Inertial Fusion: Potential benefits of Energy Research and Development

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The potential benefits of successful development of an inertial confinement fusion-based energy technology justify investment in fusion energy research and development as part of the long-term U.S. energy R&D portfolio, says a new report from the National Research Council. Although ignition of the fusion fuel has not yet been achieved, scientific and technological progress in inertial confinement fusion over the past decade has been substantial. Developing inertial fusion energy would require establishment of a national, coordinated, broad-based program, but achievement of ignition is a prerequisite.

The authors argue that “The potential for using fusion energy to produce commercial electric power was first explored in the 1950s. Harnessing fusion energy offers the prospect of a nearly carbon-free energy source with a virtually unlimited supply of fuel. Unlike nuclear fission plants, appropriately designed fusion power plants would not produce the large amounts of high-level nuclear waste that requires long-term disposal. Due to these prospects, many nations have initiated research and development (R&D) programs aimed at developing fusion as an energy source. Two R&D approaches are being explored: magnetic fusion energy (MFE) and inertial fusion energy (IFE). This report describes and assesses the current status of IFE research in the United States; compares the various technical approaches to IFE; and identifies the scientific and engineering challenges associated with developing inertial confinement fusion (ICF) in particular as an energy source. It also provides guidance on an R&D roadmap at the conceptual level for a national program focusing on the design and construction of an inertial fusion energy demonstration plant.”

The Inertial Fusion Energy

Fusion Reaction

Fusion Reaction

Fusion, nuclear fission and solar energy (including biofuels) are the only energy sources capable of satisfying the Earth’s need for power for the next century and beyond without the negative environmental impacts of fossil fuels. The simplest fusion fuels, the heavy isotopes of hydrogen (deuterium and tritium), are derived from water and the metal lithium, a relatively abundant resource. The fuels are virtually inexhaustible – one in every 6,500 atoms on Earth is a deuterium atom – and they are available worldwide. One gallon of seawater would provide the equivalent energy of 300 gallons of gasoline; fuel from 50 cups of water contains the energy equivalent of two tons of coal. A fusion power plant would produce no climate-changing gases, as well as considerably lower amounts and less environmentally harmful radioactive byproducts than current nuclear power plants. And there would be no danger of a runaway reaction or core meltdown in a fusion power plant. [2]

Simple schematic of the four stages of inertial confinement fusion via “hot spot” ignition.

Simple schematic of the four stages of inertial confinement fusion via “hot spot” ignition.

There are two alternative approaches to developing fusion as an energy source that are currently being explored: IFE and magnetic fusion energy.To initiate fusion in either approach, deuterium and tritium fuel must be heated by an external energy source to over 50 million degrees and held together long enough for the reactions to take place. Ignition occurs when the energy produced by the fusion reactions is sufficient to heat the remaining fuel to fusion reaction conditions. At that point, no additional external heating source is needed, and the reaction in essence is self-sustaining until the fuel is depleted. Tritium (heavy heavy hydrogen) and deuterium (heavy hydrogen) are the fuels with the lowest energy threshold for fusion to occur.

Schematic of the four major components of an IFE power plant. (cr: The National Academy of Sciences)

Schematic of the four major components of an IFE power plant. (cr: The National Academy of Sciences)

One liter of sea water contains enough lithium—from which tritium fuel is “bred”—and deuterium to make roughly 1 kWh of fusion energy. The two main approaches to fusion achieve these conditions differently: in magnetic confinement fusion, the low-density fuel is held indefinitely in a magnetic field while it reacts; in inertial confinement fusion (the basis of IFE), a small capsule/target of fuel is compressed and heated so that it reacts rapidly before it disassembles.

Factors Influencing the Commercialization of IFE

The board also mentioning that in order to use IFE in a Commercial scale, power production requires many integrated systems, each with technological challenges. Those systems should operate reliably and economically over many years and with minimal downtime [1]. In order to achieve that though, there is a need for a nationally development program the authors argue. “(..)  at the present time there is no nationally coordinated research and development program in the United States aimed at the development of IFE that incorporates the spectrum of driver approaches, the spectrum of target designs, or any of the unique technologies needed to extract energy from any of the variety of driver and target options. In the event that ignition is achieved at NIF or another facility, and assuming that there is a federal commitment to establish a national IFE R&D program, the DOE should develop plans to administer such a national program—including both science and technology research—through a single program office”.

“The fuel used in the fusion process is lithium and deuterium; deuterium is derived from water and therefore virtually unlimited,” explained Gerald Kulcinski, associate dean for research and director of the Fusion Technical Institute at the University of Wisconsin, Madison, who served as co-chair of the report committee. “And unlike nuclear fission plants, it would not produce large amounts of high-level nuclear waste requiring long-term disposal. The potential is for a sustainable energy source that could power the Earth for millions of years.”

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