Annular Rod Research Articles

Experimental study on flow split and pressure drop characteristics in a 3 × 3 dual-cooled annular rod bundle

In this paper, flow split and pressure loss experiments were performed in a 3 × 3 dual-cooled annular rod bundle. A novel experimental methodology was developed to obtain the flow split between the internal and external channels. The flow split ratio was close to the flow area ratio of the internal channel to the external channel but didn’t change significantly with the increase of flow rate and inlet temperature. An approximate mathematical expression was proposed to analyze the flow split mechanism. The overall and local pressure drops were also measured. The friction factor in bare rod bundle and pressure loss coefficient at the spacer grid were examined. An assessment of existing correlations for predicting the friction factor and the pressure loss coefficient at the spacer grid was carried out against the experimental data. Correlations for predicting friction factor and spacer loss coefficient were developed, which agreed well with the experimental results.

Experimental study on coupled quenching behavior in a dual-cooled annular rod channel

In this paper, a bottom reflooding experiment was performed in a single annular rod channel to investigate the coupled quench characteristics of the dual-cooled annular fuel. An indirect-heated annular rod with the axial uniform power shape was used. The asymmetric quench front propagation between the external and internal sides of the annular rod was observed. The internal cladding was quenched earlier than the external cladding, owing to heat accumulation in cylindrical shell and the blockage of the vapor flow by the grid spacers in external channel. A unique “secondary quenching” phenomenon was observed at the internal side of annular rod due to the radial heat conduction. The effects of reflooding velocity, inlet subcooling, initial cladding temperature and heating power on quenching behavior were also studied. The present study can contribute to the understanding of the coupled quenching characteristics of dual-cooled annular fuel and obtains valid data for the development of reflooding models and the validation of thermal hydraulics codes of annular fuel.

Burnup Characteristics of Transuranic Fuel With Burnable Poison in Dual Cooled Annular Rod of VVER-1000

Abstract The potentiality of Transuranic (TRU) fuel as dual cooled annular fuel rods with different types of burnable absorbers (BAs)- integrated burnable absorbers (IBAs), burnable poison rods (BPRs), coated absorbers, etc. in the hexagonal assembly of VVER-1000 was studied. Annular 7, Annular 8, and Annular 9 models were taken for various combinations of TRU fuel and BAs. Planned models were simulated in Monte Carlo particle simulation code OpenMC and lattice physics deterministic code Dragon Version5. Burnup-dependent multiplication factors (MFs) were simulated for 3000 effective full power days (EFPDs). Reactivity was calculated by taking 3% neutron leakage. The study showed that both the MF and reactivity for TRU fuel are significantly higher than conventional UO2 fuel. Linear reactivity model (LRM) was applied to find out cycle burnup, discharge cycle burnup, and cycle length. High cycle burnup, discharge burnup, and cycle length have been observed for TRU fuel compared to UO2 fuel. Burnup-dependent atomic concentration graphs showed that slight burn of Np-237, constant concentration for Cm-244, a slight increase for Am-242, and linear burnout of BAs- Gd-155, Gd-155, and Er-167. A lower concentration of Xe-135 has been observed for TRU fuel. Pin power distribution and energy-dependent neutron flux for different models and BAs combinations are also included in this study.

Experimental investigation on quenching behavior during reflooding in a 3 × 3 dual-cooled annular rod bundle

The internally and externally cooled annular fuel is an innovative fuel geometry proposal for advanced PWR, which could provide a substantial increase of power density while maintaining or improving safety margins. The quenching behavior of annular fuel during reflood phase in LOCA is more complicated than cylindrical solid fuel, owing to the geometrical difference and the coupling effect of dual-cooling. However, the investigation focusing on quenching characteristics in annular fuel geometry is very little. In the present study, an experimental study on quenching behavior of bottom reflood in a 3 × 3 dual-cooled annular rod bundle was carried out under various test conditions (reflood velocities from 0.025 to 0.15 m·s−1, inlet subcooling from 10 to 80°C, peak cladding temperature from 300 to 900°C, and linear power density from 0 to 1.58 kW·m−1). Self-designed indirect-heating annular rods were employed to provide an axial uniform power distribution in this experiment. It was found that the quenching process on external and internal surfaces of annular rod bundle was almost synchronous. The parametric effects on quenching behavior, i.e. precursory cooling rate, quench front propagation velocity (Vqf) and minimum film boiling temperature (Tmin), were investigated in detail. Earlier occurrence of quenching downstream the grid spacer was also observed under low inlet subcooling and high peak cladding temperature conditions. In addition, several correlations for Tmin were assessed against the present results. Kim correlation was in good agreement with the present data, with the mean absolute errors of 7.81% and 7.55% for outer and inner channels respectively.

Experimental Investigation on Reflooding Behavior in Annular Rod Bundle

Experimental Investigation on Reflooding Behavior in Annular Rod Bundle

Critical heat flux on zircaloy and accident tolerant fuel cladding under prototypical conditions of pressurized and boiling water reactors

First of a kind high spatial and temporal resolution temperature measurements of Pressurized Water Reactor and Boiling Water Reactor simulated fuel pins (high heat flux cosine profile heaters) in annular rod type geometry during nucleate boiling, departure from nucleate boiling and re-wetting has been performed. Distributed fiber optic measurements of the cladding axial temperature with spatial resolutions down to 2.5 mm axially at up to three equally spaced azimuthal locations per rod have demonstrated the similarities and differences of the different accident tolerant fuel cladding materials. These experiments show the performance of accident tolerant cladding with a precise measurement of the location and evolution of dryout followed by the re-wetting phenomena (see supplementary time history of a critical heat flux event). Experimental parameters varied coolant mass fluxes from 1695 to 2712 kg/m2s, pressures from 10 to 20 MPa, and inlet subcooling from 10 to 55 °C. It was found that the coatings and different material have little effect on the value of the critical heat flux. Any discrepancies between the local critical heat flux verified among the cladding material are attributed to different departure from nucleate boiling phenomena captured during the experiment with the high-resolution optical fiber temperature data. Substantial differences in the performance of the different cladding material to survive a critical heat flux event were however observed by post-test X-ray and optical inspection. External evident damage and internal cracks to the simulated fuel pin having the bare zircaloy cladding were observed in regions associated with the occurrence of the critical heat flux for longer periods. Such damages were associated with zirconium oxidation, and not noticed on the Cr coated zircaloy or FeCrAl claddings. These results indicate that the use of FeCrAl or a Cr coated zircaloy as cladding in Pressurized Water Reactor and Boiling Water Reactor may increase the survivability of the cladding material for short transients.

Experimental Investigation on Quenching Behavior During Reflooding in a 3 × 3 Dual-Cooled Annular Rod Bundle

Experimental Investigation on Quenching Behavior During Reflooding in a 3 × 3 Dual-Cooled Annular Rod Bundle

Heat transfer due to turbulent annular impinging jet with a bullet extension at the end of the inner blockage rod

The flow and thermal behavior of a turbulent annular jet impinging on a flat plane are numerically investigated to examine the effect of extending the inner rod of the annulus beyond the exit plane of the jet. The Fluent commercial code is used for conducting the computations employing the k-ε (Realizable) turbulence model. Three different shapes of the extended annular rod end, viz., cylindrical, conical, and semi-ellipsoidal, are considered. The length of the extended part is taken as 0.5, 1, and 2 times the outer jet diameter. The extension of the annular rod end modifies the flow structure and eliminates the recirculation region at the exit of the annular jet, which noticeably affects the impingement plane heat transfer. Depending on the shape and length of the bullet, the bullet extensions affect the heat transfer differently. Compared to the case without the extension, the conical extension diminishes the heat transfer, the ellipsoidal extension moderately increases the heat transfer, while the cylindrical extension enhances the heat transfer for a larger bullet length (≥1). Also, the location and the magnitude of the peak Nusselt number at the hot impingement surface vary as the shape and length of the extension change.

Assessment of the burnup characteristics of UO2 and MOX fuel in the mixed solid and annular rod configuration

Modeling and burnup analysis of Uranium dioxide (UO2) and Mixed Oxide (MOX) fuel in square assemblies comprising both solid and annular rods was carried out. The lattice pitch of the models was optimized first in terms of infinite multiplication factor (k∞) using OpenMC. The burnup analysis was performed at the optimized pitch by lattice physics code Dragon for 1620 EFPD. The burnup dependent fission rate density was studied, and the thermal fission rate was found higher for the models as compared to reference designs. The values of k∞ and reactivity were determined and higher values were found for the models at low fuel burnup period. However, models showed a higher criticality period than the reference design consisting of only the annular rod. The fuel and moderator temperature sensitivity of reactivity was investigated for different fuel burnup periods. The burnup-dependent atomic concentrations of fissionable materials, minor actinides, and neutron poisons were also studied. The production of neutron poison, namely Xe-135 and Sm-149 and minor actinides viz. Np-237, Am-241, Cm-242 and Cm-244 were found lower in models as compared to the reference designs.

Neutronics calculation of the conceptual TRISO duplex fuel rod design

• The neutronic properties of TRISO duplex fuel rod for a small block-type thorium HTR was investigated. • TRISO duplex fuel rod consists of an inner region filled with UO 2 particles and an outer layer filled with ThO 2 particles. • TRISO duplex fuel increases the discharged burnup and has a lower reactivity swing. • TRISO duplex fuel capable of maintaining a softer neutron spectrum throughout its burnup period. The duplex fuel pellet includes UO 2 components as seed and ThO 2 blanket, originally designed to increase the breeding rate of fissile materials in light water breeder reactors. However, the seed portion alone concentrates most of the energy released from the fission reaction, which can make the seed temperature too high. The duplex fuel potential for the high-temperature reactor (HTR) using TRISO fuel has never been researched. MCNPX simulation was conducted to compare the neutronics performance of normal TRISO fuel with that of TRISO duplex fuel. Two types of HTR fuel rod, the cylinder and the annular rod, were simulated and compared to see whether the duplex neutron characteristics would be better in the cylinder or annular fuel compact design. The TRISO duplex rods produced higher burnup than normal rods up to 5% higher for cylinder and 6% for annular rods. The TRISO duplex rod is also capable of maintaining longer criticality, producing smaller k inf changes and reducing the potential for plutonium build-up. The proposed TRISO duplex conceptual fuel design has an interesting neutronic properties, which offers possibilities for future studies.

Effect of fluidizing solids on wall-liquid mass transfer in a cylindrical cell with rotating central rod

Limiting current density data were obtained at point electrodes fixed flush with inner surface of the outer cylinder of an electrochemical cell in which a coaxially placed cylindrical rod is rotated at different rotational velocities in the presence of fluidizing solids. The variables covered in the present study are rpm of inner annular rod, diameter of rod, solid fraction and flow rate of the electrolyte. Mass transfer coefficients, which were computed from limiting current density data, were found to increase with an increase in the velocity of the fluid electrolyte through the annular cell in the presence of fluidizing solids. No specific trend was observed with respect to the rpm of the central annular rod. The variation in mass transfer coefficient values due to change in the rod diameter was just marginal. The bed expansion data represented Richardson-Zaki equation with an exponent of 2.15. Colburn jD-factor format has been used to correlate the data on mass transfer coefficients.

Development of model for studies on momentum transfer in electrochemical cells with entry region coil as turbulence promoter

Entry region swirl promoters gain importance in industry because of its effectiveness in augmentation of mass and heat transfer augmentation. Design of equipment needs momentum transfer data along with mass or heat transfer data. Hence an experimental investigation was carried out with coaxially placed entry region spiral coil as turbulence promoters on momentum transfer in forced convection flow of electrolyte in circular conduits. Aqueous solution of sodium hydroxide and 0.01 M equimolal Ferri-ferro cyanide system was chosen for the study. The study covered parameters like effect of pitch of the coil, effect of length of the coil, diameter of the coil, diameter of the coil wire, diameter of the annular rod. The promoter is measured by limiting current technique using diffusion controlled electrochemical reactions. The study comprises of evaluation of momentum transfer rates at the outer wall of the electrochemical cell. Pressure drop measurements were also made to obtain the energy consumption pattern. Within the range of variables covered. The results are correlated by the momentum transfer similarity function. Momentum transfer coefficients were evaluated from measured limiting currents. Effect of each parameter was studied in terms of friction factor. A model was developed for momentum transfer. The experimental data on momentum transfer was modeled in terms of momentum transfer function and Reynolds number, geometric parameters.

Process Intensification with Coaxially Placed Entry Region Vanes Assembly Turbulence Promoter in Homogeneous Flow

The entry region vane turbulence promoters are inserted at the downstream of a circular electrolytic cell and limiting current data are measured at the copper micro electrodes fixed on an electrode support. The effect of flow rate of the electrolyte, effect of velocity on mass transfer at the wall, effects of geometric parameters diameter of the vane (dv) from 0.02 m to 0.04 m, the angle of the vane (γ) from 15° to 60°, sectorial angle (α)/number of the vanes (N) from 4 to 8, diameter of the annular rod of mass transfer is investigated. The electrolyte was equimolal potassium ferricyanide, potassium ferrocyanide and excess sodium hydroxide. Limiting current data had been obtained for the reduction of potassium ferricyanide ion. The mass transfer correlation is based on the law of the wall similarity. The effect of each parameter was studied in terms of friction factor. A model was developed for mass transfer. The correlation may be extended to a wider range of parameters by virtue of the law of the wall. The experimental data on mass transfer was modelled in terms of mass transfer function and Reynolds number geometric parameters.

Numerical Investigation of heat transfer enhancement of SiO2-water based nanofluids in Light water nuclear reactor

Nanofluid performed a very crucial role in nuclear power plant for improving heat transfer. Due to high thermal conductivity of nanofluid heat transfer capacity in nuclear reactor can be thousand times larger than conventional fluids like water. So the efficiency of nuclear reactor is improving and also reducing the thermal hydraulics problems. It opens a new gateway for gaining higher energy optimization. For improving the heat transfer in light water reactor, SiO2-water based nanofluids properties were used for numerical investigation. Heat transfer of nanofluid can be functions of volume concentration, physical properties and size of nanoparticles etc. Density, thermal conductivity, specific heat and viscosity were investigated and operated as a basic data for ANSYS 14. In this numerical investigation three value of weight concentration of nanoparticles in the range of 1%, 2% and 3% were used. A uniform heat flux of 1000 (kW/m2) is applied at the wall of annular rod. The numerical method which is available in CFD package of Ansys CFX 14 has been used here. Turbulence models of k–ω has been used in this numerical analysis. Validation of result has been done by analytical equations. Numerical investigation of various effect on characteristics of heat transfer in light water nuclear reactor by using SiO2-water based nanofluid is the key objective of the study. Coefficient of heat transfer and temperature of clad wall profiles are plotted without nanofluids and with nanofluids.

Photonic Dirac point realized in two dimensional annular photonic crystals

The Dirac cones in photonic crystals have aroused much interest in the last few years. Annular photonic crystals have also been well studied for designing and controlling the band gap because they have more parameters than usual photonic crystal. In this paper, we study a two-dimensional square lattice dielectric annular photonic crystal to explore the formation of the photonic Dirac cone by the accidental degeneracy method. The theoretical tool is the plane wave expansion method. The results show that this system can provide a Dirac point in the center of the Brillouin-zone in the photonic band if both the outer radius and the inner radius of each scatterer are chosen to be appreciate values when the dielectric refractive index of the annular rod is fixed. For example, there is a Dirac point at the photonic normalized frequency f=0.438(c/a) when n=3.4, RO=0.42a, RI=0.305a, where f is the frequency, c is the light speed in vacuum, a is the lattice constant, n is the refractive index, RO is the outer radius, and RI is the inner radius. It is also found that within a confined region of outer radius RO(0.37aROa), when a Dirac point is realized in the annular photonic crystal (n>1.4), the inner radius RI and the outer radius RO obey a relation of RI=-1.104+8.167RO+(-11.439)RO2, which is unrelated to the refractive index n of the dielectric annular rod. If n is less than 1.4, this rule is not valid. At the same time, the normalized frequency at which the Dirac point is realized, decreases with increasing both refractive index n and outer radius RO. Especially, the curves of the relation between photonic frequency f and outer radius RO almost do not change their profiles but only be shifted up and down with changing the refractive index n. Based on this, we also design and predict the annular photonic crystal which provides a Dirac point. The goal is to obtain the other relative parameters (frequency f, outer radius RO and the inner radius RI) of the photonic crystal system if the refractive index n is fixed. The values of the prediction agree very well with the values obtained by the rigid theoretical calculation within a relative error of only 4%.

Progress in the studies of the advanced plutonium fuel assembly

A new assembly concept, designated APA (for A dvanced P lutonium fuel A ssembly), should make it possible to multi-recycle plutonium in pressurized water reactors. The basic idea is founded on the manufacture of a large plutonium thin annular fuel rod with an inert support, cooled on both faces. The absence of plutonium generation, combined with moderate fuel temperature should make it possible to achieve substantial burn-up fractions in these rods. The assembly is compatible with the internals of a Pressurized Water Reactor (PWR), and provides for permanent reversibility. Neutronic studies showed a compliance with actual safety/control criteria. A multi-recycling scenario was simulated for 84 years' operation with a 65 GW electrical power installed capacity, comprising forty-five 1450 MW electrical power PWRs, 32 of which are loaded with UO 2 and 13 with APAs. It showed that the plutonium inventory is controlled. Thermal-hydraulic studies showed one can find an annular rod geometry allowing one to respect both margins to Critical Heat Flux (CHF) during normal and accidental operations and void fraction limitations.

95/06054 Integrated data base report — 1993: U.S. spent nuclear fuels and radioactive waste inventories, projections and characteristics

A new assembly concept, designated APA (for Advanced Plutonium fuel Assembly), should make it possible to multi-recycle plutonium in pressurized water reactors. The basic idea is founded on the manufacture of a large plutonium thin annular fuel rod with an inert support, cooled on both faces. The absence of plutonium generation, combined with moderate fuel temperature should make it possible to achieve substantial burn-up fractions in these rods. The assembly is compatible with the internals of a Pressurized Water Reactor (PWR), and provides for permanent reversibility. Neutronic studies showed a compliance with actual safety/control criteria. A multi-recycling scenario was simulated for 84 years' operation with a 65 GW electrical power installed capacity, comprising forty-five 1450 MW electrical power PWRs, 32 of which are loaded with UO2 and 13 with APAs. It showed that the plutonium inventory is controlled. Thermal-hydraulic studies showed one can find an annular rod geometry allowing one to respect both margins to Critical Heat Flux (CHF) during normal and accidental operations and void fraction limitations.

Equivalence Resonance Integrals for Lattices of Annular Absorber Rods

Resonance integrals for lattices of annular rod absorbers can be accurately determined by ordinary equivalence relation procedures. This is demonstrated for water lattices of annular uranium rods whose inner cylindrical zone is either a void or water filled. The equivalence cross section, needed to enable the use of tabulated homogeneous integrals, is given by a formula recently developed. There are three parameters in the formula that need estimation: a Dancoff factor for the lattice, the probability of neutrons entering the inner rod zone to collide there, and a Bell factor. Ways and means to estimate these parameters are discussed and demonstrated. The interpolation of resonance integrals from entries in existing tables of homogeneous integrals is performed with an accurate technique. Results of the equivalence-based calculations are compared with results by the integral transport RABBLE code.