Volume-averaged Temperature Research Articles

On the transient thermal response of thin vapor chamber heat spreaders: Governing mechanisms and performance relative to metal spreaders

Vapor chambers can offer a passive heat spreading solution for thermal management in electronics applications ranging from mobile devices to high-power servers. The steady-state operation and performance of vapor chambers has been extensively explored. However, most electronic devices have inherently transient operational modes. For such applications, it is critical to understand the transient thermal response of vapor chamber heat spreaders and to benchmark their transient performance relative to the known behavior of metal heat spreaders. This study uses a low-cost, 3D, transient semi-analytical transport model to explore the transient thermal behavior of thin vapor chambers. We identify the three key mechanisms that govern the transient thermal response: (1) the total thermal capacity of the vapor chamber governs the rate of increase of the volume-averaged mean temperature; (2) the effective in-plane diffusivity governs the time required for the spatial temperature profile to initially develop; and (3) the effective in-plane conductance of the vapor core governs the range of the spatial temperature variation, and by extension, the steady-state performance. An experiment is conducted using a commercial vapor chamber sample to confirm the governing mechanisms revealed by the transport model; the model accurately predicts the experimental measurements. Lastly, the transient performance of a vapor chamber relative to a copper heat spreader of the same external dimensions is explored as a function of the heat spreader thickness and input power. The mechanisms governing the transient behavior of vapor chambers are used to explain the appearance of key performance thresholds beyond which performance is superior to the copper heat spreader. This work provides a foundation for understanding the benefits and limitations of vapor chambers relative to metal heat spreaders in transient operation and may inform the design of vapor chambers for improved transient performance.

Heat transport in rotating-lid Rayleigh–Bénard convection

We perform a direct numerical simulation of three-dimensional Navier–Stokes equations for a Rayleigh–Bénard convection system in a stationary cylinder with the top cold lid rotating. This convection system with an imposed swirl flow is a canonical problem for investigating axial vortices under unstable thermal gradients. The base flow is established by rotating the top lid and the fluid moves azimuthally along the side vertical wall into a meridional flow in the r − z plane. This forms an axial vortex core at the axis of the cylinder. This axial core, under a certain rotational Reynolds number (Re), breaks down to a vortex breakdown bubble whose dynamics are modified under thermal convection. We study the effect of rotation on varying Re for a Rayleigh number Ra = 2 × 105. The equations are formulated in such a way that the rotating-lid cylinder and Rayleigh–Bénard convection are extreme cases of the same numerical set up. From the present study, we find that as the rotational rate is increased, the system dynamics shift from a convection-dominated flow regime to a rotation-dominated regime. This shift in dynamics is quantified using the volume-averaged and time-averaged temperature, the heat flux, the thickness of the Bödewadt boundary layer and the relative Nusselt number. These quantities are shown to demarcate the convection- and rotation-dominated regimes, as compared to the qualitative description of flow patterns from velocity and temperature contours.

Effect of solar irradiance on photo biochemical transformation process of direct absorption methane digester

Direct absorption methane digester can accomplish the coupled process of solar heat collection and photo and biochemical reaction of microorganisms simultaneously. In present work, a numerical model was developed to determine a tool to investigate the photo biochemical transformation process for developing engineering analyses, which is a coupled one of the simplified ADM1 model and the heat and mass transfer model. The model was validated by experimental data from two groups of different experiments. The effect of solar irradiance on the photo biochemical transformation process was also investigated by the model. The results show that a good agreement has been obtained between experimental data and simulations, which can be achieved in most of time. The study found that increasing solar irradiance is an effective method to improve the biogas production rate of direct absorption methane digester. With the solar irradiance increasing, the volume average temperature increases and the rates of biogas production, substrate reaction and total propionate all turn bigger. The effect of solar irradiance on biogas production rate is bigger than the one on the rate of propionic acid. In order to increase the heat storage of digester, the slurry surface evaporation of digester should be restrained.

Simulation of microwave’s heating effect on coal seam permeability enhancement

As hydraulic fracturing was forbidden in some countries due to possible negative environmental impacts and enhanced coalbed methane (ECBM) was restricted by in-situ conditions, microwave heating was proposed to enhance coalbed permeability. One of the mechanisms of improving coal permeability with microwave irradiation is that thermal expansion caused by microwave heating. To study the influence of microwave’s heating effect of coal samples, the simulations were conducted using a coupled electromagnetic, thermal and mechanical model in this paper. The temperature, Von-Mises stress and strain distribution of coal sample are recorded every 10 s. The permeability distribution is also obtained based on the relationship between strain and permeability from articles. It was found that volume average temperature, stress, strain and permeability increase almost linearly with time. The average permeability increased from 1.65 × 10−16 m2 to 3.63 × 10−16 m2 under 2.45 GHz and 500 W microwave radiation after 300 s. The significant increase proved microwave to be effective in coal seam permeability enhancement.

Reprint of: Multiscale multiphase modeling of detonations in condensed energetic materials

Hot spots ignition and shock to detonation transition modeling in pressed explosives is addressed in the frame of multiphase flow theory. Shock propagation results in mechanical disequilibrium effects between the condensed phase and the gas trapped in pores. Resulting subscale motion creates hot spots at pore scales. Pore collapse is modeled as a pressure relaxation process, during which dissipated power by the ‘configuration’ pressure produces local heating. Such an approach reduces 3D micromechanics and subscale contacts effects to a ‘granular’ equation of state. Hot spots criticity then results of the competition between heat deposition and conductive losses. Heat losses between the hot solid-gas interface at pore's scale and the colder solid core grains are determined through a subgrid model using two energy equations for the solid phase. The conventional energy balance equation provides the volume average solid temperature and a non-conventional energy equation provides the solid core temperature that accounts for shock heating. With the help of these two temperatures and subscale reconstruction, the interface temperature is determined as well as interfacial heat loss.The overall flow model thus combines a full disequilibrium two-phase model for the mean solid-gas flow variables with a subgrid model, aimed to compute local solid-gas interface temperature. Its evolution results of both subscale motion dissipation and conductive heat loss. The interface temperature serves as ignition criterion for the solid material deflagration. There is no subscale mesh, no system of partial differential equations solved at grain scale.The resulting model contains less parameter than existing ones and associates physical meaning to each of them. It is validated against experiments in two very different regimes: Shock to detonation transition, that typically happens in pressure ranges of 50 kbar and shock propagation that involves pressure ranges 10 times higher.

Uncertainty quantification for modeling night-time ventilation in Stanford’s Y2E2 building

Natural ventilation can significantly reduce the energy consumption of modern buildings, but robust design is challenging because of the many uncertainties involved. The present work aims to predict the 4-hour nightflush in Stanford’s Y2E2 building during 4 different nights. We employ an uncertainty quantification (UQ) framework that combines an integral model and a computational fluid-dynamics (CFD) model and propagate the uncertainty in the inputs using a polynomial chaos expansion method. The integral model solves a one-dimensional equation for the thermal mass temperature and an equation for the volume-averaged air temperature inside the building. The CFD instead solves for the three-dimensional flow and temperature field in the building, hence enabling direct computation of the heat transfer and discharge coefficients. We first performed a UQ study of the integral model and found that the measured air temperature is inside the 95% confidence interval of the mean prediction ∼80% of the times. Subsequently we employed CFD to improve the accuracy of the probability distributions for the heat transfer and discharge coefficients. In the final step we updated the integral model with these new probability distributions and showed that the standard deviation of the indoor temperature could be reduced up to ∼40%. These results demonstrate that the proposed framework can effectively quantify and reduce uncertainty in models used for the design of natural ventilation systems.

The AGR-3/4 fission product transport irradiation experiment

AGR-3/4 was the combined third and fourth planned irradiations for the U.S. Department of Energy (DOE) Advanced Gas Reactor (AGR) Fuel Development and Qualification Program. The primary purpose of the AGR program is to support the development and qualification of tristructural isotropic (TRISO)-coated particle fuel for use in High Temperature Gas-cooled Reactors. AGR-3/4 was designed as a fission product transport irradiation experiment whose specific objectives were to: (1) irradiate fuel containing UCO (uranium oxycarbide) designed-to-fail (DTF) fuel particles that provide a fixed source of fission products for subsequent transport through compact matrix and structural graphite materials; (2) assess the effects of sweep gas impurities on fuel performance and fission product transport; (3) provide irradiated fuel and material samples for post-irradiation examination (PIE) and post-irradiation heating; and (4) support the refinement of fuel performance and fission product transport models. The AGR-3/4 test train was irradiated in the northeast flux trap of the Advanced Test Reactor (ATR) at Idaho National Laboratory (INL) for 369.1 effective full power days from December 2011 to April 2014. The experiment was successful in achieving its specification goals in terms of burnup and fast fluence levels reached at the end of irradiation and fuel temperature levels maintained throughout irradiation: peak compact burnup reached 15.27% fissions per initial heavy-metal atom and peak compact fast fluence reached 5.32 × 1025 n/m2 (E > 0.18 MeV), while the time-average volume-average temperatures of the compacts ranged from 854 to 1345 °C. Fission product release–to–birth ratios reached values in the 10−4–10−3 range early during irradiation as the DTF particles started to fail. Subsequent post-irradiation examination will provide information on fission product distributions in matrix and core graphite materials, enabling refinement of fission product transport models.

Multiscale multiphase modeling of detonations in condensed energetic materials

Hot spots ignition and shock to detonation transition modeling in pressed explosives is addressed in the frame of multiphase flow theory. Shock propagation results in mechanical disequilibrium effects between the condensed phase and the gas trapped in pores. Resulting subscale motion creates hot spots at pore scales. Pore collapse is modeled as a pressure relaxation process, during which dissipated power by the ‘configuration’ pressure produces local heating. Such an approach reduces 3D micromechanics and subscale contacts effects to a ‘granular’ equation of state. Hot spots criticity then results of the competition between heat deposition and conductive losses. Heat losses between the hot solid-gas interface at pore's scale and the colder solid core grains are determined through a subgrid model using two energy equations for the solid phase. The conventional energy balance equation provides the volume average solid temperature and a non-conventional energy equation provides the solid core temperature that accounts for shock heating. With the help of these two temperatures and subscale reconstruction, the interface temperature is determined as well as interfacial heat loss.The overall flow model thus combines a full disequilibrium two-phase model for the mean solid-gas flow variables with a subgrid model, aimed to compute local solid-gas interface temperature. Its evolution results of both subscale motion dissipation and conductive heat loss. The interface temperature serves as ignition criterion for the solid material deflagration. There is no subscale mesh, no system of partial differential equations solved at grain scale.The resulting model contains less parameter than existing ones and associates physical meaning to each of them. It is validated against experiments in two very different regimes: Shock to detonation transition, that typically happens in pressure ranges of 50 kbar and shock propagation that involves pressure ranges 10 times higher.

Key results from irradiation and post-irradiation examination of AGR-1 UCO TRISO fuel

The AGR-1 irradiation experiment was performed as the first test of tristructural isotropic (TRISO) fuel in the US Advanced Gas Reactor Fuel Development and Qualification Program. The experiment consisted of 72 right cylinder fuel compacts containing approximately 3×105 coated fuel particles with uranium oxide/uranium carbide (UCO) fuel kernels. The fuel was irradiated in the Advanced Test Reactor for a total of 620 effective full power days. Fuel burnup ranged from 11.3 to 19.6% fissions per initial metal atom and time-average, volume-average irradiation temperatures of the individual compacts ranged from 955 to 1136°C. This paper focuses on key results from the irradiation and post-irradiation examination, which revealed a robust fuel with excellent performance characteristics under the conditions tested and have significantly improved the understanding of UCO coated particle fuel irradiation behavior. The fuel exhibited zero TRISO coating failures (failure of all three dense coating layers) during irradiation and post-irradiation safety testing at temperatures up to 1700°C. Advanced PIE methods have allowed particles with SiC coating failure that were discovered to be present in a very-low population to be isolated and meticulously examined, which has elucidated the specific causes of SiC failure in these specimens. The level of fission product release from the fuel during irradiation and post-irradiation safety testing has been studied in detail. Results indicated very low release of krypton and cesium through intact SiC and modest release of europium and strontium, while also confirming the potential for significant silver release through the coatings depending on irradiation conditions. Focused study of fission products within the coating layers of irradiated particles down to nanometer length scales has provided new insights into fission product transport through the coating layers and the role various fission products may have on coating integrity. The broader implications of these results and the application of lessons learned from AGR-1 to fuel fabrication and post-irradiation examination for subsequent fuel irradiation experiments as part of the US fuel program are also discussed.

Heating by transverse waves in simulated coronal loops

Recent numerical studies of oscillating flux tubes have established the significance of resonant absorption in the damping of propagating transverse oscillations in coronal loops. The nonlinear nature of the mechanism has been examined alongside the Kelvin-Helmholtz instability, which is expected to manifest in the resonant layers at the edges of the flux tubes. While these two processes have been hypothesized to heat coronal loops through the dissipation of wave energy into smaller scales, the occurring mixing with the hotter surroundings can potentially hide this effect. We aim to study the effects of wave heating from driven and standing kink waves in a coronal loop. Using the MPI-AMRVAC code, we perform ideal, three dimensional magnetohydrodynamic (MHD) simulations of both (a) footpoint driven and (b) free standing oscillations in a straight coronal flux tube, in the presence of numerical resistivity. We have observed the development of Kelvin-Helmholtz eddies at the loop boundary layer of all three models considered here, as well as an increase of the volume averaged temperature inside the loop. The main heating mechanism in our setups was Ohmic dissipation, as indicated by the higher values for the temperatures and current densities located near the footpoints. The introduction of a temperature gradient between the inner tube and the surrounding plasma, suggests that the mixing of the two regions, in the case of hotter environment, greatly increases the temperature of the tube at the site of the strongest turbulence, beyond the contribution of the aforementioned wave heating mechanism.

Calculation of the fuel temperature coefficient of reactivity considering non-uniform radial temperature distribution in the fuel rod

Abstract The safe operation of a reactor is based on feedback models. In this paper we attempted to discuss the influence of a non-uniform radial temperature distribution on the fuel rod temperature coefficient of reactivity. The paper demonstrates that the neutron properties of a reactor core is based on effective temperature of the fuel to obtain the correct fuel temperature feedback. The value of volume-averaged temperature being used in the calculations of neutron physics with feedbacks would result in underestimating the probable event. In the calculation it is necessary to use the effective temperature of the fuel in order to provide correct accounting of the fuel temperature feedback. Fuel temperature changes in different zones of the core and consequently reactivity coefficient change are an important parameter for analysis of transient conditions. The restricting factor that compensates the inserted reactivity is the temperature reactivity coefficient and effective delayed neutron fraction.

Effect of Pu content on uncertainty in reactor parameters due to use of no temperature gradient in (U-Pu)O$_{2}$ fuels

Radial temperature distribution in a fuel rod is a parabolic function. Neutronics calculations are in general performed over a volume-averaged temperature by ignoring this distribution. Such an assumption results in an uncertainty in reactor design parameters. In this study, the magnitude of this uncertainty is estimated by solving the heat equation with a temperature-dependent conductivity coefficient coupled with a reactor physics code. The effect of radial fuel temperature distribution is investigated by representing the fuel region as multiregional. Uncertainty is investigated for various Pu contents of (U-Pu)O$_{2}$ fuel, a mix of depleted U and reactor-grade Pu. The effect of Pu content on the uncertainty is studied. The PWR TMI-1 unit cell case from UAM test problems is used in the calculations. Results are obtained by using the discrete ordinate method. From the results, it was observed that uncertainties in reactor parameters ($k_{\infty }$ and Doppler coefficient) due to the use of no temperature gradient and in $k_{\infty }$ due to cross-sections decrease as Pu content increases. Moreover, it was calculated that uncertainty due to uniform temperature inside the nuclear fuel is about 7% of uncertainty due to cross-sections.

Modelling the Ohmic L-mode ramp-down phase of JET hybrid pulses using JETTO with Bohm–gyro-Bohm transport

The empirical Bohm–gyro-Bohm (BgB) transport model implemented in the JETTO code is used to predictively simulate the purely Ohmic (OH), L-mode current-ramp-down phase of three JET hybrid pulses, which combine two different ramp rates with two different electron densities (at the beginning of the ramp). The modelling is discussed, namely the strategy to reduce as much as possible the number of free parameters used to benchmark the model predictions against the experimental results. Hence, keeping the gas puffing rate as measured whilst controlling the line-averaged electron density via the recycling coefficient (which in the modelling is taken at the separatrix instead of the wall), one of the many possible ways to fix the total particle source, it is shown that the BgB model reproduces well the experimental data, as far as both average quantities (plasma internal inductance and volume-averaged electron temperature) and profiles (electron density and temperature) are concerned, with relative errors remaining mostly below . The sensitivenesses with respect to the recycling coefficient, the ion effective charge, the energy of neutrals entering the plasma through the separatrix and the need to introduce a particle pinch are assessed; the necessity for a proper sawtooth model if experimental results are to be reproduced is also shown. The strong non-linear coupling in a OH plasma between density, temperature and current (essentially via interplay between the power-balance equation, Joule’s heating with a temperature-dependent resistivity and the dependence of BgB transport coefficients on profile gradients) is put in evidence and analyzed in light of modelling results. It is still inferred from the modelling that the real value of the recycling coefficient at the separatrix (basically, the so-called fuelling efficiency times the actual recycling coefficient at the wall) must become close to one in the final stages of the discharges, when the gas puffing is switched off and so recycling comes to be the only source of particles. If the wall recycling remains close to one (as standard for tokamaks), this may indicate that the fuelling efficiency also approaches unity, apparently consistent with the observed fact that the plasma is pushed towards the machine wall at the end of the current ramps.

Numerical Investigation of Influence of Electrode Immersion Depth on Heat Transfer and Fluid Flow in Electroslag Remelting Process

The influence of the electrode immersion depth on the electromagnetic, flow and temperature fields, as well as the solidification progress in an electroslag remelting furnace have been studied by a transient three-dimensional coupled mathematical model. Maxwell’s equations were solved by the electrical potential approach. The Lorentz force and Joule heating were added into the momentum and energy conservation equations as a source term, respectively, and were updated at each time step. The volume of fluid method was invoked to track the motion of the metal droplet and slag–metal interface. The solidification was modeled by an enthalpy–porosity formulation. An experiment was carried out to validate the model. The total amount of Joule heating decreases from 2.13 × 105 W to 1.86 × 105 W when the electrode immersion depth increases from 0.01 m to 0.03 m. The variation law of the slag temperature is different from that of the Joule heating. The volume average temperature rises from 1856 K to 1880 K when the immersion depth increases from 0.01 m to 0.02 m, and then drops to 1869 K if the immersion depth continuously increases to 0.03 m. As a result, the deepest metal pool, which is around 0.03 m, is formed when the immersion depth is 0.02 m.

Fluid dynamics simulations for an open-sorption heat storage drum reactor based on thermophysical kinetics and experimental observations

To gain insight into the involved thermodynamic processes of open sorption systems and aid in layout and development of future designs, two different methodologies are presented for the numerical description of adsorption reactors using moving beds. In accordance to earlier laboratory measurements, the molecular sieve Köstrolith 4AK was selected as sorption material and thermo-physical measurements using thermogravimetry with simultaneous differential scanning calorimetry were presented to extract the necessary interpolation functions for modelling the kinetic behaviour. Using discrete particle models in a Navier Stokes CFD Solver and particle simulations based on LIGGGHTS, the mixing characteristics of the rotating drum setup were accessed. Adsorption based on the thermophysical measurements was implemented into the discrete particle model. Finally, a parametric study with different temperatures and water content in the inflow air was performed using a transient porous volume approach based on the adsorption implementation and different mixing algorithms. Whereas in a simple adsorption kinetic implementation, the volume averaged temperature of the reactor was already significantly reduced after 1.5h, more realistic implementations showed a prolonged reaction time with a temperature peak at around 15min. The temperature gap between the temperature of the particles and the usable temperature level for the energy extraction was reduced by introducing a mixing algorithm. In the simulations, zeolite temperature yields could be reached between 15K and 28K, corresponding to air temperatures above the material between 21K and 33K, which compared well to the experimental observations, where temperature shifts of the process air of up to 36K were reported. The presented simulation methodology is able to identify partly unused areas in reactors. Numerical optimisation of the flow field and enhancing the particle mixing lead to improved reactor solutions.

Modelling microwave heating of discrete samples of oil palm kernels

Recently, microwave (MW) pre-treatment of fresh palm fruits has showed to be environmentally friendly compared to the existing oil palm milling process as it eliminates the condensate production of palm oil mill effluent (POME) in the sterilization process. Moreover, MW-treated oil palm fruits (OPF) also possess better oil quality. In this work, the MW drying kinetic of the oil palm kernels (OPK) was determined experimentally. Microwave heating/drying of oil palm kernels was modelled and validated. The simulation results show that temperature of an OPK is not the same over the entire surface due to constructive and destructive interferences of MW irradiance. The volume-averaged temperature of an OPK is higher than its surface temperature by 3–7 °C, depending on the MW input power. This implies that point measurement of temperature reading is inadequate to determine the temperature history of the OPK during the microwave heating process. The simulation results also show that arrangement of OPKs in a MW cavity affects the kernel temperature profile. The heating of OPKs were identified to be affected by factors such as local electric field intensity due to MW absorption, refraction, interference, the contact effect between kernels and also heat transfer mechanisms. The thermal gradient patterns of OPKs change as the heating continues. The cracking of OPKs is expected to occur first in the core of the kernel and then it propagates to the kernel surface. The model indicates that drying of OPKs is a much slower process compared to its MW heating. The model is useful to design a microwave reactor which can be used to dry a large quantity of OPKs more effectively.

Estimation of Gas Turbine Blades Cooling Efficiency

This paper outlines the results of the evaluation of the most thermally stressed gas turbine elements, first stage power turbine blades, cooling efficiency. The calculations were implemented using a numerical simulation based on the Finite Element Method. The volume average temperature of the blade and the coefficient of heat transfer from the cooling medium to the cooling channel wall were chosen as the cooling efficiency criteria. A comparison of steam and air used as coolants was done, and the calculations were performed using ANSYS Fluent software.

Evaporation of closely-spaced interacting droplets arranged in a single row

Predictive models of heating and evaporation of fuel droplets in the dense region of sprays are essential to optimize the design of combustion chambers in internal combustion engines. This topic is addressed here, based on an experimental study using lines of equally-spaced droplets evaporating in a high temperature chamber (540°C). The experimental set-up allows controlling several key parameters including the droplet size, velocity and the inter-droplet distance. The volume-averaged temperature of the droplets is measured using two-color laser-induced fluorescence, while the droplet size and velocity are deduced from a double-pulse shadowgraphy method. The combination of these measurement techniques allows evaluating the heating and evaporation rates of single-component droplets made of ethanol, n-dodecane, n-decane and isohexane. Nusselt and Sherwood numbers are estimated from the experiments and compared with the existing correlation concerning the isolated droplet, which allows quantifying the effects of droplet interactions on the heat and mass transfers. The droplet spacing appears to have a strong influence on the size and temperature evolutions. However, it also seems necessary to consider the development of a boundary layer around the chain of droplets. As the thickness of the boundary layer increases with the distance from the injector, forced convection has a more and more limited influence on the heat and mass transport. Inside the boundary layer, the transfers are mainly governed by diffusion and convection by the Stefan flow. In a first approach, these effects are partially incorporated in a reduced parameter using the concept of volume of influence. Then, a more detailed study based on numerical simulation is carried out. The Navier–Stokes equations and the vapor transport equation are solved for various periodical arrangements of droplets. A parametric study of the influence of the main characteristic numbers involved allows to infer a correlation for Nusselt and Sherwood numbers which is finally validated against the measurements.

Coastal ocean variability in the US Pacific Northwest region: seasonal patterns, winter circulation, and the influence of the 2009–2010 El Niño

A 2-km horizontal resolution ocean circulation model is developed for a large coastal region along the US Pacific Northwest (34–50N) to study how continental shelf, slope, and interior ocean variability influence each other. The model has been run for the time period September 2008–May 2011, driven by realistic surface momentum and heat fluxes obtained from an atmospheric model and lateral boundary conditions obtained from nesting in a global ocean model. The solution compares favorably to satellite measurements of sea surface temperature and sea surface height, observations of surface currents by high-frequency radars, mooring temperature time series, and glider temperature and salinity sections. The analysis is focused on the seasonal response of the coastal ocean with particular emphasis on the winter circulation patterns which have previously garnered relatively little attention. Interannual variability is examined through a comparison of the 2009–2010 winter influenced by El Nino and the winters in the preceding and following years. Strong northward winds combined with reduced surface cooling along the coast north of Cape Mendocino (40.4N) in winter 2009–2010, resulting in a vigorous downwelling season, characterized by relatively energetic northward currents and warmer ocean temperatures over the continental shelf and upper slope. An analysis of the time variability of the volume-averaged temperature and salinity in a coastal control volume (CV), that extends from 41 to 47N and offshore from the coast to the 200-m isobath, clearly shows relevant integrated characteristics of the annual cycle and the transitions between winter shelf circulation forced by northward winds and the summer circulation driven primarily by southward, upwelling-favorable winds. The analysis also reveals interesting interannual differences in these characteristics. In particular, the CV volume-average temperature remains notably warmer during January–March 2010 of the El Nino winter.

Comparison of silver, cesium, and strontium release predictions using PARFUME with results from the AGR-1 irradiation experiment

The PARFUME (PARticle FUel ModEl) code was used to predict the release of fission products silver, cesium, and strontium from tristructural isotropic coated fuel particles and compacts during the first irradiation experiment (AGR-1) of the Advanced Gas Reactor Fuel Development and Qualification program. The PARFUME model for the AGR-1 experiment used the fuel compact volume average temperature for each of the 620 days of irradiation to calculate the release of silver, cesium, and strontium from a representative particle for a select number of AGR-1 compacts. Post-irradiation examination (PIE) measurements provided data on release of these fission products from fuel compacts and fuel particles, and retention of silver in the compacts outside of the silicon carbide (SiC) layer. PARFUME-predicted fractional release of silver, cesium, and strontium was determined and compared to the PIE measurements. For silver, comparisons show a trend of over-prediction at low burnup and under-prediction at high burnup. PARFUME has limitations in the modeling of the temporal and spatial distributions of the temperature and burnup across the compacts, which affects the accuracy of its predictions. Nevertheless, the comparisons on silver release lie in the same order of magnitude. Results show an overall over-prediction of the fractional release of cesium by PARFUME. For particles with failed SiC layers, the over-prediction is by a factor of up to 3, corresponding to a potential over-estimation of the diffusivity in uranium oxycarbide (UCO) by a factor of up to 250. For intact particles, whose release is much lower, the over-prediction is by a factor of up to 100, which could be attributed to an over-estimated diffusivity in SiC by about 40% on average. The release of strontium from intact particles is also over-predicted by PARFUME, which also points towards an over-estimated diffusivity of strontium in either SiC or UCO, or possibly both. The measured strontium fractional release from intact particles varied considerably from compact to compact, making it difficult to assess the effective over-estimation of the diffusivities. Furthermore, the release of strontium from particles with failed SiC is difficult to observe experimentally due to the release from intact particles, preventing any conclusions to be made on the accuracy or validity of the PARFUME predictions and the modeled diffusivity of strontium in UCO.