Category: Science

New discoveries, the scientific method, and all matters relating to the scientific study of the physical world

Basics of gas centrifuge uranium enrichment

[U]ranium enrichment is the process that separates U-235 from U-238 in order to increase the proportion of the former isotope. Separation is measured by the kilogram separative work unit (SWU), representing the amount of uranium processed and the degree to which it is enriched. The gas centrifuge exploits the mass difference between these two isotopes (three neutrons) by spinning uranium hexafluoride gas (UF6) at extraordinarily high speeds (twice the speed of sound), forcing the lighter U-235 to the center, where it can be “scooped off” at the top. These centrifuges must be arranged in cascades, or groups of centrifuges, as each cascade enriches the material only slightly before feeding it into the next. Although this process may sound fairly simple, the specialized materials and precision engineering necessary are very difficult to achieve.

The necessary ingredient for the enrichment process, UF6, must be free of any impurities, as impurities may condense and trigger blockages in the valves and piping of the cascades, causing the centrifuges to crash. Once this gas is produced with the highest degree of purity, it is then ready to be fed into the centrifuge, a machine made of many complex parts. The main components are (1) rotor and end caps; (2) bearing and suspension systems; (3) electric motor and power supplies; (4) center post, scoops, and baffles; (5) the vacuum system; and (6) the casing. The first challenge is to acquire the specialized materials for these parts. High-strength, corrosion-resistant materials, such as maraging steel, aluminium alloys, titanium, glass-fiber resins, or carbon fiber, are essential for most of the aforementioned components. Maraging steel specifically provides not only protection but also the capacity for faster rotor speed.

The second challenge is to construct a perfectly balanced centrifuge rotor (an almost impossible task) that can rotate at supercritical speeds (about 100,000 rpm). In addition to the complex engineering necessary for the construction of other centrifuge parts, a method must be devised to control the temperature and convection in the vacuum. Now imagine replicating this precision engineering in cascades of about three thousand centrifuges.

Khan, Feroz Hassan. Eating Grass: The Making of the Pakistani Bomb. Stanford University Press; Stanford. 2012. p. 142

Open thread: additive manufacturing

I was surprised to see that I don’t seem to have ever put up a post about 3D printing, despite the variety of ways in which it’s interesting.

The Economist has recently printed a few articles:

I’ve done a little 3D printing myself, making one of Bathsheba’s free designs at the Toronto Reference Library. It would be great to be able to print in something more durable than the biodegradable plastic they offer.

Lots of significant climate news

CPSA is keeping me busy, but there have been some interesting news stories in the last few days:

Overall, recent developments are worrisome. We know how short a window there is for action capable of hitting the Paris Agreement’s targets, and yet we continue to make contradictory policy choices.

Climate change messaging

A paper by Pearce, Brown, Nerlich, Koteyko (“Communicating climate change: conduits, content, and consensus“, 2015) contains some interesting ideas about effective communication about climate change. They cite one “best practice guide” which explains that:

in order for climate science information to be fully absorbed by audiences, it must be actively communicated with appropriate language, metaphor, and analogy; combined with narrative storytelling; made vivid through visual imagery and experiential scenarios; balanced with scientific information; and delivered by trusted messengers in group settings.

It also notes that: “Messages focusing on fear and predictions of adverse events can increase skepticism, perhaps because they disrupt underlying ‘just world’ beliefs and can reduce people’s intentions to perform mitigating actions”.

This kind of research is important. Motivation may be the trickiest part of the climate challenge: getting people to care about the welfare of people impacted all over the world by climate change, and well into future generations. Then making people willing to demand political and economic change to prevent the worst potential impacts of excessive fossil fuel use.

Wandering Home: A Long Walk Across America’s Most Hopeful Landscape

My family in Vermont sent me Bill McKibben’s 2005 book (updated in 2014) as a Christmas gift. In it, he recounts a meandering trek through the Lake Champlain region of the Adirondacks. It’s part nature writing, partly an account of the history of the region and the ways his neighbours are tying to earn a living, and partly a meditation on the nature of wilderness and how it relates to human life.

McKibben talks about small-scale farmers and winemakers trying to compete against giant agribusiness corporations by securing premium prices for local food; students keen to establish major vegetable gardens at local colleges; debates about what to think and do about invasive species; strategies for social change; park rangers burning down the illegal cabins of hunters; and the ruin and ruckus caused by all-terrain vehicles and Jet Skis.

The book fits into a theme of environmentally-minded people finding ways to undertake major wilderness excursions, which I also saw among friends before leaving Facebook. I can see the plausibility in how time invested this way can help control the adverse emotions which accompany environmental activism in the face of a public wedded to consumerism and corporations and politicians vigorous in their defence of the status quo. At the same time, it’s hard to undertake when I am always behind on PhD requirements and never really financially secure enough for vacations.

In any event, the book is another good demonstration of McKibben’s eloquence and constant focus on the big questions facing humanity. I hope one day I will get to visit some of the landscape he describes.

“We won’t stop using fossil fuels tomorrow”

Sometimes paired with the fallacious argument that only people who use no fossil fuels can legitimately oppose fossil fuel development is the statement: “We won’t stop using fossil fuels tomorrow”.

The logical error associated with using this statement to defend new fossil fuel infrastructure like fracking wells and bitumen sands pipelines (as well as new fossil fuel vehicles or power plants) is so obvious that it may seem unnecessary to state, but the quip is so popular among those trying to delay adequate action on climate change that it requires a quick rebuttal.

It’s true that human society is dependent on fossil fuels, and not only for discretionary activities that people can legitimately be asked to give up. That said, it’s now entirely evident that climate change threatens human civilization if unchecked, to say nothing of the profound damage it’s already doing to non-human nature. Preventing the worst impacts of climate change requires a rapid transition away from fossil fuels, and that is fundamentally incompatible with building new fossil fuel infrastructure.

Under contraction and convergence, it is plausible that some poor places can legitimately build a modest amount of additional fossil fuel infrastructure. This is most defensible in places that have low per capita emissions, low historical emissions, and where new fossil fuel use will address basic human needs instead of luxuries. None of these conditions apply in Canada or the United States, where per capita and historical emissions are both unconscionably high, and where most citizens routinely make heavy use of fossil fuels for trivial purposes.

The line about not giving up fossil fuels tomorrow is rhetorically appealing because it makes the speaker seem like a level-headed pragmatist and suggests that anyone who disagrees is out of touch with reality. In actual fact, our existing dependence on fossil fuels is an argument against new fossil fuel infrastructure, not for it. The media, members of the public, and decision-makers need to accept this.

Writing my first book

Nothing about my PhD so far has been easy. As long-time readers may recall, my first comprehensive exam was only passed after two attempts and a lot of effort. The strike was painful, and has made me particularly question the quality of undergraduate education that U of T provides, in terms of class and tutorial sizes, the selection of professors, and support for and integration of teaching assistants into the learning process. I am now edging toward a formal research proposal for departmental approval and ethics review.

I originally wrote a longer document which talked more about methodology and many other things, but my supervisor encouraged me to write something more concise with the essential features of the proposed research project.

The plan now is to make sure the short document is a plausible nucleus for a successful PhD, including through a presentation to a brown bag lunch at the U of T Environmental Governance Lab on October 27th; to incorporate what has been left out in the older longer proposal; and to seek departmental and ethical approval before beginning first round remote interviews.

My supervisor has intelligently cautioned me about seeking too many critiques of these documents – a factor which has complicated and delayed my efforts so far, and which may be drawn from my experience as a civil servant. I have also been warned by Peter Russell that I am starting to write my thesis in the form of the proposal. So no comments please, unless they are strictly limited and focused on the process for making this proposal viable.