J. Jeon, N. Kim, Won Jun Choi, Taeseok Kim, S. J. Kim
After the Fukushima Daiichi accident, predicting lower flammability limits (LFL) as a part of hydrogen risk analysis has become an ever important task. Although many experimental studies have been conducted extensively, the LFL results for mixtures abided by the severe accident conditions are still lacking. The objective of this study is to develop a calculated non-adiabatic flame temperature (CNFT) model, which facilitates to predict the LFL of hydrogen mixtures. This model considers heat loss due to radiative heat transfer from flame to ambient environment during flame propagation. The model shows better agreement with experimental results for various mixtures than previous model, which predicts the LFL through a calculated adiabatic flame temperature. Especially, prediction accuracy for H2-air-steam mixture and mixtures at elevated initial temperature is improved substantially. Thus it is worth to evaluate the applicability of the CNFT model in the hydrogen risk analysis during severe accident. The postulated hydrogen risk in the current Optimized Power Reactor 1000 MWe (OPR1000) under Station Blackout (SBO) scenario was investigated with MELCOR 1.8.6 code. As a result, it was observed that uncertainty of hydrogen risk calculated with the MELCOR default model can be reduced by the CNFT model. This study suggests that the developed CNFT model can enhance reliability of severe accident analysis related to the flammability of hydrogen mixtures.
{"title":"Investigation of Flammability of Hydrogen Gases With Diluent Gases Under Severe Accident Conditions Using CNFT Model","authors":"J. Jeon, N. Kim, Won Jun Choi, Taeseok Kim, S. J. Kim","doi":"10.1115/ICONE26-81773","DOIUrl":"https://doi.org/10.1115/ICONE26-81773","url":null,"abstract":"After the Fukushima Daiichi accident, predicting lower flammability limits (LFL) as a part of hydrogen risk analysis has become an ever important task. Although many experimental studies have been conducted extensively, the LFL results for mixtures abided by the severe accident conditions are still lacking. The objective of this study is to develop a calculated non-adiabatic flame temperature (CNFT) model, which facilitates to predict the LFL of hydrogen mixtures. This model considers heat loss due to radiative heat transfer from flame to ambient environment during flame propagation. The model shows better agreement with experimental results for various mixtures than previous model, which predicts the LFL through a calculated adiabatic flame temperature. Especially, prediction accuracy for H2-air-steam mixture and mixtures at elevated initial temperature is improved substantially. Thus it is worth to evaluate the applicability of the CNFT model in the hydrogen risk analysis during severe accident. The postulated hydrogen risk in the current Optimized Power Reactor 1000 MWe (OPR1000) under Station Blackout (SBO) scenario was investigated with MELCOR 1.8.6 code. As a result, it was observed that uncertainty of hydrogen risk calculated with the MELCOR default model can be reduced by the CNFT model. This study suggests that the developed CNFT model can enhance reliability of severe accident analysis related to the flammability of hydrogen mixtures.","PeriodicalId":289940,"journal":{"name":"Volume 9: Student Paper Competition","volume":"55 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133456420","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Betavoltaic cells are nuclear batteries ideal for low-power applications for extended periods of time without maintenance or replacement. Betavoltaics function similarly to photovoltaic (solar) cells where instead of using sunlight, beta particles are used to generate electron-hole pairs within a semiconductor p-n junction to generate current. Even though there have been multiple demonstrations, betavoltaic performance has not been extensively studied. To accurately predict betavoltaic performance, which is important for a device in operation without maintenance for elongated periods, all parameters are required to predict potential fluctuations in cell performance, such as doping densities and resistances for semiconductor variation and absorption coefficients for beta-generated current. However, not all parameters are easily measured, especially when the p-n junction is constantly under irradiation and cannot be separated from the source. Critical parameters were characterized experimentally with the betavoltaic cell by performing capacitance-voltage to determine doping densities and performing current-voltage characterization tests to determine resistances on multiple NanoTritium™ cells, while absorption coefficients were determined from MCNP6 simulations. Experiments indicated that series resistance Rs was 1 × 106 Ω, while shunt resistance Rsh was 2 × 108 Ω from I-V characterization, while doping density ND was determined to be 1 × 1017 cm−3 from C-V characterization. Absorption coefficient α was found to vary with semiconductor material and incoming beta energy and used in conjunction with critical parameters from experimentation to accurately model betavoltaic cell performance similar to experimental results. Both implicit equations and explicit estimations were compared to model betavoltaic cell performance.
{"title":"Derivation of Critical Parameters of Betavoltaics","authors":"D. Cheu, T. Adams, S. Revankar","doi":"10.1115/ICONE26-81109","DOIUrl":"https://doi.org/10.1115/ICONE26-81109","url":null,"abstract":"Betavoltaic cells are nuclear batteries ideal for low-power applications for extended periods of time without maintenance or replacement. Betavoltaics function similarly to photovoltaic (solar) cells where instead of using sunlight, beta particles are used to generate electron-hole pairs within a semiconductor p-n junction to generate current. Even though there have been multiple demonstrations, betavoltaic performance has not been extensively studied. To accurately predict betavoltaic performance, which is important for a device in operation without maintenance for elongated periods, all parameters are required to predict potential fluctuations in cell performance, such as doping densities and resistances for semiconductor variation and absorption coefficients for beta-generated current. However, not all parameters are easily measured, especially when the p-n junction is constantly under irradiation and cannot be separated from the source. Critical parameters were characterized experimentally with the betavoltaic cell by performing capacitance-voltage to determine doping densities and performing current-voltage characterization tests to determine resistances on multiple NanoTritium™ cells, while absorption coefficients were determined from MCNP6 simulations. Experiments indicated that series resistance Rs was 1 × 106 Ω, while shunt resistance Rsh was 2 × 108 Ω from I-V characterization, while doping density ND was determined to be 1 × 1017 cm−3 from C-V characterization. Absorption coefficient α was found to vary with semiconductor material and incoming beta energy and used in conjunction with critical parameters from experimentation to accurately model betavoltaic cell performance similar to experimental results. Both implicit equations and explicit estimations were compared to model betavoltaic cell performance.","PeriodicalId":289940,"journal":{"name":"Volume 9: Student Paper Competition","volume":"38 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115692051","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The immediate heat exchanger is important for the heat utilization and hydrogen production in a very high-temperature gas-cooled reactor (VHTR). There is a 90-degree elbow passageway in the inlet passageway of immediate heat exchanger, contributing uneven flow distribution in circumference direction in the heat transfer area, which is harmful to the heat transfer tubes aging process. In this study, three inlet passageway optimization designs are put forward and their optimization effect is analyzed according to specific criterion by CFD. As the existence of spiral tube area would have coupling effect on inlet passageway flow, in the computation, the heat transfer area is assumed to be porous medium, in which the effect of heat transfer is taken into account as well. The result shows that installing flow distributer in the inlet passageway could make helium flow on circumference direction most homogenous.
{"title":"Inlet Passageway Optimization of Immediate Heat Exchanger in an HTGR","authors":"Jingdan Cui, K. Yuan, Qi Sun, W. Peng, Jie Wang","doi":"10.1115/ICONE26-81801","DOIUrl":"https://doi.org/10.1115/ICONE26-81801","url":null,"abstract":"The immediate heat exchanger is important for the heat utilization and hydrogen production in a very high-temperature gas-cooled reactor (VHTR). There is a 90-degree elbow passageway in the inlet passageway of immediate heat exchanger, contributing uneven flow distribution in circumference direction in the heat transfer area, which is harmful to the heat transfer tubes aging process. In this study, three inlet passageway optimization designs are put forward and their optimization effect is analyzed according to specific criterion by CFD. As the existence of spiral tube area would have coupling effect on inlet passageway flow, in the computation, the heat transfer area is assumed to be porous medium, in which the effect of heat transfer is taken into account as well. The result shows that installing flow distributer in the inlet passageway could make helium flow on circumference direction most homogenous.","PeriodicalId":289940,"journal":{"name":"Volume 9: Student Paper Competition","volume":"5 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116233002","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Simin Luo, Wang Xin'an, Yapei Zhang, Dalin Zhang, S. Qiu, G. Su
In-vessel-retention (IVR) has become an important subject of severe accident mitigation strategy. Up to now, many experimental and numerical investigations have been performed on the natural convection characteristics in melt pools with volumetric heating. But these studies are limited to the melt pools under static condition. As floating nuclear reactors become increasingly popular among both commercial and military ships, for successful application of IVR in this occasion, research should be done on the heat transfer characteristics of melt pool under moving conditions. Currently, the specially-designed facility is under construction in Xi'an China for the relevant experiment and numerical studies are performed beforehand. In this paper, a hemisphere with an inner radius of 0.5m, similar to LIVE experimental facility, is chosen to simulate the melt pool. Its flow behaviors under periodic rolling condition are simulated by means of CFD calculation. This work may cast a light on the melt pool characteristics under moving conditions and could be further evaluated by future experimental data.
{"title":"Numerical Research on Melt Pool Flow Characteristics Under Rolling Condition","authors":"Simin Luo, Wang Xin'an, Yapei Zhang, Dalin Zhang, S. Qiu, G. Su","doi":"10.1115/ICONE26-81994","DOIUrl":"https://doi.org/10.1115/ICONE26-81994","url":null,"abstract":"In-vessel-retention (IVR) has become an important subject of severe accident mitigation strategy. Up to now, many experimental and numerical investigations have been performed on the natural convection characteristics in melt pools with volumetric heating. But these studies are limited to the melt pools under static condition. As floating nuclear reactors become increasingly popular among both commercial and military ships, for successful application of IVR in this occasion, research should be done on the heat transfer characteristics of melt pool under moving conditions. Currently, the specially-designed facility is under construction in Xi'an China for the relevant experiment and numerical studies are performed beforehand. In this paper, a hemisphere with an inner radius of 0.5m, similar to LIVE experimental facility, is chosen to simulate the melt pool. Its flow behaviors under periodic rolling condition are simulated by means of CFD calculation. This work may cast a light on the melt pool characteristics under moving conditions and could be further evaluated by future experimental data.","PeriodicalId":289940,"journal":{"name":"Volume 9: Student Paper Competition","volume":"2013 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125673407","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In order to enhance the inherent safety of sodium-cooled fast reactors, innovative hydraulically suspended absorber rod (HSR) passive shut-down system have been proposed for China demonstration fast reactor. In this study, based on the functional and performance requirements, a full-scale experimental setup has been designed and fabricated for the analysis of the HSR as applied to the prototype reactor. The main characteristic of the test facility is the actuation of the mobile safety rod is triggered by coolant flow rate decrease in the primary loop below half the nominal value and then the rod inserts into the stationary sleeve by gravity. The objective is to investigate the dynamic performance of HSR and establish the laws of its movement at lowering the flow rate modeling the coastdown of primary circulating pump. A series of tests have been performed, including start-up, steady-state operation, loss of flow accident, sensitivity analysis and reliability test. This study also focused on the effect of various factors on scram time, the effect of pump coasting time, rod weight, gap between rod and guide tube, bypass holes, cone angle of rod, flow rate and fluid temperature are analyzed. The experimental results demonstrate the functionality and reliability of the HSR, which would lay foundation for further optimization design.
{"title":"Characterization and Experimental Investigation for the Dynamic Performance of the Hydraulically Suspended Passive Shutdown System in China Sodium-Cooled Fast Reactor","authors":"Jianping Song, Yingwei Wu, W. Tian, S. Qiu, G. Su","doi":"10.1115/ICONE26-81248","DOIUrl":"https://doi.org/10.1115/ICONE26-81248","url":null,"abstract":"In order to enhance the inherent safety of sodium-cooled fast reactors, innovative hydraulically suspended absorber rod (HSR) passive shut-down system have been proposed for China demonstration fast reactor. In this study, based on the functional and performance requirements, a full-scale experimental setup has been designed and fabricated for the analysis of the HSR as applied to the prototype reactor. The main characteristic of the test facility is the actuation of the mobile safety rod is triggered by coolant flow rate decrease in the primary loop below half the nominal value and then the rod inserts into the stationary sleeve by gravity. The objective is to investigate the dynamic performance of HSR and establish the laws of its movement at lowering the flow rate modeling the coastdown of primary circulating pump. A series of tests have been performed, including start-up, steady-state operation, loss of flow accident, sensitivity analysis and reliability test. This study also focused on the effect of various factors on scram time, the effect of pump coasting time, rod weight, gap between rod and guide tube, bypass holes, cone angle of rod, flow rate and fluid temperature are analyzed. The experimental results demonstrate the functionality and reliability of the HSR, which would lay foundation for further optimization design.","PeriodicalId":289940,"journal":{"name":"Volume 9: Student Paper Competition","volume":"29 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127048292","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Dynamic characteristics of active magnetic bearing (AMB)-flexible rotor system are closely related to control law. To analyze dynamic characteristics of flexible rotor suspended by AMBs with linear quadratic regulation (LQR) controller, a simple and effective method based on numerical calculation of unbalanced response is proposed in this article. The model of flexible rotor is established based upon Euler-Bernoulli beam theory and Lagrange’s equation. Disc on the rotor and its Gyro effect are taken into account. LQR controller based on error and its derivative is developed to control electromagnetic force of AMB at each degree of freedom (DOF) in real time. Under the unbalanced exciting force, the steady-state response and transient response in time domain of each node of flexible rotor at 0–4000 rad/s are calculated numerically. The critical speeds of rotor are obtained by identification method quickly and easily.
{"title":"Dynamic Analysis of Flexible Rotor Suspended by Active Magnetic Bearings With LQR Controller","authors":"Yi-xin Su, Yanhui Ma, Qian Shi, Suyuan Yu","doi":"10.1115/ICONE26-82347","DOIUrl":"https://doi.org/10.1115/ICONE26-82347","url":null,"abstract":"Dynamic characteristics of active magnetic bearing (AMB)-flexible rotor system are closely related to control law. To analyze dynamic characteristics of flexible rotor suspended by AMBs with linear quadratic regulation (LQR) controller, a simple and effective method based on numerical calculation of unbalanced response is proposed in this article. The model of flexible rotor is established based upon Euler-Bernoulli beam theory and Lagrange’s equation. Disc on the rotor and its Gyro effect are taken into account. LQR controller based on error and its derivative is developed to control electromagnetic force of AMB at each degree of freedom (DOF) in real time. Under the unbalanced exciting force, the steady-state response and transient response in time domain of each node of flexible rotor at 0–4000 rad/s are calculated numerically. The critical speeds of rotor are obtained by identification method quickly and easily.","PeriodicalId":289940,"journal":{"name":"Volume 9: Student Paper Competition","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-07-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129091643","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mitigation measures against severe accidents (SAs) are important from the viewpoint of safety of nuclear reactors. In some scenarios of the SAs, the core materials melt and fall into a water pool in the lower plenum as a jet. The molten material jet is broken up, and heat transfer between molten material and coolant is occurred. This process is called a fuel-coolant interaction (FCI). The aim of the present study is to clarify the liquid jet behavior falling into a shallow pool. Our focus is on the atomization conditions of a liquid jet injected into the pool with insufficient depth. In order to understand the jet behavior in a shallow pool, we performed observation of visualization with several methods and mapped observed flow regimes of jet against dimensionless numbers. As a results of observation, we succeeded visualization of internal flow.
{"title":"Penetration Behavior of Liquid Jet Falling Into a Shallow Pool","authors":"H. Yoshida","doi":"10.1115/icone26-81993","DOIUrl":"https://doi.org/10.1115/icone26-81993","url":null,"abstract":"Mitigation measures against severe accidents (SAs) are important from the viewpoint of safety of nuclear reactors. In some scenarios of the SAs, the core materials melt and fall into a water pool in the lower plenum as a jet. The molten material jet is broken up, and heat transfer between molten material and coolant is occurred. This process is called a fuel-coolant interaction (FCI).\u0000 The aim of the present study is to clarify the liquid jet behavior falling into a shallow pool. Our focus is on the atomization conditions of a liquid jet injected into the pool with insufficient depth.\u0000 In order to understand the jet behavior in a shallow pool, we performed observation of visualization with several methods and mapped observed flow regimes of jet against dimensionless numbers. As a results of observation, we succeeded visualization of internal flow.","PeriodicalId":289940,"journal":{"name":"Volume 9: Student Paper Competition","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2018-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126473949","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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