Thermal-hydraulic Aspects of the Use of Low Enrichment Uranium Fuel in the MIT Research Reactor PDF Download
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Author: Joseph B. Gehret
Publisher:
ISBN:
Category :
Languages : en
Pages : 304
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Author: Joseph B. Gehret
Publisher:
ISBN:
Category :
Languages : en
Pages : 304
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Author: Keng-Yen Chiang
Publisher:
ISBN:
Category :
Languages : en
Pages : 171
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The MIT Research Reactor (MITR) is evaluating the conversion from highly enriched uranium (HEU) to low enrichment uranium (LEU) fuel. In addition to the fuel element re-design from 15 to 18 plates per element, a reactor power upgraded from 6 MW to 7 MW is proposed in order to maintain the same reactor performance of the HEU core. Previous approaches in analyzing the impact of engineering uncertainties on thermal hydraulic limits via the use of engineering hot channel factors (EHCFs) were unable to explicitly quantify the uncertainty and confidence level in reactor parameters. The objective of this study is to develop a methodology for MITR thermal hydraulic limits analysis by statistically combining engineering uncertainties in order to eliminate unnecessary conservatism inherent in traditional analyses. This methodology was employed to analyze the Limiting Safety System Settings (LSSS) for the MITR LEU core, based on the criterion of onset of nucleate boiling (ONB). Key parameters, such as coolant channel tolerances and heat transfer coefficients, were considered as normal distributions using Oracle Crystal Ball for the LSSS evaluation. The LSSS power is determined with 99.7% confidence level. The LSSS power calculated using this new methodology is 9.1 MW, based on core outlet coolant temperature of 60 'C, and primary coolant flow rate of 1800 gpm, compared to 8.3 MW obtained from the analytical method using the EHCFs with same operating conditions. The same methodology was also used to calculate the safety limit (SL) to ensure that adequate safety margin exists between LSSS and SL. The criterion used to calculate SL is the onset of flow instability. The calculated SL is 10.6 MW, which is 1.5 MW higher than LSSS, permitting sufficient margin between LSSS and SL.
Author: Yu-Chih Ko (Ph. D.)
Publisher:
ISBN:
Category :
Languages : en
Pages : 290
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The MIT research reactor (MITR) is converting from the existing high enrichment uranium (HEU) core to a low enrichment uranium (LEU) core using a high-density monolithic UMo fuel. The design of an optimum LEU core for the MIT reactor is evolving. The objectives of this study are to benchmark the in-house computer code for the MITR, and to perform the thermal hydraulic analyses in support of the LEU design studies. The in-house multi-channel thermal-hydraulics code, MULCH-II, was developed specifically for the MITR. This code was validated against PLTEMP for steady-state analysis, and RELAP5 and temperature measurements for the loss of primary flow transient. Various fuel configurations are evaluated as part of the LEU core design optimization study. The criteria adopted for the LEU thermal hydraulics analysis for this study are the limiting safety system settings (LSSS), to prevent onset of nucleate boiling during steady-state operation, and to avoid a clad temperature excursion during the loss of flow transient. The benchmark analysis results showed that the MULCH-II code is in good agreement with other computer codes and experimental data, and hence it is used as the main tool for this study. In ranking the LEU core design options, the primary parameter is a low power peaking factor in order to increase the LSSS power and to decrease the maximum clad temperature during the transient. The LEU fuel designs with 15 to 18 plates per element, fuel thickness of 20 mils, and a hot channel factor less than 1.76 are shown to comply with these thermal-hydraulic criteria. The steady-state power can potentially be higher than 6 MW, as requested in the power upgrade submission to the Nuclear Regulatory Commission.
Author: Dakota J. Allen
Publisher:
ISBN:
Category :
Languages : en
Pages : 109
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In the framework of non-proliferation policy, the Massachusetts Institute of Technology Reactor (MITR) is planning to convert from highly enriched uranium (HEU) to low enriched uranium (LEU) fuel. A new type of high-density LEU fuel based on a monolithic U-10Mo alloy is being qualified to allow the conversion of all remaining U.S. high performance research reactors including the MITR. The purpose of this study is to understand the impact of proposed MITR LEU "FYT" fuel element fabrication tolerances on the operation and safety limits of the MITR. Therefore, the effects of fabrication specification parameters on all levels of the core, ranging from full-core alterations to individual spots on the fuel plates were analyzed. Evaluations at the design tolerances, and beyond, were conducted through neutronics and thermal hydraulics calculations. The first step was analyzing the separate effects that parameters, including enrichment, fuel mass loading, fuel plate thickness, and impurities, have on the reactor physics of the core. These analyses were used to develop curve fits to predict the effect of these parameters on the excess reactivity of fresh fuel inserted into the LEU core. These models could then be used to estimate the effect on fuel cycle length to ensure the tolerances would not cause significant changes to the operating cycle of MITR. These analyses estimated the margin to criticality present in the core and ensured that the reactivity shutdown margin (SDM) was not violated. Other parameters such as coolant channel gap and local fuel homogeneity cause primarily local impacts including the power distribution within the fuel element, and related impacts to thermal hydraulic margins. This modeling was necessary to ensure that these parameters would not cause the margin to MITR's thermal hydraulic safety limit, the onset of nucleate boiling (ONB), to be violated. The final step was a covariance analysis of the combined effects at a full-core and element level. This combined effect analysis assured that the core would maintain proper safety and operational margins with a realistic distribution of off-nominal parameters. Given the comprehensive analysis performed, the current design fabrication tolerances were determined to provide acceptable fuel cycle length and safety margins consistent with the MITR LEU preliminary safety analysis report, and a basis for updating these tolerances during planned manufacturing-scale plate fabrication demonstrations has been established.
Author: Yunzhi Diana Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 115
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The MIT Research Reactor (MITR) is in the process of conducting a design study to convert from High Enrichment Uranium (HEU) fuel to Low Enrichment Uranium (LEU) fuel. The currently selected LEU fuel design contains 18 plates per element, compared to the existing HEU design of 15 plates per element. A transitional conversion strategy, which consists of replacing three HEU elements with fresh LEU fuel elements in each fuel cycle, is proposed. The objective of this thesis is to analyze the thermo-hydraulic safety margins and to determine the operating power limits of the MITR for each mixed core configuration. The analysis was performed using PLTEMP/ANL ver 3.5, a program that was developed for thermo-hydraulic calculations of research reactors. Two correlations were used to model the friction pressure drop and enhanced heat transfer of the finned fuel plates: the Carnavos correlation for friction factor and heat transfer, and the Wong Correlation for friction factor with a constant heat transfer enhancement factor of 1.9. With these correlations, the minimum onset of nucleate boiling (ONB) margins of the hottest fuel plates were evaluated in nine different core configurations, the HEU core, the LEU core and seven mixed cores that consist of both HEU and LEU elements. The maximum radial power peaking factors were assumed at 2.0 for HEU and 1.76 for LEU in all the analyzed core configurations. The calculated results indicate that the HEU fuel elements yielded lower ONB margins than LEU fuel elements in all mixed core configurations. In addition to full coolant channels, side channels next to the support plates that form side coolant channels were analyzed and found to be more limiting due to higher flow resistance. The maximum operating powers during the HEU to LEU transition were determined by maintaining the minimum ONB margin corresponding to the homogeneous HEU core at 6 MW. The recommended steady-state power is 5.8 MW for all transitional cores if the maximum radial peaking is adjacent to a full coolant channel and 4.9 MW if the maximum radial peaking is adjacent to a side coolant channel.
Author: Thomas Henderson Newton
Publisher:
ISBN:
Category :
Languages : en
Pages : 312
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(cont.) Thermal-hydraulic calculations using the multi-channel thermal-hydraulics analysis code MULCH-II indicated that the peak power channel will remain below the Onset of Nucleate Boiling under all normal operating conditions as well as loss of flow conditions. In addition, using MCNP and the thermal-hydraulics/point kinetics code PARET it was shown that all reactivity coefficients were negative and that the LEU core could withstand a step reactivity insertion of $3.69 without reaching cladding softening temperature, thus increasing the allowable reactivity for an incore experiment. Finally, it is possible to use the proposed design to increase the neutron flux by increasing core power, but with a correspondingly reduced refueling cycle length.
Author: Yinjie Zhao
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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The MIT Research Reactor (MITR) is in the process of converting from the current 93%-enriched U-235 highly-enriched uranium (HEU) fuel to the low enriched uranium (LEU, 20%-enriched U-235) fuel, as part of the global non-proliferation initiatives. A high-density, monolithic uraniummolybdenum (U-10Mo) fuel matrix is chosen. The fuel element design is changed from 15-plate finned HEU fuel to 19-plate unfinned LEU fuel with the same geometry. The reactor power increases from 6.0 MW to 7.0 MW thermal, and primary coolant flow rate increases from 2000 gpm to 2400 gpm. Detailed analyses were completed for initial LEU core with 22 fuel elements, and demonstrated both neutronic and thermal hydraulic safety requirements are met throughout equilibrium cycles. An alternative conversion strategy is proposed which involves a gradual transition from an all-HEU core to an all-LEU core by replacing 3 HEU fuel elements with fresh LEU fuel elements during each fuel cycle. The objectives of this study are to demonstrate that the primary coolant system can be safely modified for 2400 gpm operation, and to perform steady-state and loss-of-flow (LOF) transient thermal-hydraulic analyses for the MITR HEU-LEU transitional mixed cores to evaluate this alternative conversion strategy. The primary technical challenge for the 20% increase in primary flow rate with existing piping system is flow-induced vibration. Several experiments were performed to measure and quantify vibration acceleration and velocity on three main hydraulic components to determine if higher flowrates cause excessive vibration. The test results show that the maximum vibration velocity is 9.70 mm/s, the maximum vibration acceleration is 0.98 G at the current flow rate 2000 gpm and no significant spectral change in the vibration profile at 2550 gpm. Therefore, it can be concluded that the existing piping system can safely support 2400 gpm primary flow operation. Thermal hydraulics analysis was performed using RELAP5 MOD3.3 code and STAT7 code. The MITR transitional mixed core input models were constructed to simulate the reactor primary system. Two scenarios, steady-state and loss-of-flow transient were simulated at power level of 6 MW. RELAP5 results show that during steady state, there is significant safety margin ( 10 °C) to onset of nucleate boiling for both HEU and LEU fuel. The maximum core temperature occurs at HEU fuel in Mix-core 3, the maximum wall temperature reached was 89 °C. During the LOF transient case, the result shows that The HEU fuel element is more limiting than the LEU in transitional cores. Nucleate boiling is predicted to occur only in the HEU hot channel during the first 50 seconds after the pump coastdown. The peak cladding temperatures are much lower than the fuel temperature safety limit of UAl[subscript x] fuel plates, which is 450 °C. From the STAT7 calculation results, the operational limiting power at which onset of nucleate boiling (ONB) occurs in all cases show significant margins from the Limiting System Safety Setting (LSSS) over-power level. The lowest margin for LEU element during the mixed core transition is at Mix-7, 11.43 MW with a 4.03 MW power margin. For the HEU element, the lowest margin during the transition is at Mix-2, 8.51 MW with a 1.11 MW power margin. The location at which ONB is always expected to occur is F-Plate Stripe 1 and 4 for the LEU fuel element; side plate for the HEU fuel element with the HEU element is always more limiting.
Author: Ferry Roelofs
Publisher: Woodhead Publishing
ISBN: 0081019815
Category : Science
Languages : en
Pages : 464
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Thermal Hydraulics Aspects of Liquid Metal cooled Nuclear Reactors is a comprehensive collection of liquid metal thermal hydraulics research and development for nuclear liquid metal reactor applications. A deliverable of the SESAME H2020 project, this book is written by top European experts who discuss topics of note that are supplemented by an international contribution from U.S. partners within the framework of the NEAMS program under the U.S. DOE. This book is a convenient source for students, professionals and academics interested in liquid metal thermal hydraulics in nuclear applications. In addition, it will also help newcomers become familiar with current techniques and knowledge. Presents the latest information on one of the deliverables of the SESAME H2020 project Provides an overview on the design and history of liquid metal cooled fast reactors worldwide Describes the challenges in thermal hydraulics related to the design and safety analysis of liquid metal cooled fast reactors Includes the codes, methods, correlations, guidelines and limitations for liquid metal fast reactor thermal hydraulic simulations clearly Discusses state-of-the-art, multi-scale techniques for liquid metal fast reactor thermal hydraulics applications
Author: United States. Congress. House. Committee on Science and Technology. Subcommittee on Energy Development and Applications
Publisher:
ISBN:
Category : Nuclear engineering
Languages : en
Pages : 1968
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Author:
Publisher:
ISBN: 9785936804274
Category :
Languages : en
Pages : 574
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