Paul S. Pickard

Molten-salt-cooled advanced high-temperature reactor for production of hydrogen and electricity

Abstract The molten-salt-cooled Advanced High-Temperature Reactor (AHTR) is a new reactor concept designed to provide very high-temperature (750 to 1000°C) heat to enable efficient low-cost thermochemical production of hydrogen (H2) or production of electricity. This paper provides an initial description and technical analysis of its key features. The proposed AHTR uses coated-particle graphite-matrix fuel similar to that used in high-temperature gas-cooled reactors (HTGRs), such as the General Atomics gas turbine-modular helium reactor. However, unlike the HTGRs, the AHTR uses a molten-salt coolant and a pool configuration, similar to that of the General Electric Super Power Reactor Inherently Safe Module (S-PRISM) liquid-metal reactor. Because the boiling points for molten fluoride salts are near ~1400°C, the reactor can operate at very high temperatures and atmospheric pressure. For thermochemical H2 production, the heat is delivered at the required near-constant high temperature and low pressure. For electricity production, a multireheat helium Brayton (gas-turbine) cycle, with efficiencies >50%, is used. The low-pressure molten-salt coolant, with its high heat capacity and natural circulation heat transfer capability, creates the potential for robust safety (including fully passive decay-heat removal) and improved economics with passive safety systems that allow higher power densities and scaling to large reactor sizes [>1000 MW(electric)].

Operation and analysis of a supercritical CO2 Brayton cycle.

Sandia National Laboratories is investigating advanced Brayton cycles using supercritical working fluids for use with solar, nuclear or fossil heat sources. The focus of this work has been on the supercritical CO{sub 2} cycle (S-CO2) which has the potential for high efficiency in the temperature range of interest for these heat sources, and is also very compact, with the potential for lower capital costs. The first step in the development of these advanced cycles was the construction of a small scale Brayton cycle loop, funded by the Laboratory Directed Research & Development program, to study the key issue of compression near the critical point of CO{sub 2}. This document outlines the design of the small scale loop, describes the major components, presents models of system performance, including losses, leakage, windage, compressor performance, and flow map predictions, and finally describes the experimental results that have been generated.

An Integrated Laboratory-Scale Experiment on the Sulfur-Iodine Thermochemical Cycle for Hydrogen Production

Sandia National Laboratories (SNL), General Atomics Corporation (GA) and the French Commissariat a l’Energie Atomique (CEA) have been conducting laboratory-scale experiments to investigate the thermochemical production of hydrogen using the Sulfur-Iodine (S-I) process. This project is being conducted as an International Nuclear Energy Research Initiative (INERI) project supported by the CEA and US DOE Nuclear Hydrogen Initiative. In the S-I process, 1) H2 SO4 is catalytically decomposed at high temperature to produce SO2 , O2 and H2 O. 2) The SO2 is reacted with H2 O and I2 to produce HI and H2 SO4 . The H2 SO4 is returned to the acid decomposer. 3) The HI is decomposed to H2 and I2 . The I2 is returned to the HI production process. Each participant in this work is developing one of the three primary reaction sections. SNL is responsible for the H2 SO4 decomposition section, CEA, the primary HI production section and General Atomics, the HI decomposition section. The objective of initial testing of the S-I laboratory-scale experiment was to establish the capability for integrated operations and demonstrate H2 production from the S-I cycle. The first phase of these objectives was achieved with the successful integrated operation of the SNL acid decomposition and CEA Bunsen reactor sections and the subsequent generation of H2 in the GA HI decomposition section. This is the first time the S-I cycle has been realized using engineering materials and operated at prototypic temperature and pressure to produce hydrogen.Copyright

DOE reactor-pumped laser program

FALCON is a high-power, steady-state, nuclear reactor-pumped laser (RPL) concept that is being developed by the Department of Energy. The FALCON program has experimentally demonstrated reactor-pumped lasing in various mixtures of xenon, argon, neon, and helium at wavelengths of 585, 703, 725, 1271, 1733, 1792, 2032, 2630, 2650, and 3370 nm with intrinsic efficiency as high as 2.5%. The major strengths of a reactor-pumped laser are continuous high-power operation, modular construction, self-contained power, compact size, and a variety of wavelengths (from visible to infrared). These characteristics suggest numerous applications not easily accessible to other laser types. A ground-based RPL could beam its power to space for such activities as illuminating geosynchronous communication satellites in the earths shadow to extend their lives, beaming power to orbital transfer vehicles, removing space debris, and providing power (from earth) to a lunar base during the long lunar night. The compact size and self-contained power also makes an RPL very suitable for ship basing so that power-beaming activities could be situated around the globe. The continuous high power of an RPL opens many potential manufacturing applications such as deep-penetration welding and cutting of thick structures, wide-area hardening of metal surfaces by heat treatment or cladding application, wide-area vapor deposition of ceramics onto metal surfaces, production of sub-micron sized particles for manufacturing of ceramics, wide-area deposition of diamond- like coatings, and 3-D ceramic lithography.

Supercritical CO2 Brayton Cycle Power Generation Development Program and Initial Test Results

The DOE Office of Nuclear Energy and Sandia National Labs are investigating supercritical CO2 Brayton cycles as a potentially more efficient and compact power conversion system for advanced nuclear reactors, and other heat sources including solar, geothermal, and fossil or bio fuel systems. The focus of this work is on the supercritical CO2 Brayton cycle which has the potential for both high efficiency, in temperature range (400–750 C), and for reduced capital costs due to very compact turbomachinery. The cycle achieves high efficiency due to the non-ideal behavior of supercritical CO2 , and it achieves extremely high power density because the fluid in the turbomachinery is very dense, 10%–60% the density of water. Sandia and its contractor Barber Nichols Inc. have fabricated and are operating a supercritical CO2 (S-CO2 ) compression test-loop to investigate the key technology issues associated with this cycle. The compression loop is part of a multi-year phased development program to develop a megawatt (MW) heater-class closed S-CO2 Brayton cycle to demonstrate the applicability of this cycle to heat sources above 400 C. Other portions of the program include modifications to the compression loop to operate it as a simple heated Brayton loop by adding a small turbine and a heater, but with no recuperator. The early testing of this simple Brayton cycle is under way. A more ambitious effort is currently constructing a recompression cycle Brayton loop (1) which is some times called a split-flow Brayton cycle. This cycle is used to increase the efficiency of the system by providing large amounts of recuperation using printed circuit heat exchangers. The re-compression (or split-flow) Brayton cycle is designed to operate at 1000 F (538 C) and produce up to 250 kWe with a 1.47″ OD radial compressor and a 2.68″ OD radial turbine. The current compression loop uses a main compressor that is identical to the main compressors in all the Brayton cycles that are being developed at Sandia. The key issues for the supercritical Brayton cycle include the fundamental issues of compressor fluid performance and system control near the critical point. Near the critical point very non ideal fluid behavior is observed which means that standard tools for analyzing compressor performance cannot be used. Thus one of the goals of the program is to develop data that can be used to validate the tools and models that are used to design the turbomachinery. Other supporting technology issues that are essential to achieving efficiency and cost objectives include bearing type, thrust load and thrust load balancing, bearing cooling, sealing technologies, and rotor windage losses. The current tests are providing the first measurements and information on these important supercritical CO2 power conversion system questions. Some of this data is presented in this report. In the testing to date, the turbomachinery has reached maximum speeds of 65,000 rpm, peak flow rates of over 9 lb/s and pressure ratios of just over 1.65. Compressor inlet fluid densities have been varied from 14% to 70% the density of water. Although the data from these tests are only the first results to be analyzed, they indicate that the basic design and performance predictions are sound. The loops have operated the turbo-compressor on the liquid and vapor side of the saturation curve, very near the critical point, above the critical point and even on the saturation dome. We have also operated the compressor near the choked flow regime and even in surge. At the current operating speeds and pressures, the observed performance map data agrees extremely well with the model predictions. These results have positive implications for the ultimate success of the S-CO2 cycle. In general the main compressor shows no adverse behavior while operating over a wide range of normal operating conditions. It operates reliably and with performance values that are very near the predicted results. Future efforts will focus on operating the Brayton cycle loop at sufficiently high temperatures that electrical power can be produced near the end of 2009. The compression-loop hardware is now the test bed for confirming the remaining parameters to support the next stage of development — which is the 1 MW heater-class split-flow or re-compressor Brayton cycle.Copyright

Description and Test Results from a Supercritical CO2 Brayton Cycle Development Program

The Supercritical CO2 Brayton cycle (S-CO2) can potentially offer more efficient and compact power conversion systems for advanced nuclear reactors, solar, or fossil fuel systems. The DOE Office of Nuclear Energy, Knolls Atomic Power Laboratory, and Sandia National Labs are investigating this cycle in a phased development program because it has the potential for high efficiency (in the temperature range from 400 °C to 750 °C), is very compact making it transportable, and may reduce capital costs due to the very compact turbomachinery. This paper describes resent test results from a supercritical CO2 closed Brayton cycle test loop. Sandia manufactured the loop through its contractor Barber Nichols Inc. The paper describes experimental test measurements of the main compressor performance map, the operational behavior of the supercritical loop at the critical point and below the critical point, and it illustrates the approach to break-even power production at very low turbine inlet temperatures (60 °C / 140 °F) using 78 kW of heater power.

Next Generation Nuclear Plant Phenomena Identification and Ranking Tables (PIRTs) Volume 6: Process Heat and Hydrogen Co-Generation PIRTs

A Phenomena Identification and Ranking Table (PIRT) exercise was conducted to identify potential safety-0-related physical phenomena for the Next Generation Nuclear Plant (NGNP) when coupled to a hydrogen production or similar chemical plant. The NGNP is a very high-temperature reactor (VHTR) with the design goal to produce high-temperature heat and electricity for nearby chemical plants. Because high-temperature heat can only be transported limited distances, the two plants will be close to each other. One of the primary applications for the VHTR would be to supply heat and electricity for the production of hydrogen. There was no assessment of chemical plant safety challenges. The primary application of this PIRT is to support the safety analysis of the NGNP coupled one or more small hydrogen production pilot plants. However, the chemical plant processes to be coupled to the NGNP have not yet been chosen; thus, a broad PIRT assessment was conducted to scope alternative potential applications and test facilities associated with the NGNP. The hazards associated with various chemicals and methods to minimize risks from those hazards are well understood within the chemical industry. Much but not all of the information required to assure safe conditions (separation distance, relative elevation, berms) is known for a reactor coupled to a chemical plant. There is also some experience with nuclear plants in several countries that have produced steam for industrial applications. The specific characteristics of the chemical plant, site layout, and the maximum stored inventories of chemicals can provide the starting point for the safety assessments. While the panel identified events and phenomena of safety significance, there is one added caveat. Multiple high-temperature reactors provide safety-related experience and understanding of reactor safety. In contrast, there have been only limited safety studies of coupled chemical and nuclear plants. The work herein provides a starting point for those studies; but, the general level of understanding of safety in coupling nuclear and chemical plants is less than in other areas of high-temperature reactor safety.

SULFURIC ACID DECOMPOSITION FOR THE SULFUR BASED THERMOCHEMICAL CYCLES.

Abstract In this work, we describe a novel design for a H2SO4 decomposer. The decomposition of H2SO4 to produce SO2 is a common processing operation in the sulfur-based thermochemical cycles for hydrogen production where acid decomposition takes place at 850°C in the presence of a catalyst. The combination of a high temperature and sulfuric acid creates a very corrosive environment that presents significant design challenges. The new decomposer design is based on a bayonet-type heat exchanger tube with the annular space packed with a catalyst. The unit is constructed of silicon carbide and other highly corrosion-resistant materials. The new design integrates acid boiling, superheating, decomposition, and heat recuperation into a single process and eliminates problems of corrosion and failure of high-temperature seals encountered in previous testing using metallic construction materials. The unit was tested by varying the acid feed rate and decomposition temperature and pressure.

Safety Related Physical Phenomena for Coupled High-Temperature Reactors and Hydrogen Production Facilities

High-temperature reactors are a potential low-carbon source of high-temperature heat for chemical plants—including hydrogen production plants and refineries. Unlike electricity, high temperature heat can only be transported limited distances; thus, the reactor and chemical plants will be close to each other. A critical issue is to understand potential safety challenges to the reactor from the associated chemical plant events to assure nuclear plant safety. The U.S. Nuclear Regulatory Commission (NRC) recently sponsored a Phenomena Identification and Ranking Table (PIRT) exercise to identify potential safety-related physical phenomena for high-temperature reactors coupled to a hydrogen production or similar chemical plant. The ranking process determines what types of chemical plant transients and accidents could present the greatest risks to the nuclear plant and thus the priorities for safety assessments. The assessment yielded four major observations. Because the safety philosophy for most chemical plants (dilution) is different than the safety philosophy for nuclear power plants (containment), this difference must be recognized and understood when considering safety challenges to a nuclear reactor from coupled chemical plants or refineries. Accidental releases of hydrogen from a hydrogen production facility are unlikely to be a major hazard for the nuclear plant assuming some minimum separation distances. Many chemical plants under accident conditions can produce heavy ground-hugging gases such as oxygen, corrosive gases, and toxic gases that can have major off-site consequences because of the ease of transport from the chemical plant to off-site locations. Oxygen presents a special concern because most proposed nuclear hydrogen processes convert water into hydrogen and oxygen; thus, oxygen is the primary byproduct. These types of potential accidents must be carefully accessed. Last, the potential consequences of the failure of the intermediate heat transport loop that moves heat from the reactor to the chemical plant must be carefully assessed.Copyright

CFD Modeling of Bayonet Type High Temperature Heat Exchanger and Chemical Decomposer With Different Packed Bed Designs

The present work is concerned with use of bayonet type high temperature heat exchanger as silicon carbide integrated decomposer (SID) which produces sulfuric acid decomposition product - sulfur dioxide. The product can be used within the sulfur iodine thermo-chemical cycle portion of the hydrogen production process. The chemical decomposition occurs in packed bed area of the decomposer. The engineering design of the packed bed is very much influenced by the structure of the packing matrix, which is governed by the shape, dimensions and the loading of the constituent particles. Optimum design of catalyst pellet in terms of shape configuration, packing method and available surface area can promote catalytic activity and the prevailing transport properties of the system. Knowledge of the underlying factors should enable designers to engineer the optimum design for a given system with prescribed conditions. The investigations of fluid flow and the arrangement of cylindrical and spherical pellets in packed bed are presented in the paper.Copyright