Historical research guide · 0976 · 2019
Nuclear Fusion Power Plants
Shutaro Takeda · Richard Pearson
In one minute
This is the incumbent fusion roadmap, written by two people inside it. Shutaro Takeda of Kyoto University and Richard Pearson of the Open University walk through what fusion is, how a reactor holds a plasma hot and dense enough for long enough, and what still has to be invented before a fusion power plant sells electricity. Their central number is the triple product — density times temperature times how long the heat stays in — and their central observation is that it climbed steadily from the 1970s and then stopped, because the whole field poured itself into ITER. They lay out the real bottlenecks with numbers attached: the world’s entire commercial tritium stockpile is about 30 kilograms and ITER alone wants almost 20 of it, so every future plant has to breed its own fuel from lithium, and nobody has yet demonstrated that breeding blanket. Then they name the alternatives — high-temperature superconducting tokamaks, magnetised target fusion, and the aneutronic fuels that skip tritium altogether.
Connection
Chapter 12 argues that every scheme on this site needs the same thing first, a small source of very large energy, and this chapter is the honest ledger of what the mainstream route still owes: the divertor, the breeding blanket, the neutron-tolerant wall, the magnets. Chapter 9 meets it where the plasma stops being a passive fluid and starts being a confined, self-sustaining object — magnetised target fusion, the compact private machines, and the proton-boron-11 fuel cycle that returns charged particles instead of neutrons.
From the source
Two different breakevens have to be kept apart. Scientific breakeven is a fusion energy gain of one, the moment the energy produced in the plasma equals the energy supplied to sustain it. Engineering breakeven compares the plant’s energy production against the total consumption of the whole power plant, auxiliary systems and conversion losses included — and it is engineering breakeven that is the true goal on the pathway to the realization of fusion energy.Section 2, Fundamentals of nuclear fusion science
The performance of any fusion machine reduces to one number, the triple product of plasma density, temperature and energy confinement time, known as the Lawson criterion. Plotted since the 1970s it shows a steady climb towards scientific breakeven — and then a stall: progress towards breakeven has stagnated over the past two decades, as all focus has been on ensuring ITER’s success, which has diverted funding, manpower and time from other pathways and even from alternative tokamak concepts.Sections 2 and 3.2; the Lawson diagram, Figure 5
ITER’s primary objective is to yield a fusion reaction that produces five times more energy than is needed to sustain the reaction, and to demonstrate the scientific and technological feasibility of fusion energy using tokamaks. First plasma, the start of preliminary deuterium-deuterium operation, was scheduled for 2025; the start of full-power deuterium-tritium operation, which allows the attempt at breakeven, has been pushed back almost two decades from the original date to 2035.Section 1, Introduction, closing paragraph
Fuel supply, not physics, is the binding constraint on the deuterium-tritium cycle. Tritium does not occur in nature in any significant quantity and comes only as a by-product of heavy-water CANDU fission reactors; the global stockpile available for commercial use is around 30 kilograms, and ITER alone must be supplied with almost 20 kilograms of it, while a commercial reactor would consume 55.6 kilograms per year per gigawatt of thermal output. Every future plant must therefore breed its own tritium from lithium-6 at a breeding ratio above one — and to date no proof-of-concept for tritium breeding technology has been demonstrated.Sections 5.1 and 5.5; the lithium-6 breeding reaction, Equation 7
On lithium and deuterium alone the authors estimate fusion could supply the electricity needs of humanity for 14 to 23 million years, which is what makes the resource base virtually unlimited. The scarcity sits elsewhere: beryllium, wanted as the neutron multiplier in the breeding blanket at about 400 tonnes per gigawatt of electrical output, exists in total global deposits of only 100,000 to 150,000 tonnes — far short of a 2500-gigawatt fleet — so lead-based breeder blankets are being explored as the substitute.Section 5.5, Sustainability
The authors name the routes that do not go through ITER. Magnetized target fusion, sometimes called magnetized inertial fusion, works the parameter space between magnetic and inertial confinement — higher densities than magnetic confinement, lower-power drivers than inertial — and is supported in the United States through the ARPA-E ALPHA programme. Tokamak Energy and Commonwealth Fusion Systems are building high-temperature superconducting tokamaks; General Fusion is building an acoustically driven pulsed machine; and TAE Technologies is exploring liner-driven proton-boron-11, opting to avoid the complications that arise from the deuterium-tritium fuel cycle.Sections 3.1 and 6.2, Innovative approaches by private companies
The way in
https://doi.org/10.5772/intechopen.80241How to cite it
Shutaro Takeda, Richard Pearson (2019) Nuclear Fusion Power Plants doi:10.5772/intechopen.80241