A L Qualls

Pre-Conceptual Design of a Fluoride-Salt-Cooled Small Modular Advanced High Temperature Reactor (SmAHTR)

This document presents the results of a study conducted at Oak Ridge National Laboratory during 2010 to explore the feasibility of small modular fluoride salt-cooled high temperature reactors (FHRs). A preliminary reactor system concept, SmATHR (for Small modular Advanced High Temperature Reactor) is described, along with an integrated high-temperature thermal energy storage or salt vault system. The SmAHTR is a 125 MWt, integral primary, liquid salt cooled, coated particle-graphite fueled, low-pressure system operating at 700 C. The system employs passive decay heat removal and two-out-of-three , 50% capacity, subsystem redundancy for critical functions. The reactor vessel is sufficiently small to be transportable on standard commercial tractor-trailer transport vehicles. Initial transient analyses indicated the transition from normal reactor operations to passive decay heat removal is accomplished in a manner that preserves robust safety margins at all times during the transient. Numerous trade studies and trade-space considerations are discussed, along with the resultant initial system concept. The current concept is not optimized. Work remains to more completely define the overall system with particular emphasis on refining the final fuel/core configuration, salt vault configuration, and integrated system dynamics and safety behavior.

Advanced High Temperature Reactor Systems and Economic Analysis

The Advanced High Temperature Reactor (AHTR) is a design concept for a large-output [3400 MW(t)] fluoride-salt-cooled high-temperature reactor (FHR). FHRs, by definition, feature low-pressure liquid fluoride salt cooling, coated-particle fuel, a high-temperature power cycle, and fully passive decay heat rejection. The AHTRs large thermal output enables direct comparison of its performance and requirements with other high output reactor concepts. As high-temperature plants, FHRs can support either high-efficiency electricity generation or industrial process heat production. The AHTR analysis presented in this report is limited to the electricity generation mission. FHRs, in principle, have the potential to be low-cost electricity producers while maintaining full passive safety. However, no FHR has been built, and no FHR design has reached the stage of maturity where realistic economic analysis can be performed. The system design effort described in this report represents early steps along the design path toward being able to predict the cost and performance characteristics of the AHTR as well as toward being able to identify the technology developments necessary to build an FHR power plant. While FHRs represent a distinct reactor class, they inherit desirable attributes from other thermal power plants whose characteristics can be studied to provide general guidance on plant configuration, anticipated performance, and costs. Molten salt reactors provide experience on the materials, procedures, and components necessary to use liquid fluoride salts. Liquid metal reactors provide design experience on using low-pressure liquid coolants, passive decay heat removal, and hot refueling. High temperature gas-cooled reactors provide experience with coated particle fuel and graphite components. Light water reactors (LWRs) show the potentials of transparent, high-heat capacity coolants with low chemical reactivity. Modern coal-fired power plants provide design experience with advanced supercritical-water power cycles. The current design activities build upon a series of small-scale efforts over the past decade to evaluate and describe the features and technology variants of FHRs. Key prior concept evaluation reports include the SmAHTR preconceptual design report,1 the PB-AHTR preconceptual design, and the series of early phase AHTR evaluations performed from 2004 to 2006. This report provides a power plant-focused description of the current state of the AHTR. The report includes descriptions and sizes of the major heat transport and power generation components. Component configuration and sizing are based upon early phase AHTR plant thermal hydraulic models. The report also provides a top-down AHTR comparative economic analysis. A commercially available advanced supercritical water-based power cycle was selected as the baseline AHTR power generation cycle both due to its superior performance and to enable more realistic economic analysis. The AHTR system design, however, has several remaining gaps, and the plant cost estimates consequently have substantial remaining uncertainty. For example, the enriched lithium required for the primary coolant cannot currently be produced on the required scale at reasonable cost, and the necessary core structural ceramics do not currently exist in a nuclear power qualified form. The report begins with an overview of the current, early phase, design of the AHTR plant. Only a limited amount of information is included about the core and vessel as the core design and refueling options are the subject of a companion report. The general layout of an AHTR system and site showing the relationship of the major facilities is then provided. Next is a comparative evaluation of the AHTR anticipated performance and costs. Finally, the major system design efforts necessary to bring the AHTR design to a pre-conceptual level are then presented.

Extrusion Development of Graphite-Based Composite Fuel for Nuclear Thermal Propulsion

Graphite-based composite fuel forms for Nuclear Thermal Propulsion (NTP) technology are being developed at ORNL. This effort involves process development for extrusion and heat treatment of intermediate length fuel elements representative of historical NERVA fuel. Earlier efforts at ORNL involved identifying extrusion feedstock materials, extrusion equipment, and fabrication techniques based on historical work. This information was utilized to procure representative materials and establish an extrusion capability. Using the new equipment and applying information learned during earlier lab scale work, several extrusion studies were conducted. The focus of these studies included determining appropriate blending methods for the feedstock materials, range of binder fraction, extrusion die and layoff table requirements, and the development of an interconnected carbide network during heat treatment. The results from these studies are reported including microstructural analysis and characterization of a high temperature heat treated element. SEM images of specimens both before and after heat treatment were used to determine changes in microstructure. Large regions of coalesced particles after heat treatment indicate that the desired interconnected carbide network was achieved. Additional characterization included density, compressive strength, and coefficient of thermal expansion (CTE). Since it is important that fuel elements from this work be representative of the original elements, these results were compared to historical values. Physical properties data from the recently fabricated element show good agreement with some historical data.

Coating Development on Graphite-Based Composite Fuel for Nuclear Thermal Propulsion

ORNL is currently recapturing graphite-based fuel forms for Nuclear Thermal Propulsion (NTP). Previous work at ORNL focused on reviewing historic fuel technology developed during the ROVER/NERVA programs and performing coating development at the lab scale. The current effort focuses on transitioning the coating work from the lab scale to an intermediate length, and coating an element with a more prototypic geometry to include a hexagonal cross section and multiple internal channels. A new vertical multi-zone furnace capable of coating 16” length elements was installed and the ability to deposit a ZrC coating along the full length of the element demonstrated. A chemical vapor deposition (CVD) process was used to apply a ZrC coating where zirconium metal was chlorinated insitu forming ZrCl4 as the Zr precursor and CH4 was used for the carbon source. The coating and additional diluent gases were directed through the internal channels using custom fixtures. While processing conditions were not fully optimized, good progress was made in coating development. Between the information gained and new capabilities installed, an excellent foundation for further fuel development and eventual qualification has been put into place.

Tritium Management Loop Design Status

This report summarizes physical, chemical, and engineering analyses that have been performed to support development of a test loop to study tritium migration in FLiBe (2LiF-BeF2) salts. The loop will operate under turbulent flow, and a schematic of the apparatus has been used to develop a model in Mathcad to suggest flow parameters that should be targeted in loop operation. The introduction of tritium into the loop has been discussed, as well as various means to capture or divert the tritium from egress through a test assembly. Permeation was calculated, starting with the development of a Modelica model for a transport through a nickel window into a vacuum, followed by modification of the model for a FLiBe system with an argon sweep gas on the downstream side of the permeation interface. Results suggest that tritium removal with a simple tubular permeation device will occur readily. Although this system is idealized, it suggests that rapid measurement capability in the loop may be necessary to study and understand tritium removal from the system.

Johnson Noise Thermometry System Requirements

This document is intended to capture the requirements for the architecture of the developmental electronics for the ORNL-lead drift-free Johnson Noise Thermometry (JNT) project conducted under the Instrumentation, Controls, and Human-Machine Interface (ICHMI) research pathway of the U.S. Department of Energy (DOE) Advanced Small Modular Reactor (SMR) Research and Development (R&D) program. The requirements include not only the performance of the system but also the allowable measurement environment of the probe and the allowable physical environment of the associated electronics. A more extensive project background including the project rationale is available in the initial project report [1].

Recapturing Graphite-Based Fuel Element Technology for Nuclear Thermal Propulsion

ORNL is currently recapturing graphite based fuel forms for Nuclear Thermal Propulsion (NTP). This effort involves research and development on materials selection, extrusion, and coating processes to produce fuel elements representative of historical ROVER and NERVA fuel. Initially, lab scale specimens were fabricated using surrogate oxides to develop processing parameters that could be applied to full length NTP fuel elements. Progress toward understanding the effect of these processing parameters on surrogate fuel microstructure is presented. I. Introduction HE research presented in this report is a collaborative effort between Oak Ridge National Laboratory (ORNL) and NASA to recapture manufacturing technology for full length ROVER/NERVA graphite composite fuel elements. Nuclear thermal propulsion (NTP) fuel development has been intermittently ongoing since the late 1950’s and many of the original materials used in the early fuel development are no longer available. Also, the processing capability and the art associated with the production of full-length elements have been lost. The focus of the collaboration is to recapture the capability and expertise to produce representative fuel element test samples and iteratively scale up to full-length elements. To maximize efficiency, the work was separated into two tasks, extrusion development and coating development, which were conducted in parallel. At this stage in the program, the extrusion development task is focused on recreating a representative blend of materials, evaluating blending methods, and establishing an extrusion capability. The coating task is focused on developing processing conditions and equipment to establish ZrC coating capability. This report summarizes the accomplishments and progression toward these goals. It is important to note that the results and analyses presented here are in the early stages of research (TRL 3) and should be considered preliminary.

Phenylnaphthalene as a Heat Transfer Fluid for Concentrating Solar Power: High-Temperature Static Experiments

Concentrating solar power (CSP) may be an alternative to generating electricity from fossil fuels; however, greater thermodynamic efficiency is needed to improve the economics of CSP operation. One way of achieving improved efficiency is to operate the CSP loop at higher temperatures than the current maximum of about 400 C. ORNL has been investigating a synthetic polyaromatic oil for use in a trough type CSP collector, to temperatures up to 500 C. The oil was chosen because of its thermal stability and calculated low vapor and critical pressures. The oil has been synthesized using a Suzuki coupling mechanism and has been tested in static heating experiments. Analysis has been conducted on the oil after heating and suggests that there may be some isomerization taking place at 450 C, but the fluid appears to remain stable above that temperature. Tests were conducted over one week and further tests are planned to investigate stabilities after heating for months and in flow configurations. Thermochemical data and thermophysical predictions indicate that substituted polyaromatic hydrocarbons may be useful for applications that run at higher temperatures than possible with commercial fluids such as Therminol-VP1.

Nuclear Hybrid Energy Systems FY16 Modeling Efforts at ORNL

A nuclear hybrid system uses a nuclear reactor as the basic power generation unit. The power generated by the nuclear reactor is utilized by one or more power customers as either thermal power, electrical power, or both. In general, a nuclear hybrid system will couple the nuclear reactor to at least one thermal power user in addition to the power conversion system. The definition and architecture of a particular nuclear hybrid system is flexible depending on local markets needs and opportunities. For example, locations in need of potable water may be best served by coupling a desalination plant to the nuclear system. Similarly, an area near oil refineries may have a need for emission-free hydrogen production. A nuclear hybrid system expands the nuclear power plant from its more familiar central power station role by diversifying its immediately and directly connected customer base. The definition, design, analysis, and optimization work currently performed with respect to the nuclear hybrid systems represents the work of three national laboratories. Idaho National Laboratory (INL) is the lead lab working with Argonne National Laboratory (ANL) and Oak Ridge National Laboratory. Each laboratory is providing modeling and simulation expertise for the integration of the hybrid system.

Update on Small Modular Reactors Dynamics System Modeling Tool -- Molten Salt Cooled Architecture

The Small Modular Reactor (SMR) Dynamic System Modeling Tool project is in the third year of development. The project is designed to support collaborative modeling and study of various advanced SMR (non-light water cooled) concepts, including the use of multiple coupled reactors at a single site. The objective of the project is to provide a common simulation environment and baseline modeling resources to facilitate rapid development of dynamic advanced reactor SMR models, ensure consistency among research products within the Instrumentation, Controls, and Human-Machine Interface (ICHMI) technical area, and leverage cross-cutting capabilities while minimizing duplication of effort. The combined simulation environment and suite of models are identified as the Modular Dynamic SIMulation (MoDSIM) tool. The critical elements of this effort include (1) defining a standardized, common simulation environment that can be applied throughout the program, (2) developing a library of baseline component modules that can be assembled into full plant models using existing geometry and thermal-hydraulic data, (3) defining modeling conventions for interconnecting component models, and (4) establishing user interfaces and support tools to facilitate simulation development (i.e., configuration and parameterization), execution, and results display and capture.