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ITER and Many Nuclear Fusion Startups Use Misleading Power Terms

The Nuclear Fusion industry has been working towards various kinds of milestones in energy generation and various kinds of energy breakeven.

The public only cares about the point when the fusion reactor will continually generate commercial power at a price and performance that is superior to a nuclear fission reactor or to coal.

The fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state. This is more energy in the form of heat than the energy that went into the plasma.

However, energy that goes into the plasma could be produced by lasers or ultra-high velocity projectiles which could need many times the energy to generate. The heat that is produced needs to be converted to electricity.

In 1997, the JET tokamak in the UK, at Q = (16 MW)/(24 MW) ≈ 0.67 got 67% of the plasma power input out as heat. JET (Joint European Torus) used 700 million Watts of electricity to produce fusion particles with 16 million Watts of power. JET lost 98% of the power it consumed. None of the power, heat or particles produced was converted back into electricity.

Steven B. Krivit at New Energy Times has highlighted this problem where misleading technical definitions are created and then are not explained to the public.

The condition of Q = 1, when the power being released by the fusion reactions is equal to the required heating power is called breakeven or scientific breakeven. Plasma breakeven can be 100 times away from what is needed for a practical reactor.

ITER, First Fusion and MIT Sparc All Have Misleading Public Statements

First Light Fusion in a press release claimed that by 2024 its experimental fusion reactor would achieve gain – generating more energy than is used to spark a reaction. They are referring to plasma energy gain. It does not represent getting to commercial power levels.

The Multi-billion dollar International Thermonuclear Experimental Reactor (ITER) has spent over $14 billion so far and will only reach some level of plasma energy gain for a few minutes at a time if everything works as planned.

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Brian Wang's picture

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Nathan Wilson's picture
Nathan Wilson on February 18, 2019

Yes, the fusion yield, Q must be significantly higher than 1 for a practical reactor, but things do get much better once Q reaches 5.  That's because 20% of the fusion energy (for tritium-deuterium fusion) is carried by the helium-nucleus fusion products; it is charged, so it gets trapped in the magnetic field, giving its energy to the plasma.  The other 80% is carried by the neutrons, which escape the plasma and are harvested by the power plant.

The other reason Q=1 is important is because, for modest research-sized reactors, there is a guaranteed improvement in Q just from scaling the design from research-sized to power-plant-sized.  Of course, the ITER plan was to go big from the start, which is problematics as they found out, since going big increases program bureaucracy and schedule/cost over-runs.

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