Analysis of burnup performance and temperature coefficient for a small modular molten‑salt reactor started with plutonium

In a thorium-based molten salt reactor(TMSR),it is difficult to achieve the pure 232Th–^(233)U fuel cycle without sufficient^(233)U fuel supply.Therefore,the original molten salt reactor was designed to use enriched uranium or plutonium as the starting fuel.By exploiting plutonium as the starting fuel and thorium as the fertile fuel,the high-purity^(233)U produced can be separated from the spent fuel by fluorination volatilization.Therefore,the molten salt reactor started with plutonium can be designed as a^(233)U breeder with the burning plutonium extracted from a pressurized water reactor(PWR).Combining these advantages,the study of the physical properties of plutonium-activated salt reactors is attractive.This study mainly focused on the burnup performance and temperature reactivity coefficient of a small modular molten-salt reactor started with plutonium(SM-MSR-Pu).The neutron spectra,^(233)U production,plutonium incineration,minor actinide(MA)residues,and temperature reactivity coefficients for different fuel salt volume fractions(VF)and hexagon pitch(P)sizes were calculated to analyze the burnup behavior in the SM-SMR-Pu.Based on the comparative analysis results of the burn-up calculation,a lower VF and larger P size are more beneficial for improving the burnup performance.However,from a passive safety perspective,a higher fuel volume fraction and smaller hexagon pitch size are necessary to achieve a deep negative feedback coefficient.Therefore,an excellent burnup performance and a deep negative temperature feedback coefficient are incompatible,and the optimal design range is relatively narrow in the optimized design of an SM-MSR-Pu.In a comprehensive consideration,P=20 cm and VF=20%are considered to be relatively balanced design parameters.Based on the fuel off-line batching scheme,a 250 MWth SM-MSR-Pu can produce approximately 29.83 kg of ^(233)U,incinerate 98.29 kg of plutonium,and accumulate 14.70 kg of MAs per year,and the temperature reactivity coefficient can always be lower than−4.0pcm/K.

Assembly-level analysis on temperature coefficient of reactivity in a graphite-moderated fuel salt reactor fueled with low-enriched uranium

To provide a reliable and comprehensive data reference for core geometry design of graphite-moderated and low-enriched uranium fueled molten salt reactors,the influences of geometric parameters on the temperature coefficient of reactivity(TCR)at an assembly level were characterized.A four-factor formula was introduced to explain how different reactivity coefficients behave in terms of the fuel salt volume fraction and assembly size.The results show that the fuel salt temperature coefficient(FSTC)is always negative owing to a more negative fuel salt density coefficient in the over-moderated region or a more negative Doppler coefficient in the under-moderated region.Depending on the fuel salt channel spacing,the graphite moderator temperature coefficient(MTC)can be negative or positive.Furthermore,an assembly with a smaller fuel salt channel spacing is more likely to exhibit a negative MTC.As the fuel salt volume fraction increases,the negative FSTC first weakens and then increases,owing to the fuel salt density effect gradually weakening from negative to positive feedback and then decreasing.Meanwhile,the MTC weakens as the thermal utilization coefficient caused by the graphite temperature effect deteriorates.Thus,the negative TCR first weakens and then strengthens,mainly because of the change in the fuel salt density coefficient.As the assembly size increases,the magnitude of the FSTC decreases monotonously owing to a monotonously weakened fuel salt Doppler coefficient,whereas the MTC changes from gradually weakened negative feedback to gradually enhanced positive feedback.Then,the negative TCR weakens.Therefore,to achieve a proper negative TCR,particularly a negative MTC,an assembly with a smaller fuel salt channel spacing in the under-moderated region is strongly recommended.

Fabrication and characterization of NiCr-based films with high resistivity and low temperature coefficient of resistance

As a metal alloy,NiCr films have a relatively high resistivity and low temperature coefficient of resistance (TCR) and are widely used in electronic components and sensors.However,the resistivity of pure NiCr is insufficient for high-resistance and highly stable film resistors.In this study,a quaternary NiCrAlSi target (47:33:10:10,wt.%) was successfully used to prepare resistor films with resistivities ranging from 1000 to 10 000μΩcm and TCR within±100 ppm/K.An oxygen flow was introduced during the sputtering process.The films exhibit hightemperature stability at 450℃.The films were analyzed using Auger electron spectroscopy,x-ray diffraction,time-of-flight secondary-ion mass spectrometry,and x-ray photoelectron spectroscopy.The results show that the difference in the oxide proportion of the films caused the differences in resistivity.The near-zero TCR values were considered to be due to the competition between silicon and other metals.This study provides new insights into the electrical properties of NiCr-based films containing Si,which will drive the manufacturing of resistors with high resistivity and zero TCR.

Preparation and study on performance of submicron nickel powder for multilayer chip positive temperature coefficient resistance

Base metal nickel is often used as the inner electrode in multilayer chip positive temperature coefficient resistance （PTCR）. The fine grain of ceramic powders and base metal nickel are necessary. This paper uses reducing hydrazine to gain submicron nickel powder whose diameter was 200-300 nm through adjusting the consumption of nucleating agent PVP properly. The submicron nickel powder could disperse well and was fit for co--fired of multilayer chip PTCR. It analyes the submicron nickel powder through x-ray Diffraction （XRD） and calculates the diameter of nickel by PDF cards. Using XRD analyses it obtains several conclusions： If the molar ratio of hydrazine hydrate and nickel sulfate is kept to be a constant, when enlarging the molar ratio of NaOH/Ni^2＋, the diameter of nickel powder would become smaller. When the temperature in the experiment raises to 70-80 ℃, nickel powder becomes smaller too. And if the molar ratio of NaOH/Ni2＋ is 4, when molar ratio of （C2H5O）2/Ni^2＋ increases, the diameter of nickel would reduce. Results from viewing the powders by optical microscope should be the fact that the electrode made by submicron nickel powder has a better formation and compactness. Furthermore, the sheet resistance testing shows that the electrode made by submicron nickel is smaller than that made by micron nickel.

Research on the effect of the heavy nuclei amount on the temperature reactivity coefficient in a small modular molten salt reactor

Small modular thorium-based graphite-moderated molten salt reactors (smTMSRs), which combine the advantages of small modular reactors and molten salt reactors, are regarded as a wise development path to speed deployment time. In a smTMSR, low enriched uranium and thorium fuels are used in once-through mode, which makes a marked difference in their neutronic properties compared with the case when a conventional molten salt breeder reactor is used. This study investigated the temperature reactivity coefficient (TRC) in a smTMSR, which is mainly affected by the molten salt volume fraction (VF) and the heavy nuclei concentration in the fuel salt (HN). The fourfactor formula method and the reaction rate method were used to indicate the reasons for the TRC change, including the fuel density effect, the fuel Doppler effect, and the graphite thermal scattering effect. The results indicate that only the fuel density has a positive effect on the TRC in the undermoderated region. Thermal scattering from both salt and graphite has a significant negative influence on the TRC in the overmoderated region. The maximal effective multiplication factor, which shows the highest fuel utilization, is located at 10% VF and 12 mol% HN and is still located in the negative TRC region. In addition, on increasing the heavy nuclei amount from 2 mol% HN to 12 mol% HN (VF = 10%), the total TRC undergoes an obvious change from - 11 to - 3 pcm/K, which implies that the change in the HN caused by the fuel feed online should be small to avoid potential trouble in the reactivity control scheme.

Characterization of the BaBiO_3-doped BaTiO_3 positive temperature coefficient of a resistivity ceramic using impedance spectroscopy with T_c=155℃

BaBiO3-doped BaTiO3 （BB-BT） ceramic, as a candidate for lead-free positive temperature coefficient of resistivity （PTCR） materials with a higher Curie temperature, has been synthesized in air by a conventional sintering technique. The temperature dependence of resistivity shows that the phase transition of the PTC thermistor ceramic occurs at the Curie temperature, Tc = 155℃, which is higher than that of BaTiO3 （≤ 130 ℃）. Analysis of ac impedance data using complex impedance spectroscopy gives the alternate current （AC） resistance of the PTCR ceramic. By additional use of the complex electric modulus formalism to analyse the same data, the inhomogeneous nature of the ceramic may be unveiled. The impedance spectra reveal that the grain resistance of the BB-BT sample is slightly influenced by the increase of temperature, indicating that the increase in overall resistivity is entirely due to a grain-boundary effect. Based on the dependence of the extent to which the peaks of the imaginary part of electric modulus and impedance are matched on frequency, the conduction mechanism is also discussed for a BB-BT ceramic system.

Investigation on the plastic work-heat conversion coefficient of 7075-T651 aluminum alloy during an impact process based on infrared temperature measurement technology

The plastic work-heat conversion coefficient is one key parameter for studying the work-heat conversion under dynamic deformation of materials. To explore this coefficient of 7075-T651 aluminum alloy under dynamic compression, dynamic compression experiments using the Hopkinson bar under four groups of strain rates were conducted, and the temperature signals were measured by constructing a transient infrared temperature measurement system. According to stress versus strain data as well as the corresponding temperature data obtained through the experiments, the influences of the strain and the strain rate on the coefficient of plastic work converted to heat were analyzed.The experimental results show that the coefficient of plastic work converted to heat of 7075-T651 aluminum alloy is not a constant at the range of 0.85–1 and is closely related to the strain and the strain rate. The change of internal structure of material under high strain rate reduces its energy storage capacity, and makes almost all plastic work convert into heat.

Influence of Temperature and Frequency on Minority Carrier Diffusion Coefficient in a Silicon Solar Cell under Magnetic Field

In this study, the effects of temperature and frequency on minority carrier diffusion coefficient in silicon solar cell under a magnetic field are presented. Using two methods (analytic and graphical), the optimum temperature corresponding to maximum diffusion coefficient is determined versus cyclotronic frequency and magnetic field.

Anisotropic Rock Poroelasticity Evolution in Ultra-low Permeability Sandstones under Pore Pressure,Confining Pressure,and Temperature:Experiments with Biot's Coefficient

This study aimed to show anisotropic poroelasticity evolution in ultra-low permeability reservoirs under pore pressure,confining pressure,and temperature.Several groups of experiments examining Biot's coefficient under different conditions were carried out.Results showed that Biot's coefficient decreased with increased pore pressure,and the variation trend is linear,but the decreasing rate is variable between materials.Biot's coefficient increased with increased confining pressure;the variation trend is linear,but the increasing rate varies by material as well.Generally,Biot's coefficient remains stable with increased temperature.Lithology,clay mineral content,particle arrangement,and pore arrangement showed impacts on Biot's coefficient.For strong hydrophilic clay minerals,expansion in water could result in a strong surface adsorption reaction,which could result in an increased fluid bulk modulus and higher Biot's coefficient.For skeleton minerals with strong lipophilicity,such as quartz and feldspar,increased oil saturation will also result in an adsorption reaction,leading to increased fluid bulk modulus and a higher Biot's coefficient.The study's conclusions provide evidence of poroelasticity evolution of ultra-low permeability and help the enhancing oil recovery(EOR)process.

Temperature coefficient of resistivity of TiAlN films deposited by radio frequency magnetron sputtering

Titanium aluminum nitride （TiAlN） film, as a possible substitute for the conventional tantalum nitride （TAN） or tantalum-aluminum （TaAl） heater resistor in inkjet printheads, was deposited on a Si（100） substrate at 400 ℃ by radio frequency （RF） magnetron co-sputtering using titanium nitride （TIN） and aluminum nitride （AlN） as ceramic targets. The temperature coefficient of resistivity （TCR） and oxidation resistance, which are the most important properties of a heat resistor, were studied depending on the plasma power density applied during sputtering. With the increasing plasma power density, the crystallinity, grain size and surface roughness of the applied film increased, resulting in less grain boundaries with large grains. The Ti, Al and N binding energies obtained from X-ray photoelectron spectroscopy analysis disclosed the nitrogen deficit in the TiAlN stoichiometry that makes the films more electrically resistive. The highest oxidation resistance and the lowest TCR of-765.43×10^-6 K-l were obtained by applying the highest plasma power density.

Minority Carrier Diffusion Coefficient <i>D</i>*(<i>B,T</i>): Study in Temperature on a Silicon Solar Cell under Magnetic Field

This work deals with minority carrier diffusion coefficient study in silicon solar cell, under both temperature and applied magnetic field. New expressions of diffusion coefficient are pointed out, which gives attention to thermal behavior of minority carrier that is better understood with Umklapp process. This study allowed to determine an optimum temperature which led to maximum diffusion coefficient value while magnetic field remained constant.

Thin Film Chip Resistors with High Resistance and Low Temperature Coefficient of Resistance

High resistance thin film chip resistors(0603 type) were studied,and the specifications are as follows:1 k? with tolerance about ±0.1% after laser trimming and temperature coefficient of resistance(TCR) less than ±15×10-6/℃.Cr-Si-Ta-Al films were prepared with Ar flow rate and sputtering power fixed at 20 standard-state cubic centimeter per minute(sccm) and 100 W,respectively.The experiment shows that the electrical properties of Cr-SiTa-Al deposition films can meet the specification requirements of 0603 ty...

Measurement of temperature inside die and estimation of interfacial heat transfer coefficient in squeeze casting

As an advanced near-net shape technology, squeeze casting is an excellent method for producing high integrity castings. Numerical simulation is a very effective method to optimize squeeze casting process, and the interfacial heat transfer coefficient(IHTC) is an important boundary condition in numerical simulation. Therefore, the study of the IHTC is of great significance. In the present study, experiments were conducted and a "plate shape" aluminum alloy casting was cast in H13 steel die. In order to obtain accurate temperature readings inside the die, a special temperature sensor units(TSU) was designed. Six 1 mm wide and 1 mm deep grooves were machined in the sensor unit for the placement of the thermocouples whose tips were welded to the end wall. Each groove was machined to terminate at a particular distance(1, 3, and 6 mm) from the front end of the sensor unit. Based on the temperature measurements inside the die, the interfacial heat transfer coefficient(IHTC) at the metal-die interface was determined by applying an inverse approach. The acquired data were processed by a low pass filtering method based on Fast Fourier Transform(FFT). The feature of the IHTC at the metal-die interface was discussed.

Influence of 235U enrichment on the moderator temperature coefficient of reactivity in a graphite-moderated molten salt reactor

To optimize the temperature coefficient of reactivity(TCR)for a graphite-moderated and liquid-fueled molten salt reactor,the effects of fuel salt composition on the fuel salt temperature coefficient of reactivity(FSTC)were investigated in our earlier work.In this study,we aim to provide a more comprehensive analysis of the TCR by considering the effects of the graphite-moderator temperature coefficient of reactivity(MTC).The effects of^235U enrichment and heavy metal(HM)proportion in the salt mixture on the MTC are investigated from the perspective of the six-factor formula based on a full-core model.For the MTC(labeled“αTM”),the temperature coefficient of the fast fission factors(αTM(ε))is positive,while those of the resonance escape probability(αTM(p)),the thermal reproduction factor(αTM(η)),the thermal utilization factor(αTM(f)),and the total non-leakage probability(αTM(A))are negative.The results reveal that the magnitudes ofαTM(ε)andαTM(p)for the MTC are similar.Thus,variations in the MTC with^235U enrichment for different HM proportions are mainly dependent onαTM(η),αTM(A),andαTM(f),but especially on the former two.To obtain a more negative MTC,a lower HM proportion and/or a lower 235U enrichment is recommended.Together with our previous studies on the FSTC,a relatively soft neutron spectrum could strengthen the TCR with a sufficiently negative MTC.

Effect of Temperature on Segregation Coefficients of Impurities in Phosphorus

The present work is focused on the relationship between effective segregation coefficient keff and tem- perature of melting zone for purification of phosphorus by zone melting method. Values of keff at four temperatures of melting zone are obtained for zone pass n = 1 at travel velocity of molten zone v = 5x 10^-3 m. h^-1 and initial impu- rity concentration C0〈10 μg.g-1, lnkeff is a linear function of 1/T. The keff values of A1, Ca, Cr, Fe, Cd and Sb in- crease with temperatures while that of Mg is almost constant. The purification is acceptable at lower temperature of melting zone such as 323 K. The variations of enthalpy and entropy between impurities and phosphorus in the liq- uid and solid ohases are also 19resented.

Improvement of the electrical resistivity of epoxy resin at elevated temperature by adding a positive temperature coefficient BaTiO3-based compound

The DC electrical resistivity-temperature characteristic is an important property for insulating materials to operate at a high stress level.In order to improve the DC electrical resistivity at elevated temperature in a targeted way,a positive temperature coefficient(PTC)material(Ba Ti O3-based compound(BT60))was selected as the filler in this paper,whose electrical resistivity has a PTC effect when the temperature exceeds its Curie temperature.The BT60 was treated with hydrogen peroxide and(3-Aminopropyl)triethoxysilane.Epoxy composites with different loadings of BT60 fillers(0 wt%,0.5 wt%,and 2 wt%of epoxy)were prepared,denoted as EP-0,EP-0.5,and EP-2.It was shown that BT60 was able to maintain the DC breakdown strength when its loading was less than 2 wt%of epoxy.As the temperature exceeds 60°C,BT60 will compensate for the negative temperature coefficient effect of epoxy resin to some extent.The electrical resistivity of EP-2 was improved by 55%compared with that of neat epoxy at 90°C.It was found that the potential barrier at the grain boundary of BT60 and the deep traps in the interface between BT60 and the epoxy resin hinder the migration of carriers and thus increase the electrical resistivity of epoxy composite.

Negative Temperature Coefficient of Resistivity in Bulk Nanostructured Ag

The change of the temperature coefficient of resistivity (a) with the particle size, dp, and the grain size, dc, in the nanostructured Ag bulk samples was investigated. dp and dc were controlled by heating the nano-Ag powders over the temperature range from 393 to 453 K. The electrical resistance measurements of the nanostructured Ag bulk samples obtained by compacting the Ag powders after heat treatments showed a change in the sign of a with dP and dc. When dp and dc are smaller or equal to 18 and 11 nm below room temperature or 20 and 12 nm above room temperature, respectively, the sign of the temperature coefficient of resistivity changes from positive to negative. The negative a arises mainly from the high resistivity induced by the particle interfaces with very lowly ordered or even disordered structure, a large volume fraction of interfaces and impurities existing in the interfaces, and the quantum size effect appearing in the nano-Ag grains.

Influence of Zirconium Addition on Magnetic Properties and Temperature Coefficient for Nanocomposite Nd_(10)Fe_(78.5-x)Co_5Zr_xB_(6.5) Magnets

The influence of Zr addition on magnetic properties and temperature coefficient for nanocomposite Nd10Fe78.5-xCo5ZrxB6.5 (x=0～4) bonded magnets was investigated. It was found that the room-temperature magnetic properties were remarkably improved with Zr addition due to the grain refinement and increasing volume fraction of the hard magnetic phase. The optimal magnetic properties of Jr=0.689 T, iHc=769.4 kA·m-1 and (BH)max=84 kJ·m-3 were obtained for 2.5% Zr addition. The temperature coefficient of remanence (α) increases slightly and the temperature coefficient of coercivity (β) decreases obviously with increasing Zr content for nanocomposite Nd10Fe78.5-xCo5ZrxB6.5 (x=0～4) bonded magnets.

Effect of Heat Transfer Coefficient on the Temperature Gradient for Hollow Fiber

The heat transfer coefficient h caused by blowing affects the heat transfer of fiber greatly. Especially,unsymmetrical blowing forms the unsymmetrical temperature gradient on the fiber cross.section. Based on the results of spinning simulation by computer, the changes of heat transfer coefficient on the cross-section along the spinning line and the effects on distributions of temperature gradients were discussedl It is showed that for the spinning simulation of hollow fiber under strong blowing condition, the heat transfer coetticient should bemodified as: h=0.437×10-4[ G/Vρ ( R2/ R2-n2 ) ] -o.333(V2+ 64( VYsin (θ))2)0.

Effect of Sliding／Rolling Ratio on the Temperature Distribution and Traction Coefficient of Line Contact Thermal EHL of Helical Gears

By using multi-grid method, the simultaneous Reynolds, elasticily, film-thickness,rheology, energy and thermal interface temperature equations are solved, and the numerical solution of line-ontact thermal EHL is successfully obtained and presented in this paper.In addition, the influence of sliding/rolling ratio on the distribution of temperature within the film and on the solid surface. minimum film thickness and traction coefficient are also studied. The results show that the influence of temperature on film thickness is significant and unnegligible, All mentioned above may provide a basis for further investigation of thermal EHL of helical gears.