Compact Fusion Advanced Rankine Research Articles

A preliminary study of a D—T tokamak fusion reactor with advanced blanket using the compact fusion advanced Brayton (CFAB) cycle

Preliminary key issues for a synchrotron radiation-enhanced compact fusion advanced Brayton (CFAB) cycle fusion reactor similar to the CFAR (compact fusion advanced Rankine) cycle reactor are presented. These include plasma operation windows as a function of the first wall reflectivity and related issues, to estimate an allowance for deterioration of the first wall reflectivity due to dpa effects. It was found theoretically that first wall reflectivities down to 0.8 are still adequate for operation at an energy confinement scaling of 3 times Kaye-Goldston. Measurements of the graphite first wall reflectivities at Nagoya University indicate excellent reflectivities in excess of 90% for CC-312, PCC-2S, and PD-330S in the submillimeter regime, even at high temperatures in excess of 1000 K. Some engineering issues inherent to the CFAB cycle are also discussed briefly in comparison with the CFAR cycle which uses hazardous limited-resource materials but is capable of using mercury as coolant for high heat removal. The CFAB cycle using helium coolant is found to achieve higher net plant conversion efficiencies in excess 60% using a non-equilibrium magnetohydrodynamic disk generator in the moderate pressure range, even at the cost of a relatively large pumping power, and at the penalty of high temperature materials, although excellent heat removal characteristics in the moderate pressure range need to be guaranteed in the future.

Inertial fusion reactors using Compact Fusion Advanced Rankine (CFARII) MHD conversion

This study evaluates the potential performance (efficiency and cost) of inertial fusion reactors assumed capable of vaporizing blankets of various working materials to a temperature (10,000-20,000 K) suitable for economical MHD conversion in a Compact Fusion Advanced Rankine II (CFARII) power cycle. Using a conservative model, 1-D neutronics calculations of the fraction of fusion yield captured as a function of the blanket thickness of Flibe, lithium and lead—lithium blankets are used to determine the optimum blanket thicknesses for each material to minimize CoE for various assumed fusion yields, “generic” driver costs, and target gains. Lithium-hydride blankets are also evaluated using an extended neutronics model. Generally optimistic (“advanced”) combinations of lower driver cost/joule and higher target gain are assumed to allow high enough fusion yields to vaporize and ionize target blankets thick enough to stop most 14 MeV neutrons, and to breed tritium. A novel magnetized, prestressed reactor chamber concept is modeled together with previously developed models for the CFARII Balance-of-Plant (BoP), consisting of a supersonic plasma jet, MHD generator, and “raindrop” condensor. High fusion yields (20 to 80 GJ) are found necessary to heat and ionize the Flibe, lithium, and lead-lithium blankets for MHD conversion, with initial solid thicknesses sufficient to capture most of the fusion yield. Much smaller fusion yields (1 to 20 GJ) are required for lithium-hydride blankets. For Flibe, lithium, and lead—lithium blankets, improvements in target gain and/or driver cost/joule, characterized by a “Bang per Buck” figure-of-merit of ≥ 20 joules yield per driver $, would be required for competitive CoE, while a figure-of-merit of ≥ 1 joule yield per driver $ would suffice for lithium-hydride blankets. Advances in targets/driver costs would benefit any IFE reactor, but the very low CFARII BoP costs (contributing only 3 mills/kWh to CoE) allows this type of reactor, given sufficient advances that non-driver costs dominate, to ultimately produce electricity at a much lower cost than any current nuclear plant.

Design and Safety Analysis of the CFAR Cycle Concept

The CFAR (compact fusion advanced Rankine) cycle concept for an advanced tokamak reactor consists of a high temperature blanket cooled by evaporating mercury, microwave superheaters and magnetohydrodynamic generators for direct electric power generation. The vanadium alloy blanket is designed to minimize the MHD pressure losses in the front section where the mercury is evaporating. A passive concept for condensing the mercury vapor in the event of a LOCA (loss of coolant accident) is described. It is shown that an active cooling system is required to keep the vanadium alloy structure and the front part of the blanket at acceptable temperatures during cool-down after a LOCA.

Low Cost, High Yield IFE Reactors: Revisiting Velikhov’s Vaporizing Blankets

The performance (efficiency and cost) of IFE reactors using MHD conversion is explored for target blanket shells of various materials vaporized and ionized by high fusion yields (5 to 500 GJ). A magnetized, prestressed reactor chamber concept is modeled together with previously developed models for the Compact Fusion Advanced Rankine II (CFARII) MHD Balance-of-Plant (BoP). Using conservative 1-D neutronics models, high fusion yields (20 to 80 GJ) are found necessary to heat Flibe, lithium, and lead-lithium blankets to MHD plasma temperatures, at initial solid thicknesses sufficient to capture most of the fusion yield. Advanced drivers/targets would need to be developed to achieve a “Bang per Buck” figure-of-merit ≳ 20 to 40 joules yield per driver $ for this scheme to be competitive with these blanket materials. Alternatively, more realistic neutronics models and better materials such as lithium hydride may lower the minimum required yields substantially. The very low CFARII BoP costs (contributing only 3 mills/kWehr to CoE) allows this type of reactor, given sufficient advances that non-driver costs dominate, to ultimately produce electricity at a much lower cost than any current nuclear plant.

A D-T tokamak fusion reactor with advanced blanket using compact fusion advanced Rankine (CFAR) cycle

Recent progress of a D-T tokamak fusion reactor with advanced blanket concept using CFAR (Compact Fusion Advanced Rankine) cycle is presented. High enthalpy extraction in excess of 50% was found achievable by a nonequilibrium disk-type MHD generator for gas stagnation temperatures of 3000 K superheated by synchrotron radiation, leading to a 40% overall plant efficiency with recuperative heat cycle and advanced thermoelectric converters. The stored magnetic energy of a 10 T MHD three-pairs Helmholtz-type magnet was estimated to be about 600 MJ per MHD generator. A mixture of mercury and lithium liquid flow was examined and found applicable to reduce the mercury inventory. The tritium permeation loss inherent in the relatively high temperature CFAR cycle, neutronics relating to tritium breeding and streaming through the waveguide and the MHD generator duct are discussed. Results of a 2000 h high temperature (600–700°C) mercury corrosion test of Type 304 stainless steel, a TZM alloy and four kinds of ceramic rods in refluxing mercury with 0.004 mol fraction of potassium admixture have shown no noticeable corrosion except for Type 304 stainless steel.

Study of high-performance non-equilibrium MHD generator for compact fusion advanced Rankine cycle

The conceptual design of high-performance non-equilibrium disk magnetohydrodynamic (MHD) generator for compact fusion advanced Rankine (CFAR) cycle has already been performed by the authors. In the design, however, the inlet stagnation pressure may be too high (12.8 atm), making it difficult to design the other components of the cycle. The present study, therefore, performs conceptual design of high performance MHD generator with low stagnation pressure (4 atm) for CFAR cycle. For this purpose, the distribution of magnetic flux density is dealt as unknown variable and is calculated from given inlet conditions, generator configuration and electron temperature. The calculations are performed by using quasi-one-dimensional steady-state simulation code. All conditions except the load current and seed fraction are, at first, determined by preliminary study of design conditions. Then, calculations are performed for various load currents and seed fractions to find out the generator with highest enthalpy extraction ratio. The enthalpy extraction ratio of conceptually designed generator reaches 54.5%.

Compact Fusion Advanced Rankine (CFAR II) Power Cycle

The Compact Fusion Advanced Rankine (CFARII) power cycle is a direct plasma energy conversion scheme for inertial fusion (ICF) and magnetically-insulated, inertially confined fusion (MICF) reactors...

Advanced Fusion MHD Power Conversion Using the CFAR Cycle Concept

The CFAR (compact fusion advanced Rankine) concept for a tokamak reactor involves the use of a high-temperature Rankine cycle in combination with microwave superheaters and nonequilibrium MHD disk generators to obtain a compact, low-capital-cost power conversion system which fits almost entirely within the reactor vault. The significant savings in the balance-of-plant costs are expected to result in much lower costs of electricity than previous concepts. This paper describes the unique features of the CFAR cycle and a high-temperature blanket designed to take advantage of it as well as the predicted performance of the MHD disk generators using mercury seeded with cesium.

Microwave heating of flowing slightly-ionized gases in a compact fusion advanced rankine (CFAR) cycle

A compact fusion advanced closed-Rankine cycle (CFAR) based on the less expensive “in-situ” nonequilibrium MHD (magnetohydrodynamic) conversion with assistance from synchrotron radiation superheat in the “microwave” tokamak using synchrotron radiation both for MHD energy conversion and current drive is studied for the improvement of tokamak fusion reactor economy. In this CFAR concept, superheat of flowing slightly-ionized gases by synchrotron radiation energy plays a very important role in the system cycle efficiency, using solely MHD electrical power generation. This paper describes a two-dimensional microwave superheat model and examines the above envisaged concept, which is a key issue in the CFAR cycle.

Reactor applications of the compact fusion advanced rankine (CFAR) cycle for a D-T tokamak fusion reactor

The preliminary design of a high temperature blanket and compact power conversion system for a D-T reactor utilizing a mercury Rankine cycle and nonequilibrium MHD disk generators is described. The CFAR cycle is described in detail and a blanket geometry is proposed which is designed to give good heat transfer and low pressure drops for the two-phase boiling mercury flow in the presence of strong magnetic fields. The blanket utilizes beryllium and flibe in the low-temperature breeding zone and lithium aluminate in beryllium oxide pebbles in the high-temperature breeding zone to obtain a tritium breeding ratio of 1.07. With careful choice of materials and geometry, it has been possibly to have 46% of the neutron and gamma heat deposited in the high-temperature pebble beds at the back of the blanket. The design utilizes the many advantages of liquid-metal Rankine cycles, including low pressures, mass flow rates and pumping power, and superheating along with internal regeneration to achieve good thermal efficiencies of about 35% using the microwave superheater and about 32% without the microwave superheater. The capital costs are expected to be much lower than past design concepts because the MHD power generators and the mercury condensers and heat exchangers can all be placed inside the reactor vault; preliminary cost estimates indicate a very attractive cost of electricity for this advanced concept.

Conceptual design of the blanket and superheater in compact fusion advanced rankine cycle

In reactor concepts using the Compact Fusion Advanced Rankine Cycle (CFAR), the mercury works as a coolant and starts to boil in the vicinity of the inlet of the tritium breeding zone, and fully vaporizes at the exit. The vaporized mercury is then superheated in the neutron superheating zone, after which it is subjected to further microwave superheating. Finally it generates electricity directly by a MHD generator. In the preliminary design, the Flibe and beryllium are charged in the tritium breeding zone. Though this design gave marginal results with excellent neutron multiplication ability of the beryllium, the cycle efficiency is still not satisfactory and other blanket concepts need to be studied. In the present design, the lithium-lead eutectic is proposed. Since the Q -value for neutron multiplication reaction of the lead is much more negative than the beryllium, less heat is produced in the tritium breeding zone. This means less mercury is required to cool this zone, and the final temperature of the mercury and the MHD efficiency could be increased. We performed parametric design studies for this concept to increase the plant efficiency under the condition that the tritium breeding ratio satisfies the planned value by utilizing the ANISN neutron transport code.

Preliminary study of the performance characteristics of a mhd generator for the compact fusion advanced rankine cycle

The feasibility of high enthalpy extraction from the in-situ radiation-catalyzed MHD generator is studied numerically as a part of the compact fusion advanced Rankine cycle for fusion reactors. The cesium seeded mercury is selected as the working medium, which is superheated by synchrotron radiation from the fusion plasma. In the MHD channel, electrons are heated by Joule dissipation, leading the electron temperature to be higher than that of the mercury vapor. A new type of disk configuration is proposed in the present paper, which is referred to as a disk type generator with separate channels. By using this type of generator, the enthalpy extraction ratio reaches about 59.44% in the case of multi-power take-offs. The obtained cycle efficiency is about 32.1% for a simple cycle. In the case of the recuperative cycle the efficiency becomes about 35.8%. If some amorphous thermoelectric conversion can be installed, the cycle efficiency reaches about 41.7%, which is similar to conventional steam-turbine cycles.