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[en] Three separate effect tests are performed to investigate thermal-hydraulic phenomena found in reactor coolant system in case of the loss-of-residual-heat-removal (LORHR) during mid-loop operation: off-take and slugging at the surge inlet in the hot-leg, two-phase mixture level in the pressurizer and condensation heat transfer in the U-tube. The test facilities are designed according to the scaling analysis so as to maintain scale similarities with the prototypes of nuclear power plant. A scale methodology proposed by the present study satisfies the preservation of parameters for off-take and mixture level. New experimental data and correlations are obtained through those separate-effect tests, which are used for the modifications of models in the RELAP5/MOD3 code. Modified correlations are implemented into the RELAP5/MOD3 and assessed. The effect of tube diameter is investigated using the condensation heat transfer data in the U-tube. It turns out that the flow parameter governing condensation heat transfer with noncondensible gas is the mixture Reynolds number. The off-take and slugging in the hot-leg with the surge line are experimentally tested using the off-take test facility. The scaling analysis is performed to scale down the test facility. The experimental results are categorized into three items: onset of off-take (liquid entrainment) at the branch pipes, onset of slug transition in the horizontal pipe and discharge quality at the branch pipes. It is found out that the scale effect of the branch diameter on the onset of liquid entrainment is small. While the existing correlation of onset of liquid entrainment well predicts the present data, the Taitel-Dukler correlation for the onset of slug transition does not. The onset of slug transition shows its strong influence on the discharge quality. A new correlation for onset of slug transition is developed and implemented into RELAP5/MOD3. The discharge quality is strongly affected by the flow regime - stratified or slug flow - in the horizontal pipe, which means that the onset of slug transition plays a very important role of the quality behavior by off-take. New correlations for discharge quality are developed considering the critical dependency of the onset of slugging bifurcating into high and low qualities on the boundary of flow regime transition. The liquid holdup in the pressurizer is investigated using the pressurizer test facility. The behavior in the surge line is not critical compared with phenomena in the hot-leg and the pressurizer, and merely transports two-phase fluids: the discharged flow by an off-take from the hot-leg: and the drained flow of accumulated liquids in the pressurizer. The two-phase mixture level in the pressurizer is examined, which gives the pool void fraction data. The pool void fraction is lower than the predictions by RELAP5/MOD3. Thus, the RELAP5/MOD3 code is assessed through the implementation of empirically modified correlation of drift velocity. The onset of water-draining at the surge outlet (at the bottom of the pressurizer) is also examined, which occurs at higher gas velocity as the collapsed level increases in the pressurizer. There is discrepancy between the data of onset of water-draining and the predictions from RELAP5: draining initiates at much lower gas flows in the predictions. The local heat transfer coefficients of in-tube condensation are examined in the single vertical tube with the same diameter (0.75') as that of the U-tube. These results are compared with the previous data performed with the same diameter (2.0') as that of the PCCS to investigate the diameteric scale effect on the heat transfer. Total 6 series of the data for local heat transfer coefficients are obtained. The present data uses different scaling methodologies for steam-air mixture flow rates: Reynolds number similitude, velocity similitude, and Froude number similitude. It is revealed that the similitude of mixture Reynolds number is most scalable to the wall condensation heat transfer. A new correlation unifying the previous and present data is developed using degradation factor expressed in terms of the mixture Reynolds number
[en] In the Loss-of-RHR accident during mid-loop operation reflux condensation in U-tube riser is experimentally studied. The present experimental study handles with the reflux condensation in the presence of noncondensable gas in a vertical tube. The main interest is to investigate the parametric effects such as inlet air mass fraction, system pressure and inlet steam flow rate on reflux condensation heat transfer. The test facility is mainly composed of two parts: an air-steam mixture generation part and a reflux condensation part(test section). Air is used as a noncondensable gas. Experiments are performed under the system pressure of 1 ∼ 2.5bar, inlet steam flow rate of 1.04 ∼ 2.15kg/hr and inlet air mass fraction of 0 ∼ 57.9%. From experimental results, several characteristics of parametric effects are confirmed. The presence of air causes a decrease in heat transfer coefficients and, as a result, increases the active condensation length. As the inlet steam flow rate increases, the active length slightly increases during reflux condensation. As the system pressure increases, the active condensation length somehow decreases with an increase in heat transfer coefficients in that zone. And the flooding limit for inlet mixture flow rate is much less than that of Wallis' flooding formula
[en] The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate. A single vertical tube has a geometry which is a length of 2.4 m, inner diameter of 16.56 mm and outer diameter of 19.05 mm and is made of stainless steel. Air is used as a noncondensable gas. The secondary side has a shape of annulus around vertical tube and the lost heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 11 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348∼3.282 kg/hr, of inlet air mass fraction 11.8∼55.0 percent. The investigation of the flooding is preceded to find the upper limit of the reflux condensation. Onset of flooding is lower than that of Wallis' correlation. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the increase of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed by 165 data of the local heat transfer. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17.7 percent between the results by the experiment and by the correlation. (author)
[en] A separate effect test facility consisting of hot-leg, surge line and pressurizer is installed to investigate the gas flow into the pressurizer and the entrained water holdup in the pressurizer. The collapsed and mixture levels are measured with changes of gas flow rate during the liquid holdup process. Onset of liquid collapse, CCFL and frictional drop in the surge line are examined during the water collapse process. Scaling analysis is performed to have scale similarities between test facility and real plant. CCFL and velocity similitude are applied to geometric scale parameters in the test facility. Scale similarity for the collapsed and mixture levels are examined. The collapsed level has a similarity from the present scaling methodologies. The mixture level also has a similarity in case that the void fraction is preserved. Preliminary experimental results are obtained for the liquid holdup process. The collapsed level becomes a control parameter instead of the water level in hot-leg together with the gas flow rate
[en] The local heat transfer coefficient is experimentally investigated for the reflux condensation in a countercurrent flow between the steam-air mixture and the condensate. A single vertical tube has a geometry which is a length of 2.4m, inner diameter of 16.56mm and outer diameter of 19.05mm and is made of stainless steel. Air is used as a noncondensible gas. The secondary side is installed in the form of coolant block around vertical tube and the heat by primary condensation is transferred to the coolant water. The local temperatures are measured at 15 locations in the vertical direction and each location has 3 measurement points in the radial direction, which are installed at the tube center, at the outer wall and at the coolant side. In three different pressures, the 27 sets of data are obtained in the range of inlet steam flow rate 1.348∼3.282kg/hr, of inlet air mass fraction 11.8∼55.0%. The local heat transfer coefficient increases as the increase of inlet steam flow rate and decreases as the decrease of inlet air mass fraction. As an increase of the system pressure, the active condensing region is contracted and the heat transfer capability in this region is magnified. The empirical correlation is developed represented with the 165 sets of local heat transfer data. As a result, the Jacob number and film Reynolds number are dominant parameters to govern the local heat transfer coefficient. The rms error is 17.7% between the results by the experiment and by the correlation
[en] The off-take and the liquid entrainment on the air-water interface are experimentally investigated at the T-junction of vertical-up branch on the horizontal pipe. In case of the pressurizer manway opening after the loss of residual heat removal during a shutdown operation, the steam boiled from the core flows into the pressurizer via the surge line and is discharged through the manway, where the steam flow accompanies the coolant entrainment by the off-take below the inlet of surge line. This study has a focus on a shutdown operation. Test conditions are slightly over the atmospheric pressure and at room temperature. No water flow exists. An off-take is visually observed using the transparent pipes. Scaling analysis is performed to scale down the test facility to the reference prototype, Korea standard nuclear power plant (UCN units 3 and 4). The horizontal leg and surge line geometries are scaled down as the horizontal pipe and the vertical-up branch pipe, respectively. Two different diameters of the branch pipe to have proper scalling methodologies are proposed for looking the diameter effect. The main pipe diameter (D) is 0.295m and the surge line diameters (d) are 0.05m and 0.07m. They have large scales than those of related experimental studies. Experimental data is able to have the phenomenological similarity with the reference plant by the use of the large scale facility and by the scaling analysis. With changes of an air flow and a water level, the onset of liquid entrainment (OLE) and the branch quality are investigated. The onset of slug transition (OST) in horizontal pipe is also observed and investigated for the relationship between the horizontal flow regime and the off-take phenomena. The scale effect of branch pipe exists in the OLE and the OST data. The branch quality is strongly affected by the flow regime in horizontal pipe. The stratified flow is more persistent up to large air flow than the existing model. These experimental results will be bases of studies in phenomenological modeling and the proper scaling methodologies in the future works
[en] We studied the method to gain a clear LSF using a thick aluminum sheet and to acquire the spatial resolution value with a high accuracy for a low spatial resolution imaging modality. In this study, aluminum sheets with thicknesses varying from 0.3 mm to 1.2 mm were tested to derive a modulation transfer function (MTF) for the oversampling and non-oversampling methods. The results were evaluated to verify the feasibility of the use of thick sheets for periodic quality assurance. Oversampling was more accurate than non-oversampling, and an aluminum sheet with a correction factor less than 2 at the cut-off frequency, which was less than 0.8 mm in this case, was confirmed to be suitable for MTF measurements. Therefore, MTF derivation from a thick aluminum sheet with thickness correction is plausible for a medical imaging modality.
[en] The off-take and the slug transition on air-water interface are experimentally investigated at the T-junction of the horizontal pipe with a vertical upward branch to simulate the loss-of-residual-heat-removal during a mid-loop operation in the Korea standard nuclear power plant. Scaling analysis is performed to scale down the experimental facility to the reference nuclear power plant. Two different diameters of branch pipes are used to verify the scaling laws and their scale effects. Air is used as working gaseous fluid and no water flow exists. Off-take behavior on horizontal stratified and slug flows is visually observed in the horizontal pipe. The experimental data are divided into three categories; onset of liquid entrainment at T-junctions, onset of slug transition in the horizontal pipe, and discharge quality in the branch pipe. It is found out that the scale effect of the branch diameter on the onset of liquid entrainment is small and the existing correlations for it are applicable. Also, the onset of slug transition shows a discrepancy with Taitel-Dukler's correlation and has a strong influence on the discharge quality. New correlations for discharge quality are developed considering the critical dependency of the onset of slugging. (author)
[en] The off-take and the liquid entrainment on air-water interface are experimentally investigated at the T-junction with a vertical upward branch to simulate the loss-of-residual-heat-removal (LORHR) during a mid-loop operation in the Korea Standard Nuclear Power Plant (KSNPP). Scaling analysis is performed to scale down the experimental facility to the reference nuclear power plan, UCN Unit 3 and 4. Two different diameters of branch pipe use two scaling similarities to confirm the scaling law. An air is used as working fluid and no water flow exists. An off-take behavior is visually observed using transparent pipes. Main control parameters are the water level in horizontal pipe and the air flow rate. The experimental results are divided into three categories; onset of liquid entrainment at T-junction, onset of slug transition in horizontal pipe, and discharge quality in the surge line. These results are compared with previous results related to the small-break loss-of-coolant-accident (SB-LOCA) for top-side breaks. The scale effect of branch pipe diameters (d) is investigated: no clear dependency on the pipe diameter. The existing correlation for the onset of liquid entrainment well predicts the present data. However, data of the onset of slug transition do not have good agreement with several existing correlations. The branch quality is strongly affected by the slug transition in the horizontal pipe: quality suddenly drops when the transition occurs. (authors)
[en] Computed tomography (CT) measures the attenuation coefficient of an object and converts the value assigned to each voxel into a CT number. In radiation therapy, the CT number, which is directly proportional to the linear attenuation coefficient, must be converted to an electron density for radiation dose calculations for cancer treatment. However, if various tube voltages are applied to take the patient’s CT image without applying the specific CT number to the electron density conversion curve, the accuracy of the dose calculation is not assured. In this study, changes in CT numbers for different materials due to changes in the tube voltage were demonstrated, and the dose calculation errors in the percentage depth dose (PDD), along with a clinical case were analyzed. The maximum dose difference in the PDD from the treatment planning system (TPS) dose calculation and from the Monte Carlo simulation were 1.3% and 1.1%, respectively, when applying the same CT number to the electron density conversion curve for the 80-kVp and 140-kVp images. In the clinical case, different CT number to electron density conversion curves at tube voltage of 80 kVp and 140 kVp were applied to the same image and the maximum differences in the mean, maximum, and minimum doses were 1.1%, 1.2%, and 1.0%, respectively, at the central region of the phantom and 0.6%, 0.9%, and 0.8%, respectively, at the peripheral region of the phantom.