Thermal Utilization Factor Research Articles

Multiobjective optimization of a pressurized water reactor cogeneration plant for nuclear hydrogen production

In this paper, energy, exergy, economic analysis and multiobjective optimization of a pressurized water reactor (PWR) nuclear cogeneration plant for hydrogen production through high-temperature steam electrolysis (HTSE) are carried out. HTSE requires energy in the form of both heat and electrical work. A novel parameter, namely the heat/total energy ratio, is defined, and used as a decision variable in optimization. In addition to energy ratio, hydrogen production capacity, reactor thermal power, live steam temperature, reheating mass flow rate ratio, reheating temperature and steam extraction location are considered as the decision variables to simultaneously optimize the thermal efficiency, thermal-to-hydrogen efficiency, utilization factor, exergy efficiency and total revenue of the cogeneration plant. The analysis and optimization focus on the secondary cycle of the PWR and the effects of hydrogen and electricity prices and ambient conditions are also taken into account since these prices have a significant impact on the optimum design. For a hydrogen price of 4 $/kg and an electricity price of 0.1 $/kWh, when equal preference is given to all objective functions, the optimum production capacity is 6.778 kg/s. The energy ratio has an optimum value if the optimization focuses exclusively on the thermal efficiency and total revenue.

Influences of latent heat storage heat sink integrated with solar dryer to enhance drying period

Drying is an important procedure and is popular among farmers to dry agricultural produce. However, farmers cannot dry their crops due to the limited availability of sun rays during the daytime. Because of the above issue, a solar-operated heat sink unit was designed and developed to store 40 kg of phase change material (PCM) for latent heat storage, enabling the desired drying temperature for continuous drying operation. Barium Hydroxide Octahydrate [Ba(OH)2. 8H2O] was used as a PCM which can store the energy in the daytime and release it during off-sunshine hours. The performance of PCM integrated with a solar dryer was investigated with a drying of potato chips in terms of thermal efficiency, drying rate, drying efficiency, and heat utilization factor. In the PCM-enabled dryer, the product was dried in a single day, maintaining the average drying temperature between 58 °C to 66 °C throughout the drying. In contrast, the same product was dried in next day in case of open sun drying. The developed drying system is positioned to operate effectively 4-5 hours after sunset and found a viable option for Agri industries and domestic purposes as it is nonpolluting to the environment and does not contain many more conventional energy sources. Moreover, the developed system saved 5604 kWh of electrical energy and 555.06 liters of diesel fuel each year, as well as reduced 5.49 t CO2 emissions.

Heterogeneous model based burnup and its impact on integral parameters of IAEA MTR benchmark

Computational benchmarks are an important source for verifying the codes and modeling methodology in nuclear reactor analysis. The current study aims at utilizing the newly developed burnup capability of open source code OpenMC to perform analyses of the IAEA 10-MW MTR benchmark reactor. The whole core model developed for the benchmark is verified against the Serpent results from an earlier study. The effect of the volume-weighted homogenized (VWH) unit-cell model against a fully heterogeneous fuel assembly model to obtain burnup dependent number densities is determined. It was observed that the comparison of four factors (resonance escape, fast fission, thermal utilization, and reproduction factor) for two modeling options shows relative differences which increase with burnup. These differences translate to about a 350 pcm difference in the HEU case while the LEU core shows a relatively larger difference of about 500 pcm in integral core parameters. Root Mean Square (RMS) and maximum relative error in assembly power as large as 0.83 and 2 % respectively are seen for HEU and LEU cases. Although standard fuel element (SFE) and control fuel element (CFE) are geometrically significantly different, some studies have used VWH unit-cell based on SFE to generate and use number densities for CFE as well. The effect of this modeling choice is also analyzed. This led to a relative difference of more than 20 % in the concentration of Pu-239 for both HEU and LEU studies, with SFE based number density being overpredicted. Xe-135 concentration also shows about a 20 % difference for the HEU case. The difference in the whole core neutron multiplication factor, SFE vs SFE + CFE individual burnt fuel vector, is negligible. On the other hand, power RMS error and maximum relative difference for power fraction exhibit a maximum value of 0.84 and 2.24 respectively. This study can serve as a reference for future verification efforts using the IAEA 10-MW MTR benchmark reactor.

Research of the spatial effect of PWR fuel pin with disperse particles

Fully ceramic microencapsulated (FCM) fuel is one of the most popular accident tolerant fuels (ATF) and it has a particular spatial structure, made of SiC matrix embedded with TRISO fuel particles. Fuel pin embedded with disperse burnable poison particles, has similar spatial structure. They are both double-heterogeneous and they have much unique neutronic characteristic. In this paper, efforts are made to analyze how the spatial structure of the disperse fuel particles and burnable poison particles affects their neutronic behaviors in detail, from pin-cell level, which is also referred as spatial effect. Many important neutronic parameters are discussed, including infinite multiplication factor (Kinf), four factors (fast fission factor ∊, resonance escape probability factor p, thermal utilization factor f and thermal reproduction factor η), neutron flux level, nuclides number density. They are compared with an equivalent homogeneous structure and the corresponding differences would reveal the unique spatial effect of this kind of double-heterogeneous structure. Besides, sub-regions analyses are also carried on. Finally, it is proved that the double-heterogeneous spatial structure would bring much influence on neutronic behaviors, and the spatial effect of disperse burnable poison particles would be even more serious.

Flexible demand and supply as enablers of variable energy integration

This article analyses the impact of the interplay between the demand response, wind penetration and hydropower in the Nordic power market. Long-term equilibrium model is developed, in which the thermal power capacity adjusts to the zero-profit level over varying real-time pricing adoption rates and wind power shares. The results show that an increased demand response decreases the amount of thermal power capacity and improves the utilization rate of thermal power and the value of wind power. There is a decreasing marginal gain from an increasing demand response adoption with respect to the thermal utilization and wind value factor. However, the demand response itself does not lead to lower CO2 emissions or reduced variation in hydropower generation.

The Challenging Thermophysical Issues of Fast Reactors

The article presents and analyzes the results from topical thermophysical investigations aimed at substantiating the characteristics and assessing the safety of liquid metal cooled fast reactors: an advanced largecapacity fast sodium-cooled reactor and a fast lead-cooled reactor. We also outline the results from experimental investigations into hydrodynamics and heat transfer for stratified flow of coolant, into thermal hydraulics of a large-modular “sodium–water” steam generator in different modes of reactor operation, and into the fuel assembly degradation process in the course of a severe accident involving loss of sodium flowrate in a fast reactor. The basic mechanisms governing degradation of dummy fuel rod claddings are identified; the distribution of marker materials over the fuel assembly height in its ultimate state is estimated, and the phenomena of blocking the fuel assembly flow pass section and the marker materials being thrown to beyond the assembly boundaries are studied. The article demonstrates the advisability of using a combined sodium purification system built into the reactor vessel that contains cold traps as a mandatory element along with hot traps, which serve to perform accelerated removal of oxygen during the NPP operation at its nominal parameters. The results from thermal–hydraulic tests of the lead-cooled reactor core carried out on the 6B experimental setup and of the steam generator carried out on the SPRUT experimental setup installed at the SSC RF–IPPE are presented.1 It has been found from the experiments on the thermal–hydraulic model of the lead-cooled reactor’s steam generator that the steam temperatures at the outlets from both headers are identical with each other and so are the lead temperatures at the downcomer section outlet and in the main lead path. The experiments did not show pulsations of feedwater flowrate or pressure in the loops, which points to the stable nature of operation at partial load. The state of the technology of heavy metal coolants and the prospects for its future development are considered. It is shown that there is a possibility in principle to realize the required parameters of a high-temperature sodium-cooled fast reactor for producing large quantities of hydrogen, e.g., based on one of the thermochemical cycles or high-temperature electrolysis with a high electricity thermal utilization factor. The problems that must be solved during the further thermophysical investigations are analyzed.

Flexible Demand and Flexible Supply As Enablers of Variable Energy Integration

This article analyses the impact of the interplay between the demand response, wind penetration and hydropower in the Nordic power market. We develop a long-term equilibrium model in which the thermal power capacity adjusts to the zero-profit level over varying real-time pricing adoption rates and wind power shares. Our results show that an increased demand response decreases the amount of thermal power capacity and improves the utilization rate of thermal power and the value of wind power. We show a decreasing marginal gain from an increasing demand response adoption with respect to the thermal utilization and wind value factor. However, the demand response itself does not lead to lower CO2 emissions or reduced variation in hydropower generation.

Thermal Neutron Utilization Factor Calculation by Monte Carlo

The Neutron Transport Theory is accurate in reactor engineering analysis, but the calculation process is tedious and complicated. The objective of the present study obtains the thermal utilization factor f by Monte Carlo method. The study establishes the pressurized water reactor model by MCNP program firstly, and calculates the dioxide pellets, zirconium alloy cladding and moderator’s neutron flux density distribution. The thermal neutron disadvantage factor ζ will be gained according to the definition formula. Based on the functional relationship between the above thermal neutron disadvantage factor ζ and the thermal utilization factor f, this study finally obtains the thermal utilization factor f.

Energy efficiency performance of multi-energy district heating and hot water supply system

A district heating and hot water supply system is presented which synthetically utilizes geothermal energy, solar thermal energy and natural gas thermal energy. The multi-energy utilization system has been set at the new campus of Tianjin Polytechnic University (TPU). A couple of deep geothermal wells which are 2 300 m in depth were dug. Deep geothermal energy cascade utilization is achieved by two stages of plate heat exchangers (PHE) and two stages of water source heat pumps (WSHP). Shallow geothermal energy is used in assistant heating by two ground coupled heat pumps (GCHPs) with 580 vertical ground wells which are 120 m in depth. Solar thermal energy collected by vacuum tube arrays (VTAs) and geothermal energy are complementarily utilized to make domestic hot water. Superfluous solar energy can be stored in shallow soil for the GCHP utilization. The system can use fossil fuel thermal energy by two natural gas boilers (NGB) to assist in heating and making hot water. The heating energy efficiency was measured in the winter of 2010-2011. The coefficients of performance (COP) under different heating conditions are discussed. The performance of hot water production is tested in a local typical winter day and the solar thermal energy utilization factor is presented. The rusults show that the average system COP is 5.75 or 4.96 under different working conditions, and the typical solar energy utilization factor is 0.324.

New waste heat district heating system with combined heat and power based on absorption heat exchange cycle in China

A new waste heat district heating system with combined heat and power based on absorption heat exchange cycle (DHAC) was developed to increase the heating capacity of combined heat and power (CHP) through waste heat recovery, and enhance heat transmission capacity of the existing primary side district heating network through decreasing return water temperature by new type absorption heat exchanger (AHE). The DHAC system and a conventional district heating system based on CHP (CDH) were analyzed in terms of both thermodynamics and economics. Compared to CDH, the DHAC increased heating capacity by 31% and increased heat transmission capacity of the existing primary side district heating network by 75%. The results showed that the exergetic efficiency of DHAC was 10.41% higher and the product exergy monetary cost was 36.6¥/GJ less than a CHD. DHAC is an effective way to increase thermal utilization factor of CHP, and to reduce district heating cost.

Temperature Reactivity Effects in Pebbles of a High-Temperature Reactor Fueled with Reactor-Grade Plutonium

This work presents the temperature reactivity effects occurring in pebbles of a high-temperature reactor fueled with reactor-grade plutonium, without any additional resonance absorbers. Burnup calculations are performed for pebbles loaded with various amounts of plutonium per pebble. During burnup, branching calculations are carried out to calculate k∞ as a function of the uniform temperature. For a high plutonium mass per pebble and low burnup values, k∞ decreases with uniform temperature, which indicates a negative uniform temperature coefficient of reactivity (UTC). However, for a low plutonium mass per pebble, as well as for a high plutonium mass per pebble in combination with high burnup, k∞ is maximal at a particular uniform temperature. Below this temperature, the UTC is positive, while above this temperature it is negative. Branching calculations with only a varying moderator temperature show almost the same behavior, which indicates that the contribution of the fuel temperature plays a minor role for the mentioned effect. To understand the reactivity effect, the moderator temperature coefficient (MTC) is investigated by two methods. In the first method, changes in reaction rates of individual nuclides and their corresponding contributions to the MTC are calculated, whereas in the second method the four-factor formula has been used. For the fresh fuel cases, the positive coefficient at low temperature is due to a positive coefficient for the thermal utilization factor. For high moderator temperatures, the coefficient for the resonance escape probability renders the MTC negative. This trend is basically caused by the shift of the high-energy tail of the Maxwell-spectrum toward the 1-eV resonance of 240Pu, and toward the resonances of 241Pu, which leads to an increase of the capture-to-fission ratio.

Remarks on the physics of early fuel lattices / Bemerkungen zur Physik früher Brennstoffgitter.

Neutron multiplication properties of lattices of natural uranium and heavy water, as investigated in Germany 1940-45, are discussed in terms of fast fission effect, resonance escape probability, thermal utilization, and disadvantage factor. The comparison comprises lattices of spheres and slabs with equal mean chord lengths in the fuel, and lattices of optimum dimensions for maximum neutron multiplication. Reasons for the superiority of spheres over slabs in neutron multiplication are given.

First- and Second-Law Analysis of Steam-Turbine Cogeneration Systems

The paper presents an analysis of a cogeneration plant. The performance of the plant is compared to a conventional plant with separate production of process heat and power. The analysis is first- and second-law based and, therefore, quantifies the irreversibilities of the different components of each plant. In the cogeneration plant, the heat required in the boiler can be obtained either from fuel firing (condensing or back-pressure turbine plant) or from exhaust gases of a simple gas turbine (gas turbine cogeneration plant). The present study compares the two methods. The influence of the heat-to-power ratio and the process pressure on the thermal efficiency, utilization factor, and irreversibilities of the different components of each plant is presented. The results show that the total irreversibility of the cogeneration plant is lower by 38 percent compared to the conventional plant. This reduction in the irreversibility is accompanied by an increase in the thermal efficiency and utilization factor by 25 and 24 percent, respectively. The results show that most irreversible losses are due to boiler.

Computation on Fuel Particle Size Capable of Being Regarded as Homogeneous in Nuclear Criticality Safety Analysis.

For powdered fuel processed in the nuclear fuel facilities, flooding is often thought to be the severest condition regarding the nuclear criticality safety evaluation. The reactivity of such a heterogeneous system as powdered fuel in water should be almost equal to that of the homogeneous one, when the fuel particle size is very small. The neutron multiplication factor was calculated for an infinite cubic array of slightly enriched UO2 sphere particles immersed in water with various enrichments, water to fuel ratios and fuel particle sizes. The calculations were performed with a computer code module based on the collision probability method to solve the ultra-fine energy group equations of neutrons. The change in the neutron multiplication factor from the homogeneous system is dominated first by the change in the resonance escape probability and second by the change in the thermal utilization factor; these changes and therefore their sum, depend almost completely on the mean uranium concentration (or wate...

The ignition parameter Tnτ and the energy multiplication factor k for fusioning plasmas

This paper presents some novel interpretations of fusion plasmas which may be of interest to both fission and fusion scientists and engineers. A new fusion ignition parameter (TneτE)I is proposed which is proportional to β2B4 and inversely proportional to the fusion power density (PFusion) of a reacting plasma. Curves are given for many potential nuclear fusion fuels. The energy utilization factor in existing devices is defined as f = PFusion/PLoss = (TneτL)/(TneτE)I; in experimental plasmas, f has increased by about two orders of magnitude in the past decade and now exceeds 10−4 (a “nearest” f* exceeds 10−3). The f factor is also analogous to its fission counterpart in the four-factor neutron multiplication factor k = f η ϵ p, where f is the neutron thermal utilization factor. Past, present, and future fusion experiments are discussed briefly in this context.

The effect of the anisotropic scattering on the thermal utilization factor

In calculations of the thermal utilization factor for heterogeneous reactors the anisotropic scattering is taken into account usually in the transport and sometimes in the linear-anisotropic approximations. The work of Eccleston and McCormick make doubtful the generally accepted opinion that the second angular moment of the scattering kernel has little effect on the disadvantage factor in slab cells in nuclear reactors. In the present work we have investigated the effect of the second and higher angular moments of the scattering kernel on the thermal utilization factor. The formulas appropriate for the qualitative analysis of the question under consideration are given and a set of cells was calculated by various methods. A disagreement between the data obtained and those reported by Eccleston and McCormick is shown.

Measurement of Thermal Utilization Factor in a Square Cell of UO2-H2O Lattice

Measurement of Thermal Utilization Factor in a Square Cell of UO₂-H₂O Lattice

Measurement of Thermal Utilization Factor in a Square Cell of UO2-H20 Lattice

Thermal neutron distribution in a square lattice of water moderated UO2 (enriched to 2.596 w/0 in 235U) was measured with dysprosium micro-foils. Diameters of the fuel pellet and the aluminum cladding tube were 12.5mm and 14.12mm respectively. The pitch of the square lattice was 19.56mm, and the water to fuel volume ratio 1.844. To obtain the integrated flux in the fuel and moderator regions, the solution for the P-1 diffusion equation was used. A disadvantage factor of 1.27±0.02 and a thermal utilization factor of 0.891±0.002 were obtained. The theoretical value of the disadvantage factor obtained by the 30 group integral transport theory in a square call is 1.341 and is larger than the experimental value by a discrepancy exceeding the experimental error. The result is also compared with some approximate calculations.

The Calculation of the Thermal Utilization and Disadvantage Factor in Uranium/Water Lattices

Theoretical methods for computing intracell thermal-neutron densities, disadvantage factors and thermal utilizations are presented. The topics discussed are the computation of the neutron spectra in a lattice, anisotropic scattering by water, the cylindrical cell effect, correlation of spectral moments and average one-group cross sections, one-group transport-theory methods, scattering models of water, and comparison of various theories with experiment. The lattices investigated are water moderated with slightly enriched uranium metal and oxide fuel.

Re: “Spatial Dependence of Thermal-Neutron Spectra and the Interpretation of Thermal Utilization Measurements”

"Re: “Spatial Dependence of Thermal-Neutron Spectra and the Interpretation of Thermal Utilization Measurements”." Nuclear Science and Engineering, 12(3), p. 433