Second-generation Reactor Research Articles

Scalable Production of Graphene Nanoplatelets for Energy Storage

The difficulty of scaling up the production of high-quality graphene nanoplatelets remains a major challenge for the graphene community and inhibits commercialization across a variety of market segments and applications. Here, we demonstrate a compressed, permeable reactor that produces graphene nanoplatelets via electrochemical exfoliation and controlled pressure. In contrast to prior controlled-volume reactors, the second-generation reactor allows for both direct control of pressure on the graphite source and arbitrarily large batch sizes. We have measured how graphene production is affected by the electrode type and arrangement (working electrode and counter electrode), reactor dimensions, and reaction kinetics. The data indicate that the reactor must be thin in at least one dimension to avoid diffusion limitations, but the long dimension can be scaled up without decreases in the yield. As in other batch processes, the highest production rate occurs in the initial stage followed by a plateau in conversion. An expandable graphite feedstock results in a substantial increase in yield compared to graphite flake feedstocks under identical reactor conditions.

Electroorganic Synthesis under Flow Conditions.

Despite the long history of electroorganic synthesis, it did not participate in the mainstream of chemical research for a long time. This is probably due to the lack of equipment and standardized protocols. However, nowadays organic electrochemistry is witnessing a renaissance, and a wide range of interesting electrochemical transformations and methodologies have been developed, not only for academic purposes but also for large scale industrial production. Depending on the source of electricity, electrochemical methods can be inherently green and environmentally benign and can be easily controlled to achieve high levels of selectivity. In addition, the generation and consumption of reactive or unstable intermediates and hazardous reagents can be achieved in a safe way. Limitations of traditional batch-type electrochemical methods such as the restricted electrode surface, the necessity of supporting electrolytes, and the difficulties in scaling up can be alleviated using electrochemical flow cells. Microreactors offer high surface-to-volume ratios and enable precise control over temperature, residence time, flow rate, and pressure. In addition, efficient mixing, enhanced mass and heat transfer, and handling of small volumes lead to simpler scaling-up protocols and minimize safety concerns. Electrolysis under flow conditions reduces the possibility of overoxidation as the reaction mixture is flown continuously out of the reactor in contrast to traditional batch-type electrolysis cells. In this Account, we highlight our contributions in the area of electroorganic synthesis under flow conditions over the past decade. We have designed and manufactured different generations of electrochemical flow cells. The first-generation reactor was effectively used in developing a simple one-step synthesis of diaryliodonium salts and used in proof-of-concept reactions such as the trifluoromethylation of electron-deficient alkenes via Kolbe electrolysis of trifluoroacetic acid in addition to the selective deprotection of the isonicotinyloxycarbonyl (iNoc) group from carbonates and thiocarbonates. The improved second-generation flow cell enabled the development of efficient synthesis of isoindolinones, benzothiazoles, and thiazolopyridines, achieving gram-scale for some of the products easily without changing the reactor design or reoptimizing the reaction parameters. In addition, the same reactor was used in the development of an efficient continuous flow electrochemical synthesis of hypervalent iodine reagents. The generated unstable hypervalent iodine reagents were easily used without isolation in various oxidative transformations in a coupled flow/flow manner and could be easily transformed into bench-stable reagents via quantitative ligand exchange with the appropriate acids. Our second-generation reactor was further improved and commercialized by Vapourtec Ltd. We have demonstrated the power of online analysis in accelerating optimizations and methodology development. Online mass spectrometry enabled fast screening of the charge needed for the cyclization of amides to isoindolinones. The power of online 2D-HPLC combined with a Design of Experiments approach empowered the rapid optimization of stereoselective electrochemical alkoxylations of amino acid derivatives.

Sealing of concrete confining structures of French nuclear reactors

France has a total of 58 nuclear reactors, which produce 75% of its electricity. The second-generation reactors are protected by two concentric concrete envelopes, which are separated by an annular space. Every ten years, leakage tests are performed, by inflating the confinement structure with pressurized dry air. The confining structures of several second-generation reactors are now close to their allowed leakage limit. As a consequence, several different approaches are currently being studied in order to improve their airtightness. A dedicated wall has been especially designed, by our laboratory, to simulate the leakage tests as they occur in the real in-situ confining structures. The main goal of this “apparatus” was to test different possibilities to recover a large part of the envelope tightness: application of coatings or water re-saturation of the concrete with spraying. The measured airtightness and bond strength (between the wall and coating) of two concrete prototypes revealed these to be unsatisfactory. In parallel, the spraying method allowed a high proportion of the concrete's gas tightness to be recovered. The present study provides a detailed description of the design of the prototype test wall and the results of preliminary tests, including those obtained with the “water spraying technique”.

CANDU technology for Generation III+ and IV reactors

Atomic Energy of Canada Limited (AECL) is the original developer of the CANDU ® reactor, one of the three major commercial power reactor designs now used throughout the world. For over 60 years, AECL has continued to evolve the CANDU design from the CANDU prototypes in the 1950s and 1960s through to the second-generation reactors now in operation, including the Generation II+ CANDU 6. The next phase of this evolution, the Generation III+ Advanced CANDU Reactor™ (ACR™), continues the strategy of basing next generation technology on existing CANDU reactors. Beyond the ACR, AECL is developing the Generation IV CANDU Super Critical Water Reactor. Owing to the evolutionary nature of these advanced reactors, advanced technology from the development programs is also being applied to operating CANDU plants, for both refurbishments and upgrading of existing systems and components. In addition, AECL is developing advanced technology that covers the entire life cycle of the CANDU plant, including waste management and decommissioning. Thus, AECL maintains state-of-the-art expertise and technology to support both operating and future CANDU plants. This paper outlines the scale of the current core knowledge base that is the foundation for advancement and support of CANDU technology. The knowledge base includes advancements in materials, fuel, safety, plant operations, components and systems, environmental technology, waste management, and construction. Our approach in each of these areas is to develop the underlying science, carry out integrated engineering scale tests, and perform large-scale demonstration testing. AECL has comprehensive R&D and engineering development programs to cover all of these elements. The paper will show how the ongoing expansion of the CANDU knowledge base has led to the development of the Advanced CANDU Reactor. The ACR is a Generation III+ reactor with substantially reduced costs, faster construction, and enhanced passive safety and operating margins. The ACR is also the basis for the Generation IV Super Critical Water Reactor, which extends operation to higher temperatures and pressures.

Direct Simulation Monte Carlo Analysis of Rarefied Gas Flow Structures and Ventilation of Etching Gas in Magneto-Microwave Plasma Etching Reactors

Gas flows in plasma etching reactors for semiconductor fabrication became a chief consideration in designing second-generation reactors with higher etching rates. An axisymmetrical model based on the direct simulation Monte Carlo method has been developed for analyzing rarefied gas flows in a vacuum chamber with the conditions of downstream pressure and gas flow rate. By using this simulator, rarefied gas flows with radicals and etch-products were calculated for microwave-plasma etching reactors. The results showed that the flow patterns in the plasma chamber strongly depend on the Knudsen number and the gas-supply structure. The ventilation of the etch-products in the plasma chamber was found to be improved both for higher Knudsen numbers and for gas-supply structures of the downward-flow type, as compared with those of the radial-flow or upward-flow types.

A comparison of PLW and PHW second-generation 232Th 233U reactors

The use of irradiated Th rods in 232Th 233U second-generation reactors was studied theoretically. It was found that the use of the heavy-water moderator in such reactors has considerable advantages over the use of the light-water one.

Materials and their application in the nuclear industry

During the next 25–50 years an interim energy source that minimizes the consumption of the natural resources of the world is required. Based on current technological forecasting, nuclear power can satisfy these guidelines. Today, we are undergoing an evolution in nuclear power generating sources. We have in service nuclear burners such as the light water reactors (LWR) and the gas-cooled reactors (GCR). Currently available is a second-generation reactor concept, the breeder, which has been proven feasible and will be the primary source of energy within the next 25 years. These energy sources are possible only because materials technology has been advanced through the combined efforts of both the theoreticians and engineers of the world. This paper discusses the metallurgical investigations that are being conducted at the Oak Ridge National Laboratory on materials for nuclear applications. It will concentrate on pressure vessel materials such as ASTM A 508 Class 2 and A 533 Grade B steels for LWR and concrete and prestressing tendons for the GCR. In addition, the paper discusses the liquid-metal fast breeder reactor (LMFBR) and describes the materials used in the primary containment, intermediate heat exchanger, and steam generator. This discussion of the LMFBR includes both austenitic and ferritic materials. The paper emphasizes the cooperative responsibility of the metallographer and engineer in optimizing material development and selection to ensure the safe and reliable behavior of nuclear components.