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Friday, August 30, 2013

The painful progress of fusion

I recently undertook my decennial scan of our latest efforts to extract useful amounts of energy from controlled nuclear fusion. It’s one of those subjects I feel a need to check up on every decade or so in case I miss an interesting new development.

Okay that may be a little cynical, but domestic electricity produced by nuclear fusion seems to have been thirty years away for my entire life and time is running out. My time at any rate, because I’ve finally reached an age where I may claim with some confidence that fusion power will never be viable. I mean – there is no longer much risk of my being proved wrong before coffin time is there?

So where are we now? Well is possibly the place to go for the upbeat, mainstream, big money view. Technically and as an example of human determination to succeed, it’s a mighty project. In spite of my crusty cynicism, I’m also something of a closet nerd. I simply can’t help but be impressed. I want it to work but that thirty year horizon is still with us.

ITER is not an end in itself: it is the bridge toward a first plant that will demonstrate the large-scale production of electrical power and tritium fuel self-sufficiency. This is the next step after ITER: the Demonstration Power Plant, or DEMO for short. A conceptual design for such a machine could be complete by 2017. If all goes well, DEMO will lead fusion into its industrial era, beginning operations in the early 2030s, and putting fusion power into the grid as early as 2040.

As early as 2040? Almost a whole career from now, but one hopes that is merely a coincidence. Yet if nuclear fusion is ever to yield an unlimited supply of energy at an accessible cost, then we are surely entitled to be a little hard-headed as well as taking the long view. Take this on the Hot Cell Facility for example:-

The Hot Cell Facility will be necessary at ITER to provide a secure environment for the processing, repair or refurbishment, testing, and disposal of components that have become activated by neutron exposure. Although no radioactive products are produced by the fusion reaction itself, energetic neutrons interacting with the walls of the vacuum vessel will 'activate' these materials over time. Also, materials can become contaminated by beryllium and tungsten dust, and tritium.

By the phrase components that have become activated by neutron exposure, they mean components made radioactive by the neutron flux from the fusion reaction. Although the deuterium/tritium fusion reaction is the most favourable fusion reaction energetically, it spews out a lot of neutrons which are bound to make containment materials radioactive.

So as well as the extreme technical difficulties in containing a fusion plasma at 150 million degrees, we have a radioactive waste problem which never goes away.

Not only that, but tritium is a rare isotope of hydrogen and about 300g of tritium will be required per day to produce 800 MW of electrical power. The plan is to generate this in situ via lithium and that neutron flux, but this too has yet to be tested on a sufficiently large scale. According to Wikipedia, commercial demand for tritium is 400 grams per year, costing about US $30,000 per gram.

So as ever, fusion power has many hurdles to overcome, but a serious fusion plant is being built and more lessons will be learned. Somehow though, it all sounds ominously expensive even though costs will be driven down if the technique ever goes commercial.

Will it ever go commercial though?

Something inside me says not, but maybe that’s because I’ve waited such a long time for this particular egg to hatch. For me it has acquired the queasy feel of a colossal vanity project.

Ho hum – maybe I’ll take another gander in 2023.

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Paddington said...

It's not vanity, more curiosity. Besides, we already have human-generated fusion. The problem is control.

A K Haart said...

Paddington - I take your points. Something niggles me about this project though - maybe it's the PR gloss.