Numerous experiments were conducted to address when and how the core can lose its original geomet... more Numerous experiments were conducted to address when and how the core can lose its original geometry, what geometries are formed, and in what processes the core materials are transported to the lower plenum of the reactor pressure vessel during a severe accident. Core degradation progresses along the line of clad ballooning, clad oxidation, material interaction, metallic blockage, molten pool formation, melt progression, and relocation to the lower head. Relocation into the lower plenum may occur from the lateral periphery or from the bottom of the core depending upon the thermal and physical states of the pool. Determining the quantities and rate of molten material transfer to the lower head is important since significant amounts of molten material relocated to the lower head can threaten the vessel integrity by steam explosion and thermal and mechanical attack of the melt. In this paper the focus is placed on the melt flow regime on a cylindrical fuel rod utilizing the LAMDA (Lumped Analysis of Melting in Degrading Assemblies) facility at the Seoul National University. The downward relocation of the molten material is a combination of the external film flow and the internal pipe flow. The heater rods are 0.8 m long and are coated by a low-temperature melting metal alloy. The electrical internal heating method is employed during the test. External heating is adopted to simulate the exothermic Zircaloy-steam reaction. Tests are conducted in several quasi-steady-state conditions. Given the variable boundary conditions including the heat flux and the water level, observation is made for the melting location, progression, and the mass of molten material. Finally, the core melt progression model is developed from the visual inspection and quantitative analysis of the experimental data. As the core material relocates downwards a blockage may be formed and grow both radially and axially. The velocity of the melt can be calculated from a force balance between the gravity and frictional losses at the melt-rod interface. When the heater rod is uncovered completely, the melt progression is initiated at the mid-point, which is the hot spot in the rod. However, the melting location is elevated as the water level rises because of the downward heat transfer. Considering the melt flow as a film, the steady-state film thickness on the cylindrical heater rod and the average velocity are computed. The steady-state film flow rate is determined in terms of the density, film thickness, and film velocity.
Previously determining the fuel loading pattern is based on the trial and error method. For a can... more Previously determining the fuel loading pattern is based on the trial and error method. For a candidate pattern, the core analysis is performed and the pattern is examined whether it satisfies the imposed constraints such as the power peaking or not. The pattern, then, is revised by the shuffling of assemblies and the revision is repeated until all of the conditions are met. This method unavoidably requires many iterative diffusion calculations, computing times and accumulated experiences. To overcome these disadvantages, a new method which is called backward diffusion calculation is introduced. If the most desirable power distribution is already known, the optimal loading pattern can be obtained by solving the backward diffusion equation with simple calculation. In this study, the basic equation for the backward diffusion calculation is derived and the optimal power and fuel distributions are searched in one-dimensional cylindrical geometry by using the proposed method. In addition...
A new fast-running analytic model has been developed for analyzing the load follow operation. The... more A new fast-running analytic model has been developed for analyzing the load follow operation. The new model was based on the neural network theory, which has the capability of modeling the input/ output relationships of a nonlinear system. The new model is made up of two error back-propagation neural networks and procedures to calculate core parameters, such as the distributions and density of xenon in a quasi-steady-state core like load follow operation. One neural network is designed to retrieve the axial offset of power distribution, and the other is for reactivity corresponding to a given core condition. The training data sets for learning the neural networks in the new model are generated with a three-dimensional nodal code and, also, the measured data of the first-day test of load follow operation. Using the new model, the simulation results of the 5-day load follow test in a pressurized water reactor show a good agreement between the simulation data and the actual measured data. Required computing time for simulating a load follow operation is comparable to that of a fast-running lumped model. Moreover, the new model does not require additional engineering factors to compensate for the difference between the actual measurements and analysis results because the neural network has the inherent learning capability of neural networks to new situations.
Photorefractive materials like SrBaNb (SBN) have optical properties that can have several militar... more Photorefractive materials like SrBaNb (SBN) have optical properties that can have several military applications. To improve the figures of merit for these materials, it is very important to have better control of Cr dopant in the SBN. Since the amount of Cr dopant is so small, the usual analytical techniques are not adequate to analyze this material. In this report, the incorporation of Cr into SBN using secondary ion mass Abstract spectrometry (SIMS) measurement with an electron gun is confirmed.
While nickel ohmic contacts to n-type silicon carbide have good electrical properties, the physic... more While nickel ohmic contacts to n-type silicon carbide have good electrical properties, the physical contact, and therefore the reliability, can be poor. An approach is described for using the good electrical properties of Ni ohmic contacts while using another metal for its desired mechanical, thermal and/or chemical properties. In the present work, once the Ni contacts have been annealed forming nickel silicides and achieving low contact resistance, they are etched off. Removing the primary Ni contacts also eliminates the poor morphology, voids, and at least some of the excess carbon produced by the Ni/SiC reaction. The Ni contacts are then replaced by a second contact metal. This second metal displays low contact resistance as-deposited, indicating that the critical feature responsible for the ohmic contact has not been removed by the primary contact etch. Not only does this approach provide more flexibility for optimizing the contact for a given application, it also provides some ...
Use of instruments in severe accident guidance is focused on cooling of the reactor core and heat... more Use of instruments in severe accident guidance is focused on cooling of the reactor core and heat removal from the containment. The large uncertainties and extreme conditions involving the severe accident render the measurement and interpretation of the data difficult enough. There presently exist some parameters relevant to monitoring the accident initiation and progression and to preparing necessary measures and strategies to prevent further aggravation and to mitigate the consequence of the accident at hand. One of the accident management guidance parameters for the KSNP (Korean Standard Nuclear Plant) is the core exit temperature (CET). Though the fuel rod temperature is perhaps the most important parameter to determine the phase of accident progression, there is currently no means to read it directly from the core. A best alternative, thus, is to guess the fuel temperature from the measured CET data. The severe accident management guidance (SAMG) suggest that the transition criterion from the emergency operating procedure is the CET of 650 K. The fuel temperature begins to escalate from the time of core uncovery. When the temperature reaches 930 K, hydrogen is generated by oxidation of the cladding whose reaction is accelerated drastically with temperatures exceeding 1500 K. Because the oxidation reaction is exothermal, the core temperature increases rapidly. Although the CET is lower than the fuel temperature, the increase rate will tend to follow that for the fuel rod temperature. In this paper, the focus is placed on the plant damage state during a severe accident. The accident initiator is a small-break loss-of-coolant accident (LOCA). The MAAP4 calculations were carried out to analyze the plant state and accident sequence such as the core uncovery time, the CET, and the primary system pressure. It is concluded that the CET will prove to be a reasonable criterion for recognizing severe core damage. However, when the temperature exceeds 950 K the CET reading may not be reliable so that one needs alternatively to infer the degree of core damage by reading the reactor water level and the hydrogen generation rate.
A hyperbolic two-phase, two-fluid equation system developed in the previous work has been impleme... more A hyperbolic two-phase, two-fluid equation system developed in the previous work has been implemented in an existing nuclear safety analysis code, MARS. Although the implicit treatment of interfacial pressure force term introduced in momentum equation of the hyperbolic equation system is required to enhance the numerical stability, it is very difficult to implement in the code because it is not possible to maintain the existing numerical solution structure. As an alternative, two-step approach with stabilizer momentum equations has been selected. The results of a linear stability analysis by Von-Neumann method show the equivalent stability improvement with fully-implicit solution method. To illustrate the applicability, the new solution scheme has been implemented into the best-estimate thermal-hydraulic analysis code, MARS. This paper also includes the comparisons of the simulation results for the perturbation propagation and water faucet problems using both two-step method and the...
10th International Conference on Nuclear Engineering, Volume 3, 2002
ABSTRACT Analysis was performed for a large-break loss-of-coolant accident (LOCA) in the APR1400 ... more ABSTRACT Analysis was performed for a large-break loss-of-coolant accident (LOCA) in the APR1400 (Advanced Power Reactor 1400 MWe) with the thermal-hydraulic analysis code RELAP5/ MOD3.2.2 and the severe accident analysis code MAAP4.03. The two codes predicted different sequences for essentially the same initiating condition. As for the break flow and the emergency core cooling (ECC) flow rates, MAAP4.03 predicted considerably higher values in the initial stage than RELAP5/ MOD3.2.2. It was considered that the differing break flow and ECC flow rates would cause the LOCA sequences to deviate from one another between the two codes. Hence, the break flow model in MAAP4.03 was modified with partly implementing the two-phase homogeneous critical flow model and adopting a correction term. The ECC flow model in MAAP4.03 was also varied by changing the hardwired friction factor through the sensitivity study. The modified break flow and ECC flow models yielded more consistent calculational results between RELAP5/MOD3.2.2 and MAAP4.03. It was, however, found that the resultant effect is rather limited unless more mechanistic treatments are done for the primary system in MAAP4.03. (authors)
Most of the corrosive degradations in steam generator tubes of nuclear power plants are closely r... more Most of the corrosive degradations in steam generator tubes of nuclear power plants are closely related to the residual stress existing in the local region of a geometric change, that is, an expansion transition, u-bend, ding, dent, bulge, etc. Therefore, accurate information on a geometric anomaly in a tube is a prerequisite to the activity of a non destructive inspection for a precise and earlier detection of a defect in order to prevent a failure during an operation, and also for a root cause analysis of a failure. In this paper, a newly developed eddy current technique of a three-dimensional profilometry is introduced and the proof for the applicability of the technique to a plant inspection is provided. The quantitative profile measurement using a new eddy current probe was performed on steam generator expansion mock-up tubes with various geometric anomalies typically observed in the operating power plants, and the accuracy of the measured data was compared with those from the ...
ÐFive sesquiterpene lactones, 8-acetylarteminolide (1), artanomaloide (2), arteminones (3 and 4),... more ÐFive sesquiterpene lactones, 8-acetylarteminolide (1), artanomaloide (2), arteminones (3 and 4), and dehydromatricarin (5), were isolated from the methanolic extract of the¯ower of Artemisia sylvatica and characterized on the basis of their spectral data. New sesquiterpene lactone 1 was identi®ed as a con®gurational isomer of artanomaloide (2), and the new arteminones 3 and 4 are determined as stereoisomers. 8-Acetylarteminolide (1) strongly inhibited FPTase with an IC 50 of 1.8 mM, however, the other sesquiterpene lactones mildly inhibited the transferase with an IC 50 of 22±300 mM.
Three steroidal glycosides, wondosterols A-C (1–3) have been isolated from a marine two-sponge as... more Three steroidal glycosides, wondosterols A-C (1–3) have been isolated from a marine two-sponge association. Their stereostructures were elucidated on the basis of the spectroscopic analysis of natural wondosterol and its derivatives.
A gas chromatography/mass spectrometry (GC/MS) method is described which uses negative ion chemic... more A gas chromatography/mass spectrometry (GC/MS) method is described which uses negative ion chemical ionization (NCI) and tandem mass spectrometry (MS/MS) for the determination of eight anabolic steroids in human urine. Eight anabolic steroids were derivatized by heptafluorobutyric anhydride (HFBA), and were determined using GC/NCI-MS and GC/NCI-MS/MS. The linear correlation coefficients for calibration in NCI-MS/MS were in the range 0.9880-0.9988. This method of derivatization with HFBA for use with GC/NCI was useful in determinations of 19-norandrosterone, boldenone, 19-noretiocholanolone, 2-methylandrosterone, nandrolone, 1-methyleneandrosterone, 1-methylandrosterone, 4-dihydroboldenone and mesterolone. The detection limits of this procedure were 5-20 ppb at a signal-to-noise (S/N) ratio of 3.
The interfacial area concentration (IAC) is one of the most important parameters in the two-fluid... more The interfacial area concentration (IAC) is one of the most important parameters in the two-fluid model for two-phase flow analysis. The purpose of this study is to develop the local IAC measuring method by using the five-sensor conductivity probe. In this paper, the mathematical approach of the five-sensor conductivity probe method for measuring the local time averaged IAC is described, and numerical simulations are carried out for cap bubbles and two types of ellipsoidal bubbles, as well as spherical bubbles, in order to evaluate the new method. The sizes and locations of the bubbles are determined by using random number generators. To investigate the probe size effect on the accuracy of IAC measurement, three cases for length scales of the probe are applied to the simulations. The simulations show that the five-sensor conductivity probe method proposed in this paper produces better results than the four-sensor method.
This study is concerned with development of a coupled calculation methodology with which to conti... more This study is concerned with development of a coupled calculation methodology with which to continually and consistently analyze progression of an accident from the design-basis phase via core uncovery to core melting and relocation. Experiments were performed to investigate the core coolant inventory depletion after safety injection failure during a large-break loss-of-coolant accident in a cold leg utilizing the Seoul National University Facility (SNUF). The SNUF is an integral test loop scaled down to 1/6.4 in length and 1/178 in area from the Advanced Power Reactor 1400 MWe (APR1400). The SNUF tests are simulated with the RELAP5/MOD3.3 code. The test results revealed that the core coolant inventory decreased five times faster during the sweepout in the downcomer than after termination of the sweepout. The sweepout was observed to take place on top of spillover from the downcomer region to expedite the depletion of the core coolant inventory. The calculation results of RELAP5/MOD3.3 deviated from the experimental data in terms of entrainment from the surface of core coolant, condensation and sweepout in the downcomer. Thereby, the core coolant level was computed to decrease faster than the measured from the experiment due to the overestimated spillover by the evaporation of the entrained droplets by the uncovered heaters. Notwithstanding the occasional disparities, the code prediction is in reasonable agreement with the overall behavior of the tests.
Numerous experiments were conducted to address when and how the core can lose its original geomet... more Numerous experiments were conducted to address when and how the core can lose its original geometry, what geometries are formed, and in what processes the core materials are transported to the lower plenum of the reactor pressure vessel during a severe accident. Core degradation progresses along the line of clad ballooning, clad oxidation, material interaction, metallic blockage, molten pool formation, melt progression, and relocation to the lower head. Relocation into the lower plenum may occur from the lateral periphery or from the bottom of the core depending upon the thermal and physical states of the pool. Determining the quantities and rate of molten material transfer to the lower head is important since significant amounts of molten material relocated to the lower head can threaten the vessel integrity by steam explosion and thermal and mechanical attack of the melt. In this paper the focus is placed on the melt flow regime on a cylindrical fuel rod utilizing the LAMDA (Lumped Analysis of Melting in Degrading Assemblies) facility at the Seoul National University. The downward relocation of the molten material is a combination of the external film flow and the internal pipe flow. The heater rods are 0.8 m long and are coated by a low-temperature melting metal alloy. The electrical internal heating method is employed during the test. External heating is adopted to simulate the exothermic Zircaloy-steam reaction. Tests are conducted in several quasi-steady-state conditions. Given the variable boundary conditions including the heat flux and the water level, observation is made for the melting location, progression, and the mass of molten material. Finally, the core melt progression model is developed from the visual inspection and quantitative analysis of the experimental data. As the core material relocates downwards a blockage may be formed and grow both radially and axially. The velocity of the melt can be calculated from a force balance between the gravity and frictional losses at the melt-rod interface. When the heater rod is uncovered completely, the melt progression is initiated at the mid-point, which is the hot spot in the rod. However, the melting location is elevated as the water level rises because of the downward heat transfer. Considering the melt flow as a film, the steady-state film thickness on the cylindrical heater rod and the average velocity are computed. The steady-state film flow rate is determined in terms of the density, film thickness, and film velocity.
Previously determining the fuel loading pattern is based on the trial and error method. For a can... more Previously determining the fuel loading pattern is based on the trial and error method. For a candidate pattern, the core analysis is performed and the pattern is examined whether it satisfies the imposed constraints such as the power peaking or not. The pattern, then, is revised by the shuffling of assemblies and the revision is repeated until all of the conditions are met. This method unavoidably requires many iterative diffusion calculations, computing times and accumulated experiences. To overcome these disadvantages, a new method which is called backward diffusion calculation is introduced. If the most desirable power distribution is already known, the optimal loading pattern can be obtained by solving the backward diffusion equation with simple calculation. In this study, the basic equation for the backward diffusion calculation is derived and the optimal power and fuel distributions are searched in one-dimensional cylindrical geometry by using the proposed method. In addition...
A new fast-running analytic model has been developed for analyzing the load follow operation. The... more A new fast-running analytic model has been developed for analyzing the load follow operation. The new model was based on the neural network theory, which has the capability of modeling the input/ output relationships of a nonlinear system. The new model is made up of two error back-propagation neural networks and procedures to calculate core parameters, such as the distributions and density of xenon in a quasi-steady-state core like load follow operation. One neural network is designed to retrieve the axial offset of power distribution, and the other is for reactivity corresponding to a given core condition. The training data sets for learning the neural networks in the new model are generated with a three-dimensional nodal code and, also, the measured data of the first-day test of load follow operation. Using the new model, the simulation results of the 5-day load follow test in a pressurized water reactor show a good agreement between the simulation data and the actual measured data. Required computing time for simulating a load follow operation is comparable to that of a fast-running lumped model. Moreover, the new model does not require additional engineering factors to compensate for the difference between the actual measurements and analysis results because the neural network has the inherent learning capability of neural networks to new situations.
Photorefractive materials like SrBaNb (SBN) have optical properties that can have several militar... more Photorefractive materials like SrBaNb (SBN) have optical properties that can have several military applications. To improve the figures of merit for these materials, it is very important to have better control of Cr dopant in the SBN. Since the amount of Cr dopant is so small, the usual analytical techniques are not adequate to analyze this material. In this report, the incorporation of Cr into SBN using secondary ion mass Abstract spectrometry (SIMS) measurement with an electron gun is confirmed.
While nickel ohmic contacts to n-type silicon carbide have good electrical properties, the physic... more While nickel ohmic contacts to n-type silicon carbide have good electrical properties, the physical contact, and therefore the reliability, can be poor. An approach is described for using the good electrical properties of Ni ohmic contacts while using another metal for its desired mechanical, thermal and/or chemical properties. In the present work, once the Ni contacts have been annealed forming nickel silicides and achieving low contact resistance, they are etched off. Removing the primary Ni contacts also eliminates the poor morphology, voids, and at least some of the excess carbon produced by the Ni/SiC reaction. The Ni contacts are then replaced by a second contact metal. This second metal displays low contact resistance as-deposited, indicating that the critical feature responsible for the ohmic contact has not been removed by the primary contact etch. Not only does this approach provide more flexibility for optimizing the contact for a given application, it also provides some ...
Use of instruments in severe accident guidance is focused on cooling of the reactor core and heat... more Use of instruments in severe accident guidance is focused on cooling of the reactor core and heat removal from the containment. The large uncertainties and extreme conditions involving the severe accident render the measurement and interpretation of the data difficult enough. There presently exist some parameters relevant to monitoring the accident initiation and progression and to preparing necessary measures and strategies to prevent further aggravation and to mitigate the consequence of the accident at hand. One of the accident management guidance parameters for the KSNP (Korean Standard Nuclear Plant) is the core exit temperature (CET). Though the fuel rod temperature is perhaps the most important parameter to determine the phase of accident progression, there is currently no means to read it directly from the core. A best alternative, thus, is to guess the fuel temperature from the measured CET data. The severe accident management guidance (SAMG) suggest that the transition criterion from the emergency operating procedure is the CET of 650 K. The fuel temperature begins to escalate from the time of core uncovery. When the temperature reaches 930 K, hydrogen is generated by oxidation of the cladding whose reaction is accelerated drastically with temperatures exceeding 1500 K. Because the oxidation reaction is exothermal, the core temperature increases rapidly. Although the CET is lower than the fuel temperature, the increase rate will tend to follow that for the fuel rod temperature. In this paper, the focus is placed on the plant damage state during a severe accident. The accident initiator is a small-break loss-of-coolant accident (LOCA). The MAAP4 calculations were carried out to analyze the plant state and accident sequence such as the core uncovery time, the CET, and the primary system pressure. It is concluded that the CET will prove to be a reasonable criterion for recognizing severe core damage. However, when the temperature exceeds 950 K the CET reading may not be reliable so that one needs alternatively to infer the degree of core damage by reading the reactor water level and the hydrogen generation rate.
A hyperbolic two-phase, two-fluid equation system developed in the previous work has been impleme... more A hyperbolic two-phase, two-fluid equation system developed in the previous work has been implemented in an existing nuclear safety analysis code, MARS. Although the implicit treatment of interfacial pressure force term introduced in momentum equation of the hyperbolic equation system is required to enhance the numerical stability, it is very difficult to implement in the code because it is not possible to maintain the existing numerical solution structure. As an alternative, two-step approach with stabilizer momentum equations has been selected. The results of a linear stability analysis by Von-Neumann method show the equivalent stability improvement with fully-implicit solution method. To illustrate the applicability, the new solution scheme has been implemented into the best-estimate thermal-hydraulic analysis code, MARS. This paper also includes the comparisons of the simulation results for the perturbation propagation and water faucet problems using both two-step method and the...
10th International Conference on Nuclear Engineering, Volume 3, 2002
ABSTRACT Analysis was performed for a large-break loss-of-coolant accident (LOCA) in the APR1400 ... more ABSTRACT Analysis was performed for a large-break loss-of-coolant accident (LOCA) in the APR1400 (Advanced Power Reactor 1400 MWe) with the thermal-hydraulic analysis code RELAP5/ MOD3.2.2 and the severe accident analysis code MAAP4.03. The two codes predicted different sequences for essentially the same initiating condition. As for the break flow and the emergency core cooling (ECC) flow rates, MAAP4.03 predicted considerably higher values in the initial stage than RELAP5/ MOD3.2.2. It was considered that the differing break flow and ECC flow rates would cause the LOCA sequences to deviate from one another between the two codes. Hence, the break flow model in MAAP4.03 was modified with partly implementing the two-phase homogeneous critical flow model and adopting a correction term. The ECC flow model in MAAP4.03 was also varied by changing the hardwired friction factor through the sensitivity study. The modified break flow and ECC flow models yielded more consistent calculational results between RELAP5/MOD3.2.2 and MAAP4.03. It was, however, found that the resultant effect is rather limited unless more mechanistic treatments are done for the primary system in MAAP4.03. (authors)
Most of the corrosive degradations in steam generator tubes of nuclear power plants are closely r... more Most of the corrosive degradations in steam generator tubes of nuclear power plants are closely related to the residual stress existing in the local region of a geometric change, that is, an expansion transition, u-bend, ding, dent, bulge, etc. Therefore, accurate information on a geometric anomaly in a tube is a prerequisite to the activity of a non destructive inspection for a precise and earlier detection of a defect in order to prevent a failure during an operation, and also for a root cause analysis of a failure. In this paper, a newly developed eddy current technique of a three-dimensional profilometry is introduced and the proof for the applicability of the technique to a plant inspection is provided. The quantitative profile measurement using a new eddy current probe was performed on steam generator expansion mock-up tubes with various geometric anomalies typically observed in the operating power plants, and the accuracy of the measured data was compared with those from the ...
ÐFive sesquiterpene lactones, 8-acetylarteminolide (1), artanomaloide (2), arteminones (3 and 4),... more ÐFive sesquiterpene lactones, 8-acetylarteminolide (1), artanomaloide (2), arteminones (3 and 4), and dehydromatricarin (5), were isolated from the methanolic extract of the¯ower of Artemisia sylvatica and characterized on the basis of their spectral data. New sesquiterpene lactone 1 was identi®ed as a con®gurational isomer of artanomaloide (2), and the new arteminones 3 and 4 are determined as stereoisomers. 8-Acetylarteminolide (1) strongly inhibited FPTase with an IC 50 of 1.8 mM, however, the other sesquiterpene lactones mildly inhibited the transferase with an IC 50 of 22±300 mM.
Three steroidal glycosides, wondosterols A-C (1–3) have been isolated from a marine two-sponge as... more Three steroidal glycosides, wondosterols A-C (1–3) have been isolated from a marine two-sponge association. Their stereostructures were elucidated on the basis of the spectroscopic analysis of natural wondosterol and its derivatives.
A gas chromatography/mass spectrometry (GC/MS) method is described which uses negative ion chemic... more A gas chromatography/mass spectrometry (GC/MS) method is described which uses negative ion chemical ionization (NCI) and tandem mass spectrometry (MS/MS) for the determination of eight anabolic steroids in human urine. Eight anabolic steroids were derivatized by heptafluorobutyric anhydride (HFBA), and were determined using GC/NCI-MS and GC/NCI-MS/MS. The linear correlation coefficients for calibration in NCI-MS/MS were in the range 0.9880-0.9988. This method of derivatization with HFBA for use with GC/NCI was useful in determinations of 19-norandrosterone, boldenone, 19-noretiocholanolone, 2-methylandrosterone, nandrolone, 1-methyleneandrosterone, 1-methylandrosterone, 4-dihydroboldenone and mesterolone. The detection limits of this procedure were 5-20 ppb at a signal-to-noise (S/N) ratio of 3.
The interfacial area concentration (IAC) is one of the most important parameters in the two-fluid... more The interfacial area concentration (IAC) is one of the most important parameters in the two-fluid model for two-phase flow analysis. The purpose of this study is to develop the local IAC measuring method by using the five-sensor conductivity probe. In this paper, the mathematical approach of the five-sensor conductivity probe method for measuring the local time averaged IAC is described, and numerical simulations are carried out for cap bubbles and two types of ellipsoidal bubbles, as well as spherical bubbles, in order to evaluate the new method. The sizes and locations of the bubbles are determined by using random number generators. To investigate the probe size effect on the accuracy of IAC measurement, three cases for length scales of the probe are applied to the simulations. The simulations show that the five-sensor conductivity probe method proposed in this paper produces better results than the four-sensor method.
This study is concerned with development of a coupled calculation methodology with which to conti... more This study is concerned with development of a coupled calculation methodology with which to continually and consistently analyze progression of an accident from the design-basis phase via core uncovery to core melting and relocation. Experiments were performed to investigate the core coolant inventory depletion after safety injection failure during a large-break loss-of-coolant accident in a cold leg utilizing the Seoul National University Facility (SNUF). The SNUF is an integral test loop scaled down to 1/6.4 in length and 1/178 in area from the Advanced Power Reactor 1400 MWe (APR1400). The SNUF tests are simulated with the RELAP5/MOD3.3 code. The test results revealed that the core coolant inventory decreased five times faster during the sweepout in the downcomer than after termination of the sweepout. The sweepout was observed to take place on top of spillover from the downcomer region to expedite the depletion of the core coolant inventory. The calculation results of RELAP5/MOD3.3 deviated from the experimental data in terms of entrainment from the surface of core coolant, condensation and sweepout in the downcomer. Thereby, the core coolant level was computed to decrease faster than the measured from the experiment due to the overestimated spillover by the evaporation of the entrained droplets by the uncovered heaters. Notwithstanding the occasional disparities, the code prediction is in reasonable agreement with the overall behavior of the tests.
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Papers by Un-chul Lee