So as stated in my last post, I'm reading "The Watchman's Rattle" by Rebecca Costa, which, while it's hitting a lot of good psychological points, seems to be simply incoherent on energy issues.
I've gotten to Ms. Costa's story concerning space-based solar power, claiming that it's a fine example of what she calls "Silo Thinking".
Silo thinking, or bunkering, as I've called it at work, is essentially when the wall you have to throw ideas over to collaborate are a bit taller than your arm is strong. It's what happens when you have territorial management. It's a clear point, it happens fractally as you escalate the scope of organization, and it's something that restricts the ability of an organization to handle large and complex projects.
The problem isn't with the example, which, if true, would be a prime example of the issue. The problem is, she's over-selling space-based solar.
I won't bother quoting the book. Her explanation is pretty bad where it hits details, and pretty light on the details in general.
Space-based solar is a simple concept: you throw a satellite into geosynchronous orbit*, unfurl a PV or heat capturing device, convert the incoming energy into electricity, and fire a microwave laser at the earth's surface where, hopefully, there's an energy capture dish.
There are obvious potential safety issues with the concept, but they're entirely soluble with good engineering. Meanwhile, materials science helps as well with potential efficiency.
However, Costa sells this as "unlimited free energy", which it isn't, at least, no more than rooftop solar is. She also sells space-based solar as having efficiencies "magnitudes greater than what we achieve by laying solar panels on our roofs".
Solar flux is limited to about 450 watts / sq picoradian. That equates to about 1 kW / m^2 at the equator on a sunny day, or 1.4 kW / m^2 at geostationary orbit. To convert this flux, we use either a heat engine or photovoltaics. Neither solution has very high efficiencies: 33% for thermal, 25% for PV. Both ground-based and geostationary solar is only active about 1/3 of every 24 hour cycle. Ground-based has about a 50% duty cycle even from that, due to weather conditions. Space based solar must then transmit the power down to earth, at an efficiency of about 84%.
Now, while that means that space-based solar can be as much as 3.1 times as efficient, that's only a single order of magnitude if you're using e (which I do endorse, as it's a more "natural" growth measure), but I believe the conventional wisdom is that a 10x improvement constitutes an order of magnitude.
Then there's the cost. Even assuming the use of lightweight, thin-film solar panels, held out using a minimum scaffolding, you're still only talking about 300 W/kg, at ~$3/W for panel capacity alone ($9/W to accommodate the 33% duty cycle), and a cost to orbit of about $1200/kg.
In power generation, we talk about dollars per watt (Power cost). The current prevailing limit of profitability for electricity production is at about $3/W. SBSP, including just those factors, is $13/W. That is not free. That has to be re-spent every time the panels get too degraded by micrometeors, an estimated 10 years. That's $0.14/kWh just for generation, without profit added - which is currently more than I pay for all electricity-related service.
It's no secret I'm a fan of nuclear power, and moreover of LFTR. The reason for this is that I've looked into solar, wind, and even the lame "magnetic motor perpetual motion" self-delusions that people have, and have found them to be too diffuse, too expensive, too variable, or any combination of the three. Nuclear power, well executed**, is an effective solution to climate change.
* Or use geosync sats as relays for giant SBSPs at the leading and trailing lagrange points of the earth.
** i.e., with reprocessing where it's needed, and with a focus on building reactors that continuously reprocess, such as LFTR.
Saturday, March 5, 2011
Thursday, March 3, 2011
I'm presently reading The Watchman's Rattle by Rebecca Costa. It's a good read, so far, concerning largely the differences in the way we address about problems, the difficulties that come from complexity, and the way cognitive shortfalls can doom societies.
Unfortunately, she stepped on a pet peeve. I'm not a nuclear engineer. I'm not in the field. But I have done quite a bit of study on the subject so as to elevate my knowledge on the subject past that of a layman. So when I got to the bits about Costa's problems with nuclear energy, I just had to say something.
Although not widely known, nuclear power plants must shut down approximately every eighteen months to replace their fuel rods. The old fuel rods contain short-lived, low-level poisons as well as a highly toxic, radioactive material called Np-237, which has a half-life of more than two million years. Not counting nuclear facilities already on the drawing board, today we produce the “equivalent of one-hundred double-decker buses” of nuclear waste every year—waste that has to be stored somewhere.
The Watchman's Rattle, pg 42This is entirely true, if partial. There's a lot more toxic, radioactive stuff in there than Neptunium. Were we to reprocess our nuclear waste, as France does, the actinides - those elements that are heavier than Uranium - remain in the return fuel stream to be burned up. Depending on the implementation, we may even exclude Np-237.
There's actually a market for Np-237: when NASA sends out satellites to explore deep space (which they have sadly not done recently), they use what are called radioisotope thermoelectric generators. These run on Pu-238, a metal that, while not fissile like it's Highly Weaponable big brother, Pu-239 (of Demon Core and Operation Crossroads fame), is nonetheless an alpha (high-energy helium atom) emitter that - well shielded - generates about 0.5W/g of material, with a half-life of 87.7 years (i.e., a 200W fueled RITE generator will only be producing 100W). The primary production mode for Pu-238 is via the neutron bombardment of Np-237.
No, the nastiest isotope in the mix is Cs-137. It can substitute itself for potassium in many biological processes - up to the point where it fails and causes problems; it's got a half-life of 30 years, giving it high radioactivity (@0.6MeV/beta decay) with a 300 year backgrounding time; it decays to Barium, which, depending on what it was bonded to at the time, can result in serious toxicity.
On the up side, nuclear waste is solid and stays where you put it.
It turns out that nuclear energy isn’t clean at all. We’re simply putting pollution into the ground instead of releasing it into the air.
The Watchman's Rattle, pg 42I'm not sure what planet you live on. See, I live on Earth, a planet that has a core heated largely by nuclear decay. But I was talking about reprocessing, wasn't I?
For the United States, producing roughly 810 TWh / year in 2008, it's true that we generate approximately 10,000 tonnes of spent nuclear fuel per year. Of that spent fuel, only about 100 tonnes is actually unusable in the nuclear fuel cycle - the rest can be put right back into a reactor.
The cry I always hear about reprocessing is that it enables proliferation. I haven't gotten that far in the book yet, but I wouldn't be surprised to see it show up. To cut it off: the argument from proliferation screams ignorance about the problem of proliferation. That is to say, if you're concerned about nuclear proliferation, you might care to know what is being proliferated aside from "nuclear material".
Little secret: anything that undergoes spontaneous nuclear reactions is nuclear material. Think about that next time you inhale an atom of Carbon-14.
I'll scare you proper with the train of thought that normally shuts down conversations about nuclear reprocessing.
In spent fuel from any commercial light water reactor, the average breeding of plutonium isotopes for a 1% burn-up is about 0.6%. The prevailing method of reprocessing, PUREX, separates this plutonium from the Uranium and fission product streams.
At this point you're meant to say, "OMG PLUTONIUM! T3H ENERGY COMPANIES ARE MAKIN' DEMON COR3Z!"
If you recall, above, I specifically called out Pu-239 as the isotope of choice for weapons. Spent fuel plutonium - "reactor grade" - does contain Pu-239, but only at an average of about 50%. The rest is a mix of Pu-240 and Pu-241. Pu-240 has a high spontaneous fission rate - which means that if there's any appreciable quantity of it in a weapon core, it's likely that the weapon will prematurely detonate. Pu-241 has a different problem: with its short half-life of 14 years, it decays quickly to Am-237, which is a heavy gamma emitter.
Gamma emitters are bad, especially if you need to, you know, control you nuclear weapon. Gammas interfere with electronics and kill people. High contamination of Pu-241 in a weapon core renders it deadly to the weapon's operator - and builder.
There is a trope going around that a weapon was made from "reactor grade plutonium" in the 1980's - but the fuel in question was right at the edge of what's called "reactor grade" - about 80% Pu-239. Spent fuel from commercial reactors contains nowhere near those concentrations.
Then there's the argument that reactor grade plutonium can be enriched to the needed amounts. To that, I say, "So what?" As a nation or terrorist organization, you can enrich natural uranium to the 90% required to be considered "weapons grade" near as easily as plutonium (*SWU), but without the step of diverting it from bureaucratically monitored and well-secured channels.
So there it is: we should be reprocessing our nuclear fuel, working towards a fuel cycle that doesn't product so much of it (LWRs are terribly fuel inefficient, which is what leads to reprocessing being necessary), and simply burying the fission products for the 300 or so years it'll take them to background.
Not a typo. I did say 300. The quarter-million to several millions of years it takes to background our existing nuclear fuel stream is largely caused by neptunium and plutonium isotopes - which means that if we're just plowing those fissile and breedable materials back into the fuel cycle, we're dealing with them on reasonable time scales.
We're not yet digging holes to bury our nuclear fuel; no one can yet agree on Yucca Mountain. At the moment, most of our nuclear fuel is stored on-site at the power plants at which it's produced. It's my suspicion that Yucca Mountain is meant to be a spring board for governmentally run reprocessing operation, and that there's serious political hand-wringing - gridlock, if I may - concerning the topic. Honestly, I can think of no bigger waste than burying what is essentially 99% fuel and 1% hot trash, just because the hot trash is seriously neutron absorbent.
Chu smiled warmly and in a soft voice mentioned that if every roof and road were painted white, it would be the equivalent of taking eleven billion cars off the road for eleven years.“It’s a cheapie,” he added.Rather than build hundreds more nuclear power plants producing more radioactive waste, wouldn’t we rather paint our roofs and roads white? We could practically do it overnight, and the results would be immediate. Cars would remain cooler and use less energy. Cooler roads also mean less tire wear. The sun’s rays would be reflected rather than absorbed, so there would be an immediate temperature reduction around the globe. The demand for household air conditioning would drop 20 percent.
The Watchman's Rattle, pg 43I applaud efforts at conservation, but as you had mentioned just pages earlier:
When I show up at the local water board meetings and attempt to explain why conservation is not a permanent solution but rather a short-term mitigation, everyone’s eyes roll back in their heads. “Get rid of your grass and replace your landscaping with drought-tolerant plants,” they say.
The Watchman's Rattle, pg 17Anyway, that's as far as I had gotten before electing to weigh in. I'll continue reading, and likely comment as I see fit. I have high hopes for the book, especially if it manages to nail down what you mean by "insight" as a process beyond the symptomatic "eureka" moment.
I really think you should rethink, or restudy nuclear. When I did, the issue of climate change crystallized for me from feeling like an insoluble, murky, overwhelming issue of doom to being a simple matter of acting quickly on technology we'd not yet fully explored. I found that conventional wisdom on nuclear energy is largely based on misunderstood statements and political wrangling.
I won't call it conspiracy - that would assume a level of subject-matter competency among anti-nuclear activism that just isn't there. The problem is fear and ignorance.
*SWU: It's orders of magnitude easier to enrich to 50% than it is to enrich from 50%. Why? Say you have a box of red and white marbles, mostly white. If you shake the box around, and grab at the patch that look the most white, you've just enriched your box's red content. If, on the other hand, you've got lots of red and few white, you're going to have a harder time enriching your red. Since the particles are macroscopic, you can pick them out - but for nuclear chemistry, it's not so easy.
at 5:52 PM