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JNC TN9400 2000-008, 323 Pages, 2000/02
JNC-TN9400-2000-008.pdf:25.2MB
This rport presents numerical results on theemal striping characteristics at a tee junction of LMFBR coolant pipe, carried out using a direct numerical simulation code DINUS-3. In the numerical investigations, it was considered a tee junction system consisted of a main pipe (1.33 cm
) with a 90
elbow and a branch pipe, and four parameters, j.e., (1)diameter ratio 
between both the pipes, (2)flow velocity ratio 
between both the pipes, (3)angle 
between both the pipes, and (4)Reynolds number Re. From the numerical investigations, the following characteristics were obtained: (1)According to the decreasing of the diameter ratio, significant area of second-order moments was expanded in the fixed condition of =1.0. (2)Significant second-order moments area was expanded for the increasing of the flow velocity ratio specified by varying of the main pipe velocity in the case of a = 1.0 constant condition. 0n the other hand, the area was expanded for the decreasing of the velocity ratio defined by varying of the branch pipe velocity in the case of a = 3.0 constant condition. (3)Maximum second-order moments values were generated in the case of = 180 due to the influence of interactions between main pipe flows and jet flows from the branch pipe. (4)According to the increase of Reynolds number, significant area of second-order moments was expanded due to the activation of turbulence mixing in the main pipe.
; ; Kamide, Hideki
JNC TN9400 2000-026, 70 Pages, 1999/11
JNC-TN9400-2000-026.pdf:10.93MB
The phenomena on a thermal-hydraulic field inside/outside the porous blockage has been investigated by the experiment employed the 4-subchamlel geometry water test facility. From existing experimental and numerical studies, it was shown that the now field around the blockage had significant effect on the temperature distribution inside the blockage. Therefore, We conducted the experiment of flow visualization with 4-subchannel geometry water test facility. The flow visualization showed that the recirculation flow and a lateral flow existed at the side of the porous blockage. The region of recirculation flow extended to the downstream side with increasing of the flow rate. The mixing due to the convection was dominant in the region of recirculation flow, and was getting effective as increasing of the flow rate. ln the wake region, the flow was unstable due to the interaction between the flows in the unplugged and plugged subchannels. The coolant was provided from the unplugged subchannels and also through the inside of porous blockage. These results obtained from the flow visualization gathering with the numerical simulation will be reflect to the evaluation of the local blockage issue of large scale Fast Breeder Reactor.
; ; ; ; Kamide, Hideki
JNC TN9400 2000-025, 78 Pages, 1999/11
JNC-TN9400-2000-025.pdf:2.24MB
Local blockage issue in a fuel subassembly is one of initiation of local fault in a fast reactor core. ln existing studies, it is shown that blockage in a wire-spacer type pin bundle will consist of small particles coming through the bundle and will be porous. ln order to evaluate the integrity of fuel pins covered by the porous blockage, we have to predict thermohydraulics in the blockage and also in the pin bundle. ln this study sodium experiments were carried out using a 37-pin bundle test section with a porous blockage. The fueI pins are modeled by electric heater pins of 8.5 mm in diameter (full scale). The blockage is formed by stainless steel spheres of 0.3 mm in diameter. The blockage is set in the two rows of subchannels along one side of hexagonal wrapper tube. The length of blockage in axial direction is 35 mm and corresponds to 1/6th of wire wrapping pitch. The experimental parameters were power of the heater pins. The heater power was varied from 14% to 43% of the maximum linear heat rate of a real reactor (
420W/cm). The flow rate in the subassembly was set at 430 l/min corresponding to 93% of the Reynolds number in a fuel subassembly of real reactor under full power condition. The experimental results showed that the highest temperature was measured on the pin surface covered by the blockage and faced to the subchannel which was surrounded by the blockage. The height of peak temperature point was nearly top of the blockage. lt means that the temperature field in the blockage is influenced by flow filed in the blockage significantly. The non-dimensional temperature profile in the blockage and in the pin bundle is independent on heater power.
Tokuhiro, Akira; Kimura, Nobuyuki;
JNC TN9400 2000-014, 86 Pages, 1999/06
JNC-TN9400-2000-014.pdf:11.72MB
Experiments were performed using the WAJECO facility to investigate the thermohydraulic mixing of multiple jets flowing out of a LMFBR core. Mixing is the root of the thermal striping problem. The multiple jets are typically at different velocities and temperatures and may induce thermal stresses upon components they impinge. In our study we modeled the mixing of three vertical jets, the central at a lower temperature than the two adjacent jets at equal temperatures. The jets are quasi-planar. The parameters were the average exit jet velocities (Uo,av) and the temperature difference between the "cold" and "hot" jets (
Thc=Thot-Tcold). Measurements of the liquid velocity, initially using laser Doppler velocimetry (LDV) and later ultrasound Doppler velocimetry (UDV), for both our reference single-jet and the triple-jet configuration, comprised Phase I of the experiments (up to 1994). Two reports (TN9410 96-181 and TN9410 96-296; in Japanese) reported on the hydraulic and heat tra