Core Heat Research Articles

The preliminary design of emergency core cooling scheme and loss-of-coolant accident analysis for Tsinghua high flux reactor

This paper proposes the preliminary emergency core cooling scheme for Tsinghua High Flux Reactor. According to the thermohydraulic characteristics of high flux reactors, forced circulation needs to be maintained by emergency pumps in the early stage. When the decay power is low enough, natural circulation between core and the reactor pool is initiated to remove the residual core heat. The sources of safety injection are accumulators and reactor pool. Accumulator injection can ensure core safety in the early stage and reactor pool injection can maintain long time stable forced circulation. To avoid emptying the reactor pool, the waterproof zone needs to be built. The waterproof zone consists of reactor pool and several finite volume dry pools. All pipelines and equipment in the reactor coolant system are placed in the dry pools. Once break accident occurs, the dry pool where the break is located can collect the leaked coolant. With the increase of break back pressure, the break flow is restricted. The current scheme is modeled by Relap5 and different size breaks at four locations (namely core inlet, core outlet, primary heat exchanger inlet and main pump inlet) are assumed. According to the response characteristics of the scheme, the accident process can be divided into five stages: non-shutdown stage, high-injection stage, low-injection stage, stable forced circulation stage and natural circulation stage. Critical heat flux predicted by Sudo CHF correlations is adopted as the primary safety criterion. Through analysis, a success path is found to maintain core safety for a wide range of loss-of-coolant accident scenarios.

Spatiotemporal changes of urban heat island effect relative to land surface temperature: a case study of Jinan City, China.

The urban heat island (UHI) effect has become increasingly prevalent and significant with the accelerated pace of urbanization, posing challenges for urban planners and policymakers. To reveal the spatiotemporal variations of the urban heat island effect in Jinan City, this study utilized Landsat satellite images from 2009, 2014, and 2019, employing the classic Mono-Window algorithm to extract land surface temperature (LST). Additionally, Geodetector was introduced to conduct a detailed analysis of the relationship between LST in Jinan City and land cover types (vegetation, water bodies, and buildings). The results indicate a significant increase in the severity of the urban heat island effect in Jinan from 2009 to 2019, with the central urban area consistently exhibiting a high-intensity core heat island. Suburban areas of Jinan show a clear trend of merging their heat island effects with the central urban area. The combined area of strong cool island effect zones and cool island effect zones within water bodies reaches 89.7%, while the combined proportion of heat island and strong heat island effect zones in building areas is 62.2%. Vegetation cover (FVC) exerts the greatest influence among all factors on the intensity level of the urban heat island effect. These findings provide a reliable basis for decision-making related to urban planning and construction in Jinan City.

Numerical study of the particle-scale heat transfer in the HTR-PM pebble bed based on GPU-DEM

An essential aspect of the design of a pebble bed high-temperature gas-cooled reactor (HTGR) is the consideration of heat transfer. A particle-scale heat transfer model was developed based on the previous GPU-DEM numerical model. This model includes the heat conduction of the particles in contact, the radiative heat transfer among particles, and unidirectional convection heat transfer in the flow field. The comparison of the predicted results with the results of the TF-PBEC experiment demonstrates the accuracy of the conduction and radiation modules within the current model. Based on the current model and the porous media model, a numerical study of the natural convection heat transfer in the High-Temperature gas-cooled Reactor-Pebble-bed Module (HTR-PM) after reactor shutdown is performed. This paper systematically introduces the model design, pebble bed generation, flow field calculation, and heat transfer simulation. The results indicate that natural convection contributes to removing residual heat in the reactor core, and a higher pressure leads to better convection heat transfer. At extremely low Reynolds numbers (Re < 10), convection heat transfer is comparable to conduction and radiation, while for pressurized pebble beds (Re = 50–500), convection heat transfer dominates. Furthermore, the influence of different models used to calculate the Nusselt number of the results is compared and analyzed. For most cases, the differences in the temperature distribution of the pebble bed obtained from the different correlations are minor. However, the impact of porosity on the local Nusselt number cannot be ignored in the extremely low Reynolds numbers flows. Overall, the particle-scale heat transfer model can provide more effective reference information for the design and construction of an HTGR.

Three-dimensional CFD analysis of PHWR exposed core under postulated severe accident condition

A three-dimensional steady-state thermal–hydraulic analyses of a large sized Pressurized Heavy Water Reactors (PHWRs) with varying levels of exposure is carried out for degraded core heat transfer assessment and presented in this paper. Low-frequency postulated severe accident without mitigating actions leads to exposure of fuel channels in PHWRs. Such exposure of fuel channels leads to their heat-up, governed by interdependent heat transfer mechanisms such as radiation, convection and conduction heat transfer and thermo-chemical interactions among the core constituents. In order to understand such complex behavior and plan the severe accident management guidelines, numerical analyses of the exposed core are of necessary. This paper illustrates the influence of the temperature and velocity profiles vis-à-vis different regions of the exposed core on the fuel channel heat-up. The interesting interdependency of convection and radiation heat transfer on fuel channel heat-up is reported. The dominance of convection heat transfer is observed for initial exposures of the fuel channels. However, the advanced stages of fuel channel exposures are observed to be dominated by radiation heat transfer. Intriguingly, it is observed that the convective cooling of exposed fuel channels by steam flow is counter-acted by exothermic heat generation from Zircaloy-made calandria tube surface and steam interaction. This leads to supplemental power addition for fuel channel heat-up. Moreover, it is interesting to note that the heat-up of fuel channels is restricted to central regions of the exposed core due to degraded steam cooling and higher-powered fuel channels. It is worth noting that fuel channel disassembly is observed in the advanced levels of fuel channel exposures. Moreover, fuel channel length equivalent to nearly 7–8 fuel bundle lengths undergo disassembly depending upon the fuel channel elevation and location in the core. The calandria vault water is observed to undergo film boiling at the onset of fuel channel disassembly.

Thermal-hydraulic analysis of a full-scale lead-bismuth cooled fast reactor core considering inter-wrapper flow

The Lead-bismuth cooled Fast Reactors (LFR) utilizes wrapped hexagonal fuel assemblies arranged in a honeycomb pattern. The inter-wrapper flow (IWF) between adjacent assemblies has a significant influence on the core thermal-hydraulics. In this paper, the LFR core assembly analysis model, inter-wrapper flow and heat transfer model, and multi-scale coupling analysis model were developed and were implemented into the previously self-developed subchannel-level three-dimensional thermal hydraulic analysis code CorTAF-LBE for whole core of LFR, which is based on the OpenFOAM computational fluid dynamics simulation platform. The inter-wrapper flow and heat transfer model was validated against the KALLA-IWF experiment. Whole core steady state operating condition and low flow rate condition simulations were performed with reference to the 19-rod bundle geometry from KALLA laboratory and typical LFR core assembly arrangement. The whole core steady state distribution laws of key thermal-hydraulic parameters were obtained, and the influence of low flow rate operation on safety parameters such as cladding and pellet temperatures was analyzed. Under low flow rate operating conditions, the IWF heat transfer was accounted for 4.87% of the core thermal power, which was 315.6 kW higher than that under normal operating conditions, playing an important role in core heat removal and safe operation. This work provides important insights into LFR core design and the assessment of the role of IWF under low flow rate conditions.

Analysis of transient characteristics and design improvement of the passive residual heat removal system of NHR-200-II

NHR-200-II is a small integrated pressurized water reactor with 200 MW core thermal power. The core heat is transferred to two independent intermediate circuits via fourteen in-vessel primary heat exchangers (PHE), and the heat in the intermediate circuits is transferred to feedwater by two steam generators (SG) in the two intermediate circuits respectively. A passive residual heat removal (PRHR) branch is connected to each intermediate circuit to remove core decay heat under postulated accidents. During normal operation, PRHR branches are isolated by valves while SG branches in intermediate circuits are open. The valves in PRHR branches will be opened and the isolation valves of SG branches will be closed during decay heat removal scenarios. The decay heat removal capacity of NHR-200-II PRHRS could be seriously deteriorated once the isolation valves for SG branches fail to close, which was confirmed in a scaled integral test loop previously. Current understanding of PRHRS’s thermal-hydraulic characteristics with possible isolation failure in SG branches is limited. In this paper, the NHR-200-II PRHRS is modeled with RELAP5 considering the case of success and fail to isolate SG branches. A series of numerical simulations are carried out to study the impact of various parameters, such as the initial temperature, the size of the intermediate circuits’ header, and the initial flow direction in the intermediate circuits. Oscillatory flow is found when SG branches fail to be isolated under certain parameters combinations. An improved PRHRS design is purposed to eliminate possible flow oscillations, and the purposed improved design are tested by numerical simulations.

A Hyperactive Geomagnetic Field in the Late Visean (Early Carboniferous) From the Late Asbian Stratotype Section in Northwest England, UK

Plain Language SummaryNearly synchronous global changes in geomagnetic polarity give both a detailed irregular pacing to geological time and provide a glimpse into heat transfer processes across the core—mantle boundary which drives the Earth's geodynamo. Although the Late Carboniferous is characterized by some well‐studied reversals, details of the tempo of polarity changes in the Early Carboniferous are unknown. This work addresses this by providing a detailed record of polarity changes over a ∼2 million year interval at around 334.5–332.5 million years ago‐from the Trowbarrow Quarry section in NW England. We demonstrate that these limestones likely preserve magnetization from close to their time of formation and record at least 31 polarity reversals. These observations support the idea that the Earth's dynamo was in a hyperactive reversing state similar to those sustained for tens of Myr in the Late Jurassic, parts of the Cambrian and the Late Ediacaran. It further corroborates a ∼200 Myr cyclicity in paleomagnetic field behavior since the Precambrian, potentially linked to variable core heat flow forced by mantle convection.

Lorenz number and transport properties of Fe: Implications to the thermal conductivity at Earth's core-mantle boundary

Abstract The electrical resistivity (ρ) and thermal conductivity (κ) of the Earth's core compositions are essential parameters for constraining the core's thermal state, the inner core age, and the evolutionary history of the geodynamo. However, controversies persist between experimental and computational results regarding the electronic transport properties (ρ and κ) of the Earth's core. Iron is the major element in the core, and its transport properties under high pressure and high temperature conditions are crucial for understanding the core's thermal state. We measured the ρ values of solid iron using the four-wire van der Pauw method at 300 K and pressures ranging from 3 to 26 GPa within a multi-anvil press. For comparison, we calculated the ρ and κ values of hexagonal close-packed (hcp) iron at conditions of 300-4100 K and 22-136 GPa using the first-principles molecular dynamics (FPMD) method. Our calculations generally align with prior studies, indicating that the electrical resistivity of solid hcp iron at Earth's core-mantle boundary (CMB) conditions is ~76-83 μΩ∙cm. The resistivity of hcp iron changes small as it melts from solid to liquid at pressures from 98 to 134 GPa. The impact of temperature and pressure on the Lorenz numbers of solid hcp iron are investigated according to our calculation results and previous studies. Under the CMB's pressure conditions, the κ of hcp iron initially decreases with increasing temperature and subsequently increases. The electron-electron scattering plays a dominant role at low temperatures and causes the decrease in κ. At high temperatures, the increase of electronic specific heat significantly increases the Lorentz number and κ. Overall, we estimate the κ of solid hcp iron at CMB's condition to be 114 ± 6 W/m/K, slightly lower than the room temperature value of 129 ± 9 W/m/K at the same pressure. Our model shows that a 0-525 km thickness of a thermally stratified layer may exist beneath the Earth's CMB depending on the core's heat flow and thermal conductivity.

A rapid heat treatment for nanocrystallization of amorphous Fe75.1Cu1Nb1.5Si15.5B6.9 and Fe83Cu1Nb4B12 tape wound cores

A rapid annealing technique for soft magnetic Fe75.1Cu1Nb1.5Si15.5B6.9 and Fe83Cu1Nb4B12 tape wound cores is presented. Its effectiveness for creating a fine-grained nanocrystalline structure is demonstrated by measurements of the magnetic hysteresis loops as well as by structural investigations done by X-ray diffraction. The results show that the technique reduces the average crystallite sizes from about 27 nm to 17 nm for Fe75.1Cu1Nb1.5Si15.5B6.9, and from about 52 nm to 15 nm for Fe83Cu1Nb4B12. The coercivity after the rapid annealing is about three times lower for the Fe75.1Cu1Nb1.5Si15.5B6.9 alloy and up to one order of magnitude lower for the Fe83Cu1Nb4B12 alloy compared to the coercivity after the standardized long-time heat treatment. The improved heat treatment is outstanding in the way that it produces better soft magnetic properties in high-performance alloy cores within much shorter time than the standard core heat treatments.

Constraints onBose–Einsteincondensate stars as neutron stars models from new observational data

AbstractWe evaluate the feasibility of Bose–Einstein condensate stars (BECS) as models for the interior of neutron stars (NSs). BECS are compact objects composed of bosons, formed through the spin‐parallel pairing of neutrons. Here, we utilize the astronomical data from GW170817, XMMU J173203.3‐344518 (the lightest NS known), and a novel lower limit on NS core heat capacity to scrutinize the compatibility of BECS with these recent observations of NSs. Our specific focus is to constrain the values of the scattering length , parameter determining the strength of particle interactions in the model. Our analysis suggests that if the stars involved in GW170817 were BECSs, the scattering length of their constituent bosons should fall within the to fm range. Additionally, at a scattering length of fm, stars with mass and radius characteristics akin to XMMU J173203.3‐344518 are identified. Moreover, we find that the heat capacity depends on the mass and temperature of BECS, and surpasses the established lower bound for NS cores when fm. In summary, our results endorse BECS models with fm, providing NS observables in agreement with diverse observations and contributing to the understanding of NS interiors.

Improvement of core heat transport in NBI plasmas of heliotron J using high-intensity gas puffing

Controlling the heat transport profile is important for high performance in magnetically confined fusion plasmas. In this study, improved electron heat transport was achieved in neutral beam injection plasmas by applying high-intensity gas puffing (HIGP) on a stellarator/heliotron device called Heliotron J. Compared with conventional gas puffing (GP) fueling discharge, a higher and more peaked electron temperature profile was obtained, and the core ion temperature was slightly higher but similarly shaped. Using similar parameters, the electron density profile for HIGP remained similar and differed from the hollow density profile observed in electron cyclotron heating-eIBT plasma. Transport analysis using the FIT3D and TR-snap codes showed a clear reduction in the effective electron heat transport coefficient in the plasma core region. However, more detailed experiments are required to understand the mechanisms underlying this improvement fully.

Core temperature and surface heat flux during exercise in heat while wearing body armor

Core temperature and surface heat flux during exercise in heat while wearing body armor

Analysis Options for Urban Green Spaces Based on Unified Urban Masks: Selected Results for European Cities

At a time of rising urbanisation and climate change, urban green spaces (UGSs) are an essential element to help adapt to extreme weather events. Especially in urban core areas, heat and drought are regarded as human stress factors. The delineation of such areas constitutes an important reference geometry in topographic geodata (urban mask). This article deals with possibilities for investigating UGSs in European cities—based on unified urban masks—by applying city-wide metrics to Copernicus data (Urban Atlas including the Street Tree Layer). Both public and tree-covered urban green spaces are examined in detail. Selected results are presented for 30 European cities that display a wide range of urban structures. The spatial reference to uniformly delineated urban masks places the analytical focus of city-wide metrics onto corresponding core areas. In general, the values of UGS metrics vary considerably between cities, indicating the strong influence of city-specific factors on urban structures in Europe. For the comparative analysis of tree-covered urban areas, the Urban Green Raster Germany and a municipal tree register are used to provide additional data sources. The regular updating of the Copernicus dataset means that green spaces in European cities can be monitored, also using urban masks.

An evaluation of a healthy participant laboratory model of epidural hyperthermia: a physiological study

BackgroundHyperthermia complicates 21% of cases of intrapartum epidural analgesia, but the mechanism is unclear. One hypothesis is that blockade of cholinergic sympathetic nerves prevents active vasodilation and sweating, thus limiting heat loss. Because labour increases heat production, this could create a situation in which heat production exceeds loss, causing body temperature to rise. This physiological study tested a novel laboratory model of epidural-related hyperthermia, using exercise to simulate the increased heat production of labour and surface insulation to simulate the effect of epidural analgesia. MethodsTwelve healthy non-pregnant participants (six female) cycled an ergometer for two hours at 20 Watts (W) on two occasions: once with surface insulation (intervention) and once without (control). Core temperature, skin temperature (eight sites), and heat loss (eight sites) were recorded. Mean body temperature and heat production were calculated. Values are mean (SD). ResultsExercise increased heat production on both visits (intervention 38 (18) W; control 37 (31) W; P = 0.94). Total heat loss was less on the intervention visit (intervention 115 (19) W; control 129 (23) W; P = 0.002). Core temperature increased on both visits (intervention 0.21 (0.37)°C; control 0.19 (0.27)°C; P < 0.001). The increase in mean body temperature was greater on the intervention visit (intervention 0.47 (0.41)°C; control 0.25 (0.19)°C; P = 0.007). ConclusionsThis laboratory model predicts that labour epidural analgesia limits heat loss by >14 W. Once the model is validated, it could be used to test the efficacy of potential interventions to prevent and treat epidural-related maternal hyperthermia.

Core nuclear design and heat transfer analysis of a megawatt-level SiC coated particle based vehicular micro reactor

As a versatile and diversified source of new energy, transportable micro reactors can offer high flexibility and the ability to provide power services even in remote areas. When utilizing coated fuel particles and supercritical carbon dioxide (S-CO2) coolant, the transportable micro reactor core achieves exceptional inherent safety and high power generation efficiency, rendering it incredibly competitive within the nuclear market. The Vehicular Micro Reactor (VMR) previously investigated is an integrated micro-reactor cooled by S-CO2, which employs TRistructural ISOtropic (TRISO) fuel particles dispersed in a conventional graphite matrix to generate 5 MW of power output. However, its drawback lies in the low fuel loading capacity. In recent year, the application of high-strength SiC materials in the field of nuclear energy has been developing continuously. In this paper, a new type of double-layered SiC coated fuel particle is designed, based on which a SiC-based Vehicular Micro Reactor (SVMR) is proposed and explored. It represents an improved design of VMR, with the main difference being its utilization of SiC as a matrix and filling by the two-layered SiC-coated fuel particle to achieve higher fuel loading than the VMR. In this paper, both the neutronic and heat transfer characteristics of the SVMR are discussed. The neutronic simulation is conducted using SCALE code based on Monte Carlo method, the module KENO IV was used to analyze the effective neutron multiplication factor (keff), and SCALE/TRITON (Transport Rigor Implemented with Time-Dependent Operation for Neutronic Depletion) coupled by 2-D radiation transport code NEWT and ORIGEN for burn-up calculation. By optimizing the assembly size and SiC-coated fuel particle size, the SVMR core achieves high fuel loading capacity and superior fuel utilization efficiency. The results of the heat transfer analysis also demonstrate that the SVMR core, which is entirely SiC-based, exhibits exceptional heat transfer capability. The excellent neutron economy and inherent safety make SVMR a more competitive micro reactor concept.

Investigation of neutronic and thermal–electric coupling phenomenon in a 100 kWe-level nuclear silent heat pipe-cooled reactor

Heat pipe-cooled reactors are attractive because of their compact structure, high power capacity and reliability, and inherent safety features. These reactors are distinguished by the use of high-temperature heat pipes that directly bridge the reactor core and energy conversion devices, thus creating a tightly knit modular system. However, comprehensive coupled analysis of these reactors remains challenging because of the intricate multiphysics interactions involved. To address this, the neutronic and thermoelectric coupled phenomena of heat pipe-cooled reactors are investigated in this study. Models are introduced for the point reactor kinetics, core heat transfer, channel heat transfer, two-phase two-dimensional heat pipes, thermoelectric coupling, and cold plates. The channel heat transfer is refined in a 100 kWe-level nuclear silent heat pipe-cooled reactor and a model for the three-dimensional heat transfer process in its thermoelectric matrix established, which effectively resolves the calculation distortions of the lumped model. The maximum deviation between the calculation results from the proposed model and the verification data for a full-system coupled computation is less than 10 K. The core temperature difference from the three-dimensional model is five times that of the lumped model with a maximum average fuel temperature difference of 225.7 K. The maximum and average thermoelectric conversion efficiencies are 15.56 % and 14.43 %, respectively. The failures of one, five, and nine heat pipes are analysed. The failure of a single heat pipe has negligible effects with a peak fuel temperature surge of only 121 K. In contrast, a failure involving nine heat pipes leads to a peak fuel temperature spike of 778 K and a 47.1 % increase in the maximum heat transfer power, marking a critical operational threshold. It is therefore imperative to consider the safety margin in the potential failure of multiple central heat pipes during the preliminary design stages.

A Coupling System for Prediction of Physiological Parameters in an Immersed Condition

This study’s major aim is to use a coupling system to predict the physiological parameters of a person wearing a life preserver in an immersion condition. The coupling system is made up of a thermal manikin that can simulate the human body’s thermoregulatory response in an immersion environment, coupled to a multi-segment human thermal model. By comparing the results with those of the subjects, the coupled system’s predictions were shown to be accurate. The core temperature, skin temperature, and heat flow density of ten healthy men were all continuously measured while they wore life preservers and were exposed to the same temperature of air and water. The coupling system demonstrated accurate predictions of heat production and core temperature compared to real measures, with RMSD of 18.91 W and 0.12 °C, respectively. The majority of the predicted values for mean skin temperature were within SD of the measured values, and the paired sample t-test with a significance level of 0.05 showed good agreement with a maximum temperature difference of 1 °C. Also, the coupling system predicted results and the measured results showed some good accuracy for predicting local skin temperatures.

Effect of nano-crystallization and atomic substitution on electronic and heat properties of Bi2Te3

The specific heat of nano-crystalline (NC) Bi2Te3 (20 nm) in the temperature range of 150 K to 300 K is theoretically studied and compared with the specific heat of the bulk Bi2Te3 materials. Carrier concentration and Hall coefficient are also evaluated using free electron model and compared with experimental results. Lattice (phonon) specific heat has been observed with an overlap repulsive potential with the help of Debye model. For Nano Crystalline materials having high interface volume ratio, the Debye temperature and phonon frequencies are reasonably less at the interfaces than at the core of nano-crystal. Such softening of phonon frequencies at interfaces results in enhancement of Specific Heat in nano-structures. Total specific heat would include interface, core and electronic specific heat. The temperature derivative of the internal energy yields the electronic contribution to specific heat. The present analysis based on the softening of phonon frequencies mechanism is sufficient to describe the enhancement in specific heat by nano-crystallization.

Research on Initiating Events Analysis of Small Helium-Xenon Gas Cooled Nuclear Reactor

Initiating event analysis is an essential prerequisite of conducting probabilistic safety assessment for nuclear reactors, which plays an important role in improving the core design, identifying fault, and guiding operation. In order to determine the initiating event list of SIMONS (Small Innovative helium-xenon cooled Mobile Nuclear power System), preliminary researches on the initial event of SIMONS were carried out using the MLD (Main Logic Diagram) analysis method and referring to the initial event list and initial event analysis theory of other nuclear reactors such as HTGR (High Temperature Gas-cooled Reactor), MSR (Molten Salt Reactor), and PWR (Pressurized water reactor). With employing these methods, a total of 31 initial events are identified for SIMONS based on its latest conceptual design. These initial events are then divided into six groups according to the accident types, which are core heat removal increase, core heat removal decrease, abnormal reactivity and power distribution, pipeline crevasse and equipment leakage, anticipated transients without scram, and disasters (internal and external). The obtained results can provide a theoretical basis for the further safety analysis of SIMONS.

The modulation effect of ice thickness variations on convection in icy ocean worlds

ABSTRACT It has been long puzzling whether the ice thickness variations observed on Enceladus can be sustained solely by a polar-amplified bottom heating. The key to this question is to understand how the upward heat transport by convective plumes would be interfered by the temperature and salinity variations beneath the ice due to the ice thickness variations, which, however, has yet to be explored. Here, we find that the horizontal temperature variation induced by the ice topography can easily be orders of magnitude greater than the vertical temperature variation induced by bottom heating using scaling analysis. Due to the dominance of horizontal temperature gradient, convective plumes are completely shut off by a stratified layer under the thin ice formed out of baroclinic adjustment, largely slowing down the vertical tracer transport. The stratified layer will also deflect almost all of the core-generated heating towards the regions with thicker ice shell, destroying the ice thickness gradient. These results allow us to put an upper bound on the core-generated heating on Enceladus, which is crucial for the estimate of habitability. Scaling laws for the bottom heat flux to penetrate the stratification are derived and examined. This scaling can be used to constrain the maximum ice thickness variations induced by heterogeneous bottom heating on icy satellites in general, which can be used to differentiate icy satellites that generate the majority of heat in the ice shell from those that generate the majority of heat in the silicate core.