Monthly Archives: September 2013

Fast Reactors—No Free Lunch

nuke plant cropped

Cooling towers at a thermal reactor plant.

(A slightly technical post; but I find this subject pretty fascinating. This post is more-or-less an extension of my last post, “The Nuke Post” ; I’m going to assume that readers have read that first.)

As I alluded to in my last post and comments, whether breeder reactors are affordable or possible is perhaps a key to the question of the practicality and desirability of nuclear power as we go forward. So, the following is my take on the current state of the field, gleaned from quite a few different sources. Bottom line—1) they do exist and can be built, and 2) we probably can’t afford too many of them.

Breeder reactors are more appropriately called “fast reactors”, so I’m going to use that terminology. And to understand why they’re called fast reactors, we have to step back just a bit and look at “standard” nuclear reactors that are used to generate electricity, the vast majority of which are one form or another of a light-water reactor (LWR). (The “light” refers to regular water, instead of “heavy” water, the latter of which is a different molecular structure that doesn’t naturally occur in large quantities.) These reactors use fuel rods that are enriched to 3%-5% U-235, which are typically interspersed with graphite or carbon control rods, which can be slid in and out of the core to control the speed of the reaction. When they are slid out, the fissile elements (typically U-235) approach critical mass, with neutrons being released that cause, in turn, more neutrons to be released.

Fuel pellet. Reactor fuel is typically enriched to 3%-5% U-235.

Fuel pellet. Reactor fuel is typically enriched to 3%-5% U-235.

Now, in case you’re wondering why the chain-reaction doesn’t accelerate out of control—there are different degrees of critical mass, such as sub-critical, delayed subcritical, and prompt-critical. In most nuclear chain-reactions, some of the neutrons released have a delay that ranges from a few milliseconds to several minutes. In a power reactor this allows control rods time to control the reaction. Fuel in a power generation reactor could never reach a prompt-critical state (necessary for a nuclear explosion), even if the control rods were pulled and left out. The reactor would suffer a melt-down, or even a small explosion, but it wouldn’t be a nuclear explosion, per se. Nuclear weapons typically use plutonium, combined with conventional explosives, to achieve a prompt-critical state.

But back to light-water reactors—when a nuclear chain-reaction begins, the neutrons released have so much energy that they don’t tend to cause fission when they hit other U-235 atoms. They do this much better if they are slowed down, or “moderated”. Thus, the importance of water as a coolant, because water (light or heavy) is an excellent moderator. In LWR’s, water flows through the core, moderating the neutrons, and enabling them to more effectively split other U-235 atoms. A moderated neutron is sometimes called a “thermal” neutron, because its temperature (and therefore energy) has been reduced to that of the coolant. Thus, LWR’s are sometimes called “thermal reactors”.

Idaho National Laboratory's Advanced Test Reactor, a light-water reactor (LWR)

Idaho National Laboratory’s Advanced Test Reactor, a light-water reactor (LWR)

So, that’s that. LWR’s are pretty standard, make quite a bit of electricity around the world, and, unfortunately, leave a lot of high-level nuclear waste behind, as much as 27 tons a year for a 1 GW reactor. Typically about 97% of the original uranium remains in a “spent” fuel rod, along with those fission products I discussed in the last post. In fact, that’s one reason the rod is considered spent—the fission products are all excellent neutron absorbers, and as they build up, the reactor works less and less well, until it has to be shut down and the rods replaced (typically done in thirds, each rod spending three years total in the reactor, but with a third of the rods replaced each year).

This form of operation is considered an “open fuel cycle”; the rods are used once and then disposed of. (In the U.S., no one wants them, so each reactor facility stores them, first in pools of water until their radioactivity subsides some, and then in casks on-site) Now, many consider this to be a total waste, as it is possible for the spent rods to be reprocessed and the fission products removed, and the remainder mixed with new uranium and reused. But, plutonium is typically separated out as part of reprocessing, and proliferation fears caused a ban on reprocessing during the Carter administration in the 1977, and this ban still stands.

So, back to where we began, to fast reactors. They’re called fast reactors because, unlike all of those LWR’s, they don’t moderate the fast neutrons. By letting the neutrons keep their energy, they are much more likely to hit a fertile (but not fissile) U-238 atom, and transform it into fissile P-239. Thus, potentially making more fuel than they use. (Though it’s not some sort of free-lunch—they still need to be fueled with U-238). The cores have to use highly-enriched (17%-26%) uranium, or plutonium, (called “start-up fuel”) and then the core is surrounded with a “blanket” of fertile U-238 where the plutonium is made. That plutonium can’t be used for power until the blanket is reprocessed, though, but I’ll get to this is a bit. Continue reading

The Nuke Post

Testing newly-mined cores for uranium content.

Testing newly-mined cores for uranium content.

Ok, so what to think of nuclear power as a path forward? It’s an extensive and complicated subject, and one that doesn’t lend itself to definitive pronouncements. But, I’ve figured out quite a few things, much of it from a single long blog post by Tom Murphy, “Nuclear Options“, and from that page’s well-moderated and even longer list of comments from highly-educated professionals in the field. I highly recommend reading both if you’re interested in the subject, but if you don’t have a few hours to digest it, here are some important points, as I understand them (the unattributed quotes in this post come from his page)—

The biggest point of all—we can’t just take what we have and scale it up. After my post about Vermont Yankee quite a few people have expressed their opinion to me that we need to take France as a model and start scaling up nuclear power as a (relatively) carbon-free energy source. But, there simply isn’t enough uranium to power a full-scale switch to nuclear fission as we know it, even aside from safety and other concerns. Depending on how you figure it, the world’s 13 TW energy appetite would use up all the uranium in somewhere between six years and a few decades. This is because fissionable U-235 makes up only .7% (that’s point seven percent) of naturally-occurring uranium, which is nearly all “impotent” but fertile (as opposed to fissile) U-238. As such, something like a million tons of natural uranium a year would need to be mined.

Two ways out of this particular dilemma seem to be 1) to use breeder reactors, which can use the U-238 indirectly by converting it to plutonium, and 2) to use thorium, instead of uranium, as a fuel, in reactors (also breeder reactors) that can convert thorium into U-233 (U-233 being the second, but not naturally-occurring, fissile isotope of uranium). Thorium is several times more abundant than uranium in the Earth’s crust, and either of these approaches could extend the available fuel supply to an extent that it would become much less of an issue, or even a non-issue.

(Some other “ways out”—extracting uranium from seawater, or even common granite. At present I believe these options are quite theoretical, with no proven way to extract uranium on a large scale. There is potential there, because fissile materials have a million times the energy density of chemical fuels (oil), but at present these are not realistic options. Then, of course, there is fusion, which is so complex and difficult that I don’t think we’ll ever achieve it on a commercial scale.)

So, back to the “two ways out”—the problem with breeder reactors is mainly that they are expensive and less safe, due to proliferation and other concerns, and as such haven’t been fully developed for power generation. But breeders (sometimes called “fast reactors”) have some advantages. First, they can use both of the naturally-occurring isotopes of uranium, which would extend the available uranium supply by a factor of 140. They can also be designed as “burners”, which are reactors that are specifically designed to use up spent fuel. Because they use fuel differently, spent fuel from fast reactors is also less of a long-term hazard. This point deserves a few lines of explanation, because it’s one of the key advantages of breeder reactors. When a neutron hits a uranium atom and causes it to split, it splits into two “daughter” atoms of various elements, with atomic weights of about 95 and 135. These materials are also referred to as  “fission products”. But, some uranium atoms absorb the neutron without splitting, and become transuranics (sometimes called “actinides”). Both of these, the fission products and the transuranics, remain in the spent fuel. But, they are vastly different in terms of their long-term hazards—fission products have much shorter half-lives, and are more-or-less fully degraded after a relatively short 300 years. The transuranics, however, have half-lives that make them dangerous for tens of thousands, or even hundreds of thousands, of years. BUT—breeder reactors can be built to burn up these transuranics. (I believe GE’s new S-PRISM designs, which are on the verge of being constructed in both the U.S. and Britain, are reactors of this type). So, therein lie the advantages of breeders—they can utilize nearly all of naturally-occurring uranium, they can burn up high-level radioactive waste from non-breeding reactors, and they leave spent fuel that is less hazardous over the long term.

There are disadvantages to breeders, as well. They make plutonium as part of their fuel cycle, and as such raise concerns over proliferation, especially as fuel is reprocessed. But, it also seems that this plutonium isn’t pure enough to be usable in weapons (though all nuclear material of this sort is “pure enough” to be used in dirty bombs); such weapons-grade plutonium is more often made in reactors specially built for this purpose. Breeder reactors are also more complex than standard reactors, and as such, even more expensive. They aren’t unworkable, but of the 430 or more nuclear reactors currently in operation worldwide, only a tiny handful are breeders, notably Russia’s BN-600 reactor, a 560 MW plant that has been operating since 1980. Many more breeder reactors have been built but later shut down, such as France’s Super-Phoenix, and Germany’s SNR-300, the latter a $19-billion plant that was completed, never started, and then decommissioned. Because such reactors aren’t common, a path forward using nuclear to make large proportions of our power would require further research and development (and quite a few countries are currently moving in this direction). It is expense that keeps fast reactors from being more common now, they would only pay off if the price of uranium was substantially higher than it currently is (the cost of fuel is NOT currently one of the big expenses in nuclear power). Continue reading

Et Tu, Time?

Yes, it's still disappearing.

Yes, it’s still disappearing.

Really, Time Magazine? As if the section in The Economist wasn’t enough, I open up Time magazine last night, and see a great big “60%” in their “Briefing” section (Sept. 23 edition), with this text underneath (along with clip-art of a shivering penguin)—

” [60%] Increase in ice-covered ocean water since last year, leading some scientists to believe that the planet is actually undergoing ‘global cooling’.”

It took a whole twenty seconds online to figure out the story behind this, but apparently Time doesn’t have that kind of time. A whole host of articles (all written a week or more before the Time edition), with telling headlines, from reputable sources, spell out the details. Just a few of them—

No, The World Isn’t Cooling“, by Phil Plait on Slate.

With Climate Science Like This, Who Needs Fiction? – Discover Magazine.

Arctic Sea Ice Delusions Strike the Mail on Sunday and Telegraph – The Guardian.

Apparently a notable climate denier named David Rose wrote the original deeply-flawed piece in the Mail, a conservative British tabloid, and it was then picked up by the Telegraph, and from there by various outlets in the U.S. But I’m deeply disappointed in Time; they should be embarrassed by this lapse. If commentators the world over figured it out within days, I just don’t see why they couldn’t have figured it out in a week.

Image credit: muola / 123RF Stock Photo

Hang On, Indeed

Lordy, Lordy. I was just getting my head wrapped around the nuclear question, but before I could write about it the whole deal about the role of small-scale ag came up. So, I’m just getting my head wrapped around that, but before I could write about it, THIS comes up—

Economist coverAn entire special section in The Economist, with endearing cover image and catchy title, about how humans need to grow the economy, in order to save the planet.

Arg. I’m not sure where to begin with this, because my gut feeling is that they’re wrong, or, at a minimum, that the argument needs to be much more nuanced than they present it. But, without days and days to dig into it, I’m not sure I can write with surety. (Not that I’m ever completely sure about anything, as the multiple-stage morphings of my last post  attest to.)

But, a few off-the-cuff thoughts—

First, the articles say that global warming might be one of the more serious threat that species face, along with habitat destruction. Unfortunately, economic growth is tied almost in lockstep with energy growth (see post “A Matter of Limits“). And, despite tremendous gains in renewable capacity in recent years, humans are still using ever more fossil fuel. To paraphrase Bryan Walsh from Time, humans are losing the race to decarbonize. So, if those two things are true, then we need to be very, very careful about issuing blank checks for more economic growth. Burning ever-increasing amounts of fossil fuel just isn’t an answer. (NOTE April 2016– in the years since I wrote this, we have begun to decouple fossil fuel use from economic growth. We aren’t out of the woods yet by any measure, but we’re doing better….)

The articles also give, fairly I think, a great deal of credit to the environmental movement for recent gains. Calls for habitat protection, sustainability, conservation, and the like have moved governments and NGOs alike to enact many changes that have been beneficial. In fact, the entire collection of articles is upbeat in tone, and they urge humanity onward to more economic growth.

But, GDP can be a pretty blunt measure, counting as it does McMansions and Hummers in the rich world right along with better roads and communications for poor African nations. All growth is not equal. There is no doubt that economic growth can help many of the world’s poorest lead dramatically better lives, and there’s no doubt that the very poor trash their environments (as Mr. X never tires of pointing out to me, concern for the environment is the luxury of wealthy nations). But, more urban sprawl and planet-trashing consumption in the rich world is NOT part of the answer, and I’m afraid that a quick read of this section of the magazine by most will do more harm than good, as many will take it as a blank check for more business-as-usual.

In the end, we need to keep and continue all those changes that environmental movements have achieved in rich and poor countries alike, but go easy on these prescriptions for unfettered growth. Rich nations have indeed done some good things with regard to the environment and biodiversity, but they have, and continue to, exact a huge environmental toll, much of it in faraway and poor places. The global warming impact of the wealthy world is also huge—the average American uses something like 40 times the energy that the average person from the world’s poorer nations uses. Even with lower overall population numbers, the consumption in rich nations is at the root of many of the world’s environmental problems.

We aren’t decoupled, and all actions have consequences. Continuing to mushroom the human footprint and impact, if we aren’t careful, is going to have the biggest consequence of all.

Backward and Forward

(Note– I’m deleting nearly everything that I wrote in this post, including the comments; my conversations with Ben Falk and others have caused me to rethink my ideas about the topics in the book. What remains is the much shorter version. -tb)

(Note #2-– I discuss my “rethinking” in a later post, “The Role of Self-Sufficiency“. )

More about nuclear power soon; I’m making progress. But first, since I was just discussing efficiency, a short review of this new book about permaculture that I just bought—”The Resilient Farm and Homestead”, by Ben Falk.

Ben Falk bookFalk’s farm and property, a focus of the book, is just over the mountain from me, in Moretown, Vermont. The book is beautiful, and focuses on how to design and build a largely self-sufficient, regenerative, resilient, rural homestead. From fish and duck ponds, to nut trees, heating water with compost, herbal medicines, gravity-fed water systems, mowing with scythes, and all matter of activities in between, this book is a pleasure to read, and a valuable addition to my library. Along with Mark Shepard’s “Restoration Agriculture”, it presents quite a complete range of permaculture topics.



Cloudy Day Pause

snowy DC

Gray days to deal with.

Mr. X thinks my vision of a future without nuclear power is “too hard” (“Needed: The Hard Path“). I was all set to write a post arguing about it, but something that’s not too uncommon here has given me pause—a dark and cloudy day. This is because a big part of the entire argument of whether we need nuclear power hinges, for most people, on whether or not we can make enough power from renewable sources. And THAT entire argument hinges on the question of intermittency, which is what the cloudy day reminded me of. Solar arrays can make plenty of power on a sunny day, and wind turbines can make plenty of power on a windy day, but what about all those other times? If we depended entirely on wind and solar and hydroelectric, what would we do on short winter days when the entire East coast might be having a cloudy and windless day? Or worse, a week of such days? If the energy constraints in such a system were dramatic, or if such a system was too difficult to build, it might result in that path that would be “too hard”.

So, Mr. X had a variety of points, but his main ones, including whether or not I was being consistent in my thinking, hinge around this “too hard” piece. In general, there are two broad lines of thinking here-

Line-of-thinking #1—We will need nuclear power as we move toward carbon-free sources, because wind and solar and other renewable sources are intermittent, and we will need nuclear power for baseload power. Or, related, we will need nuclear power as a transitional power source, until we build out enough wind and solar and/or develop grid-scale storage capacity.

Line-of-thinking #2—We can indeed switch over to renewable power, and the intermittency problems can be solved, and the money we would have had to spend developing safer “Gen IV” nuclear power would have been better spent on developing the truly safe and sustainable renewable system that we will need for the long term.

So, who is right? Could we make the system work with just renewable power? After some contemplation, I’ve decided that we probably can, though I admit that it will be difficult, as it will involve some fundamental changes. Some factors that make me lean in this direction—

— I think we need to undergo a paradigm shift with regard to how people expect their electricity to be delivered; the new systems will not just mimic the old. Customers today expect electricity to be generated by the utility and made continually available, in any amount, at a set rate. The system of the future might function dramatically differently from this, with the utility companies buying power from thousands or tens of thousands of producers, aggregating that power, and then making it available at a continually varying spot price. Consumers will be able to monitor this price via smart meters, and will be able to use this information to shift their demand.  And, they will indeed shift their demand, because prices might vary dramatically. (And, because the generation is so dispersed, it will help moderate demands on transmission infrastructure.) This change alone would go a long way toward solving the intermittency problem—we might someday see tremendous electricity consumption during sunny hours, as people choose that time when power is plentiful (and cheap) to charge their EV’s, heat or cool their homes, run their water heaters, run their air conditioners, or, factories choose that time to conduct energy-intensive operations.

— Wind and solar complement each other really well. Germany is a good example of this—the country has 32 gw of installed solar, and about 30 gw of wind. Their solar peaks in spring and summer months, when daily solar production is about eight times higher than in December and January. But wind production is nearly the exact opposite, and the seasonal fluctuations largely balance out. (For a visual of this, see pages 13,14, and 16 of this presentation. It takes half a minute or so to load this page, but worth the wait.) Other factors also help, such as the fact that daily demand peaks in most systems during midday hours, and seasonally during the summer, exactly when solar production peaks.

Kaprun hydro-electric dam, Salzburg, Austria.

Kaprun hydroelectric dam, Salzburg, Austria.

— Hydroelectric power could be held back during the day, when solar power is at its maximum, and used during nighttime hours. In many locations it can even be held back seasonally, if required. Pumped-storage systems are used in similar ways; filled when power is cheap, then used for generation when power is expensive. Other forms of utility-scale storage are being developed at a rapid rate, from compressed air storage in abandoned mines, to grid-scale liquid-metal batteries, to ideas about lifting whole mountains (TEDx Talk here), or putting together used EV battery packs in stationary locations for grid-scale battery storage. In all storage situations, the higher the difference between low and high electricity rates, the more profitable the storage—another prime situation where market-forces will help to solve a problem.

— Roofs everywhere need solar panels, even if they don’t have optimum orientations. Panels facing east and west on rooftops (and not just south) spread solar production more evenly across the course of the day (…though in the Southern Hemisphere they put solar on the northern sides of their roofs).

— The larger the geographic area that is tied together by a smart grid, the easier it is to balance power and loads. Over large areas, solar insolation averages out, as does wind production. DC transmission lines are capable of delivering power for well over 1,000 miles, and such transmission corridors could link the production from the windiest areas in the Midwest and offshore to urban centers where it would be needed, and from the sunniest parts of the country to the less-sunny (see post “This is Interesting…“). Continue reading