The Experts below are selected from a list of 18999 Experts worldwide ranked by ideXlab platform
Toru Obara - One of the best experts on this subject based on the ideXlab platform.
-
Burnup performance of MOX and Pu-ROX fuels in small pebble bed reactor with accumulative fuel Loading Scheme
Annals of Nuclear Energy, 2018Co-Authors: Irwan Liapto Simanullang, Toru ObaraAbstract:Abstract Pebble bed reactors (PBRs) are among the promising designs for future nuclear power plants. There are several fuel management strategies for PBRs. The accumulative fuel Loading Scheme was introduced as the simplest fueling strategies for a PBR. In this study, mixed-oxide (MOX) and plutonium-rock like oxide (Pu-ROX) fuels were introduced as starting materials. The MVP-BURN code was used to calculate the burnup performance of these fuels. The optimum fuel composition of MOX fuel was 5 g HM/pebble when uranium-plutonium ratio was 70:30. In the case of MOX fuel, the maximum discharged burnup was 172 GWd/t over 6 years of operation time. On the other hand, the optimum fuel composition for Pu-ROX fuel was 3 g HM/pebble. The results showed that the maximum discharged burnup was 550 GWd/t with an operation time of 12.7 years. The maximum excess reactivity occurred in the initial condition for both fuels. Moreover, the results of initial excess reactivity for both fuels were quite similar. The use of burnable poison materials to compensate for the initial excess reactivity of both fuels was not effective. A negative temperature coefficient was achieved for both MOX and Pu-ROX fuels throughout the operation period.
-
Burnup performance of rock-like oxide (ROX) fuel in small pebble bed reactor with accumulative fuel Loading Scheme
Annals of Nuclear Energy, 2017Co-Authors: Irwan Liapto Simanullang, Toru ObaraAbstract:Abstract The Japan Atomic Energy Agency (JAEA) has proposed rock-like oxide (ROX) fuel as a new, once-through type fuel concept. Here, burnup performance using ROX fuel was simulated in a pebble bed reactor with an accumulative fuel Loading Scheme. The MVP-BURN code was used to simulate the burnup calculation. Fuel of 5 g-HM/pebble with 20% 235 U enrichment was selected as the optimum composition. Discharged burnup could reach up to 218 GWd/t, with a core lifetime of about 8.4 years. However, high excess reactivity occurred in the initial condition. Initial fuel enrichment was therefore reduced from 20% to 4.65% to counter the initial excess reactivity. The operation period was reduced by the decrease of initial fuel enrichment, but the maximum discharged burnup was 198 GWd/t. Burnup performance of ROX fuel in this reactor concept was compared with that of UO 2 fuel obtained previously. Discharged burnup for ROX fuel in the PBR with an accumulative fuel Loading Scheme was as high as UO 2 fuel. Maximum power density could be lowered by introducing ROX fuel compared to UO 2 fuel. However, PBR core lifetime was shorter with ROX fuel than with UO 2 fuel. A negative temperature coefficient was achieved for both UO 2 and ROX fuels throughout the operation period.
-
Burnup Performance of a PBR with an Accumulative Fuel Loading Scheme Utilizing Burnable Poison Particles in UO2 and ROX Fuels
Energy Procedia, 2017Co-Authors: Irwan Liapto Simanullang, Toru ObaraAbstract:Abstract The accumulative fuel Loading Scheme is a promising design for pebble bed reactors (PBRs). In a previous study, burnup analysis for such a reactor was performed using UO2 fuel and the results showed that the maximum burnup and operation period were 223 GWD/t and 10.2 years, respectively. In this study, rock-like oxide (ROX) fuel was analyzed in PBR with an accumulative fuel Loading Scheme. The results showed that a maximum burnup and operation period of 218 GWd/t and 8.4 years, respectively. However, high excess reactivity occurred in the initial condition for both UO2 and ROX fuels. In this study, burnable poison (BP) particles were used to suppress the initial excess reactivity. Several BP materials such as B4C, Gd2O3, Er2O3 and CdO were investigated. In case of UO2 fuel, the combination of B4C and Gd2O3 was found to be optimal for flattening the reactivity swing in the initial condition. However, due to the fissile density of ROX fuel being about five times lower than that of UO2 fuel, single-material BP particles (B4C) seemed to be optimal for flattening the reactivity swing. By utilizing the BP particles at the initial condition, the results of UO2 and ROX fuels showed that maximum keff was decreased from 1.423 to 1.068 and from 1.357 to 1.033, respectively. On the other hand, the maximum discharge burnup value and core lifetime were quite similar to the results for the reactor that did not use BP particles at the initial condition.
-
Improvement of core design of small pebble bed reactor with accumulative fuel Loading Scheme
Annals of Nuclear Energy, 2016Co-Authors: Irwan Liapto Simanullang, Toru ObaraAbstract:Abstract Innovative nuclear power plant designs and high-efficiency utilization of nuclear fuel are important issues in the field of nuclear power. Pebble bed reactors with an accumulative fuel Loading Scheme have been introduced to obtain high burnup and efficient uranium utilization. Monte Carlo codes, MVP/MVP-BURN, were used to perform the neutron transport and burnup calculation. Optimum fuel composition was obtained in the finite geometry using 6-g HM of uranium per pebble ball with 20% 235 U enrichment. The results show that the maximum burnup was 223 GWd/t with 10.2 years of operation. However, a large amount of excess reactivity occurred in the initial condition. One of the options for minimizing this was to reduce the enrichment of 235 U from 20% to 3.42%, only for the initial condition. The result showed a relatively small amount of excess reactivity during the operation period. However, the maximum burnup decreased to 199 GWd/t with 8 years of operation.
-
Decay heat removal without forced cooling on a small simplified PBR with an accumulative fuel Loading Scheme
Annals of Nuclear Energy, 2013Co-Authors: Dwi Irwanto, Toru ObaraAbstract:Abstract In this study, we analyzed the passive safety features of a small simplified pebble bed reactor with an accumulative fuel Loading Scheme for decay heat removal after reactor shutdown without a forced cooling system. The accumulative fuel Loading Scheme has unique characteristics that make it different from Multipass or Once Through Then Out (OTTO) fuel Loading Schemes. In this fueling Scheme, significant changes of power distributions occur in a limited area at the top of the reactor core, where new fuel pebbles are inserted during reactor operation. We analyzed three different reactor conditions: different heights of the active core at the beginning, middle, and end of life as a consequence of the accumulative fuel Loading Scheme. In the analysis of a depressurized loss-of-flow accident, it was assumed that no natural circulation was possible, so that heat would be transferred through conduction and radiation with the last heat sink being the ground. Our analysis obtained temperature distributions inside the reactor core for each condition. The maximum temperature achieved in our simulation was 1287 °C, which is lower than the safety limit of 1600 °C.
Irwan Liapto Simanullang - One of the best experts on this subject based on the ideXlab platform.
-
Burnup performance of MOX and Pu-ROX fuels in small pebble bed reactor with accumulative fuel Loading Scheme
Annals of Nuclear Energy, 2018Co-Authors: Irwan Liapto Simanullang, Toru ObaraAbstract:Abstract Pebble bed reactors (PBRs) are among the promising designs for future nuclear power plants. There are several fuel management strategies for PBRs. The accumulative fuel Loading Scheme was introduced as the simplest fueling strategies for a PBR. In this study, mixed-oxide (MOX) and plutonium-rock like oxide (Pu-ROX) fuels were introduced as starting materials. The MVP-BURN code was used to calculate the burnup performance of these fuels. The optimum fuel composition of MOX fuel was 5 g HM/pebble when uranium-plutonium ratio was 70:30. In the case of MOX fuel, the maximum discharged burnup was 172 GWd/t over 6 years of operation time. On the other hand, the optimum fuel composition for Pu-ROX fuel was 3 g HM/pebble. The results showed that the maximum discharged burnup was 550 GWd/t with an operation time of 12.7 years. The maximum excess reactivity occurred in the initial condition for both fuels. Moreover, the results of initial excess reactivity for both fuels were quite similar. The use of burnable poison materials to compensate for the initial excess reactivity of both fuels was not effective. A negative temperature coefficient was achieved for both MOX and Pu-ROX fuels throughout the operation period.
-
Burnup performance of rock-like oxide (ROX) fuel in small pebble bed reactor with accumulative fuel Loading Scheme
Annals of Nuclear Energy, 2017Co-Authors: Irwan Liapto Simanullang, Toru ObaraAbstract:Abstract The Japan Atomic Energy Agency (JAEA) has proposed rock-like oxide (ROX) fuel as a new, once-through type fuel concept. Here, burnup performance using ROX fuel was simulated in a pebble bed reactor with an accumulative fuel Loading Scheme. The MVP-BURN code was used to simulate the burnup calculation. Fuel of 5 g-HM/pebble with 20% 235 U enrichment was selected as the optimum composition. Discharged burnup could reach up to 218 GWd/t, with a core lifetime of about 8.4 years. However, high excess reactivity occurred in the initial condition. Initial fuel enrichment was therefore reduced from 20% to 4.65% to counter the initial excess reactivity. The operation period was reduced by the decrease of initial fuel enrichment, but the maximum discharged burnup was 198 GWd/t. Burnup performance of ROX fuel in this reactor concept was compared with that of UO 2 fuel obtained previously. Discharged burnup for ROX fuel in the PBR with an accumulative fuel Loading Scheme was as high as UO 2 fuel. Maximum power density could be lowered by introducing ROX fuel compared to UO 2 fuel. However, PBR core lifetime was shorter with ROX fuel than with UO 2 fuel. A negative temperature coefficient was achieved for both UO 2 and ROX fuels throughout the operation period.
-
Burnup Performance of a PBR with an Accumulative Fuel Loading Scheme Utilizing Burnable Poison Particles in UO2 and ROX Fuels
Energy Procedia, 2017Co-Authors: Irwan Liapto Simanullang, Toru ObaraAbstract:Abstract The accumulative fuel Loading Scheme is a promising design for pebble bed reactors (PBRs). In a previous study, burnup analysis for such a reactor was performed using UO2 fuel and the results showed that the maximum burnup and operation period were 223 GWD/t and 10.2 years, respectively. In this study, rock-like oxide (ROX) fuel was analyzed in PBR with an accumulative fuel Loading Scheme. The results showed that a maximum burnup and operation period of 218 GWd/t and 8.4 years, respectively. However, high excess reactivity occurred in the initial condition for both UO2 and ROX fuels. In this study, burnable poison (BP) particles were used to suppress the initial excess reactivity. Several BP materials such as B4C, Gd2O3, Er2O3 and CdO were investigated. In case of UO2 fuel, the combination of B4C and Gd2O3 was found to be optimal for flattening the reactivity swing in the initial condition. However, due to the fissile density of ROX fuel being about five times lower than that of UO2 fuel, single-material BP particles (B4C) seemed to be optimal for flattening the reactivity swing. By utilizing the BP particles at the initial condition, the results of UO2 and ROX fuels showed that maximum keff was decreased from 1.423 to 1.068 and from 1.357 to 1.033, respectively. On the other hand, the maximum discharge burnup value and core lifetime were quite similar to the results for the reactor that did not use BP particles at the initial condition.
-
Improvement of core design of small pebble bed reactor with accumulative fuel Loading Scheme
Annals of Nuclear Energy, 2016Co-Authors: Irwan Liapto Simanullang, Toru ObaraAbstract:Abstract Innovative nuclear power plant designs and high-efficiency utilization of nuclear fuel are important issues in the field of nuclear power. Pebble bed reactors with an accumulative fuel Loading Scheme have been introduced to obtain high burnup and efficient uranium utilization. Monte Carlo codes, MVP/MVP-BURN, were used to perform the neutron transport and burnup calculation. Optimum fuel composition was obtained in the finite geometry using 6-g HM of uranium per pebble ball with 20% 235 U enrichment. The results show that the maximum burnup was 223 GWd/t with 10.2 years of operation. However, a large amount of excess reactivity occurred in the initial condition. One of the options for minimizing this was to reduce the enrichment of 235 U from 20% to 3.42%, only for the initial condition. The result showed a relatively small amount of excess reactivity during the operation period. However, the maximum burnup decreased to 199 GWd/t with 8 years of operation.
Dwi Irwanto - One of the best experts on this subject based on the ideXlab platform.
-
Decay heat removal without forced cooling on a small simplified PBR with an accumulative fuel Loading Scheme
Annals of Nuclear Energy, 2013Co-Authors: Dwi Irwanto, Toru ObaraAbstract:Abstract In this study, we analyzed the passive safety features of a small simplified pebble bed reactor with an accumulative fuel Loading Scheme for decay heat removal after reactor shutdown without a forced cooling system. The accumulative fuel Loading Scheme has unique characteristics that make it different from Multipass or Once Through Then Out (OTTO) fuel Loading Schemes. In this fueling Scheme, significant changes of power distributions occur in a limited area at the top of the reactor core, where new fuel pebbles are inserted during reactor operation. We analyzed three different reactor conditions: different heights of the active core at the beginning, middle, and end of life as a consequence of the accumulative fuel Loading Scheme. In the analysis of a depressurized loss-of-flow accident, it was assumed that no natural circulation was possible, so that heat would be transferred through conduction and radiation with the last heat sink being the ground. Our analysis obtained temperature distributions inside the reactor core for each condition. The maximum temperature achieved in our simulation was 1287 °C, which is lower than the safety limit of 1600 °C.
-
burnup characteristics of a peu a peu fuel Loading Scheme in a 110mwt simplified pebble bed reactor
Journal of Nuclear Science and Technology, 2011Co-Authors: Dwi Irwanto, Toru ObaraAbstract:The efficient use of nuclear fuel is one of the important issues in the current development of nuclear reactors due to the limitation of natural uranium resources and the need for overall economy. Simplicity in the reactor design could further increase its economy while making it easier to operate. A pebble bed reactor is one of the most promising reactor systems to fulfill these criteria. The purpose of this study was to design a simplified pebble bed reactor by removing the unLoading devices from the system and then optimizing the fuel composition and reactor configuration so that the system could achieve better burnup and use scarce uranium resources more effectively. A computer code based on the Monte Carlo method was developed and used in this study in order to obtain precise calculation results due to the weakness of the diffusion method in treating the large cavity region in the core during most of the reactor operation. With this code, analysis and optimization were performed for a 110MW simplifie...
-
Preliminary Study of Burnup Characteristics for a Simplified Small Pebble Bed Reactor
2010Co-Authors: Dwi Irwanto, Yukikata Kato, Ichiro Yamanaka, Toru ObaraAbstract:Simplification of the pebble bed reactor by removing the unLoading device from the system was peformed. For this reactor design, a suitable fuel‐Loading Scheme is the Peu a Peu (little by little) fueling Scheme. In the Peu a Peu modus, there is no unLoading device; as such, the fuels are never discharged and remain at the bottom of the core during reactor operation. This means that the burnup cycle and reactivity is controlled by the addition of fuel. The objectives of the the present study were to find a means of carrying out the exact calculations needed to analyze the Peu a Peu fuel‐Loading Scheme and to optimize the fuel composition, and fuel‐Loading Scheme to achieve better burnup characteristics. The Monte Carlo method is used to perform calculations with high accuracy. Before the calculation of the whole core, the analysis for the infinite geometry was performed. The power generated per mass consumed for each combination of the uranium enrichment and packing fraction was analyzed from the parametri...
Cyril Leung - One of the best experts on this subject based on the ideXlab platform.
-
an efficient power Loading Scheme for ofdm based cognitive radio systems
IEEE Transactions on Vehicular Technology, 2010Co-Authors: Yonghong Zhang, Cyril LeungAbstract:We study the bit and power-allocation problem for an orthogonal frequency-division multiplexing (OFDM)-based cognitive radio (CR) system in which the spectrum is licensed to a primary user (PU) pair consisting of one transmitter and one receiver. CR pairs (CRPs) may use both active and nonactive PU bands as long as the generated interference powers are within the interference temperature limits of the PUs. The optimal solution and a low-complexity suboptimal solution are proposed. It is found that significant improvements can be achieved compared with systems in which CRPs only use the nonactive PU bands.
-
Subchannel Power-Loading Schemes in Multiuser OFDM Systems
IEEE Transactions on Vehicular Technology, 2009Co-Authors: Yonghong Zhang, Cyril LeungAbstract:Achievable bit rates for a number of continuous and discrete bit-Loading Schemes for multiuser orthogonal frequency-division multiplexing (OFDM) systems are studied. A computationally efficient simple-to-implement discrete bit-Loading Scheme based on equal-power allocation is proposed and shown to provide close-to-optimal performance. The proposed Scheme provides a significant improvement over the traditional discrete equal-power allocation Scheme used by medium-access control layer resource-allocation algorithms, particularly when the average user subchannel gains are quite different.
-
Performance of Equal Power Subchannel Loading in Multiuser OFDM systems
2007 IEEE Pacific Rim Conference on Communications Computers and Signal Processing, 2007Co-Authors: Yonghong Zhang, Cyril LeungAbstract:The difference in total subchannel bits loaded between the optimal water-filling subchannel power Loading Scheme and a simple equal power subchannel Loading Scheme for a multiuser OFDM system is studied. It is found that this difference is generally quite small and decreases with the number of users and the average subchannel signal-to-noise ratio.
Wolfgang Ertmer - One of the best experts on this subject based on the ideXlab platform.
-
Beating the density limit by continuously Loading a dipole trap from millikelvin-hot magnesium atoms
Physical Review A, 2012Co-Authors: M. Riedmann, Hrishikesh Kelkar, T. Wübbena, A. Pape, Andre Kulosa, Klaus Zipfel, Dominika Fim, Steffen Ruhmann, J. Friebe, Wolfgang ErtmerAbstract:We load ${10}^{5}$ magnesium atoms in a dipole trap from a millikelvin-hot magneto-optical trap (MOT) using a continuous-Loading Scheme. Light-assisted two-body processes limit the maximum achievable density in a MOT, resulting in a reduced transfer efficiency into a dipole trap when using the conventional sequential Scheme. It is overcome in a continuous-Loading Scheme where a loss channel is opened in the MOT. This allows the accumulation of atoms in the dipole trap over the trap lifetime, determined by collisions with the background gas. This results in a significantly higher number of trapped atoms even at a lower steady-state peak density in the MOT.
-
Beating the density limit by continuously Loading a dipole trap from millikelvin-hot magnesium atoms
Physical Review A, 2012Co-Authors: M. Riedmann, Hrishikesh Kelkar, T. Wübbena, A. Pape, Andre Kulosa, Klaus Zipfel, Steffen Ruhmann, J. Friebe, Wolfgang ErtmerAbstract:We load 10 5 magnesium atoms in a dipole trap from a millikelvin-hot magneto-optical trap (MOT) using a continuous-Loading Scheme. Light-assisted two-body processes limit the maximum achievable density in a MOT, resulting in a reduced transfer efficiency into a dipole trap when using the conventional sequential Scheme. It is overcome in a continuous-Loading Scheme where a loss channel is opened in the MOT. This allows the accumulation of atoms in the dipole trap over the trap lifetime, determined by collisions with the background gas. This results in a significantly higher number of trapped atoms even at a lower steady-state peak density in the MOT. Confinement of neutral atoms in a trap based on the optical dipole force has become a widespread tool for Bose-Einstein condensation [1], condensed matter studies in lattices [2], performance of high-resolution spectroscopy [3], and many other studies. Compared to magnetic traps, dipole traps provide higher trapping frequencies and the possibility to trap nonmagnetic states. Usually, the depth of these traps is below 1 mK with trapping volumes far below those of magnetic traps. Loading atoms into such traps requires efficient cooling techniques and high atomic densities as starting conditions. Continuous-Loading Schemes have proven useful in several cases where these conditions cannot be met. Here, we demonstrate a continuous-Loading Scheme for a more efficient Loading of magnesium atoms in a dipole trap from a millikelvin-temperature magneto-optical trap (MOT). Our Scheme generates a continuous flux of atoms in a dark state that is insensitive to MOT light and magnetic fields. The dipole trap overlapped with the MOT acts like an energy filter and continuously captures the low-energy tail of the flux. The Scheme allows Loading times up to the background-gas collision-limited trap lifetime. We compare this approach to a stepwise-Loading Scheme and show that a significantly higher number of atoms can be trapped using the former approach. The latter is severely restricted by density-limiting processes occurring in the MOT. Related Schemes have been applied to calcium [4] and strontium [5]. In the case of calcium, a reservoir of atoms in a metastable state was created to fill the dipole trap by spatially selective depumping. The number of captured atoms in this case is limited by the size of the reservoir. In the case of strontium, the atoms from the MOT were drained into a metastable dark state using two additional laser beams overlapped with the MOT. The optimization possibilities offered by our Scheme (as discussed in later sections) are not possible in that case since the MOT configuration of [5] cannot be simultaneously optimized for a higher number of atoms and efficient Loading of the dipole trap. The two processes are inherently coupled. Continuous-Loading Schemes have been used to load magnetic traps as well [6–8]. The continuous