Breakthrough or More Con Fusion?

December 12, 2022

A lot of chatter about a fusion “breakthrough”, and as far as the lab is concerned, that’s probably right.
A reminder that nuclear fission was achieved several decades before a working fission reactor went commercial.

Wilson Ricks, a PhD candidate at Princeton, has a reality check.

Wilson Ricks on Twitter:

The National Ignition Facility (NIF) has achieved net energy gain from fusion! This is incredibly exciting scientifically, but what does it mean for the future of energy? 

In all likelihood, very little.

A thread:

NIF uses inertial confinement fusion, which involves shooting ultra high-powered lasers into a small capsule containing a deuterium-tritium fusion fuel pellet. The surface the pellet heats, causing an implosion that crunches the interior until (hopefully) fusion is achieved

n this particular instance, it appears that NIF successfully induced a fusion reaction that generated more energy than was originally delivered to the pellet via the lasers. 

This is Net Gain, a milestone that fusion engineers have been pursuing for half a century. 

So as a scientific and symbolic achievement, this is huge. But how much closer does it put us to ‘limitless clean energy’? 

Unfortunately not much closer at all. For inertial confinement fusion, there’s a VERY long way to go between net gain and viable electricity generation. 

To explain just how far, let’s look at the power balance of this experiment. If the reports are correct, the fusion reaction generated 2.5 MJ, compared to 2.1 MJ of laser power. 

BUT, the huge lasers at NIF are less than 1% efficient, so to generate more fusion energy than actual input energy to the facility, you’d need to increase the yield 100x… 

Plus, the fusion power is in the form of heat and radiation, and needs to be converted back to electricity. Assuming a 40% steam cycle efficiency, that’s another 2.5x increase in required yield. So we need a fusion reaction *250x MORE POWERFUL* to achieve true electric net gain.

Now, future lasers might be able to achieve something like 10% efficiency. That’s still a 25x increase in fusion power needed just for NIF to break even from an electricity standpoint. And to actually *generate* power, you of course need much more 

This of course doesn’t even get into the cost of that power, which requires an absolutely enormous facility running shots in rapid succession. NIF’s huge lasers need their optics serviced after only a few shots, but even if it could perform one shot per second…

..the gross continuous power generation at the current yield level would be just 2.5 MW. 

NIF cost about $3.5 billion to build.

Basically, we’re many orders of magnitude away from an inertial confinement power plant along every possible dimension. 

So is fusion power a pipe dream? Not by any means! While inertial confinement fusion may never be a practical power source, *magnetic confinement* fusion holds some real promise.

The ITER project and a number of private companies are aiming to achieve net gain from magnetic confinement fusion within the next decade, and without the horribly inefficient lasers, net gain means a lot more for a magnetic confinement plant than an inertial one. 

So in short, don’t lose hope that fusion could one day power our civilization! On the other hand, don’t expect future fusion plants to look anything like NIF. 

This is partially to be expected, since NIF was designed to study fusion bombs, not energy:

And even if we can ‘solve fusion’, it won’t necessarily monopolize the energy sector. To learn more about the role it might play alongside other resources in a decarbonized electricity grid, check out our recent working paper:


2 Responses to “Breakthrough or More Con Fusion?”

  1. neilrieck Says:

    One shot per second? I have attended a couple of public lectures on “inertial confinement” and was led to believe that the current mode of operation only involved test shots where they tweak external parameters for each event. If this technology ever made it into production then it would be like your v8 gas guzzler in that there would be hundreds of events per second (just drop them in, ignite them via the 192 lasers, then the debris just falls out the bottom). Too much heat? Stop dropping fuel. Easy-peazy!

    I always worried that “magnetic confinement” (as found it tokamaks) might not work properly since they can only confine charged particles. What happens to the wayward uncharged particles like neutrons? BTW, this is not an issue in stars which work by “gravitational confinement”.

  2. John Oneill Says:

    There was a proposal years ago for a fission-fusion hybrid, that would only have to cycle a couple of times a day to produce multiple Gigawatts of power. The lasers would compress uranium to critical density for fission, and that would compress a large lithium deuteride pellet (as well as blasting it with neutrons to make tritium). The whole thing would be in a huge underground cavern, lined with steel, half full of molten salt. The salt would also cascade down the walls, to absorb radiation and shock waves. A steam turbine at the surface would draw off as much salt as needed to be pumped to match demand. Thorium targets would generate enough uranium 233 from neutron capture to supply the fission trigger.
    Not exactly the ‘Mr Fusion’ of ‘Back to the Future’, but it was all possible with 1950s level physics and engineering – probably. Fission without the fusion was judged to be much simpler and cheaper to build. That’s liable to stay true even after the ITER behemoth sparks up, in another decade or two.

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