Commercial Reactor Research Articles

A Commercial Reactor Simulation for the Slurry-Phase Hydrocracking of Heavy Oil with a Mineral Catalyst Using Distillation Lumps and SARA-Based Kinetic Models

A Commercial Reactor Simulation for the Slurry-Phase Hydrocracking of Heavy Oil with a Mineral Catalyst Using Distillation Lumps and SARA-Based Kinetic Models

Human intrusion dose assessment for the safe disposal of radioactive spent resin mixed waste at disposal facilities

This study explores the feasibility of safely disposing of spent resin mixed waste from which pure beta emitters(14C, 3H) have been removed 95 % at near-surface disposal facilities and evaluates the radiation dose to the public in the event of human intrusion after the management period of the disposal site. The decommissioning of Wolsong Unit 1, Korea's first commercial heavy water reactor, marks a critical juncture in the field of nuclear energy, highlighting the imperative for advancements in the methodologies of decommissioning, decontamination, and stewardship of mixed spent resin radioactive waste. To this end, six human intrusion scenarios are examined, and a cross-validation is performed using GENII and RESRAD-ONSITE simulation codes to confirm that the public dose criterion of 1 mSv/y is not exceeded under any of the scenarios. This result suggests that the safe disposal of waste from which beta radionuclides have been removed is possible, carrying significant implications for waste management and environmental protection. Such assessments provide scientific evidence for establishing waste disposal strategies and can serve as foundational data for the sustainable utilization of nuclear energy.

Development of GeSn epitaxial films with strong direct bandgap luminescence in the mid-wave infrared region using a commercial chemical vapor deposition reactor

Germanium tin (GeSn) is a material of interest for electronic and photonic device applications, but its development and commercialization have been limited by material quality issues and lack of availability from epitaxy suppliers. In this paper, we report initial studies in optimizing GeSn films deposited on a Ge buffer layer grown on 200-mm diameter silicon (Si) substrates with an ASM Epsilon 2000 chemical vapor deposition reactor designed for commercial production. Using a single-step growth process, a Sn content up to 22% near the surface of a GeSn film was achieved due to the increase in Sn incorporation via strain relaxation. A two-step growth process resulted in a bilayer structure with a nearly 100% relaxation on the first layer, followed by a higher quality GeSn layer with 18% Sn as evident by a high photoluminescence intensity emitting in the mid-wave infrared region at 3.2 μm at 20 K.

Integrating 3DVAR and ANN for inversion optimization of physical models of fuel-assembly bowing

This study introduces a novel inversion optimization method for the core physical model of fuel-assembly bowing, integrating measurement data based on three-dimensional variational (3DVAR) data assimilation and artificial neural network (ANN) techniques. Recognizing the deviation between theoretical physical models and actual core conditions due to factors like uneven coolant distribution and fuel-assembly bowing, this work aims to enhance model reliability and simulation accuracy. By generating a dataset through random perturbation and employing ANN for training, the method establishes a relationship between the core physical model and model-simulated values corresponding to measurement data. The construction of the cost function, essential for optimizing the inversion process, is executed using 3DVAR. To verify its validity, the method is implemented, and an inversion optimization process is developed using our self-developed Bamboo-C code system. The optimization process, validated through application in a commercial pressurized water reactor (PWR) in a nuclear power plant (NPP) in China, demonstrates a significant reduction in the relative errors of power distribution, thus affirming the method’s efficacy in achieving a more realistic model of fuel-assembly bowing. The integration of measurement data into the optimization process addresses the critical need for accurate core physical models in nuclear engineering, offering a promising avenue for enhancing the safety and efficiency of nuclear reactor operations.

Development of a boron-containing reduced activation Ferritic-Martensitic (B-RAFM) steel

Steel will be an essential part of any commercial fusion reactor design. Applications in this area involve extreme conditions, imposing particular performance requirements, such as high operational temperature and creep resistance, and also a limitation on the elements that can be used due to the activation that occurs on interaction with irradiation. This work begins with a steel developed for conventional power plant applications, the IBN1 grade developed by IMPACT (a UK consortium of industrial and academic research organisations). This grade has shown excellent properties at high temperature due to high temperature-stable precipitate phases, but contains several elements that would become radiologically active to a degree that is incompatible with the required disposal routes after exposure to the fusion reactor environment. In this study, modifications of the composition are made to remove these elements, and thermodynamic modelling and experimental assessment of the phases that form are undertaken. In this, we have paid particular attention to the prediction of transformation temperatures (to understand if normalisation and tempering can be applied successfully) and the precipitates, to see if suitable phases that are likely to impart creep strength and other desirable properties would be formed. The modifications made include the removal of Nb, Mo, Ni, Co, Cu and Al from the starting alloy, and the substitution of Ta (intended to form carbides, replacing the effect of Nb). Modifications of the amount of retained elemental components, such as C, Mn and Cr, have been made with Thermo-Calc modelling, to ensure preservation of comparable phase transformation temperatures and microstructures. The predicted changes to the alloy are compared to the observations from experimental investigation, finding that tantalum can substitute for niobium in these systems and form similar carbides with similar distribution in the material, and that reduction of Cr to 8 wt% and increase of C to 0.12 wt% raises the Ae4 temperature to allow a high-temperature heat treatment without δ-ferrite formation. While assessment of the mechanical properties of this alloy would be required, the perspectives for these alloys to perform at high temperature that can be inferred from the microstructure are discussed.

Preliminary study of transuranic transmutation in a small modular chloride salt fast reactor

The management of radioactive waste poses a significant challenge to the sustainable development of nuclear energy. Efficient transmutation of nuclear wastes is crucial to minimize their accumulation. A small modular chloride salt fast reactor (sm-MCFR) capable of transmuting transuranic elements (TRU) is proposed in this paper, combining the advantages of the small modular reactor (SMR) and the molten salt reactor (MSR). The sm-MCFR is characterized by a high fuel loading and a compact core structure that can be quickly deployed around large commercial reactors to achieve TRU transmutation. To evaluate the TRU burnup capability of the sm-MCFR, several fuel salts and reprocessing modes were analyzed using the internally developed TRITON MODEC Coupled Burnup Code (TMCBurnup) tool. NaCl-MgCl3 with 98 % enrichment in 37Cl is chosen as carrier salt for the sm-MCFR, which can achieve 76.7 % TRU transmutation rate in average and 355 kg·GW−1·a−1 TRU transmutation quality at a continuous reprocessing rate of 10 L/d for 50 operation years. The optimized sm-MCFR reduced the radioactive toxicity of TRU by 84 %, thereby simplifying waste reprocessing. In addition, the sm-MCFR has a negative temperature feedback coefficient of −7.195 pcm/K, favoring safe reactor operation.

Efficient Electrochemical Reduction through Flow Cells Using Spherical-Polymer Based Carbon Supported Catalysts as Fixed-Bed Electrode

The transition to economically friendly feedstocks and the electrification of chemical synthesis reactions gained much attention in the recent years. To be able to compete with the conventional processes, it is crucial not only to concentrate on the electrochemical reactions itself but also to constantly improve the reactor concepts. A vast variety of designs are imaginable and already well-described – from a simple, undivided beaker cell setup to a divided flow cell with separate electrolytes at cathode and anode. [1] As electrode material not only flat metal electrodes are studied, but also the concept of using carbon supported metal nanoparticles is well-known to employ high dispersion to lower the total amount of required metal. [2,3] While there are already commercial flow reactors and electrodes available for electrosynthesis with flat standard electrodes, reactors using a fixed-bed of porous carbon with nanodispersed metals as electrode just recently started to attract attention. [4] Dealing with the pressure drop over the catalyst bed, while the electrical contact is still ensured, are key challenges for this reactor design. Spherical polymer-based carbons (SPBC) combine porous carbons properties with a high purity and especially spherical character. [5] While these advantages led already to commercial products for chromatographic applications (e.g. Carboxen®) the potential regarding flow-electrochemistry has not been leveraged. Key developments for this are reproducible synthesis procedures to deposit active metal on the SPBCs and the design of an electrochemical flow cell using these catalysts in a fixed-bed electrode configuration.The first part of this work presents the deposition of Cu through different impregnation and reduction procedures on a SPBC (Carboxen® 1032, 50 µm, Merck). The carbon was characterized by physisorption, TPD-MS, TPO, Raman and SEM. The resulting metal-impregnated carbon catalysts were additionally investigated regarding the metal loading. Using the applied impregnation and reduction parameters targeted metal loadings (3 – 20 wt%) could be well achieved. The second part focuses on the design and commissioning of a flow-cell for the application of the SPBC-supported catalysts as a fixed-bed at the cathode side. Electrochemical synthesis reactions are targeted in the cell and the reduction of 5-HMF to BHMF was chosen as the test reaction in this work. In the framework of the cell development multiple aspects not only regarding the construction but also reaction engineering issues had to be considered: material stability of the pump, fixation and pressure drop of catalyst bed, choice of electrolyte, effect of dissolved oxygen in the catholyte, optimal flow rate, reliable electrochemical protocol and selection of contact material. The latter has to be a compromise between chemical inertness and an enhanced electron transfer between the catalyst bed and the contact material (e.g. soft foil vs. hard metal). Figure 1A shows the current voltage characteristics of two possible contact materials (graphite foil, boron-doped diamond (BDD)) in the targeted electrolyte (0.5M borate buffer with 0.25M potassium chloride). Here, the graphite foil clearly shows a higher activity towards the hydrogen evolution reaction which may result in a less effective electrolysis later on. The comparison of BDD as contact material without and with a catalyst bed (Carboxen® 1032 loaded with 20 wt% Cu) resulted in a significant shift in the current voltage characteristic to lower overpotentials. Therefore, the electronic contact with the carbon bed is clearly enabled and the carbon spheres loaded with copper catalyze the reaction. Figure 1B presents the results of the test reaction with the conversion of the educt 5-HMF as well as the selectivity to the targeted product BHMF over the reaction time with BDD as contact material without and with a fixed bed of Cu/SPBC catalyst. The experiments prove full 5-HMF conversion within 23 h on stream in combination with a high selectivity towards BHMF with the catalyst bed. The mass-based productivity reaches values of up to 1.78 mmol h-1 gCu -1 and is therefore about 15 times higher compared to the use of conventional Cu foil (Pliterature = 0.11 mmol h-1 gCu -1 [6]). It is possible that due to the metal-support approach in the fixed-bed configuration, the copper is leveraged more efficiently and small amounts allow to provide sufficient metal surface area for the catalytic reaction.

Horizontal homing laser for high repetitive inertial fusion

For a commercial laser inertial fusion energy reactor, a highly repetitive operation in which many fuel pellets must be illuminated by laser spots. One of the most efficient ways to achieve this is to control the laser pointing by following fluctuations of the target position. The paper shows the precise control of laser pointing in the horizontal direction with a repetition rate of 10 Hz. Free-falling test pellets of 1 mm in diameter have been illuminated by a laser of 1.6 mm in diameter with cancellation of horizontal fluctuation over 4 mm. The difference in centroids between the laser spot and the illuminated test pellets is 86 μm (standard deviation). This corresponds to a 92% engagement within a 0.15 mm difference, which is a condition for successful nuclear fusions at the Hamamatsu facility. This is the proof-of-principle demonstration of the target-supply tracking and homing laser at a repetition rate of 10 Hz for the actualization of a commercial reactor.

Thermomechanical analysis of tungsten-copper joints for fusion applications using digital image correlation

The European DEMOnstration Fusion Power Plant DEMO represents a significant milestone in the progression towards sustainable fusion energy and a critical phase between ITER and commercial fusion reactors, aiming to demonstrate sustained net positive electricity production. Thanks to its properties, tungsten is a promising material for divertor armor. Coupled with copper alloys as heatsinks, they offer robust thermal management properties to deal with intense thermomechanical loads and irradiation damage. Understanding the thermomechanical behaviour of tungsten-copper joints during their application is then necessary for divertor design.This study presents experimental analysis on tungsten-copper brazed materials subjected to thermomechanical solicitations to simulate mono-block conditions with heat fluxes expected to reach 20 MW/m2 and so to face potential creep-fatigue failure. The experimental tests were coupled with Digital Image Correlation up to 400 °C to analyse the thermomechanical behaviour of these joints, providing insights into their thermal behaviour, structural integrity, damage accumulation, joint failure and identification of strains required for creep-fatigue assessment using design codes.

Optimization of lithium vapor box divertor evaporator location on NSTX-U using SOLPS-ITER

Commercial fusion reactors will be faced with extremely high divertor target heat fluxes that will require mitigation. Simulations of detachment in an NSTX-U scenario projected to have 92 MW m−2 unmitigated peak target heat flux are presented, which reaches sub-10 MW m−2 target heat flux using a highly dissipating lithium vapor box divertor design. The lithium vapor box is a detached divertor design which employs lithium vapor evaporation and condensation to contain lithium below the X-point. Previous SOLPS modeling has indicated a lithium vapor box can reduce the heat flux down to 10 MW m−2 via simultaneous evaporation from the Private Flux Region (PFR) and the Common Flux Region (CFR) sides of the vapor box. It is found here that PFR evaporation has improved access to the separatrix leading to significantly more efficient power dissipation than CFR evaporation. Simulations of target evaporation with an evaporation distribution that is self-consistent with the temperature of a Capillary Porous System with Fast flowing liquid lithium could reach nLi / ne∼ 0.025–0.030 at the Last Closed Flux Surface (LCFS) depending on the liquid metal flow speeds and lithium sputtering yield, while PFR-side evaporation can reach acceptable heat fluxes with nLi / ne∼ 0.038 at the LCFS. However, PFR evaporator performance can be improved if the target is allowed to be hot enough such that it reflects lithium, reaching nLi / ne∼ 0.028 and reducing required lithium evaporation. Ultimately PFR evaporation and target evaporation are found to have similar ability to produce acceptable heat flux solutions with minimal upstream concentration.

Evaluation of heat transfer conditions during polydisperse gas–solid flow in an industrial fluidised bed reactor

Knowledge of heat transfer conditions in large-scale circulating fluidised bed reactors plays an essential role in their proper design and optimization of theirs. This work presents an evaluation of the heat transfer conditions taking into account the coordinate height of the furnace chamber and the fluidised bed flow regime in the reactor. Experimental tests used method and measurement technique that provides reliable temperature data. The vertical and horizontal temperature profiles were obtained at different 966MWth fluidised bed reactor operating conditions. Four characteristic areas can be distinguished in the furnace chamber: the bottom region with a high-temperature gradient from 10.6 °C/m to 22.7 °C/m; the dense region with a medium temperature gradient from 4.7 °C/m to 7.3 °C/m; the dilute area with the lowest temperature gradient from 0.7 °C/m to 3.1 °C/m and the exit region with a temperature gradient (4.3 °C ≤ grad T ≤ 9.6 °C) similar to dense region. The horizontal temperature profiles confirmed a core-annular flow structure inside the furnace chamber. At the pressure drop below 5 kPa, the low variation of average temperature (from ±0.7 °C to ±4.2 °C) inside the furnace chamber of the CFB reactor was observed. As a result of fly ash recirculation of 3.86 kg/s, the lowest temperature gradient 0.2 °C/m was achieved in the bottom region of the furnace chamber. In the range of bed material circulation rates of 32 to 68 were registered temperature fluctuations 115 °C. The experimental results also showed the variation of the bed temperature was small and kept at a very low level of ±13 °C whereas the fluidised bed reactor was operated with a fluidisation velocity range of 1.8 to 2.4. Obtained findings provide unique data on heat transfer conditions in industrial facilities and thus fill the gap in literature data for CFB reactors. Based on main tests carried out in a large-scale CFB reactor, it can be concluded that detailed experimental data on thermal conditions provide important information to validate guidelines and for verifying empirical relationships, which are used in the design, optimization, and scaling of heat transfer surfaces in commercial fluidised bed reactors.

Selective electrochemical oxidation of organic compounds in a mass transfer-enhanced electrochemical flow reactor (e[sbnd]NETmix)

eNETmix stands as an electrochemical flow reactor engineered to enhance mass transfer. This study aimed at assessing the performance of the eNETmix reactor in the realm of organic electrosynthesis. Specifically, the research focused on the selective electrochemical oxidation of 4-methoxybenzyl alcohol (4-MBA) to p-anisaldehyde (PAA) using a bare fluorine-doped tin oxide (FTO) anode. The efficiency of the process was assessed for distinct current densities (j), Reynolds numbers (Re), supporting electrolyte contents, and substrate initial contents. The eNETmix reactor was extensively compared to a commercial electrochemical flow reactor (MicroFlowCell from ElectroCell, Denmark). eNETmix facilitated the use of a broader range of j (0.8–2.0 mA cm−2versus 0.8 mA cm−2) together with smaller Re (≥190 versus >1750), supporting electrolyte contents (≥1 mM versus ≥30 mM), and substrate initial contents (≥2.0 mM versus ≥3.0 mM) with no loss of PAA production or energy consumption. These findings underscore a remarkable suitability of eNETmix as a reactor for organic electrosynthesis.

Biocarbon Production Using Three-Stage Pyrolysis and Its Preliminary Suitability to the Iron and Steel Industry

There has been a rising interest in the iron and steel industry in replacing fossil-based carbon carriers in their processes because they are the main origin of the anthropogenic carbon emissions within the industry. The use of bio-based carbon carriers could be one solution to partly tackle this challenge. Conventionally, biocarbon is produced by pyrolysis with fixed heating rate, pyrolysis temperature, and retention time. Although the mechanisms behind the formation of biocarbon and the decomposition temperatures of the main compounds of biomass-based materials are known, this knowledge is rarely being utilized in the design of commercial pyrolysis reactors, even though the pyrolysis mechanism-based approach increases the biocarbon yield. In this study, the mechanistic pathway of carbonization of lignocellulosic biomass is taken into account to produce biocarbon with higher yield and quality than conventional pyrolysis with the same process time. Results show that when the process time is the same in both methods, segmented pyrolysis increases biocarbon yield up to 5.4% within a pyrolysis temperature range from 300 °C to 900 °C. Also, fixed carbon yield increased 1.5% in this temperature area. When using segmented pyrolysis, the most suitable pyrolysis temperature is 700 °C based on the characteristics of the produced biocarbon.

Reactor neutrino background in next-generation dark matter detectors

Third-generation dark matter detectors will be fully sensitive to the B8 solar neutrino flux. Because of this, the characterization of such a background has been the subject of extensive analyses over the last few years. In contrast, little is known about the impact of reactor neutrinos. In this paper, we report on the implications of such a flux for dark matter direct-detection searches. We consider five potential detector deployment sites envisioned by the recently established XLZD Consortium: SURF, SNOLAB, Kamioka, LNGS, and Boulby. By using public reactor data, we construct five reactor clusters—involving about 100 currently operating commercial nuclear reactors each—and determine the net neutrino flux at each detector site. Assuming a xenon-based detector and a 50 ton-year exposure, we show that in all cases the neutrino event rate may be sizable, depending on energy recoil thresholds. Of all possible detector sites, SURF and LNGS are those with the smallest reactor neutrino background. On the contrary, SNOLAB and Boulby are subject to the strongest reactor neutrino fluxes, with Kamioka being subject to a more moderate background. Our findings demonstrate that reactor neutrino fluxes should be taken into account in the next round of dark matter searches. We argue that this background may be particularly relevant for directional detectors, provided they meet the requirements we have employed in this analysis. Published by the American Physical Society 2024

Machine Learning Based Compton Suppression for Nuclear Fusion Plasma Diagnostics

Diagnostics are critical on the path to commercial fusion reactors, since measurements and characterisation of the plasma is important for sustaining fusion reactions. Gamma spectroscopy is commonly used to provide information about the neutron energy spectrum from activation analysis, which can be used to calculate the neutron flux and fusion power. The detection limits for measuring nuclear dosimetry reactions used in such diagnostics are fundamentally related to Compton scattering events making up a background continuum in measured spectra. This background lies in the same energy region as peaks from low-energy gamma rays, leading to detection and characterisation limitations. This paper presents a digital machine learning Compton suppression algorithm (MLCSA), that uses state-of-the-art machine learning techniques to perform pulse shape discrimination for high purity germanium (HPGe) detectors. The MLCSA identifies key features of individual pulses to differentiate between those that are generated from photopeaks and Compton scatter events. Compton events are then rejected, reducing the low energy background. This novel suppression algorithm improves gamma spectroscopy results by lowering minimum detectable activity (MDA) limits and thus reducing the measurement time required to reach the desired detection limit. In this paper, the performance of the MLCSA is demonstrated using an HPGe detector, with a gamma spectrum containing americium-241 (Am-241) and cobalt-60 (Co-60). The MDA of Am-241 improved by 51% and the signal to background ratio improved by 49%, while the Co-60 peaks were partially preserved (reduced by 78%). The MLCSA requires no modelling of the specific detector and so has the potential to be detector agnostic, meaning the technique could be applied to a variety of detector types and applications.

Utility of argon as a static charge and wall fouling suppressant in atmospheric gas-solid fluidized beds

This work aimed to study the usability of argon to mitigate electrostatic charging and fouling of polyethylene resin fluidized in a stainless-steel column. Nitrogen, argon, and their binary mixtures of various concentrations were utilized to fluidize polyethylene. Successive and intermittent fluidizations with argon and nitrogen were also carried out to explore the feasibility of using argon in commercial reactors. Fluidization with pure argon resulted in the lowest specific charge and substantially reduced the fouling by 90% relative to pure nitrogen. The results for the mixture trials showed a decreasing non-linear trend as the concentration of argon increased. Even presence of 10 vol% argon in the mixture reduced the wall fouling by 50%. Successive and intermittent fluidization also yielded fouling and specific charge values comparable to pure argon. The results are attributed to argon's relatively low dielectric strength and subsequent localized gas discharge within the particle-dense section of the bed.

Core Optimization for Extending the Graphite Irradiation Lifespan in a Small Modular Thorium-Based Molten Salt Reactor

The lifespan of core graphite under neutron irradiation in a commercial molten salt reactor (MSR) has an important influence on its economy. Flattening the fast neutron flux (≥0.05 MeV) distribution in the core is the main method to extend the graphite irradiation lifespan. In this paper, the effects of the key parameters of MSRs on fast neutron flux distribution, including volume fraction (VF) of fuel salt, pitch of hexagonal fuel assembly, core zoning, and layout of control rod assemblies, were studied. The fast neutron flux distribution in a regular hexagon fuel assembly was first analyzed by varying VF and pitch. It was demonstrated that changing VF is more effective in reducing the fast neutron flux in both global and local graphite blocks. Flattening the fast neutron flux distribution of a commercial MSR core was then carried out by zoning the core into two regions under different VFs. Considering both the fast neutron flux distribution and burnup depth, an optimized core was obtained. The fast neutron flux distribution of the optimized core was further flattened by the rational arrangement of control rod channels. The calculation results show that the final optimized core could reduce the maximum fast neutron flux of the graphite blocks by about 30% and result in a more negative temperature reactivity coefficient, while slightly decreasing the burnup and maintaining a fully acceptable core temperature distribution.

R&D in advanced technology fuels (ATFs) in Spain

Accident Tolerant Fuels, also known as Advanced Technology Fuels (ATFs), have the potential to improve the safety and economic performance of commercial nuclear reactors as well as to provide additional operational flexibility for responding to variations in system energy demand.The design, fabrication and in-pile behaviour of currently operating and innovative nuclear fuels to enable a reliable and safe operation of nuclear power plants is a priority for the nuclear industry. The Spanish nuclear professionals (public and private companies, academia, and research centres) have achieved significant advances in this area. Both irradiation programs in commercial reactors, along with experimental and modelling activities, were focused into comprehending and modelling different ATF concepts to understand and predict the behaviour under normal and off-normal conditions.The International Atomic Energy Agency (IAEA) sub-program “Nuclear Power Reactor Fuel Engineering” is strongly involved in the development and validation of computer codes for ATF fuel design and the valuable Spanish contribution to this sub-program is described in this article.The future Spanish R&D in this field is expected to be focused on further improvements on ATF product development and performance knowledge.

Engine performance and emissions from a fumigated hydrogen/ammonia compression ignition engine with a hydrogen peroxide pilot

The study investigates, numerically, the potential use of introducing aqueous H2O2 as an ignition promoter in a statistically homogeneous NH3/H2 fuelled, medium speed (1250 rpm), 4-stroke, 1.3 litre cylinder displacement, mildly boosted CI engine with a compression ratio of 17.6:1. The H2 is considered to be produced on-board from ammonia cracking. An extensive campaign is undertaken using the commercial stochastic reactor model, SRM Engine Suite, which allowed the modelling of temporal, temperature and spatial stratification in the cylinder. The engine performance, combustion phasing, maximum pressure rise rate and emissions (NOx, N2O and unreacted NH3) are investigated in view of: (i) the share of molecular hydrogen in the initial NH3/H2 mixture from 10 to 40 percent; (ii) the mass of aqueous H2O2 introduced from 0.1 to 16 mg; (iii) the start of injection (−10 to ＋6 CAD aTDC) and duration of injection (1, 4 and 8 CAD); (iv) the amount of exhaust gas recirculation (up to 30 percent by mass); (v) the share of energy from the H2O2 in the aqueous solution mixture at less than 0.5 percent of that in the main fuel; (vi) engine load corresponding to a variation in the equivalence ratio from 0.32 to 1.2 by changing the mass of the NH3/H2 mixture in the combustion chamber. A wide range of loads (evaluated against the engine’s rated power when operated with diesel and at its rated boost levels) can be achieved (44%–93%) with the energy share of H2O2 being as little as equivalent to 2.7% vol% that of the main fuel, ammonia, which is introduced into the cylinder. This implies that the required storage volume of the H2O2 is low, at a few percent that of the main ammonia tank. NOx emissions peak between ϕ=0.6−0.65 and rapidly decrease as the equivalence ratio increases or decreases reaching values marginally above the Tier III standard at high loads (>90%) while ammonia slip and N2O emissions are generally extremely low (10−12 mg for NH3 and < 0.01 mg/kWh for N2O).

Evaluating Material Attractiveness of Minor Actinide Nuclear Fuel Intended for a Waste Transmutation Lead-Cooled Fast Reactor

Long-lived high-level waste from commercial nuclear power reactors is a problem that concerns stakeholders and scientists working in the back end of the nuclear fuel cycle. Nuclear waste transmutation is under investigation to tackle this problem, transforming nuclides that represent a long-term source of radioactivity, radiotoxicity, and heat into short-lived or stable nuclides. However, the transmutation process will require that several long-lived isotopes be separated from the spent nuclear fuel, which raises proliferation concerns. In this paper, we perform an investigation of the attractiveness characteristics related to the material used in a lead-cooled fast reactor system concept designed to burn minor actinides before and after irradiation. The materials evaluated are separated uranium, neptunium, plutonium, americium, and curium. We also evaluated grouped product materials, neptunium + americium and neptunium + plutonium. Additionally, we present potential safeguards and physical protection implications for the proposed materials. The main conclusion of this paper is that the separated neptunium and plutonium generated by the fast reactor are materials that deserve attention mainly related to physical protection measures.