductive part did not change. We concluded that we captured the saturation process of dried fractures near the drift wall by closure of drift as an electrical resistivity response.
Kato, Masashi*; Matsushita, Yoshinori*; Ichimura, Masaya*; Hatayama, Tomoaki*; Oshima, Takeshi
Japanese Journal of Applied Physics, 51(2), p.028006_1 - 028006_2, 2012/02
Times Cited Count：16 Percentile：55.56(Physics, Applied)Excess carrier lifetimes in as-grown and low-energy electron irradiated p-type 4H-SiC epitaxial layers were investigated using the microwave photoconductivity decay method. The carrier lifetime increased with increasing excitation density in the epilayers. This results suggests that the dominant recombination center in the epilayers has larger capture cross section for electrons than capture cross section for holes. The carrier lifetime in the epilayer decreased by the low-energy electron irradiation decreases. The decrease in lifetime in the electron irradiated samples showed recovery after annealing at 1000 
C.
Matsushita, Yoshinori*; Kato, Masashi*; Ichimura, Masaya*; Hatayama, Tomoaki*; Oshima, Takeshi
Materials Science Forum, 645-648, p.207 - 210, 2010/00
Silicon carbide (SiC) is a promising material for radiation hardness devices. In this study, we evaluated excess carrier decay curves in both as-grown and electron-irradiated p-type 4H-SiC layers by the microwave photoconductivity decay (
-PCD) method. The samples used in this study were an Al-doped p-type epitaxial layer grown on a Si-face B doped bulk p-type 4H-SiC. The samples were irradiated with electrons at an energy of 160 keV and at a doses of 1
10
cm
(ele-16) and 110
cm (ele-17). As a results of -PCD measurements, the lifetimes of free carriers for as-grown, ele-16 and ele-17 were estimated to be 0.14 s, 0.07 s and 0.04 s, respectively. This result indicates that defects acting as recombination centers were introduced by the electron irradiation.
Kato, Masashi*; Matsushita, Yoshinori*; Ichimura, Masaya*; Hatayama, Tomoaki*; Oshima, Takeshi
no journal, ,
no abstracts in English
Masumoto, Kazuhiko*; Matsushita, Tomoaki*; Takeuchi, Ryuji
no journal, ,
no abstracts in English
Masumoto, Kazuhiko*; Matsushita, Tomoaki*; Takeuchi, Ryuji
no journal, ,
The monitoring of groundwater condition in fractures around the rock cavern is important for safety assessment for high level radioactive waste. The GPR (Ground Penetrating Radar) method is unique technique to survey the water condition in fractures, indirectly, and with no disturbance of original groundwater condition. The authors conducted the GPR monitoring of infiltration of saline water on the side wall of the 500m access tunnel of Mizunami Underground Research Laboratory. The results showed that the difference of saline concentration in fractures caused the change of the reflection wave form and the intense of spectrum due to the results of spectrum analysis of reflection wave.
Ozaki, Yusuke; Matsushita, Tomoaki*; Masumoto, Kazuhiko*; Imasato, Takehiko*
no journal, ,
In Mizunami Underground Research Laboratory, Groundwater REcovery Experiment in Tunnel (GREET) is performed to capture the post closure behavior of geoenvironment near the test drift. For the evaluation of physical property near the drift wall, repetitive electrical resistivity surveys are performed. The tomography results indicate the resistivity change following to the change in water saturation in the host rock. In this study, we convert the resistivity value to the saturation by using the equation proposed by Kusumi et al., (2006) to clear the degree of change in saturation. Estimated saturation clearly shows the abrupt rise and gentle reduction after drift closure and release of drift, respectively.
Torikawa, Tomoaki*; Odaira, Naoya*; Ito, Daisuke*; Ito, Kei*; Saito, Yasushi*; Matsushita, Kentaro; Ezure, Toshiki; Tanaka, Masaaki
no journal, ,
On free surface of a sodium cooled fast reactor, gas entrainment can be caused by free surface vortices, which may result in disturbance in core power. It is important to develop an evaluation model to predict accurately entrained gas flow rate. In this study, the effect of pressure gradient in vortex axis direction on the gas entrainment flow rate is investigated in a simple gas experimental apparatus, in which upper and lower tanks are connected by a suction pipe. As a result, it was observed that there are two flow regime: swirling annular flow regime shows the tendency that only the gas entrainment flow rate increases with almost constant pressure gradient, then, when liquid plug is induced by the development of free surface disturbance, the gas entrainment flow rate increases as the pressure gradient increases. In addition, it was confirmed that the transformation of those two flow regimes is advanced by higher liquid level in the upper tank.
