Posts Tagged ‘Nuclear Fusion’

Fusion Energy breakthrough? Not so much.

December 15, 2022

Click on Image for a larger version. The ‘breakthrough’ was the front page of the BBC News Website. Apparently this was the most important story in the world.

Friends, I find myself lost for words. Why? Because I am apoplectic with disappointment at the breathtakingly bad reporting about the recent ‘fusion breakthrough’ in the US.

Every media organisation whose output I have read has simply regurgitated the line they have been fed by the press office of Lawrence Livermore National Laboratory (LLNL). The BBC made this their headline story with the byline:

The technology is a potential source of near-limitless clean power….

In this article I will outline what actually happened in this ‘breakthrough’, and then explain why this technology will never ever, ever, ever, ever, ever, ever, ever, ever be useful as a power source.

At the end of the article is a list of resources I consulted. Links below to the panel discussion are to timed locations within the video.

The Experiment

The experiment comprised firing a bunch of lasers split into 192 beams at a tiny, hollow, diamond sphere suspended inside an open-ended cylindrical metal capsule. Both the sphere and cylinder were manufactured to extraordinary specifications in terms of their dimensions and surface finish. These extreme specifications are necessary to ensure that the energy is reflected from the inner surface of the cylinder onto the sphere uniformly.

Click on Image for a larger version. Left. The cylinder with the diamond sphere at it’s centre. Right. Illustration of the way in which ultraviolet lasers illuminate the inner surface of the cylinder, which then bathes the diamond sphere in X-rays.

At the panel discussion which followed the press conference, Mark Herman, the LLNL Director for Weapons Physics and Design refused to assign a monetary value to the target, but reasonably it must be on the order of a million dollars per target.

This sphere and cylinder were placed with nanometre precision in the centre of a chamber, and cooled to cryogenic temperatures (less than 20 K). At these low temperatures, the inside surface of the sphere was coated with roughly 60 micrograms (~0.03 mm) of a solid mixture of deuterium and tritium.

When the ultraviolet laser blast hit the metal cylinder, it vaporised and irradiated the sphere with X-rays. The pressure of this blast was so great and so uniform that it rapidly compressed the 4 mm diameter diamond sphere to around 0.1 mm ( from a “basketball to a pea“), accompanied by extreme heating to temperatures in excess of 100 million degrees Celsius.

This extreme temperature and pressure were sufficient to transiently cause the nuclei of deuterium and tritium to collide and fuse, with each fusion releasing 17 MeV (million electron volts) of energy. In more familiar units this amounts to 2.8 x 10^-12 joules per fusion event.

The energy in the laser pulse was estimated to be 2.05 MJ (million joules). I’m afraid I don’t know how that was measured. The energy of the resulting explosion was estimated to be 3.15 MJ. This estimate is made in several ways, but one technique involves putting a metal sphere near the fusion centre. When irradiated by neutrons from the fusion reaction, nuclear reactions cause the metal sphere to be come transiently radioactive, and measurements of this induced radioactivity allow an estimate of the number of neutrons to which it was exposed. This neutron flux is directly linked to the number of fusion events.

The difference between 3.15 MJ and 2.05 MJ = 1.1 MJ is inferred to come from deuterium-tritium fusion reactions. Dividing this yield by the energy per fusion reaction suggests that there were roughly 3.9 x 10^17 fusion reactions. At the panel discussion it was stated that this was 4% of the number of possible fusions, and so this allows us to estimate that there around 10^19 molecules of D and T in the sphere with a volume (in the solid state) of around 4 cubic millimetres.

Energy and Power

Is 1.1 MJ a lot or a little? The answer depends on what you compare it with.

A familiar unit of energy for consumers is the kilowatt hour (kWh) – the units in which we are billed for our gas and electricity. One kilowatt hour is 3.6 MJ, so 1.1 MJ is an appreciable amount of energy. Enough to boil around 3 litres of water.

1 MJ is also the typical energy content of a stick of dynamite. A stick of dynamite weighs ~ 190 grams whereas this same energy was released by ~ 60 micrograms of deuterium-tritium mixture. This gives a sense of the extraordinary power density available in nuclear reactions, and why they make such powerful explosives.

Unsurprisingly, these explosions damage the chamber in which they occur and the optics of the laser used to focus the beams onto the target needs to be repaired after each shot.

Breakeven: the problems emerge.

The hype surrounding this event arose because for the first time an experimental fusion reaction  produced more energy than was required to initiate the reaction.

As was made clear at the panel discussion, this 1.1 MJ of excess energy was the result of the laser imparting 2.05 MJ to the experiment, but the laser itself consumed roughly 300 MJ of electrical power, and this itself would have been derived from around 600 MJ of primary energy, mostly from burning methane in gas-fired power stations.

If we wanted to “improve” this facility so that the same laser produced enough thermal energy to run a power plant that could generate the electrical energy (at 33% efficiency) to run itself, then we would need to increase the yield by a factor 3 x 300 MJ/1.1 ~800. Where might this gain come from?

  • Only 4% of the deuterium-tritium in the experiment reacted so we could gain a factor 25 by arranging for the all the deuterium-tritium charge to burn. Now we just need a factor 33.
  • We might increase the efficiency of the laser from 1% to (optimistically) 20% and then we would just need a factor 1.6 from ‘somewhere’ to break even.

For the sake of argument, let’s assume we got that factor 1.6 somehow – perhaps by increasing the charge of deuterium-tritium. We would then have a system that could in raw energy terms sustain itself. But we would not yet be generating any extra energy at all!

At this point we would have an experiment that once every few weeks could produce an explosion yielding 900 MJ i.e. the equivalent of 900 sticks of dynamite or about 200 kg TNT.

No feasible path to a reactor.

Let’s suppose we want a fusion reactor which can produce 100 MW of electrical power to an external load. This is a small generating plant on a national scale – the UK peak requirement is around 40,000 MW (40 GW) and the planned Hinkley C reactor (if it ever operates) should produce 3,200 MW (3.2 GW).

To achieve 100 MW of electrical output we would need to generate around 300 MW of thermal power to operate a turbine and generator set with an output of 100 MW of electricity. This means that having gone to considerable trouble to generate energy via fusion we would then throw away two thirds of it as heat!

300 MW of thermal power corresponds to 300 MJ/second so assuming that we can (somehow) produce 900 MJ explosions, we need one explosion every 3 seconds to generate enough electricity to ‘breakeven’ i.e. just to operate the plant! So an additional 300 MW of heat would be required to make electricity for other uses: this would require an explosion every 1.5 seconds.

So to summarise, to produce a power plant outputting 100 MW of electricity the designers would need to:

  • Find a way to manufacture tritium.
  • Find a way to capture the energy of the explosions and turn it into heat.
  • Improve laser efficiency by a factor 20 and improve repetition rate by a factor 80,000 from around 1 laser pulse per day to around 1 laser pulse per second.
  • Build a chamber which could withstand a small nuclear explosion (0.2 tonnes of TNT equivalent) every second for (say) 30 years. Remember that the reaction chamber itself would become intensely radioactive and no human could enter it once its service life began.
  • Within this chamber a cryogenically-cooled target must be put in place with nanometre precision once a second.
  • No debris from the previous explosion can remain because this would affect the path of the lasers.
  • To achieve electricity output at a cost of $1 per kWh – around 10 times current use US prices – the cost of the target could not exceed $40. More realistically – considering the other costs involved, the target would need to cost ~$4 and around 58,000 would be required every day.

In short, there is no feasible path to turn this physics experiment into a reactor. And even if all the achievements above were somehow solved, the electricity would still be extraordinary expensive.

Why the hype?

Friends, we are being ‘gaslighted‘.

As Wikipedia puts it:

This term may also be used to describe a person (a “gaslighter”) who presents a false narrative to another group or person, thereby leading them to doubt their perceptions and become misled, disoriented or distressed. Often this is for the gaslighter’s own benefit.

Lawrence Livermore National Laboratory is a nuclear weapons research institute, and one can see how being able to create ‘mini’ nuclear explosions might be useful for them. And that is what this facility is for. As Mark Herman, the LLNL Director for Weapons Physics and Design said in the panel discussion .

“... the ignition work we’re doing is for stockpile stewardship. Our thermonuclear weapons have Fusion ignition … and so studying Fusion ignition is something we do to support the stockpile stewardship program.

In other words it is a technology which allows the US to design and test nuclear weapons without contravening the Comprehensive Nuclear Test Ban Treaty.

Any attempt to frame this technology as having any application whatsoever to energy generation is a deception.

The answers to our energy needs are already available to us.

And finally…

My comments in this article refer to Inertial Confinement Fusion (ICF). In contrast, Magnetic Confinement Fusion (MCF) does have an unlikely, but conceivable path to making a power plant.

In July 2020 I wrote about MCF in this article: Are fusion scientists crazy? The article includes a précis of (and a link to) an excellent talk from Zach Hartwig which I think is the best summary of all approaches to fusion that I have seen.

My other articles about fusion – dating back to 2013! – can be found here:

If you liked this article, you will likely be disappointed with the following articles that I looked at while preparing this:

Are fusion scientists crazy?

July 8, 2020

Preamble

I was just about to write another article (1, 2, 3) about the irrelevance of nuclear fusion to the challenges of climate change.

But before I sharpened my pen, I thought I would look again to see if I could understand why a new breed of fusion scientists, engineers and entrepreneurs seem to think so differently. 

Having now listened to two and a half hours of lectureslinks at the bottom of the page – I have to say, I am no longer so sure of myself.

I still think that the mainstream routes to fusion should be shut down immediately.

But the scientists and engineers advocating the new “smaller faster” technology make a fair case that they could conceivably have a relevant contribution to make. 

I am still sceptical. The operating conditions are so extreme that it is likely that there will be unanticipated engineering difficulties that could easily prove fatal.

But I now think their proposals should be considered seriously, because they might just work.

Let me explain…

JET and ITER

Deriving usable energy from nuclear fusion has been a goal for nuclear researchers for the past 60 years.

After a decade or two, scientists and engineers concluded (correctly) that deriving energy from nuclear fusion was going to be extraordinarily difficult.

But using a series of experiments culminating in JET – the Joint European Torus, fusion scientists identified a pathway to create a device that could release fusion energy and proceeded to build ITER, the International Thermonuclear Experimental Reactor.

ITER is a massive project with lots of smart people, but I am unable to see it as anything other than a $20 billion dead end – a colossal and historic error. 

Image of ITER from Wikipedia modified to show cost and human being. Click for larger view.

In addition to its cost, the ITER behemoth is slow. Construction was approved in 2007 but first tests are only expected to begin in 2025; first fusion is expected in 2035; and the study would be complete in 2045.

I don’t think anyone really doubts that ITER will “work”: the physics is well understood.

But even if everything proceeds according to plan, and even if the follow-up DEMO reactor was built in 2050 – and even if it also worked perfectly, it would be a clear 40 years or so from now before fusion began to contribute low carbon electricity. This is just too late to be relevant to the problem of tackling climate change. I think the analysis in my previous three articles still applies to ITER.

I would recommend we stop spending money on ITER right now and leave it’s rusting carcass as a testament to our folly. The problem is not that it won’t ‘work’. The problem is that it just doesn’t matter whether it works or not.

But it turns out that ITER is no longer the only credible route to fusion energy generation.

High Temperature Superconductors

While ITER was lumbering onwards, science and technology advanced around it.

Back in 1986 people discovered high-temperature superconductors (HTS). The excitement around this discovery was intense. I remember making a sample of YBCO at Bristol University that summer and calling up the inestimable Balázs Győrffy near to midnight to ask him to come in to the lab and witness the Meissner effect – an effect which hitherto had been understood, but rarely seen.

But dreams of new superconducting technologies never materialised. And YBCO and related compounds became scientific curiosities with just a few niche applications.

But after 30 years of development, engineers have found practical ways to exploit them to make stronger electromagnets. 

The key property of HTS that makes them relevant to fusion engineering is not specifically the high temperature at which they became superconducting. Instead it is their ability – when cooled to well below their transition temperature – to remain superconducting in extremely high magnetic fields.

Magnets and fusion

As Zach Hartwig explains at length (video below) the only practical route to fusion energy generation involves heating a mixture of deuterium and tritium gases to immensely high temperatures and confining the resulting plasma with magnetic fields.

Stronger electromagnets allow the ‘burning’ plasma to be more strongly confined, and the fusion power density in the burning plasma varies as the fourth power of the magnetic field strength. 

In the implementation imagined by Hartwig, the HTS technology enables magnetic fields 1.74 times stronger, which allows an increase in power density by a factor 1.74 x 1.74 x 1.74 x 1.74 ≈ 9. 

Or alternatively, the apparatus could be made roughly 9 times smaller. So using no new physics, it has become feasible to make a fusion reactor which is much smaller than ITER. 

A smaller reactor can be built quicker and cheaper. The cost is expected to scale roughly as the size cubed – so the cost would be around 9 x 9 x 9 ~ 700 times lower – still expensive but no longer in the billions.

[Note added on 8/2/2021: I think this large factor is justified: see my response to the comment from Dr Brian VonHerzen for an explanation]

And crucially it would take just a few years to build rather than a few decades. 

And that gives engineers a chance to try out a few designs and optimise them. All of fusion’s eggs would no longer be in one basket.

The engineering vision

Dennis Whyte’s talk (link below) outlines the engineering vision driving the modern fusion ‘industry’.

A fusion power station would consist of small modular reactors each one generating perhaps only 200 kW of electrical power. The reactors could be produced on a production line which could lower their production costs substantially.

This would allow a power station to begin generating electricity and revenue after the first small reactor was built. This would shorten the time to payback after the initial investment and make the build out of the putative new technology more feasible from both a financial and an engineering perspective.

The reactors would be linked in clusters so that a single reactor could come on-line for extra generation and be taken off-line for maintenance. Each reactor would be built so that the key components could be replaced every year or so. This reduces the demands on the materials used in the construction. 

Each reactor would sit in a cooling flow of molten salt containing lithium that when irradiated would ‘breed’ the tritium required for operation and simultaneously remove the heat to drive a conventional steam turbine.

You can listen to Dennis Whyte’s lecture below for more details.

But…

Dennis Whyte and Zach Hartwig seem to me to be highly credible. But while I appreciate their ingenuity and engineering insight, I am still sceptical.

  • Perhaps operating a reactor with 500 MW of thermal power in a volume of a just 10 cubic metres or so at 100 million kelvin might prove possible for seconds, minutes or hours or even days. But it might still prove impossible to operate 90% of the time for extended periods. 
  • Perhaps the unproven energy harvesting and tritium production system might not work.
  • Perhaps the superconductor so critical to the new technology would be damaged by years of neutron irradiation

Or perhaps any one of a large number of complexities inconceivable in advance might prove fatal.

But on the other hand it might just work.

So I now understand why fusion scientists are doing what they are doing. And if their ideas did come to fruition on the 10-year timescale they envision, then fusion might yet still have a contribution to make towards solving the defining challenge of our age.

I wish them luck!

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Videos

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Video#1: Pathway to fusion

Zach Hartwig goes clearly through the MIT plan to make a fusion reactor.

Timeline of Zach Hartwig’s talk

  • 2:20: Start
  • 2:52: The societal importance of energy
  • 3:30: Societal progress has been at the expense of CO2 emissions
  • 3:51: Fusion is an attractive alternative in principle. – but how to compare techniques?
  • 8:00: 3 Questions
  • 8:10: Question 1: What are viable fusion fuels
  • 18:00 Answer to Q1: Deuterium-Tritium is optimal fuel.
  • 18:40: Question 2: Physical Conditions
    • Density, Temperature, Energy confinement
  • 20:00 Plots of Lawson Criterion versus Temperature.
    • Shows contours of energy ration Q
    • Regions of the plot divided into Pointless, possible, and achieved
  • 22:35: Question 3: Confinement Methods compared on Lawson Criterion/Temperature plots
    1. Cold Fusion 
    2. Gravity
    3. Hydrogen Bombs
    4. Inertial Confinement by Laser
    5. Particle accelerator
    6. Electrostatic well
    7. Magnetic field: Mirrors
    8. Magnetic field: Magnetized Targets or Pinches
    9. Magnetic field: Torus of Mirrors
    10. Magnetic field: Spheromaks
    11. Magnetic field: Stellerator
    12. Magnetic field: Tokamak
  • 39:35 Summary
  • 40:00 ITER
  • 42:00 Answer to Question 3: Tokamak is better than all other approaches.
  • 43:21 Combining previous answers: 
    • Tokamak is better than all other approaches.
  • 43:21 The existing pathway JET to ITER is logical, but too big, too slow, too complex: 
  • 46:46 The importance of magnetic field: Power density proportional to B^4. 
  • 48:00 Use of higher magnetic fields reduces size of reactor
  • 50:10 High Temperature Superconductors enable larger fields
  • 52:10 Concept ARC reactor
    • 3.2 m versus 6.2 m for ITER
    • B = 9.2 T versus 5.3 T for ITER: (9.2/5.3)^4 = 9.1
    • Could actually power an electrical generator
  • 52:40 SPARC = Smallest Possible ARC
  • 54:40 End: A viable pathway to fusion.

Video#2: The Affordable, Robust, Compact (ARC) Reactor: and engineering approach to fusion.

Dennis Whyte explains how improved magnets have made fusion energy feasible on a more rapid timescale.

Timeline of Dennis Whyte’s talk

  • 4:40: Start and Summary
    • New Magnets
    • Smaller Sizes
    • Entrepreneurially accessible
  • 7:30: Fusion Principles
  • 8:30: Fuel Cycle
  • 10:00: Fusion Advantages
  • 11:20: Lessons from the scalability and growth of nuclear fission
  • 12:10 Climate change is happening now. No time to waste.
  • 12:40 Science of Fusion:
    • Gain
    • Power Density
    • Temperature
  • 13:45 Toroidal Magnet Field Confinement:
  • 15:20: Key formulae
    • Gain 10 bar-s
    • Power Density ∝ pressure squared = 10 MW/m^3
  • 17:20 JET – 10 MW but no energy gain
  • 18:20 Progress in fusion beat Moore’s Law in the 1990’s but the science stalled as the devices needed to be too big.
  • 19:30 ITER Energy gain Q = 10, P = 3 Bar, no tritium breeding, no electricity generation.
  • 20:30 ITER is too big and slow
  • 22:10 Magnetic Field Breakthrough
    • Energy gain ∝ B^3 and ∝ R^1.3 
    • Power Density ∝ B^4 and ∝ R 
    • Cost ∝ R^3 
  • 24:30 Why ITER is so large
  • 26:26 Superconducting Tape
  • 28:19 Affordable, Robust, Compact (ARC) Reactor. 
    • 500 MW thermal
    • 200 MW electrical
    • R = 3.2 m – the same as JET but with B^4 scaling 
  • 30:30 HTS Tape and Coils.
  • 37:00 High fields stabilise plasma which leads to low science risks
  • 40:00 ARC Modularity and Repairability
    • De-mountable coils 
    • Liquid Blanket Concept
    • FLiBe 
    • Tritium Breeding with gain = 1.14
    • 3-D Printed components
  • 50:00 Electrical cost versus manufacturing cost.
  • 53:37 Accessibility to ‘Start-up” entrepreneurial attitude.
  • 54:40 SP ARC – Soomest Possible / Smallest Practical ARC to Demonstart fusion
  • 59:00 Summary & Questions

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