Reactor Fuel Research Articles

Steady-State Subchannel Thermalhydraulic Assessment of a Full-Scale Pressurized Water Reactor-Small Modular Reactor Fuel Assembly With Conventional and Advanced Fuels

Abstract Thermalhydraulic analyses using subchannel codes (e.g., ASSERT-PV) are performed as a support tool to evaluate safety margins and the key parameters. Advanced fuels have recently attracted the international community's interest to improve safety margins during normal operation and accident scenarios by utilizing special coatings and barriers in a heterogeneous, multiregion, multicoating, multiclad annular fuel. In addition, advanced fuels improve the performance characteristics such as a higher burnup and better uranium utilization. Therefore, there is a need to understand the implications of such advanced unconventional fuels for the landscape of the Canadian nuclear industry and Canadian policy for energy development. In this work, subchannel thermalhydraulic analysis of a small modular reactor based on pressurized water reactor technology (PWR-small modular reactor (SMR)) core is performed using ASSERT-PV. A benchmark of a 17 × 17 fuel assembly with conventional fuel elements in comparison to PWR-SMR specification was conducted. The advanced fuel element system is also investigated and compared with the conventional one. The results indicated that the advanced fuel achieves a significant reduction in fuel element temperature by 15%. In addition, the results revealed that the proposed advanced fuel could achieve a minimum critical heat flux ratio (MCHFR) higher than the conventional fuel by 17%.

Physics Modeling for Conceptual Designs of Proposed Experiments in the Zero Energy Deuterium-2 Critical Facility for Testing Small Modular Reactor-Type Fuels

Abstract To enable the deployment of small modular reactors (SMRs) in Canada, Canadian Nuclear Laboratories (CNL) is interested in the applicability of zero energy deuterium-2 (ZED-2) experiments for validation of Monte Carlo reactor physics codes and models for SMR reactor fuels. This applicability is investigated here by considering potential ZED-2 experiments for testing fuel assemblies (FAs) for two different SMR technologies: the pressurized-water reactor (PWR), and the fluoride-salt-cooled high-temperature reactor (FHR). Each proposed set of mixed-lattice substitution experiments uses driver fuel channels containing CANDU flexible low enriched uranium/recovered uranium (CANFLEX-LEU/RU) fuel bundles. Simulation results indicate that a number of critical core configurations are possible, and should provide suitable reactor physics measurement data that can be used for physics design verification, and also for benchmarking and validation of computational reactor physics codes used in the design, operations, and safety analysis of SMRs based on PWR or FHR technologies.

SiC and FeCrAl as Potential Cladding Materials for APR-1400 Neutronic Analysis

The aim of this study is to investigate the potential improvement of accident-tolerant fuels in pressurized water reactors for replacing existing reference zircaloy (Zr) fuel-cladding systems. Three main strategies for improving accident-tolerant fuels are investigated: enhancement of the present state-of-the-art zirconium fuel-cladding system to improve oxidation resistance, replacement of the current referenced fuel-cladding system material with an alternative high-performance oxidation-resistant cladding, and replacement of the current fuel with alternative fuel forms. This study focuses on a preliminary analysis of the neutronic behavior and properties of silicon carbide (SiC)-fuel and FeCrAl cladding systems, which provide a better safety margin as accident-tolerant fuel systems for pressurized water reactors. The typical physical behavior of both cladding systems is investigated to determine their general neutronic performance. The multiplication factor, thermal neutron flux spectrum, 239Pu inventory, pin power distribution, and radial power are analyzed and compared with those of a reference Zr fuel-cladding system. Furthermore, the effects of a burnable poison rod (Gd2O3) in different fuel assemblies are investigated. SiC cladding assemblies present a softer neutron spectrum and a lower linear power distribution compared with the conventional Zr-fuel-cladding system. Additionally, the SiC fuel-cladding system exhibits behaviors that are consistent with the neutronic behavior of conventional Zr fuel-cladding systems, thereby affording greater economic and safety improvements.

Development of a Sodium Fast Reactor Cartridge Loop Testing Capability for the Versatile Test Reactor

The objective of the Versatile Test Reactor (VTR) is to enable testing of advanced reactor fuels and materials in a fast spectrum neutron environment. Internal cartridge loop testing capabilities are being developed that will allow the cartridge coolant to be isolated from the reactor coolant. This approach will allow various cartridge coolants to be investigated, thereby maximizing testing capability. A sodium cartridge loop testing capability is being developed by a team that includes Argonne National Laboratory (Argonne) as the laboratory partner, Framatome Inc. as the industrial partner, and Purdue University along with the University of Wisconsin–Madison as university partners. Specific elements of the current work include overall cartridge loop design development that is being led by Framatome, Inc. Coolant chemistry monitoring and control are key elements of any high-pedigree irradiation testing capability; the University of Wisconsin is leading this effort by developing and experimentally verifying methods for achieving this capability in pile. Purdue University is developing a scaling methodology, and on that basis, a thermal-hydraulic testing capability to validate fluid flow and heat transfer models for the cartridge that will be used to support design and safety analysis activities. Argonne has focused on developing and testing technologies specifically targeted at simplifying VTR operations, as well as developing modeling tools to support cartridge loop design and safety analysis. The purpose of this paper is to summarize the current status of the sodium fast reactor cartridge development, including details on the cartridge functional requirements, physical design, chemistry control, operations, and safety.

Evaluation of the energy balance of chemical looping combustion of solid fuels using CuO-based oxygen carriers

Chemical looping combustion (CLC) can inherently capture the CO2 generated during thermal energy production. When using CuO-based oxygen carriers, the reactions in both the fuel reactor (FR) and air reactor (AR) are exothermic, facilitating autothermal operation. To prevent the oxygen carrier from becoming agglomerated while ensuring a sufficient oxygen release rate, it is necessary to predict the FR temperature and remove an appropriate amount of heat from the AR when burning high-rank fuels. In this work, the energy balance of a CuO-based CLC system firing various solid fuels (biomass, coal, and petroleum coke) was investigated by establishing a thermodynamic model using FactSage. The energy distribution characteristics of the FR were quantified based on a virtual five-step thermodynamic sequence. The effects of fuel properties, oxygen carrier properties, and operating conditions on the energy balance were evaluated systematically. The results indicate that the temperature difference between the FR and AR is not very sensitive to the heating value of the fuel, while the CuO loading of the oxygen carrier, the heat capacity of the support material, and the flow rate of the fluidizing gas have significant impact. The insights obtained in this work will help improve the design and heat management of CLC.

Fluidization Dynamics of a New Two-Staged Fuel Reactor for Chemical Looping Gasification

A new staged fuel reactor (FR), which integrates a bubbling bed and a spouted fluidized bed, is proposed in the present work with regard to lowering the pressure drop of the staged FR during chemical looping applications. In order to gain insights into the gas–solid fluid dynamics of the new design, a cold experimental setup was established. The fluidization dynamics of the staged FR was investigated based on the pressure pulsation signal analysis using time domain analysis, power spectral density analysis, wavelet analysis, and the Hurst exponent analysis by the R/S method. There are four flow types of funnel-like flow, spout-fluidization, spouting motion, and unsteady spouting motion to be classified, and the transition boundaries of the corresponding flow types were determined. The design provides a way to lower the overall pressure drop of FR and then reduces the fan energy consumption to hold the oxygen carrier particle circulation.

Structural, electronic, mechanical and thermodynamic properties of U–Si intermetallic compounds: A comprehensive first principles calculations

Uranium silicides are proposed as the prominent accident tolerant fuels for the light water reactors (LWR) due to their high metal density and high thermal conductivity. Among the U–Si alloys, the alloy with high U:Si ratio is more favorable for nuclear fuel application due to the higher uranium density. Thus, the crystal structure, mechanical property, electronic structure, phonon band structure and thermodynamic property of U3Si, U3Si2 and USi compounds, along with the thermodynamic reaction between U–Si intermetallic compounds are systematically studied in our work. The optimized structural parameters of these U–Si alloys are comparable with previous results. Besides, all of them are metallic in nature. Since the calculated elastic constants satisfy the Born stability criteria, one can know U–Si alloys are mechanically stable. The phonon dispersion curves are obtained based on the density functional perturbation theory (DFPT). Accordingly, various thermophysical properties, such as Helmholtz free energy, heat capacity, internal energy and entropy are calculated. Furthermore, the reaction energies related to the formation of U3Si, U3Si2 and USi as well as transformation between them are calculated. It is revealed at the same chemical environment the reaction to form USi occurs more easily, whereas the high temperature and sufficient uranium environment are more in favor for fully silicification of uranium metal into U3Si. Theoretical investigation of this work is expected to provide some new insights for the application of uranium silicides as nuclear fuels and future exploration on the design and synthesis of new-type uranium silicides.

Identifying chemically similar multiphase nanoprecipitates in compositionally complex non-equilibrium oxides via machine learning

Characterizing oxide nuclear fuels is difficult due to complex fission products, which result from time-evolving system chemistry and extreme operating environments. Here, we report a machine learning-enhanced approach that accelerates the characterization of spent nuclear fuels and improves the accuracy of identifying nanophase fission products and bubbles. We apply this approach to commercial, high-burnup, irradiated light-water reactor fuels, demonstrating relationships between fission product precipitates and gases. We also gain understanding of the fission versus decay pathways of precipitates across the radius of a fuel pellet. An algorithm is provided for quantifying the chemical segregation of the fission products with respect to the high-burnup structure, which enhances our ability to process large amounts of microscopy data, including approaching the atomistic-scale. This may provide a faster route for achieving physics-based fuel performance modeling.

Thermal hydraulic modeling of solid fueled nuclear thermal propulsion reactors Part I: Development and verification

This paper focuses on the development and demonstration of a modern thermal–hydraulic engineering tool to design nuclear thermal propulsion reactors. Low enriched uranium nuclear thermal propulsion reactors are currently being invested to appease regulatory and proliferation concerns, and consequently rendering the previous highly enriched uranium designs inapplicable. Sparse experimental data from the previously designed highly enriched uranium designs may be non-ideal for benchmarking low-enriched uranium designs. Computational fluid dynamics codes provide an affordable and expeditious alternate route for the verification of thermal–hydraulic engineering tools. Verification of engineering tools is crucial as they will be implemented in coupled neutronic and thermal–hydraulic simulations to ascertain the thermal and safety margins of a given design. Extensive research was performed on the optimization and design of nuclear thermal propulsion reactors, but there is limited publicly available description of currently adopted thermal–hydraulic solution procedures used for the design of contemporary nuclear thermal propulsion reactors. More specifically, the modelling assumptions, geometric simplifications, correlations, and iterative procedures are not always well understood or documented. The purpose of this paper is to provide a clear explanation of our thermal hydraulic modelling approach, clarify the impacts of commonly used assumptions on engineering-based tools, and demonstrate the importance of thermal–hydraulic solutions on neutronics. These objectives are achieved through the newly developed ntpThermo computational tool. This tool is verified against the high-order computational fluid dynamics code OpenFoam, which serves as the reference solution following a successful validation against experimental data. The results indicate that the reduced order-modeling approach implemented in ntpThermo can provide valuable engineering design support and be used for coupled neutronic and thermal–hydraulic simulations.

Construction of Fe3O4 bridged Pt/g-C3N4 heterostructure with enhanced solar to fuel conversion

In this study, we report the effects of co-catalysts of Pt nanoparticles and Fe3O4 clusters on photocatalytic behaviors of g-C3N4 (CN) and the use of the resulting photocatalyst for CO2 photoreduction to solar fuels in a flow reactor operated at room-temperature. In presence of H2O vapors, the selectivity of photogenerated electrons was emphasized, and found that the yield rate and selectivity of CH4 were improved by deposition of Pt on CN. With further inclusion of Fe3O4 over Pt/g-C3N4 (PtCN), the CH4 yield rate was significantly enhanced and H2 formation inhibited simultaneously, resulting in improved CH4 selectivity. Results show that the optimized Fe3O4/Pt co-decorated CN (0.50 %FPtCN) heterostructure possesses significantly enhanced CO and CH4 yield rates of 1.83 μmolg−1h−1 and 0.532 μmolg−1h−1, respectively, which were 9 and 38 times superior to pure CN, attributed predominantly synergistic effects of Pt, Fe3O4, and CN. Owing to exceptional conductivity and electron-sink function, Pt NPs are an excellent electron transporter, which facilitates interfacial charges transfer and prohibits their recombination, while, the Fe3O4 clusters can synergistically promote the CO2 photoreduction by effectively using electrons as the oxidation − reduction center. Finally, insight obtained from results is used to propose a possible underlying mechanism for superior photocatalytic performance.

Numerical investigation of CH4/H2/air flame bifurcations in a micro flow reactor with controlled wall temperature profile

Flame characteristics of CH4/H2/air (CH4:H2=1:1) mixture in a cylindrical micro flow reactor with a controlled wall temperature distribution were numerically studied. Bifurcation phenomena were captured in both stable flame regime and FREI (Flame with Repetitive Extinction and Ignition) regime. For the stable flame regime, a normal flame and a weak flame co-exist in upstream and downstream of the channel, respectively. Analysis of reaction paths demonstrates that H2 competes with CO for OH radical in upstream normal flame, which causes incomplete combustion and produces CO residual. When the residual CO moves to farther downstream with a higher wall temperature, CO and OH react completely and a weak flame is formed. For the unstable flame regime, twice bifurcations occur during one period of FREI. The first bifurcation mainly results from residual O2 and CO after the re-ignition point, while the formation mechanism of the second bifurcation is similar to that of the co-existing weak flame which bifurcates from upstream stable flame. In a word, the present study discovered complex flame characteristics of CH4/H2 blended fuels in a micro flow reactor with wall temperature gradient and revealed the underlying mechanisms responsible for these flame phenomena.

Flow and Heat Transfer Simulation in a Complete Pressurized Water Reactor Fuel Assembly Using Wall-Modeled RANS

Abstract Reproduction of turbulent flow and heat transfer inside a pressurized water reactor (PWR) fuel assembly is a challenging task due to the complex geometry and the huge computational domain. Capability of a wall-modeled Reynolds-averaged Navier–Stokes (RANS) simulation approach has been examined, which had already been validated against the measurements of the MATiS-H experiment. The method is here expanded to a larger computational domain aiming to reproduce flow and thermal field in the entire PWR fuel assembly. Namely, in the first part of this study, wall-modeled RANS is performed in a relatively short section of the representative PWR fuel assembly containing one single mixing grid with an array of 15 × 15 fuel rods. Linear and nonlinear eddy-viscosity turbulence models have been applied; however no significant difference is observed in the predicted pressure drop in the fuel assembly. The obtained predictions revealed an interesting pattern of swirl flow as well as diagonal cross flow downstream the mixing grid, which is driven by the applied design of split-type mixing vanes. In the second part, the computational model is extended to a domain representative of a complete PWR fuel assembly with ten mixing grids, inlet and outlet sections. Pressure drop and flow field are analyzed together with the predicted temperature and potential hot spots. In spite of a relatively coarse spatial resolution of the applied approach, the wall-modeled RANS provided promising results at least for the qualitative prediction of the pressure, flow field, and location of hot spots.

8 Rivers advances decarbonization plans

The decarbonization technology company 8 Rivers Capital has won a $100 million investment from SK Group and signed a deal with Johnson Matthey to integrate the two firms’ hydrogen technologies. 8 Rivers is developing the Allam-Fetvedt power generation cycle, which burns carbon-based fuels in a pure-oxygen reactor using CO 2 as the working fluid. CO 2 capture is facilitated by eliminating the need to separate it from nitrogen gas. The SK investment is the largest in a carbon-capture provider to date, SK and 8 Rivers say.

Comparison of the minor actinide transmutation efficiency in models of a fast neutron uranium-thorium fueled reactor

In terms of nuclear raw materials, the issue of involving thorium in the fuel cycle is hardly very relevant. However, in view of the large-scale nuclear power development, the use of thorium seems to be quite natural and reasonable. The substitution of traditional uranium-plutonium fuel for uranium-thorium fuel in fast neutron reactors will significantly reduce the production of minor actinides, which will make it attractive for the transmutation of long-lived radioactive isotopes of americium, curium and neptunium that have already been and are still being accumulated. Due to the absence of uranium-233 in nature, the use of thorium in the nuclear power industry requires a closed fuel cycle. At the initial stage of developing the uranium-thorium cycle, it is proposed to use uranium-235 instead of uranium-233 as nuclear fuel. Studies have been carried out on the transmutation of minor actinides in a fast neutron reactor in which the uranium-thorium cycle is implemented. Several options for the structure of the core of such a reactor have been considered. It has been shown that heterogeneous placement of americium leads to higher rates of its transmutation than homogeneous placement does.

CFD Modelling of the Fuel Reactor of a Chemical Loping Combustion Plant to Be Used with Biomethane

To realize a carbon negative power production technology, it is interesting the option of coupling a Chemical Loping Combustor to a gas turbine. The development of this technology foreseen in the project GTCLC-NEG has some technical barriers, the most important of which is the operation of the chemical looping combustor at high temperature and high pressure conditions. To overcome these limits CFD modeling can be performed to optimize the behavior of the combustor and its design process. This work models the FUEL reactor of a chemical looping combustion plant working in batch mode and based on the reactor available at the Instituto de Carboquimica in Zaragoza, Spain. It is used an oxygen carrier mainly based on 60% mass Fe2O3 and 40% mass Al2O3. Biomethane is fed to the bottom of the fluidized bed with different velocities and mass flows and the composition of the gases at the outlet of the fuel reactor is measured. The results show that it is possible to model a 2 min duration reduction cycle by running the model for a time comprised between a minimum of 4 h and a maximum of 2 days of simulation. Another important result is the modeling of the chemical reactions happening in the reactor. Kinetics is modelled based on Activation energy (66 kJ/mol) and Pre-exponential factor (4.34 × 101 m3n mol−n s−1). The simple kinetic scheme gives reasonable first approximations and can be used to determine the duration of the reaction, the composition of the exhaust gases and the biofuel conversion.

An attempt to describe the swelling of U3Si 2 fuel by a simple formula

Abstract Fuel swelling is a key parameter to be studied in the process of qualifying a fuel for use in reactors. Generally, test irradiations are performed to quantify the swelling. However, all reactor conditions can often not be simulated in tests. This situation occurs, for example, when a fuel shall be used in a new reactor where the fission rate is higher than in existing reactors available for the qualification tests. The swelling under the conditions of the new reactor must be predicted based on the data found under these test conditions. For this prediction a formula is required. Such a formula is derived for one of the most popular fuels for high flux reactors: U3Si2.

Finely Divided Metal as Nuclear Reactor Fuel

A new form for metallic nuclear reactor fuel is proposed consisting of finely divided particles (tens of micrometers) mixed with sodium for thermal bond. Fuel pins filled with this form of fuel would have greater fuel density than with solid slugs fabricated at 75% smear density. Greater fuel density reduces enrichment requirements for initial fuel loading. A larger surface-to-volume ratio allows more fission product gases and metallic fission products to diffuse out of fuel particles, resulting in less swelling, greater burnup before processing, and simple preliminary thermomechanical spent fuel processing steps that might be used several times before the more expensive pyroelectric process develolped for the Experimental Breeder Reactor II (EBR-II). Less frequent pyroelectric processing, simple preliminary processing, and a larger surface-to-volume ratio reduce total processing cost. Preliminary processing produces separate fission products, in particular cesium and strontium, in metallic rather than salt or mineral form, thereby simplifying and reducing storage cost. Intrinsically structurally weak fuel would not rupture fuel pin cladding by swelling. The expense and complexity of the process would be offset by reduced total system cost.

Effects of Temperature, Operation Mode, and Steam Concentration on Alkali Release in Chemical Looping Conversion of Biomass-Experimental Investigation in a 10 kWth Pilot.

Alkali release was studied in a 10 kWth chemical looping pilot operated with a Linz–Donawitz (LD) slag oxygen carrier (OC) and three biomass fuels. Experiments were performed at three temperatures and in three operation modes: chemical looping combustion (CLC), chemical looping gasification (CLG), and oxygen-carrier-aided combustion (OCAC). Gas-phase alkali release was measured with a surface ionization detector (SID). Fuel reactor (FR) gas-phase alkali emissions increased with the temperature. This occurred as a result of increased evaporation of KCl and enhanced decomposition of alkali salts during char conversion. Air reactor (AR) alkali emissions were lower than in the FR and independent of the operating temperature. In comparison of operating modes, CLC and CLG modes resulted in similar gas-phase alkali emissions due to the similar extent of char conversion. In contrast, operation of the reactor system in OCAC mode resulted in significantly lower levels of gas-phase alkalis. The difference in alkali emission was attributed to the steam-rich atmosphere of CLC. The effect of steam was further investigated in CLC and OCAC tests. Lowering steam concentrations in CLC operation resulted in lower gas-phase alkali emissions, while introducing steam to the FR during OCAC operation resulted in higher alkali emissions. It was concluded that steam likely enhances gas-phase K release through a reaction of K2CO3 within the fuel char with steam to produce KOH(g). Solid sampling and analysis for K content was used along with SID measurements to develop a K mass balance for the reactor system. Mass balance results for the straw pellet fuel tests showed that LD slag OC absorbs approximately 15–51% of fuel K, 2.2% of fuel K is released to the gas phase, and up to 3.4% of fuel K is captured in the AR fly ash. The residual 40–80% of fuel K was determined to leave the FR as K-rich fly ash.

Development of the Versatile Test Reactor Probabilistic Risk Assessment

The Versatile Test Reactor (VTR) is a fast spectrum test reactor currently being developed in the United States under the direction of the U.S. Department of Energy (DOE), Office of Nuclear Energy (DOE-NE). The mission of the VTR is to enable accelerated testing of advanced reactor fuels and materials required for advanced reactor technologies. The conceptual design of the 300-MW(thermal), sodium-cooled, metallic-fueled, pool-type fast reactor has been led by U.S. national laboratories in collaboration with General Electric-Hitachi and Bechtel National Inc. To facilitate risk-informed design and authorization activities during the conceptual development phase, a conceptual design probabilistic risk assessment (PRA) was performed for the VTR. This paper provides an overview of the development of the VTR conceptual design PRA, including key DOE and industry standards and the PRA analysis approach and structure. In addition, the results of the VTR conceptual design PRA are provided, which include its use within authorization documentation and design decisions, along with important lessons learned during the process. The work reported in the paper is the result of studies supporting a VTR conceptual design, cost, and schedule estimate for DOE-NE to make a decision on procurement. As such, it is preliminary.

Editorial: Reactor Fuels, Materials and Systems Under Extreme Environments

The safe and economical operation of any nuclear power system relies, to a great extent, on the success of the fuel and the materials of construction (Allen et al., 2010). Distinct from conventional power generation methods, a nuclear reactor is characterized by a harsh level of irradiation, very high operating temperature, and extremely corrosive environments. The behavior of fuels and materials as well as systems for fission reactors is thus complex due to the changes that the extreme environments generate on them. These kinds of changes may be seldom seen in other engineering disciplines, but this poses demanding requirements over reactor fuels, materials and systems. The design of reactor fuels, materials and systems subject to extreme environments is a major obstacle to enhancing reactor safety and economic performance of nuclear power systems. It is also essential in increasing innovation for current reactor operation improvement and future reactor design optimization. To address the challenges related to extreme reactor environments, the team of editors organizes the Research Topic "Reactor Fuels, Materials and Systems under Extreme Environments" in the journal Frontiers in Energy Research. Finally, 28 articles are collected, covering the theoretical, numerical and experimental studies on reactor fuels, materials and systems under extreme environments.