Conceptual design of long-cycle boron-free small modular pressurized water reactor with control rod operation

This paper presents a new conceptual design of soluble-boron-free small modular pressurized water reactor (SMPWR) core with the following singular features: long operation cycle, axially heterogeneous adjuster control rods, and ring-type burnable absorbers (R-BAs) coated on the outside of cladding materials. The core loads 37 Westinghouse-type 17 × 17 fuel assemblies (FAs) of active fuel height 200 cm and produces 180 MW of nominal thermal power during a cycle length of 1555 effective full power days (EFPDs). Three types of burnable absorbers (BAs) are used to address the excess reactivity and obtain a long cycle: 2 w/o and 8 w/o enriched Gd₂O₃ integral-type BA (IBA), natural gadolinium R-BA, and 80 w/o enriched ¹⁰B Al₂O₃/B₄C wet annular burnable absorber (WABA). Two types of 200 cm long axially heterogeneous adjuster control rods are used to control the reactivity and the offset in axial power distribution. The first rod type adopts HfB₂ with 80 w/o enriched ¹⁰B for the bottom 140 cm and stainless steel for the top 60 cm. The second rod type uses HfB₂ (natural boron) for the bottom 100 cm and HfB₂ (80 w/o enriched ¹⁰B) for the top 100 cm. A detailed safety parameter analysis is conducted to verify the imposed design limits, namely, axial shape index of less than ±0.4, 3D power peaking factor of smaller than 5.09, required shutdown margin of greater than 3000 pcm, and negative isothermal temperature coefficient during the entire reactor operation. It is successfully demonstrated that the proposed novel SMPWR design satisfies all the design limits and the target cycle length of 1500 EFPDs.     

Conceptual core design study of an innovative small transportable lead‐bismuth cooled fast reactor (SPARK) for remote power supply

An innovative small transportable lead‐bismuth cooled fast reactor, named SPARK, with rated power of 20 MWth is proposed to operate for 20 years without refueling as a remote power supply. The SPARK core neutronics and thermal‐hydraulics design and preliminary safety analysis were performed in the current study. In order to achieve a compact and light‐weight core design with enhanced transportability and passive safety, the selection of reflector materials, the optimization of fuel assembly design and radial core zoning loading, and the reactivity control system design were accomplished. MgO was selected as the optimal reflector material due to its good neutron reflecting characteristics and low density. The fuel assembly design was optimized to obtain a long lifetime of core and low peak cladding surface temperature. To flatten radial power distribution, 3 radial zones were designed with different fuel pin diameters. A liquid absorber control system was implemented using ⁶Li‐enriched liquid lithium as the neutron absorber, which significantly reduces the core height. To reduce the initial excess reactivity, fixed absorbers were installed in the scram assemblies for the first half life and then replaced by fixed reflectors for the second half life. Based on the parametric study, the optimized core design was determined, and the core neutronics and thermal‐hydraulics performances were evaluated. The objective core lifetime of 18 effective full power years was fulfilled with the compact and light‐weight core design, and the thermal design constraints were satisfied during the whole life. Both the control and scram systems proved to independently provide sufficient shutdown margins. Using the quasi‐static reactivity balance method, the passive safety characteristics of the optimized core design were analyzed based on 5 anticipated transients without scram. Passive shutdown was achieved due to the negative reactivity feedback. The critical design constraint of the peak cladding surface temperature was satisfied for all transients.     

Neutronics optimization and characterization of a long‐life SCO2‐cooled micro modular reactor

This paper presents a neutronics optimization study of a supercritical CO₂‐cooled micro modular reactor (MMR). The MMR is a fast‐spectrum reactor designed to be an extremely compact, integrated, and truck‐transportable reactor with 36.2‐MWth power and a 20‐year lifetime without refueling. The reactor uses a drum‐type primary control system and a single absorber rod located at the core center as the secondary ultimate shutdown system. In order to maximize the fuel inventory in a compact fast reactor, hexagonal fuel assemblies are adopted in this work. We compare two types of MMR: One is using U¹⁵N fuel, and the other one is based on UC fuel. In addition, the minimization of the core excess reactivity to less than 1 dollar is also achieved in this study by a unique application of a replaceable fixed absorber in order to enhance safety of the MMR core by preventing the possibility of a prompt criticality accident. Moreover, the required number of primary control drums is also reduced through minimization of the excess reactivity. Several important safety parameters such as control rod/drum worth, reactivity coefficients, and power peaking factors are also characterized as a function of core burnup. The neutronics analyses and depletion calculations are all performed using the continuous‐energy Monte Carlo Serpent code with the latest evaluated nuclear data file (ENDF/B‐VII.1) library. Copyright © 2016 John Wiley & Sons, Ltd.     

Preliminary design of a medium‐power modular lead‐cooled fast reactor with the application of optimization methods

Based on research and development experience from Gen III, Gen III+, and Gen IV reactor concepts, a 1000‐MWt medium‐power modular lead‐cooled fast reactor M²LFR‐1000 was developed by University of Science and Technology of China (USTC), aiming at achieving a reactor design fulfilling the Gen IV nuclear system requirements and meanwhile emphasizing application of optimization methods in preliminary design phase. By using the optimization methods presented, primarily considering the safety design limits (the maximum coolant velocity, the maximum cladding temperature, and the maximum burn‐up limited by the cladding radiation damage permitted), the preliminary design of 1000‐MWth medium‐power modular lead‐cooled fast reactor M²LFR‐1000 was carried out, including the design of fuel rods, fuel assemblies, reactivity control system, primary system, secondary system, decay heat removal system, and so on. The analysis of neutron characteristics (including reactivity feedback coefficients) and thermal hydraulics characteristics (the maximum fuel temperature and the maximum cladding outer surface temperature) of the core under normal steady‐state condition was carried out to evaluate the core design. Also, the analysis of 2 typical protected transients (protected transient over power accident and protected loss of flow accident) was conducted. Other analysis work of the reactor is to be done, such as the transient analysis via computational fluid dynamic codes and the seismic response analysis of the reactor. But the preliminary analysis results obtained so far under normal steady state and transient conditions confirm the inherent safety characteristics of the reactor design.     

Fabrication of oxide pellets containing lumped Gd2O3 using Y2O3‐stabilized ZrO2 for burnable absorber fuel applications

In this paper, the fabrication of novel burnable absorber fuel concepts with oxide pellets, containing either a lumped Gd₂O₃ rod, a mini‐pellet, or a spherical particle in the centerline of the oxide pellet, is investigated to propose the lumped Gd₂O₃ burnable absorber fuel concept to improve nuclear fuel performance with longer fuel cycle lengths and better fuel utilization. The unique characteristic of the lumped Gd₂O₃ burnable absorber fuel is its high spatial self‐shielding factor that reduces its burnout rate and, therefore, improves the reactivity control. Oxide pellets containing lumped Gd₂O₃ were fabricated by using a combination of cold isostatic pressing and microwave sintering at 1500°C to understand the potential technical issues in the fabrication of duplex burnable absorber fuel. The effect of the sintering temperature on the densification and phase transformation of 8 wt.% yttria‐stabilized zirconia, a surrogate for UO₂, was investigated. Spherical Gd₂O₃ particles were fabricated by the drip casting of a Gd₂O₃‐based Na alginate solution. The fabrication of duplex oxide pellets by using presintered Gd₂O₃ mini‐pellets resulted in internal cracks at the interface between the Gd₂O₃ and 8 wt.% yttria‐stabilized zirconia layers because of the mismatch of their densification. However, the formation of interfacial cracks was eliminated by controlling the initial sintered density of the lumped Gd₂O₃.     

Impacts of an ATF cladding on neutronic performances of the soluble-boron-free ATOM core

This article is mainly concerned with the impacts of various accident tolerant fuel (ATF) claddings on neutronics performances of a soluble-boron-free (SBF) small modular reactor (SMR) core. There are two ATF cladding concepts which are evaluated here: (a) coating Zircaloy-4 cladding with a thin layer of Cr or Cr alloys; (b) high-strength and oxidation-resistant claddings: stainless steel and FeCrAl. Comparisons between Zircaloy-4 and ATF claddings are done in terms of the cycle length, discharge burnup, pin peaking factor (PPF), burnup reactivity, and spectral change. Moreover, the ATF claddings are also compared in view of the rim effect, neutron absorption by the cladding and He production in the cladding. In addition, a linear reactivity model is used to estimate the required U-235 enrichment so that the cycle length with ATF claddings should be equivalent to that with the reference Zircaloy-4 case. Furthermore, impacts of a selected ATF cladding are then analyzed in a centrally shielded burnable absorber (CSBA)-loaded FA in terms of PPF, burnup reactivity, and spectral change. Based on the CSBA-loaded FA analysis, a minor modification of burnable absorber loading strategy in the SBF autonomous transportable on-demand reactor module core is proposed to adopt the selected ATF cladding without compromising the core performance. The lattice calculations are done using the Monte Carlo Serpent 2 code with the ENDF/B-VII.1 nuclear library, while the 3-D multi-physics core calculations are performed using a Monte Carlo-diffusion hybrid procedure.     

Neutronic/thermal‐hydraulic design features of an improved lead‐bismuth cooled small modular fast reactor

Lead‐based fast reactors (LFRs) have unique advantages in the development of a SMR, which has attracted a lot of attention in recent years. In this paper, an optimized design for a lead‐bismuth small modular reactor was studied on the basis of the design of SUPERSTAR. This paper aims to propose an improved LFR core scheme to enhance the neutronic performance as well as the thermal‐hydraulic safety of the reference reactor. Advanced nitride fuel is adopted in which the plutonium is used as the driven fuel, while thorium is used as the fertile fuel. Subchannel analysis was performed in the assembly design using an in‐house subchannel code, SUBAS, and an 11 × 11 scheme with a pitch‐to‐diameter (P/D) ratio of 1.4 was chosen. Using the modified assembly, the core was redesigned using the coupled code MCORE. The active core was divided into four zones with different enrichment of ²³⁹Pu to extend the core lifetime and flatten the power distribution. The main kinetic parameters and reactivity coefficients were obtained. Neutronic performance at different operation times was also studied. The maximum radial power peak factor was 1.28, while the maximum total power peak factor was 1.737. During the whole lifetime, the reactivity swing was 0.926$, which was below the limit of 1$. The subchannel study of the core flow distribution showed that a flow distributor is needed to further improve the flow distribution capability. The peaking cladding temperature was 508.7°C, and the maximum fuel center temperature was 723.4°C, both of which do not exceed the limit temperature. Compared with features of SUPERSTAR, the peaking cladding temperature was well improved and the lifetime extended.     

Environmentally friendly application of hydrides to nuclear reactor cores

Abstract

As new environmentally friendly techniques, hydride materials have been proposed to be introduced to fast reactor (FR) cores in this paper. Hydrogen atoms in metal hydride can efficiently moderate fast neutrons. Based on this fact, some metal hydrides have been investigated for their potential environmentally friendly application as nuclear materials to be used in FR cores. Two types of utilisation of metal hydrides in FR cores are discussed in this paper. One is the application of hafnium hydride as neutron absorber in FR cores. The core design has been carried out to examine its characteristics as well as to evaluate the cost reduction effect. Demonstration of the fabrication of hydride pins has been performed using hydride pellets and stainless steel claddings. The coating technique of the inner cladding surface has also been developed to reduce the permeation of hydrogen through the stainless steel cladding. The physical and chemical properties of the pellet have been measured for the purpose of designing a hafnium hydride pin. Irradiation test of the hydride pins has been performed in the experimental FR, JOYO, Japan Atomic Energy Agency. The other application is the utilisation as a transmutation target of long lived nuclear wastes. Hydride fuel containing ²³⁷Np, ²⁴¹Am and ²⁴³Am has been studied for a candidate transmutation target to be used to reduce the radioactivity of long lived nuclides contained in the nuclear wastes, which are obtained after reprocessing spent fuels.     

Core design of long‐cycle small modular lead‐cooled fast reactor

A core design of small modular liquid‐metal fast reactor (SMLFR) cooled by lead‐bismuth eutectic (LBE) was developed for power reactors. The main design constraint on this reactor is a size constraint: The core needs to be small enough so that (1) it can be transported in a spent nuclear fuel (SNF) cask to meet the electricity demands in remote areas and off‐grid locations or so that (2) it can be used as a power source on board of nuclear icebreaker ships. To satisfy this design requirement, the active core of the reactor is 1 m in height and 1.45 m in diameter. The reactor is fueled with natural and 13.86% low‐enriched uranium nitride (UN), as determined through an optimization study. The reactor was designed to achieve a thermal power of 37.5 MW with an assumption of 40% thermal efficiency by employing an advanced energy conversion system based on supercritical carbon dioxide (S‐CO₂) as working fluid, in which the Brayton cycle can achieve higher conversion efficiencies and lower costs compared to the Rankine cycle. The outer region of the core with low‐enriched uranium (LEU) performs the function of core ignition. The center region plays the role of a breeding blanket to increase the core lifetime for long cycle operation. The core working fluid inlet and outlet temperatures are 300°C and 422°C, respectively. The primary coolant circulation is driven by an electromagnetic pump. Core performance characteristics were analyzed for isotopic inventory, criticality, radial and axial power profiles, shutdown margins (SDM), reactivity feedback coefficients, and integral reactivity parameters of the quasi‐static reactivity balance. It is confirmed through depletion calculations with the fast reactor analysis code system Argonne Reactor Computation (ARC) that the designed reactor can be operated for 30 years without refueling. Preliminary thermal‐hydraulic analysis at normal operation is also performed and confirms that the fuel and cladding temperatures are within normal operation range. The safety analysis performed with the ARC code system and the UNIST Monte Carlo code MCS shows that the conceptual core is favorable in terms of self‐controllability, which is the first step towards inherent safety.     

Experimental study on sulfur trioxide decomposition in a volumetric solar receiver–reactor

Process conditions for the direct solar decomposition of sulfur trioxide have been investigated and optimized by using a receiver–reactor in a solar furnace. This decomposition reaction is a key step to couple concentrated solar radiation or solar high‐temperature heat into promising sulfur‐based thermochemical cycles for solar production of hydrogen from water. After proof‐of‐principle a modified design of the reactor was applied. A separated chamber for the evaporation of the sulfuric acid, which is the precursor of sulfur trioxide in the mentioned thermochemical cycles, a higher mass flow of reactants, an independent control and optimization of the decomposition reactor were possible. Higher mass flows of the reactants improve the reactor efficiency because energy losses are almost independent of the mass flow due to the predominant contribution of re‐radiation losses. The influence of absorber temperature, mass flow, reactant initial concentration, acid concentration, and residence time on sulfur trioxide conversion and reactor efficiency has been investigated systematically. The experimental investigation was accompanied by energy balancing of the reactor for typical operational points. The absorber temperature turned out to be the most important parameter with respect to both conversion and efficiency. When the reactor was applied for solar sulfur trioxide decomposition only, reactor efficiencies of up to 40% were achieved at average absorber temperature well below 1000°C. High conversions almost up to the maximum achievable conversion determined by thermodynamic equilibrium were achieved. As the re‐radiation of the absorber is the main contribution to energy losses of the reactor, a cavity design is predicted to be the preferable way to further raise the efficiency. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermal‐hydraulic design and analysis of a small modular molten salt reactor (MSR) with solid fuel

A 20 MWth, 540 EFPD once through fuel cycle small modular molten salt reactor with solid fuel is proposed by Massachusetts Institute of Technology for off‐grid applications. In this paper, various thermal‐hydraulic analysis methods including computational fluid dynamics, Reactor Excursion Leak Analysis Program (RELAP5), and DAKOTA are adopted step‐by‐step for the reactor design based on the neutronic analysis results. First, 1/12th full core thermal hydraulic analysis is performed by using STAR CCM⁺ with most conservative considerations. Second, the transient safety behaviors of reactor system with risky assumptions are conducted by using REALP5. Finally, due to the unknown factors affecting reactor thermal‐hydraulic characteristics, the uncertainty quantification and sensitivity analysis for the designed reactor is performed with DAKOTA code coupled with RELAP5. Numerical results show that a more uniform temperature distribution with reduced peak temperatures of fuel and coolant across the reactor core has been achieved. Enough safety margin is maintained even under most severe transient accident. The uncertainties in the heat transfer coefficient and helium gap conductivity factor are the most remarkable contributors to the statistical results of peaking fuel temperature. All above results preliminarily indicate the feasibility of the current small modular molten salt reactor design and provide the further optimization direction from reactor thermal‐hydraulic prospective.     

Hydrogen storage materials for hydrogen and energy carriers

Hydrogen storage technology is essentially necessary to promote renewable energy. Many kinds of hydrogen storage materials, which are hydrogen storage alloys, inorganic chemical hydrides, carbon materials and liquid hydrides have been studied. In those materials, ammonia (NH₃) is easily liquefied by compression at 1 MPa and 298 K, and has a highest volumetric hydrogen density of 10.7 kg H₂/100 L. It also has a high gravimetric hydrogen density of 17.8 wt%. The theoretical hydrogen conversion efficiency is about 90%. NH₃ is burnable without emission of CO₂ and has advantages as hydrogen and energy carriers.     

A review on growth optimization of spray pyrolyzed Cu2ZnSnS4 chalcogenide absorber thin film

The progress of solar cell technology in the development of clean and economic quaternary compound copper zinc tin sulfide (CZTS)‐based absorber thin films using the spray pyrolysis technique are presented in this review. CZTS (Cu₂ZnSnS₄) is the only potential competitor for the existing solar thin film absorbing materials owing to its environment‐friendly Earth abundant constituents. Even though different nonvacuum thin film technologies have been developed for the large area fabrication of this nontoxic absorber material, spray pyrolysis technique offers more versatility in changing the process parameters which has a direct impact on the cell efficiency. It can be used for depositing a wide variety of materials even with complex composition with good crystallinity, and the method has the advantage of being flexible and straightforward to design and can be quickly adopted for extensive area deposition. A survey on the effects of experimental conditions as well as the nature of precursors on the structural, morphological, electrical, and optical properties on the spray pyrolyzed CZTS thin films is discussed in detail. This analysis certainly could provide a potential to obtain new insights in the fabrication of high‐efficiency CZTS‐based solar cells and to launch it into the commercial market to satisfy the ever‐growing future energy demand.     

CZTS based thin film solar cells: a status review

Abstract

Today’s thin film photovoltaic technologies comprising CuInS₂ (CIS), CuInGaSe₂ (CIGS) and CdTe rely on elements that are costly and rare in the earth’s crust (e.g. In, Ga, Te) and are toxic (e.g. Cd). Hence, in future cost reduction and increased production, using abundantly available non-toxic elements, seem to be the main issues. Cu₂ZnSnS₄ (CZTS), having the kesterite structure, is one of the most promising absorber layer candidates for low cost thin film solar cells, because of its suitable direct band gap between 1·4 and 1·5 eV and large absorption coefficient, over 10⁴ cm^?1. Also it is composed of earth abundant and non-toxic elements, promising price reductions in future. Recently, research in this area has gained momentum due to the desirability of producing Ga, In and Cd free absorber layers and the potential to obtain new insights. Hence, a review of recent literature is urgently warranted. The CZTS progress and present status of CZTS thin film solar cells has been reviewed, with the hope of identifying new paths for productive research.     

Evaporated copper sulphide layers for all-vacuum evaporated CuxS/CdS solar cells

Copper sulphide layers have been prepared by vacuum evaporation from a single Cu_xS source, as an alternative to the chemiplating technique for fabricating the upper Cu_xS layer in Cu_xS/CdS solar cells. Deposition rates of less that 150 Å/min have been shown to produce Cu_xS layers with chalcocite being the major phase. Higher deposition rates increase the copper content of the layer which dominates its optoelectrical properties. Layers free from excess copper have a chalcocite-related phase transition between 75 and 80°C, room temperature resistivity between 10⁻² and 10⁻³ Ω cm and evidence of direct and indirect band gaps of 2.25 and 1.25 eV, respectively. With well controlled evaporation conditions the layers deposited on hot CdS thin film substrates are found to have highly reproducible characteristics, and are well suited for use as the absorber for the Cu_xS/CdS solar cell. Open-circuit voltages up to 0.58 V have been produced in cells with efficiencies in excess of 7%.     

Theoretical analysis of the thermal performance of all-glass evacuated tube solar collectors with absorber coating on the outside or inside of the inner tube

Theoretical efficiencies (η) and thermal behaviour of all-glass Evacuated Tube solar Collectors with an Internal Absorber Film (ETCIAF), i.e. the absorber film deposited in the inner surface of the inner tube, are compared and contrasted with the traditional design of all-glass Evacuated Tube solar Collectors with an External Absorber Film (ETCEAF), using the absorber film on the external surface of the inner tube. The values of η of the ETCIAF are unacceptably lower than that of ETCEAF for any particular value of the heat transfer coefficient (h_b) for the annular space, except in the case of a highly leaky ETCEAF, with h_b > 2.6 W/m² K. However, it is shown that the use of a transparent conductive coating with moderately low emittance 0.1−0.25 on the outside of the absorber tube of ETCIAF can offer efficiences 0.75−0.63, respectively, for f = 0.1 °C m²/K, competing well (η = 0.76) with the ETCEAF design operating under best conditions (α = 0.91, = 0.05, and h_b = 0.026 W/m² K).     

Hydrogen Storage in the Form of Methylcyclohexane

Abstract

The use of compounds, such as toluene, that can store hydrogen with a specific volume of 46 kgH₂/m³ in the form of methylcyclohexane, has been already shown to be potentially feasible for both mobile and stationary applications. Thus, produced hydrogen by the dehydrogenation of methylcyclohexane to toluene could be a very attractive option to be adopted for these applications. In this study, dehydrogenation of methylcyclohexane reaction for hydrogen production was investigated. The catalytic experiments were made in a tubular pyrex glass fixed bed reactor. The experiments were performed between 380°C and 440°C under the total pressure of about 1 atm with a Pt/Re/Al₂O₃ (sulfided) catalyst (UOP) (UK). Power law rate models were tested for the experimental data. r = k.P^m _MCH was found as an appropriate model for the experimental data of this study.     

Experimental study on the heat transfer characteristics of fluoride salt in the new conceptual passive heat removal system of molten salt reactor

A new conceptual design of a passive residual heat removal system (PRHRS) has been proposed for molten salt reactor. High‐temperature heat pipes are used in this new design to improve the system inherent safety and make the PRHRS more compact. An experimental system using fluoride salt FLiNaK has been constructed to validate and support the future design of PRHRS of molten salt reactors. In this research, tests on the natural convection heat transfer of FLiNaK in the drain tank with an inclined heat pipe inserted at different heights were performed. The temperature distribution of fluoride salt in the tank was analyzed. The height of heat pipe and the bulk temperature of FLiNaK have little influence on the normalized salt temperature distribution. However, with the height of heat pipe increasing, the temperature difference of molten salt decreases and heat transfer coefficient of natural convection increases. In addition, the empirical correlations of natural convection heat transfer between liquid FLiNaK and inclined heat pipe are obtained within the range of Rayleigh numbers from 3.97 × 10⁶ to 1.16 × 10⁷. The comparisons show that a good agreement with less than 5% deviation is obtained between the proposed correlations and the test data.     

Performance characteristics of spray-pyrolysed selective cobalt-oxide coated tubular absorber operated with a linear solar concentrator

Spray-pyrolysed selective cobalt-oxide (CoO_x) coatings were prepared on the surface of a bright nickel-plated copper tubular absorber (α = 0.89–0.91 and ?_100°C = 0.18) for operation in conjunction with a prototype linear Fresnel reflector solar concentrator (LFRSC). Some preliminary tests were conducted to study the optical and thermal performance characteristics of the selective cobalt-oxide coated absorber in the concentrated solar flux. The tests conducted included determination of the overall heat loss coefficient U_L of the absorber at temperatures from 50 to ～ 120°C, and the optical efficiency η_o of the concentrator-absorber system, and measurement of the stagnation temperature of the absorber with the prototype solar concentrator. Based on the results of U_L and η_o measurements, the thermal efficiency η of the concentrator-absorber system at a working temperature of 115°C has been determined for a typical beam radiation I_b of 600 W/m². Further, comparison of the results of this study with those obtained using a dimensionally identical black-painted absorber indicates that the performance of the selective cobalt-oxide coated absorber is considerably superior to that of an ordinary black-painted absorber.     

Optimization of the tubular absorber using a compound parabolic concentrator

The paper deals with the optimization of the tubular absorber of a compound parabolic concentrator (CPC) solar collector. In order to minimize the radiation thermal losses from the absorber, a modified absorber with multi-cavities is proposed. The cavities are introduced at the circumferential area with relatively high solar intensities. These areas were determined by the use of a ray-tracing technique. This has been adopted using the AutoCAD^® package. The analysis was carried out and applied to a CPC with an acceptance angle of 10 and a concentration ratio of × 4.0.