Reactor Outlet Temperature Research Articles

High-Performance Supercritical Carbon Dioxide Cycle for Next-Generation Nuclear Reactors

Supercritical carbon dioxide cycles are a promising power conversion option for future nuclear reactors operating with a reactor outlet temperature in the range of 550 to 650°C. The recompression cycle version operating with ~20-MPa turbine inlet pressure achieves similar cycle efficiencies as helium Brayton cycles operating at ~250°C higher turbine inlet temperature. The simplicity and high efficiency of the recompression cycle makes it a prime option from among the family of supercritical carbon dioxide cycles. The elimination of the need for intercooling due to the small required compressor work (because of the high density close to the critical point) makes the recompression cycle even simpler than helium Brayton cycles, which require intercooling to achieve attractive efficiencies. The high operating pressure reduces the size of the plant components significantly, making it a promising power cycle for low-cost modularized electricity-generating nuclear systems. However, the real gas behavior that improves the cycle efficiency presents a challenge for part-load operation. The traditional inventory control used for helium Brayton cycles may not be feasible. Bypass control is thus the prime option for part-load operation, making the cycle less efficient than during base-load operation. Since nuclear power plants are operated almost exclusively in base load, this drawback is not a disqualifying blemish.

Numerical Simulation of MHD Power Generation Systems Using ICF Reactor

It is known that fusion reactions are fueled by deuterium and tritium, which are found easily in water and are known as unlimited energy resource, would release enormous energy for driving power generation system. The aim of this study is to examine and compare the plant efficiency of power generation systems using magnethydrodynamic (MHD) generator, Gas Turbine (GT), Steam Turbine (ST) and Inertial Confine-ment Fusion (ICF) reactor as heat source to generate electrical power. Three systems were considered including the MHD single system, the MHD/GT system and the MHD/ST system, and the highest plant efficiency of each system was 61.06%, 58.34% and 60.76% respectively. This result showed that the MHD single system could be expected as the most effective system because of the highest plant efficiency and the simplest system. However, it also showed that the plant efficiency decreased with the increase of the reactor outlet temperature because of the reactor's blanket limit temperature. For this reason, it was under-stood that too high a reactor outlet temperature was not desirable. The temperature of 1999K and enthalpy extraction of 33.5% would be most preferable parameters to MHD single system.

Optimum utilization of nuclear fuel with gas and vapor core reactors

Gas and Vapor Core Reactors (G/VCR) are externally reflected and moderated nuclear energy systems fueled by stable uranium compound in gaseous or vapor phase. In G/VCR systems the functions of fuel and coolant are combined and the reactor outlet temperature is not constrained by solid fuel-cladding temperature limitations. G/VCRs can potentially provide the highest reactor and cycle temperature among all existing or proposed fission reactor designs. Furthermore, G/VCR systems feature a low inventory and fully integrated fuel cycle with exceptional sustainability and safety characteristics. With respect to fuel utilization, there is practically no fuel burn-up limit for gas core reactors due to continuous recycling of the fuel. Owing to flexibility in nuclear design characteristics of cavity reactors, a wide range of conversion ratio from almost solely a burner to a breeder is achievable. The continuous recycling of fuel in G/VCR systems allows for continuous burning and transmutation of actinides without removing and reprocessing of the fuel. The only waste product at the backend of the gas core reactors' fuel cycle is fission fragments that are continuously separated from the fuel. As a result the G/VCR systems do not require spent fuel storage or reprocessing. G/VCR systems also feature outstanding proliferation resistance characteristics and minimum vulnerability to external threats. Even for comparable spectral characteristic, gas core reactors produce fissile plutonium two orders of magnitude less than Light Water Reactors (LWRs). In addition, the continuous transmutation and burning of actinides further reduces the quality of the fissile plutonium inventory. The low fuel inventory (about two orders of magnitude lower than LWRs for the same power generation level) combined with continuous burning of actinides, significantly reduces the need for emergency planning and the vulnerability to external threats. Low fuel inventory, low fuel heat content, and online separation of fission fragments are among the key constituent safety features of G/VCR systems.

Catalytic combustion of gasified biomass in a platinum monolith honeycomb reactor

The characteristics of catalytic ignition and reaction of single and multiple fuels including simulated gasified biomass are investigated both experimentally and numerically. A two-dimensional channel flow code with the multi-step gas phase and surface reaction mechanisms is used to clarify the detailed interaction mechanism of the main gasified biomass species on the surface. The light-off characteristics for single and multiple fuels with varying concentrations and global residence times are identified. For gasified biomass, the preheat temperature needed for light-off is found to be determined by carbon monoxide, which has the largest adsorption probability on platinum surface. The observed two-step rising of the reactor outlet temperature also provides evidence for the promotion of methane light-off by hydrogen and carbon monoxide. The operational domain for catalytic combustion of gasified biomass in a platinum monolith honeycomb reactor is bounded by curves of carbon monoxide concentration for ignition, residence time and methane concentration for conversion ratio, and the sinter temperature of the catalyst.

Tuning Proportional−Integral Controllers for Processes with Both Inverse Response and Deadtime

Many tuning methods have been proposed over the last half-century. Most apply to deadtime/lag processes, but several have studied either integrating processes or inverse response processes. Very few have explored processes in which both deadtime and inverse responses occur. This type of response is observed in adiabatic tubular reactors when reactor outlet temperature Tout is the controlled variable and reactor inlet temperature Tin is the manipulated variable. Typically the control structure uses a cascade arrangement in which the secondary loop uses furnace heat input or heat-exchanger bypassing to control Tin. This paper addresses the problem of controlling processes that exhibit both inverse response and deadtime. The Ziegler−Nichols tuning method recommended in the literature is shown to give poor performance at both small and large values of deadtime and positive-zero time constant. A new tuning method is proposed in which the PI tuning constants are presented as functions of the positive zero τz and the deadtime D. Results are given in the form of easy-to-use tuning charts.

Inferential estimation of polymer quality using bootstrap aggregated neural networks

Inferential estimation of polymer quality in a batch polymerisation reactor using bootstrap aggregated neural networks is studied in this paper. Number average molecular weight and weight average molecular weight are estimated from the on-line measurements of reactor temperature, jacket inlet and outlet temperatures, coolant flow rate through the jacket, monomer conversion, and the initial batch conditions. Bootstrap aggregated neural networks are used to enhance the accuracy and robustness of neural network models built from a limited amount of training data. The training data set is re-sampled using bootstrap re-sampling with replacement to form several sets of training data. For each set of training data, a neural network model is developed. The individual neural networks are then combined together to form a bootstrap aggregated neural network. Determination of appropriate weights for combining individual networks using principal component regression is proposed in this paper. Confidence bounds for neural network predictions can also be obtained using the bootstrapping technique. The techniques have been successfully applied to the simulation of a batch methyl methacrylate polymerisation reactor.

A modeling and simulation study on a naphtha reforming unit with a catalyst circulation and regeneration system

A steady state and a dynamic flowsheet for a naphtha reforming unit with a catalyst circulation and regeneration system were built using SPEEDUP. A rigorous modeling of reactors, a regenerator, and a catalyst circulation system was achieved in the flowsheets by creating non-standard algorithms. With the steady state flowsheet, we calculated each reactor outlet temperature and obtained more precise temperature profiles than those of previous works with a relative error within 1.2%. The steady state flowsheet was directly used to predict the product yields and operating conditions. Two case studies were provided for an application to the actual plant operations. With the dynamic flowsheet, the best gain value in the first hopper level controller was obtained from the sensitivity analysis of control tuning parameters, and the best tuning parameters were directly used in DCS system of the real process. We could shorten the level stabilization time by half and also get more stable operations.

Operating temperatures for an FBR

Structural mechanics aspects related to operating temperatures of a typical pool type 500 MWe fast breeder reactor are discussed. The critical high temperature components are analysed in detail based on elastic, inelastic and viscoplastic deformation theories, and life is predicted in accordance with the rules of design code RCC-MR 87. Analysis indicates that the control plug is the most critical component in the reactor which limits the reactor outlet temperature to 820 K with a temperature rise of 160 K across the core.

Neural Network Based Estimators for a Batch Polymerization Reactor

Inferential estimation of polymer quality in a batch polymerization reactor using neural networks is described in this paper. Number average molecular weights, weight average molecular weights, polymerization rate, and conversion are estimated from reactor temperature, jacket inlet and outlet temperatures, and the coolant flow rate through the jacket which are easily measurable. Neural networks with mixed types of hidden neurons are used in this study and they are trained by a sequential orthogonal training algorithm. The results reported in this paper demonstrate that difficult-to-measure polymer quality variables can be estimated with acceptable accuracy from easy-to-measure process variables.

Upgrading of wakefield browncoal from south Australia

A sample of Wakefield browncoal, which is of very poor quality, was subjected to various treatments to improve the calorific value and remove contaminants. The best coal product, with a calorific value of 30 MJ/kg, was obtained by hydrothermal upgrading: 91% of the combustibles present in the feedstock were concentrated in 34% of the original weight. Moreover, an amount of liquid products was generated in a yield of up to 10 wt% on dry intake. Via a Fleissner treatment ca. 70% of the inherent moisture was removed as a liquid, leaving a product whose calorific value is expected to be almost 20 MJ/kg. Via carbonization smokeless fuels can be produced with a heating value of ca. 28 MJ/kg and yields of 50–60%, depending on the temperature. From this particular browncoal, most of the silica fraction of the mineral matter was extracted by rinsing with water, thus reducing the ash content by 50% and the ash fusion temperature by almost 200°C. By combined thermal upgrading and washing, most of the contaminants, i.e., sodium and chlorine, and half of the amount of oxygen and sulphur were removed. On the basis of experiments with micro-gasification test equipment, Wakefield browncoal and its upgraded product seem attractive feedstocks for gasification from a reactivity point of view. The lowering of the ash fusion temperature as observed in washed products is important for the reduction of the reactor outlet temperature when gasifying under slagging conditions, which has a favourable effect on the thermal efficiency.

The Effect of Coolant Orificing on the Core Performance of a Heterogeneous Liquid-Metal Fast Breeder Reactor

The effect of orificing on the core performance of a commercial-size heterogeneous liquid-metal fast breeder reactor was studied analytically. The thermal power output was flattened at beginning of life, and the coolant flow rate was chosen such that the maximum inner cladding temperature of a driver fuel and a blanket fuel was less than or equal to 620/sup 0/C at both beginning of equilibrium life (BOEL) and end of equilibrium life (EOEL). The difference between reactor outlet temperatures at BOEL and EOEL was then calculated for six core configurations: one homogeneous core configuration and five heterogeneous ones. The results showed that the core outlet temperature variation due to the change of the power profile of the radial heterogeneous core configurations is similar to that of the homogeneous one, even when a single type of orificing is used in each core zone, and it will not be necessary to use the more detailed orificing in each zone of a heterogeneous core configuration. The study concludes that for the present design, especially the thermal design, of some heterogeneous core configurations, it is feasible to control the change of the reactor outlet temperature with burnup, even when a single type of orificing ismore » used in each core zone.« less

Liquefaction of coal by SRC‐II process: Part IV: Steady‐state thermal behavior of the reactor

AbstractAn axial dispersion thermal model of an SRC‐II reactor is developed. The model is validated by simulation of steady‐state temperature profiles in the Fort Lewis (Tacoma, Washington) pilot‐plant SRC‐II reactor. The simulation shows that normal operations of the SRC‐II reactors are thermally unstable. Changes in the process conditions can be utilized to achieve thermal stability for the reactor at normal SRC‐II operating temperatures, i.e., reactor outlet temperature of less than 465°C and average reactor temperature of about 455°C. However, thermal stability of the reactor would always result in reduction in the rate of reaction. Regions of unstable steady‐state reactor temperature over large ranges of ash concentrations in the reactor and reactor feed temperatures are also illustrated.

Steady state thermal behavior of an adiabatic three phase slurry reactor—coal liquefaction under slow hydrogen consumption reaction regime

This paper presents an axial dispersion model for illustrating the steady state thermal behavior of an adiabatic three phase coal liquefaction reactor. The model predicted temperature profiles are shown to be in very good agreement with experimental data. The model is used to illustrate the effects of various scale up variables on the hydrogen consumption and temperature rise in an adiabatic coal liquefaction reactor with and without a single gas quench. An interstage recirculation model is also developed and used to examine the effects of these variables. The predictions of the interstage recirculation model agree reasonably well with those of the axial dispersion model even when only four stages are considered in the former case. The effects of reactor variables on the critical amount of quench required to maintain a constant reactor outlet temperature are illustrated.

Optimization of helium-steam binary cycles for HTGRs

This paper describes techniques for determining optimum plant configuration and operating conditions for complex binary cycles employing feedwater heaters, moisture separators, multi-stage compressors, and a regenerator. A model describing the efficiency of binary cycles is developed in a form suitable for optimization. As part of the optimization procedure, the system is partitioned into Brayton and Rankine portions by fixing coupling variables, and then for fixed values of coupling variables the two cycles are optimized separately. Dynamic programming is used in the Rankine portion of the binary cycle and a modified search technique in the Brayton cycle. For the range of reactor outlet and boiler saturation temperatures examined, and for boiler exit temperature up to 536°C, binary cycle efficiencies become optimum at 371°C boiler saturation temperature, 110°C to 170°C superheat, no regeneration for reactor exit temperatures below 1170K and appreciable amount of regeneration above 1170K. Optimum binary cycle efficiencies are 0.506, 0.533 and 0.560 for reactor exit temperatures of 1060 K, 1170 K and 1280 K, respectively.

Abstracts of contributed papers for annual meeting Professional Group on Nuclear Science October 6 and 7, 1954

The problem of designing a constant reactor outlet temperature control system for a thermal reactor power plant is considered. The dynamic control characteristics of the power plant are described in terns of (1) the response of reactivity to variations of reactor inlet coolant temperature, (2) the heat transfer characteristics of the reactor and boiler, and (3) the time lags of the reactor coolant loop. It is shown how the inherent characteristics of the power plant may be used to advantage by constant reactor outlet temperature control systems employing the reactor inlet and outlet temperatures as control variables. An important feature of these control systems is the computation of the reactor inlet temperature from the boiler outlet temperature or the steam plant variables using recently developed transport delay circuits to compensate for the boilerto-reactor coolant transport delay.