Fuel Temperature Rise Research Articles

Research on the performance enhancement of accident tolerant fuel for eliminating core melting based on ISAA

Based on the Integrated Severe Accident Analysis (ISAA) code, this paper studies the influence of thermo-physical properties of Accident Tolerant Fuel (ATF) materials on the plant responses to severe accidents, and further proposes the requirements of eliminating core melting on ATF performance and reactor components. The equation of fuel temperature rise is derived from the steady-state heat conduction equation of fuel rods, and three fuel properties, including thermal conductivity, density and specific heat capacity, which affect core melting, are obtained. By selecting ATF with IMDP(Inert Matrix Dispersion Pellet) as the core material and SiC as the cladding material and changing different physical parameters, it is found that fuel density and cladding density have the greatest influence on the fuel temperature rise, and appropriately increased fuel density can extend the core melting time. In addition, to eliminate core melting, the ATF parameters in ISAA are modified step by step to improve the thermodynamic properties of the fuel, and the core is finally made to reach thermal equilibrium and to realize the safety of nuclear power plants without human intervention. According to the calculation results, the supporting capacity of the cladding, the supporting capacity of the core supporting plate, and the melting point of the fuel are the main factors limiting the core melting, which can be eliminated by appropriately improving these properties.

Research on Transient Characteristics of Scramjet Engine during Starting Sequence

Transient characteristics of entire engine system affect control method of the engine system. A quasi-transient simulator called Hypersonic Engine Dynamic Simulator (HEDS) was developed for the purpose of analyzing the transient behavior of a scramjet engine system. The simulator was constructed using the volume junction method, which is a type of finite volume method, and was introduced with a parallel computing function using the MPI library. In this study, the transient characteristics at the starting sequence of a scramjet engine equipped with an expander cycle was analyzed. In the startup transient analysis, two factors (the time from high-speed airflow inflow to the main valve opening and the time from the main valve opening to ignition) that affect the system startup were focused. In addition, constraints on the system were set to evaluate results of the analysis. As a result, there existed cases in which the maximum rotational speed of the turbo pump was much higher than expected when the interval between the inflow of high-speed airflow and the opening of the main valve was increased. In addition, there was also a delay time between ignition and fuel temperature rise. Therefore, the time from the main valve opening to ignition should be as short as possible. In the control phase, it was necessary to manipulate those two factors appropriately in order to bring the system to a steady state in a short time. HEDS was found to be a very effective tool for understanding the behavior of the system at the operating point and constructing a control method.

Sub-channel analysis code development and core thermal calculation for fast reactor refueling cycle

Sub-channel analysis is an indispensable method for core safety evaluation. As a part of the fast reactor program series, development of SAC-SUB (System analysis code – SUB channel) program has been completed. Experiments performed with a 19-rod test assembly in the fuel failure mockup (FFM) sodium loop in Oak Ridge National Laboratory (ORNL) was selected as the benchmark to verify the SAC-SUB program capability. The maximum outlet temperature deviation is within 5%, which preliminarily verifies the availability of the program for fast reactor. Then the code was used to analyze CEFR thermal response during refueling cycle and MOX equilibrium state. During each refueling cycle, highest sodium temperature occurs in the fourth flow zone, and highest fuel temperature rise occurs in the first flow zone. The highest sodium temperature is 606.8 °C appearing in 3rd cycle, and the highest fuel temperature rise is 880.93 °C appearing in 4th cycle. Maximum temperature rise across the cladding and film do not change much. After reaching MOX core equilibrium state, all the key temperature will reach a lower level compared with refueling transition process, which indicating that the power distribution and flow distribution of the core are more matched in the equilibrium state.

Performance and Emission Characteristics of VCR Diesel Engine with Pre Heated Lemon Grass Biodiesel as Fuel

Under this experimental analysis the lemon grass oil was considered, it’s converted into biodiesel as lemon grass biodiesel methyl ester (LGB) through transesterification process. The Kirloskar TV1 was used as the reference fuel in the fuel injection system 4-stroke diesel engine. The lemon grass biodiesel methyl ester (LGB B20) blend B20 is selected because it nearest to the diesel value. The lemon grass biodiesel is preheated at 60°C temperature that is (LGB B20 preheating @ 60°C). The results of the test showed that LGB B20 kinematic viscosity and density gradually decreased with fuel temperature rise. The performance characteristics of Preheating biodiesel is increased the BTE and slightly reduce the BSFC at noted in the full load condition. And the emission characteristics at full load condition of CO, HC and smoke density as decreased, it was observed slight increase of NOx emission.

Modelling and reducing fuel flow pulsation of a fuel-metering system during pump mode switching in a turbofan engine

In this research, the transient characteristics of a new type fuel metering system for aircraft turbofan engines using two types of pumps, a gear pump and a centrifugal pump, were studied by modelling and simulation. This new fuel metering system is capable of hydraulically unloading the operating state of each pump by the pump mode switching mechanism within the permissible range of the pump rotation speed and the fuel flow rate and it is possible to reduce the fuel temperature rise due to the pressure loss in the circuit in the operation region of the entire fuel system. In addition to this, by using a small centrifugal pump that can realize high discharge flow rate, it is possible to reduce weight compared to the conventional fuel system. However, when the pump mode is switched, unexpected fluctuation in the fuel flow rate can occur when a large change in the inlet pressure of the system occurs, the pressure control unit cannot follow the change, and the transient phenomenon cannot be suppressed. At this time, the pressure waveform generated at the time of changing the pump mode includes a high frequency component such that the pressure control unit, which plays a role of keeping the metering valve differential pressure constant, cannot follow up. Therefore, in this paper, we focused on the frequency of the pressure change waveform when the pump mode was changed and studied the model of the fuel system inlet pressure in the gear pump mode. Based on that model, we propose a method to reduce the frequency characteristics of the pressure change occurring at the time of pump mode change.

Station Blackout Analysis of HTGR-Type Experimental Power Reactor

The National Nuclear Energy Agency of Indonesia has decided to build an experimental power reactor of high-temperature gas-cooled reactor (HTGR) type located at Puspiptek Complex. The purpose of this project is to demonstrate a small modular nuclear power plant that can be operated safely. One of the reactor safety characteristics is the reliability of the reactor to the station blackout (SBO) event. The event was observed due to relatively high disturbance frequency of electricity network in Indonesia. The PCTRAN-HTR functional simulator code was used to observe fuel and coolant temperature, and coolant pressure during the SBO event. The reactor simulated at 10 MW for 7200 s then the SBO occurred for 1-3 minutes. The analysis result shows that the reactor power decreases automatically as the temperature increase during SBO accident without operator’s active action. The fuel temperature increased by 36.57 °C every minute during SBO and the power decreased by 0.069 MW every °C fuel temperature rise at the condition of anticipated transient without reactor scram. Whilst, the maximum coolant (helium) temperature and pressure are 1004 °C and 9.2 MPa respectively. The maximum fuel temperature is 1282 °C, this value still far below the fuel temperature limiting condition i.e. 1600 °C, its mean that the HTGR has a very good inherent safety system.

Cooling design of an aero-engine fuel centrifugal pump at shut-off

Because of the problem of a high fuel temperature rise at shut-off, a conventional centrifugal pump could not be used as an aero-engine fuel pump for the afterburner fuel supply. In this study, a c...

Spray development and droplet characteristics of high temperature single-hole gasoline spray

As increasing fuel injection pressure in GDI (Gasoline Direct Injection) engines has been used for improving atomization quality, raising fuel temperature is also receiving more and more attention as another promising method to improve mixing quality and combustion process. In order to understand atomization process with increased fuel temperatures, spray development and droplet characteristics of high fuel temperature spray were investigated by using back-illumination imaging technique and Phase Doppler Particle Analyzer (PDPA) with fuel temperature up to 376°C as supercritical state. Results show that sprays dispersed more widely and became more transparent with increasing fuel temperature. Spray penetrations had some reduction and spray cone angle had obvious increase with increased fuel temperature not more than critical temperature. While droplet arithmetic mean diameter (D10) and Sauter Mean Diameter (SMD) was reduced from about 10μm to 1.5μm and from 30μm to 3μm as fuel temperature rise from 25°C to 261°C, high temperature more than 261°C resulted in droplets became too small to be measured by the PDPA instrument.

Numerical Study of a Fuel Centrifugal Pump with Variable Impeller Width for Aero-engines

AbstractAs typical pump with large flow rate and high reliability, centrifugal pumps in fuel system of aero-engines mostly regulate flow rate by flow bypass, which leads to low efficiency and large fuel temperature rise especially at low flow rate. An innovative fuel centrifugal pump with variable impeller width is a more effective way to regulate flow rate than flow bypass. To find external characteristics of the centrifugal pump with variable impeller width proposed in this paper, flow domain within the pump is simulated numerically and some primary performance parameters and their correlation are analyzed. Results show that flow rate of the pump can be regulated by variable impeller width and that efficiency for this scheme is higher than that for flow bypass. The higher outlet static pressure the pump runs at, the wider range of flow rates can be obtained with stronger nonlinear relationship between flow rate and impeller width.

S1150304 定圧型油圧源を有するジェットエンジン燃料制御機構の燃料ポンプ切り替えのシミュレーション

In order to reduce a weight of a fuel system and decrease the fuel temperature rise generated by a fuel system itself, the fuel system which has both a gear pump and a centrifugal pump with operation mode switching capability for a turbofan engine were studied. The fuel system can decrease the work of pumps by unloading one of pumps and can be configured without a variable displacement pump that has a complicated structure and sensitive for contaminant. During mode switching of fuel pumps, inlet fuel flow rate or inlet fuel pressure of a fuel metering unit is varied by mode switching valves. Pulsated fuel flow or fuel pressure affect the metered fuel flow that should be kept within tolerance. In this paper, mode switching procedures that can reduce fuel flow drift are proposed. Validity of the procedures is evaluated by AMESim simulation.

Subchannel analysis of fuel temperature and departure of nucleate boiling of TRIGA Mark I

An evaluation of fuel temperature and departure of nucleate boiling as a function of bulk pool temperature was performed at the Texas A&M University Nuclear Science Center’s TRIGA Mark I reactor. A subchannel analysis code was written with the support of experimentally determined correlations, including the development of a gap conductance model. The code was validated for predicting peak fuel temperature at all operational power levels. The peak fuel temperature was calculated using different correlations for forced and natural convection flows for pool temperatures of 30°C and 60°C. The forced convection correlation predicted a fuel temperature rise of 2°C for the difference in pool temperatures, contrary to the predicted rise of 26°C from natural convection relationships. Experimental data shows that the relationship of fuel temperature rise with increasing pool temperature is more accurately represented by the natural convection correlation. The peak fuel temperature, for the validated natural convection relationship, is predicted to be 441°C and 457°C at a pool temperature of 30°C and 60°C, respectively. The minimum departure of nucleate boiling ratio is calculated as 2.14 and 1.72 for a pool temperature of 30°C and 60°C, respectively, using the Bernath correlation.

Development of Double Gear Fuel Pump for Heat Management Improvement

A unique double gear fuel pump system with operation mode switching capability for aircraft engines was developed to solve the heat management problem of current high efficiency turbofan engines and improve specific fuel consumption (SFC). Mode switching from parallel operations to series operations was found to reduce the discharge flow and pump work to nearly half. This resulted in the reduction of the rise in fuel temperature due to the fuel recirculation at the high altitude low Mach number flight condition. Air cooled oil cooler (ACOC) is usually required for sufficient oil cooling at descent or approach flight conditions. Since fuel consumption at those conditions is not very high, most of the gear pump discharge fuel flow proportional to the engine speed is returned to the fuel pump inlet resulting in significant heating. The ACOC that provides additional cooling capability degrades SFC due not only to the increased weight but also to the wasted fan discharge air. By reducing fuel temperature rise at the pump at those flight conditions, the necessity of ACOC may be eliminated. Further, it is shown that a reduction by half of the double gear pump weight can be achieved by increasing pump speed twice without incurring a durability penalty. Extensive tests showed sufficient steady state pump performance, switching characteristics, and durability.

ULOF and UTOP Analyses of a Large Metal Fuel FBR Core Using a Detailed Calculation System

ULOF and UTOP analyses of a large metal fuel FBR core (1,500 MWe, averaged discharge burnup: 150 GWd/t) are conducted. The effect of core radial expansion is considered as the major negative feedback during the transient. A detailed analysis system is used, in which a transient core thermal-hydraulic code is coupled with three dimensional core radial deformation and reactivity feedback calculation codes, in order to calculate the radial expansion feedback. In ULOF analysis, the pump flow halving time is assumed to be 10 s, which is reasonably long and effective in avoiding too large power to flow ratio. The reactivity insertion during UTOP is set to be 34¢, based on the control rod reactivity design. As the analysis results, it is found that the core shows benign responses to both events, owing largely to the radial expansion feedback. No significant coolant boiling or fuel failure is predicted. The response during ULOF is compared to that of an oxide fuel core of similar design, and it is confirmed that the negative Doppler effect associated with the fuel temperature rise plays the major role in the quick power decrease.

ULOF and UTOP Analyses of a Large Metal Fuel FBR Core Using a Detailed Calculation System.

ULOF and UTOP analyses of a large metal fuel FBR core (1,500 MWe, averaged discharge burnup: 150 GWd/t) are conducted. The effect of core radial expansion is considered as the major negative feedback during the transient. A detailed analysis system is used, in which a transient core thermal-hydraulic code is coupled with three dimensional core radial deformation and reactivity feedback calculation codes, in order to calculate the radial expansion feedback. In ULOF analysis, the pump flow halving time is assumed to be 10 s, which is reasonably long and effective in avoiding too large power to flow ratio. The reactivity insertion during UTOP is set to be 34¢, based on the control rod reactivity design. As the analysis results, it is found that the core shows benign responses to both events, owing largely to the radial expansion feedback. No significant coolant boiling or fuel failure is predicted. The response during ULOF is compared to that of an oxide fuel core of similar design, and it is confirmed that the negative Doppler effect associated with the fuel temperature rise plays the major role in the quick power decrease.

Optimization Method of Rod-Type Burnable Poisons for Nuclear Designs of HTGRs.

In block-type HTGRs, control rod insertion depths into cores had to be maintained as small as possible at full power operations, to avoid a fuel temperature rise. Thus, specifications (poison atom density (NBP) and radius (r)) of rod-type burnable poisons (BPs) had to be optimized so that the effective multiplication factor (keff) would be constant at a minimum value throughout a planned burnup period.However, the optimization had been a time-consuming work until now since survey calculations had to be done for most possible combinations of NBP and r. To solve this problem, I have found a optimization method consisting of two steps. In the first step, approximation formulas describing a time-dependent relation among effective absorption cross sections (ΣaBP), NBP and r are used to select promising combinations of NBP and r beforehand. In the second step, the best combination of NBP and r is determined by a comparison between ΣaBP of each promising combination and expected one. The number of survey calculations was reduced to about 1/10 by the optimization method. The change in keff for 600 burnup days was reduced to 2%Δk by the method. Hence, it was made possible to operate reactors practically without inserting the control rods into cores.