Development, Verification, and Validation of an OpenFOAM-Based Solver for Modeling Inertial Fusion Energy Chambers

Radwaste volume in lithium and Flibe thick liquid wall and comparison to conventional SW concepts

In the APEX (Advanced Power Extraction) studies, the conventional first solid wall facing the plasma is replaced with a fast flowing layer of a thin liquid wall. The concept of a free-surface first liquid wall concept is a revolutionary concept. The first liquid wall flows very fast and detains charged particles, and is followed by the thick liquid wall (blanket) which flows slowly and absorbs generated energy and converts it to heat. In the study, the flowing molten salt (i.e., first wall and blanket) is composed of Flibe (Li2BeF4) and is considered the main constituent mixed with different mole fractions (0–12%) of heavy metal salt (ThF4 or UF4) to increase the energy multiplication. Self-sufficient tritium breeding ratio (TBR > 1.05) was taken into account to determine the upper limit of the fraction of heavy metal salt in the mixture. Design and calculations of APEX were carried out as 3-D torus by using MCNP-4B computer code. Copyright © 2011 John Wiley & Sons, Ltd.

The key feature of liquid wall chambers is the use of a renewable liquid layer to protect chamber structures from target emissions. Two primary options have been proposed and studied: wetted wall chambers and thick liquid wall (TLW) chambers. With wetted wall designs, a thin layer of liquid shields the structural first wall from short ranged target emissions (x-rays, ions and debris) but not neutrons. Various schemes have been proposed to establish and renew the liquid layer between shots including flow-guiding porous fabrics (e.g., Osiris, HIBALL), porous rigid structures (Prometheus) and thin film flows (KOYO). The thin liquid layer can be the tritium breeding material (e.g., flibe, PbLi, or Li) or another liquid metal such as Pb. TLWs use liquid jets injected by stationary or oscillating nozzles to form a neutronically thick layer (typically with an effective thickness of {approx}50 cm) of liquid between the target and first structural wall. In addition to absorbing short ranged emissions, the thick liquid layer degrades the neutron flux and energy reaching the first wall, typically by {approx}10 x x, so that steel walls can survive for the life of the plant ({approx}30-60 yrs). The thick liquid serves as the primary coolant and tritium breeding material (most recent designs use flibe, but the earliest concepts used Li). In essence, the TLW places the fusion blanket inside the first wall instead of behind the first wall.

The molten salt Flinabe (LiF-NaF-BeF2) is proposed as a liquid wall material for future fusion reactors because of its many attractive aspects. High-temperature Flinabe gases (plasmas) appear in the inertial fusion energy chamber over a wide range of temperatures and pressures because of the absorption of X-rays and debris, emitted from the target microexplosion, within a very thin surface layer of the Flinabe liquid wall. The deposited energy heats the surface edge of the Flinabe wall to very high temperatures where vaporization, dissociation, and ionization take place and high-temperature plasma is generated. Equation-of-state (EOS) and ionization equilibrium data of the resulting high-temperature gas are needed to perform gas dynamics calculations and the required assessments of many research and development issues in nuclear fusion. Nevertheless, data for Flinabe EOS or ionization states are missing in the literature, and there is an immediate need to model and estimate these properties. In this paper, a self-consistent model for the ionization equilibrium and EOS of weakly nonideal high-temperature Flinabe gas is presented and used to compute the ionization equilibrium data and EOS of such an important material. Nonideality effects have been taken into account in terms of depression of the ionization potentials, coulombic correction to plasma kinetic pressure, and truncated partition functions. A reduced formulation and efficient algorithm to solve the set of nonlinear Saha equations subjected to the constraints of electroneutrality and conservation of nuclei have been used to generate ionization equilibrium and Flinabe EOS over a wide range of temperatures and pressures. A criterion for the validity of the assumption of local thermodynamic equilibrium (LTE) is applied to the results showing the regions of pressure-temperature phase-space over which the LTE assumption can be justified and accepted. Estimates of high-temperature Flinabe EOS and ionization states are presented and discussed.

Renaissance Fusion proposes thick liquid metal walls as plasma-facing components for future commercial fusion reactors. It designs and operates proof-of-concept experiments aiming at actively suspending and stabilizing a flowing free-surface liquid metal layer against gravity using Lorentz forces. The first operating prototype consists of a 1-m-diameter chamber in the presence of a magnetic field of the order of 0.3T. A GaInSn flow is injected into the chamber, and it is actively suspended due to the injection of currents up to 3kA. To simulate the prototype, a numerical tool capable of modeling magnetohydrodynamics phenomena in two-phase flows has been developed to reproduce and interpret the experimental results. The tool considers the low-magnetic Reynolds assumption, implements the Volume-of-Fluid method for tracking the free-surface, and couples the electric potential in both fluid and solid domains. Tables 2, Figs 5, Refs 14.

Free surface heat transfer and innovative designs for thin and thick liquid walls

In this paper, we quantitatively assess the advantages offered by thick liquid wall (LW) concepts over conventional solid wall (SW) concepts in terms of the substantial reduction in radiation damage as well as activation to solid structure with subsequent reduction in radwaste volume and hazard. The conventional SW FW/blanket considered is made of Li/V with a peak neutron wall load of 5 MW/m/sup 2/ (3.5 MW/m/sup 2/ ave.) and is compared to a thick liquid lithium with a peak neutron wall load of 10 MW/m/sup 2/ (7 MW/m/sup 2/ ave.). Fixed Radii and Fixed Fusion Power configurations are considered. To have a consistent comparison, the two blankets were optimized first such that adequate tritium breeding ratio is obtained and the same level of magnet protection against radiation damage is reached.

This paper presents an update of the work done at University of California, Berkeley (UCB) on thick-liquid protection of inertial fusion energy (IFE) chambers. UCB is focusing on microsecond, millisecond, and quasi-steady phenomena. Over microsecond time scales, numerical simulations, performed with the code TSUNAMI permit modeling of IFE chambers gas dynamics. For the millisecond range, the liquid jets response to the fusion reaction impulse loading is being studied for both Z-Pinch and HYLIFE-II-type chambers. A new mineral oil has been identified that allows scaled molten salt experiments with low distortion. Vortex tube flow, a key liquid structure of the 2002 Robust Point Design has been investigated in scaled experiments using the mineral oil, while a new design for thick liquid wall protection is under development. In quasi-steady phenomena, recent work has measured the Flibe vapor pressure and composition at near melting point temperature using mass spectrometry.

This report summarizes the further findings from the assessments of current status and future needs in code qualification and licensing of reference structural materials and new advanced alloys for advanced recycling reactors (ARRs) in support of Advanced Fuel Cycle Initiative (AFCI). The work is a combined effort between Argonne National Laboratory (ANL) and Oak Ridge National Laboratory (ORNL) with ANL as the technical lead, as part of Advanced Structural Materials Program for AFCI Reactor Campaign. The report is the second deliverable in FY08 (M505011401) under the work package 'Advanced Materials Code Qualification'. The overall objective of the Advanced Materials Code Qualification project is to evaluate key requirements for the ASME Code qualification and the Nuclear Regulatory Commission (NRC) approval of structural materials in support of the design and licensing of the ARR. Advanced materials are a critical element in the development of sodium reactor technologies. Enhanced materials performance not only improves safety margins and provides design flexibility, but also is essential for the economics of future advanced sodium reactors. Code qualification and licensing of advanced materials are prominent needs for developing and implementing advanced sodium reactor technologies. Nuclear structural component design in the U.S. must comply with the ASME Boiler and Pressure Vessel Code Section III (Rules for Construction of Nuclear Facility Components) and the NRC grants the operational license. As the ARR will operate at higher temperatures than the current light water reactors (LWRs), the design of elevated-temperature components must comply with ASME Subsection NH (Class 1 Components in Elevated Temperature Service). However, the NRC has not approved the use of Subsection NH for reactor components, and this puts additional burdens on materials qualification of the ARR. In the past licensing review for the Clinch River Breeder Reactor Project (CRBRP) and the Power Reactor Innovative Small Module (PRISM), the NRC/Advisory Committee on Reactor Safeguards (ACRS) raised numerous safety-related issues regarding elevated-temperature structural integrity criteria. Most of these issues remained unresolved today. These critical licensing reviews provide a basis for the evaluation of underlying technical issues for future advanced sodium-cooled reactors. Major materials performance issues and high temperature design methodology issues pertinent to the ARR are addressed in the report. The report is organized as follows: the ARR reference design concepts proposed by the Argonne National Laboratory and four industrial consortia were reviewed first, followed by a summary of the major code qualification and licensing issues for the ARR structural materials. The available database is presented for the ASME Code-qualified structural alloys (e.g. 304, 316 stainless steels, 2.25Cr-1Mo, and mod.9Cr-1Mo), including physical properties, tensile properties, impact properties and fracture toughness, creep, fatigue, creep-fatigue interaction, microstructural stability during long-term thermal aging, material degradation in sodium environments and effects of neutron irradiation for both base metals and weld metals. An assessment of modified versions of Type 316 SS, i.e. Type 316LN and its Japanese version, 316FR, was conducted to provide a perspective for codification of 316LN or 316FR in Subsection NH. Current status and data availability of four new advanced alloys, i.e. NF616, NF616+TMT, NF709, and HT-UPS, are also addressed to identify the R&D needs for their code qualification for ARR applications. For both conventional and new alloys, issues related to high temperature design methodology are described to address the needs for improvements for the ARR design and licensing. Assessments have shown that there are significant data gaps for the full qualification and licensing of the ARR structural materials. Development and evaluation of structural materials require a variety of experimental facilities that have been seriously degraded in the past. The availability and additional needs for the key experimental facilities are summarized at the end of the report. Detailed information covered in each Chapter is given.

A power plant based on a spheromak device using liquid walls is analyzed. We assume a spheromak configuration can be made and sustained by a steady plasma gun current, which injects particles, current and magnetic field, i.e., helicity injection, which are transported into the core region. The magnetic configuration is evaluated with an axisymmetric freeboundary equilibrium code, where the current profile is tailored to support an average beta of 10%. An injection current of 100 kA (125 MW of gun power) sustains the toroidal current of 40 MA. The magnetic flux linking the gun is 1/1000th of the flux in the spheromak. The geometry allows a flow of liquid, either molten salt, (flibe–Li2BeF4 or flinabe–LiNaBeF4), or liquid metal such as SnLi, which protects most of the walls and structures from damage arising from neutrons and plasma particles. The free surface between the liquid and the burning plasma is heated primarily by bremsstrahlung, line radiation, and some by neutrons. The temperature of the free surface of the liquid is calculated and then the evaporation rate is estimated from vapor-pressure data. The impurity concentration in the burning plasma, about 0.8% fluorine, is limited to that giving a 20% reduction in the fusion power. The divertor power density of 620 MW/m2 is handled by high-speed (100 m/s) liquid jets. Calculations show the tritium breeding is adequate with enriched 6Li, and a design is given for the walls not covered by flowing liquid (~15% of the total). We identified a number of problem areas needing further study to make the design more self-consistent and workable, including lowering the divertor power density by expanding the flux tube size.

Thin and thick liquid walls provide an attractive solution to the challenging material issues facing the heavy-ion applications of the inertial fusion energy (IFE) concept. Given the many advantages of liquid-protected chambers, there are several nuclear-related concerns that are discussed in detail for the thick liquid wall option in particular. These are the ability to protect the steel-based structure from radiation damage and high activation, the feasibility of rewelding the structure, and the pulse-related problems. These issues have a profound impact on the ARIES-IFE thick-liquid protected chamber design.

Thick liquid wall blankets appear to be of great promise for heavy ion pellet fusion reactors. They avoid the severe problems of intense radiation and blast damage that would be encountered with solid blanket structures. The liquid wall material can be chosen so that its vapor pressure at the working temperature of the power cycle is well below the value at which it might interfere with the propagation of the heavy ion beam. The liquid wall can be arranged so that it does not contact any surrounding solid structure when the pellet explosion occurs, including the ends. The ends can be magnetically closed just before the pellet explosion, or a time phased flow can be used, which will leave a clear central zone into which the pellet is injected. Parametric analysis comparing three candidate liquid wall materials were carried out. The three materials were lithium, flibe, and lead (with a low concentration of disolved lithium). Lead appeared to be the best choice for the liquid wall, although any of the three should allow a practical reactor system. The parametric analyses examined the effects of pellet yield (0 to 10 GJ), pellet mass (3 g to 3 kg), liquid wall thickness (10 cm to 80 cm), vapor condensation time (0 to 10 milliseconds), degree of neutron moderation in the pellet (none to 100%), liquid wall chamber size (radius of 1.5 meters to 4 meters), Pb/Li/sup 6/ ratio (100 to 5,000), and thickness of graphite moderating zone behind the liquid wall.

On the exploration of innovative concepts for fusion chamber technology

The Ransom water faucet problem has become one of the most important benchmark tests to study two-fluid/phase flow because it exists an analytical discontinuous solution. The water faucet problem is a gravity-driven wave problem and its analytical solution is derived from the liquid free fall motion. In this paper, the opposite gravity-driven wave problem named the reversed water faucet problem where the liquid admits a rising motion with reduced speed driven by gravity is studied. With assumptions of decoupled phasic pressures, approximate incompressible flow, no liquid pressure gradient, no phase change, no wall and interfacial drag, the analytical solutions of the gas volume fraction and liquid velocity distribution are derived. From the gas volume fraction analytical solution, there is a moving discontinuity which is a very important point for testing accuracy of the numerical scheme and its stability near discontinuities. Two-fluid seven-equation two-pressure model is of particular interest due to the nature of inherent well-posed advantage in all situations. What’s more, high-order accuracy schemes have attracted great increasing attention to overcome the challenge of serious numerical diffusion from 1st-order scheme for accurately simulating many nuclear thermal-hydraulics applications such as long term transient natural circulation problems. In this paper, the solution algorithms with high-order accuracy in space and time are developed for this well-posed two-fluid model and its robustness and accuracy are verified and assessed against the derived analytical solutions. The numerical results show that high-order schemes could prevent excessive numerical diffusion and are more accurate than first-order time and space schemes; the space high-order scheme could give more accurate numerical results than the time high-order scheme for discontinuous solutions.

A fusion reactor design with a liquid first wall and divertor