Category Archives: Nuclear Power

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

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

Oh My


Mr. X has taken me roundly to task for my Vermont Yankee post. He has some strong points, and suggests that my entire line of thought, throughout my posts, is in danger of contradicting itself. I think he’s wrong, but I’m going to have to do some thinking in order to explain why.

In the meantime, I turn on the computer this morning and see a shocking article on CNN written by an international nuclear consultant, “Why Fukushima is Worse Than You Think“. Oh my, indeed.

I haven’t followed the Fukushima story particularly closely, but my rough understanding of the incident before I read the article was this—after the tsunami the reactors lost power, which caused the cores to begin to overheat, and TEPCO eventually, at great risk to some workers, was able to pump water onto the cores to stabilize them, power was eventually restored to the area and total meltdown was avoided, but the water had become radioactive and had run into the basements, and had to be pumped into temporary holding tanks. Meanwhile, airborne releases of radioactivity did waft over hundreds of square miles, but mandatory evacuations kept most of the population there from being exposed. The incident caused no deaths, and recent reports have shown that radiation exposure to the Japanese population was minimal.

Indeed, everyone seems to discuss Fukushima in the past tense, as in this passage from a Time Magazine article, “According to a recent U.N. report, there will likely be no detectable health impacts from the radiation released by the Fukushima meltdown. The  biggest catastrophe in nuclear power since Chernobyl has turned out less catastrophic than it seemed.”

Well, apparently we haven’t been following this closely enough. If the CNN article is to be believed, and it certainly appears to have been written by someone who clearly knows what he’s talking about, Fukushima is far from over. The pumping of the cooling water has never stopped, and highly radioactive water still runs through the melted cores and into the basements at a rate of 400 tons a day. It is pumped from there to temporary tanks on-site, which currently store 400,000 tons of water. Some of the tanks and hoses leak, and hundreds of tons of radioactive water have soaked into the ground or run into the Pacific. No one can enter the reactors because the radiation is lethal, no one knows how far the containment was breached, and if they stop pumping the water the spent fuel would heat up and ignite, causing a release of radiation “dozens of times worse than Chernobyl.” Worse, I get the impression that no one quite knows how to fix it, and the author of the article is calling for an international crisis team to be assembled.

So, I’ll do some thinking about the “hard path” I outlined in the Vermont Yankee post, but this only reinforces my gut feeling that I’d rather live a simpler life powered by clean wind and solar, than an extravagant one powered at the risk of disasters like Fukushima.

In the balance, a better option.

In the balance, a better option.

9 Sept 13- Clarification— Apparently part of the 400 tons of water that accrues each day comes from groundwater flowing into the basements, where it mixes with the radioactive water that is already there, which is what the “ice wall” that has been in the news is designed to stop. The reactor cores themselves have been in “cold shutdown” since Dec. 2011, and part of the delay seems to be a normal multi-year pause before decommissioning begins, to allow radiation levels in the cores to stabilize. However, water must be maintained in the reactors cores and the spent fuel pools, and apparently some of the containments still leak into the basement. How much of the 400 tons a day comes from which source I can’t seem to figure out, but either way it’s a mess.

Image credit: swisshippo / 123RF Stock Photo
Image credit: tonarinokeroro / 123RF Stock Photo

Needed: The Hard Path

Vermont Yankee.

Vermont Yankee.

Vermont Yankee is closing. While I normally have no real shortage of opinions on many issues, I don’t really have an opinion about this one.

If you aren’t aware, Vermont Yankee is an aging, 540-megawatt reactor in Vernon, Vermont, on the banks of the Connecticut River. It has been a lightning rod for those who oppose nuclear power in the Northeast, and the site of numerous spills, leaks, and small mishaps (though many would argue that opponents regularly make mountains out of molehills whenever this particular plant is concerned). The drive to shut it down has moved to the courts, and the battles there are ongoing. But, in the midst of this, low U.S. natural gas prices (themselves largely the result of another controversial arena, fracking) seem to have sealed Yankee’s fate, and owner Entergy just announced that the plant will be closed next year.

And here the mixed feelings begin. On one hand, nuclear power plants seem vulnerable to terrorism, have the potential to wreak havoc on huge areas (think Fukushima, Chernobyl), use fuel that is non-renewable and difficult to extract, and produce waste that is problematic. On the other hand, they have, on the whole, solid safety records, small footprints, and produce carbon-free power. Then, there is even more potential benefit when you move beyond considering just current reactors (so-called “Generation II” and “Generation III” reactors) and look at newer designs that could be built to shut themselves down if things go wrong, or, like fast-breeder-reactors, use fuel much more efficiently. (A good Time Magazine article here.)

If CO2 emissions and the resulting warming are serious problems, and if the energy in fossil fuels is difficult to replace with renewable power (posts: “A Matter of Limits” and “The Magic-Wand Question“), then nuclear power might, just perhaps, be a big part of the solution. More than a few former critics of nuclear power have come to this conclusion, and have become supporters. A recently released documentary by Robert Stone, “Pandora’s Promise”, focuses on some of these individuals. Trailer–

Not everyone agrees with this viewpoint, and the reviews of the film have been mixed. Brian Walsh of Time, whose opinion I tend to respect, feels that it is important, and writes that it should be seen, especially by environmentalists. Others are more critical. I haven’t seen the film yet, but I get the gist of it.

So all of this gives me some things to ponder.

First, some issues are just complex and difficult to be definitive about, issues where all-or-nothing pronouncements tend to be intellectually dishonest. I’d put nuclear power into this group, along with fracking and GMOs. All are problematic, yet all have the potential to be part of the solution.

Second, there is the issue of whether R&D money put into nuclear power wouldn’t be better spent elsewhere. The “promise” of nuclear power hasn’t been fully realized; newer “Gen IV” designs are not ready to go into full production, and much investment would be required. These billions might be better spent doing research on permaculture, or utility scale storage, or any of a thousand other needed efforts.

But third, call me crazy, but we need the curtailment that will come with switching to renewables. It will impose self-discipline; the comparative scarcity of this power will force efficiency and conservation. Humanity has huge problems in addition to energy, like deforestation and pollution and overfishing and groundwater depletion, and many of these can only be solved by reducing the human footprint on the planet (at least until we decouple; see post “Free Lunch and the Holy Grail“); which will require true paradigm shifts with regard to human behavior. If by some miracle we could actually provide what the nuclear supporters of the 70’s envisioned, “electricity too cheap to meter”, I’m afraid it would just allow humanity to plow ahead with profligate wastefulness and business-as-usual.

So in the end, perhaps I do have an opinion. I’m afraid, though, that it is an opinion that might not be popular. Hard paths never are. We must be disciplined, we must be focused, and if we are going to work hard, we might as well think big, and work toward a planet powered by clean, renewable power, with reduced consumption and a reduced focus on material things; a world of wind turbines, solar panels, permaculture, highly-efficient buildings, and more intentional living. That’s the clean, safe, healthy future we need.

 Image credit: Wikimedia Commons


“We are all complicit. Have we all asked ourselves—are we driving the most fuel-efficient car we can afford? Have we taken steps to halve our own carbon emissions?” -Dr. Alan Betts, at SolarFest.

Early morning SolarFest

Early morning SolarFest

Your live, on-the-spot reporting from SolarFest here—many dreadlocks, much protest-music playing, sandals, Reggae music and Prius driving, henna tattoos, sprinkled with an occasional dose of suspicion of the government (ha, just like the far right), all wrapped up with a layer of techno-pop-Woodstock ambiance. But a great many products and workshops; ideas that could carry us a long way forward if they were applied across the board, from savannah farming to

Henna tattoos.

Henna tattoos.

carbon-zero houses and all manner of solar and wind products. But also on display—the problem we have that I’ve been writing about all along—many, many cases of the right hand not talking to the left. No one seems to have a workable master plan. On one side of the SolarFest lot, we have groups that are adamantly opposed to nuclear power, and particularly want the closure of Vermont Yankee. I’m not sure what their plans are to replace the power from today’s nuclear plants. My guess would be “consume less”, which, unfortunately, is everyone’s answer (I spoke with them after I wrote this, but I’ll save all that for future posts). Then on another side we have groups that oppose the new solar fields on Route 7 in Vermont, referring to this as “solar sprawl”. Then we have, which seems to oppose everything, and still other groups that oppose utility-scale wind here in Vermont. I spent some time talking to Lukas Snelling of Energize Vermont, a group that opposes all utility-scale wind on Vermont’s ridges. He had stacks of huge photographic prints of blasting and road construction and the huge access roads that are being built in Lowell, VT, in order to get the parts of these towers up the mountains. I will readily admit that the impact of these roads is substantial. These roads do not match one’s mental picture of “access roads”, they look more like four-lane highways prior to paving, complete with huge infills and equally huge blasting cuts, all in formerly pristine mountain landscapes. But as bad as this is, I’m also pretty sure this is a case of a failure to see the whole picture.

So let’s step back. How exactly are we going to save the planet? What exactly are our plans with regard to energy? The very short consensus by those who have looked at this—we’re going to need to phase out fossil fuels, and use power more efficiently, and, even with this (here’s the kicker)—double the production of electricity. Somehow. This after phasing out electricity generation from coal and natural gas . The amount of energy in fossil fuels is tremendous, almost staggering, and to replace it, even with serious conservation and efficiency, is going to take a massive effort.

Part of this will, and should, come from the one thing that everyone does seem to agree on—distributed, roof-mounted solar. I agree as well, for every roof to have solar on it would be a great start. But it wouldn’t be enough. The sun doesn’t shine at night, and, here in the relative north, it doesn’t shine much in the winter months. So, something else is going to have to take up the slack, and it’s going to have to be big, and it’s going to have to be carbon-free. And there’s no doubt in my mind that a big chunk of that needs to be from wind. Small-scale solar works, but small-scale wind doesn’t work nearly as well—there are huge economies of scale and efficiencies inherent in the larger wind projects. I will even allow that nuclear power might need to stay, at least for a while.

peace wallSo, more on this topic soon—Lukas is going to send me the files for some of his photographs of the Lowell wind project, and I’d like to post them; they are thought-provoking, and there is much to this that needs discussing.

But back to Solarfest—many good ideas, many dedicated people, mixed in with a few loonies and a few earth-types who could stand to shower a bit more often. It was all a bit messy, with not many clear answers, but perhaps that in itself makes it a miniature version of the problems we face.

Until next year.

Until next year.