Like many of you, I’ve been closely following the developments at the Fukushima reactor complex. Below is a set of links to articles I’ve written for the Stranger, as the events have unfolded.

3/12/2011
Explosion at Fukushima Nuclear Plant, Cesium Detected

3/14/2011
Don’t Panic

Geiger Counter Readings Rise in Tokyo

3/15/2011
What’s on Fire at the Fukushima Reactor?

Will Radioactive Particles from the Leaking Reactor Reach Washington State?

The Fukushima Fifty

3/16/2011
“We believe that radiation levels are extremely high” (A discussion of acute radiation injury)

3/17/2011
Video from a Helicopter Flyover of the Fukushima Plant

The Health Effects of Radioactive Isotopes from Fukushima

3/20/2011:
Radiation from Fukushima, in Seattle

3/24/2011:
How Radiation Is Measured

3/27/2011:
Radiation From Fukushima, in Seattle, Tells the Story

Surplus power generated in one interconnection, at this time, cannot be transferred to another. Further, the parts of the continent most promising for wind, solar and geothermal power (i.e. the greenest power choices available right now) are far from where the bulk of power is consumed (the East and West coasts).

Enter the Tres Amigas project–a plant build a superconducting triangle of powerlines to connect these three grids. Using high temperature superconductors allows the power to be transmitted as direct current with similar efficiencies to alternating current. (Mashing together alternating currents from disparate grids is quite problematic, due to issues of phase. Using DC to connect the grids alleviates this problem. Superconductors alleviate some of the inefficiencies of transmitting DC over long distances.)

This is good news from the perspective of green energy. Connecting the East and West coasts to the areas most promising for wind and solar power will boost the economic viability of such projects in the near future. In the negative, this allows for all sorts of new games to be played by energy traders in the largely unregulated energy market.

A landmark Energy Department project to bury carbon dioxide produced by humans has begun as workers sunk a huge drill bit into Illinois ground this week, signaling continued support for a climate change mitigation strategy that has fallen out of favor in many circles.

The start of drilling marks the launch a geological sequestration project that will deposit a million metric tons of carbon dioxide into the ground by 2012.

While that’s nothing compared to the several billion tons of CO2 that humans emit yearly, it’s the geology of the site that makes the development exciting. The CO2 will be piped into a geological formation that underlies parts of Illinois, Indiana and Kentucky that could eventually hold more than 100 billion tons of CO2.

While I find the term ‘clean coal‘ to be absurd, I still think this sort of technical investment is critical for the future health of the climate. Thanks to years of foot-dragging on alternatives, the entire world has gone on a fossil-fueled power plant building spree. Carbon sequestration may never pan out. It’s, sadly, one of our few remaining shots at averting environmental catastrophe.

Take Shell’s move today, as a portent:

Shell will no longer invest in renewable technologies such as wind, solar and hydro power because they are not economic, the Anglo-Dutch oil company said today. It plans to invest more in biofuels which environmental groups blame for driving up food prices and deforestation.
….
The company said it would concentrate on developing other cleaner ways of using fossil fuels, such as carbon capture and sequestration (CCS) technology. It hoped to use CCS to reduce emissions from Shell’s controversial and energy-intensive oil sands projects in northern Canada.

Well, what of the alternatives? Wind is going to be a challenge, particularly in the context of climate change. Biofuels–at least fuels from bioengineered organisms–are intriguing, but we’ll have to get around our discomfort of genetic modification of organisms.

And then, there is nuclear power. (For a primer, I suggest my series on nuclear power, written a bit ago.) The Obama administration paused work on the Yucca mountain waste repository, exacerbating the waste problem (perhaps in a good way, for the long term.)

A growing consensus of scientists, however, are recognizing nuclear power as one of our better shots out of this mess:

Nuclear power is safe, affordable, and the waste problems are much more manageable than the public realizes. That was the take-home message from this year’s American Association for the Advancement of Science meeting in Chicago, where a group of experts from the US and EU participated in a session called “Keeping the Lights On: The Revival of Nuclear Energy for Our Future.”

My personal impression is slightly less rosy–with a deeper concern about waste management–but I still believe we should be investing massively in nuclear technologies.

We’re well past the point of being able to consider only the most pleasant energy sources. Looking at the number of people on the planet, and the increasingly dire reports of damage caused by the burning of fossil fuels, we need to be realistic. These steps, by the scientific community and the Obama administration, are heartening steps in what seems the right direction.

A modern windmill is pretty fantastic. Blades half as long as a football field slowly rotate around a hub to generate an astonishing three megawatts of electricity. Over a year, that’s about as potent as twelve-thousand barrels of oil.

All windmills get their energy from slowing down the wind a bit, capturing energy as rotational force. To generate much energy, you need many windmills distributed regularly where the wind blows. Almost all of the investment and cost is upfront–during the manufacturing, placement and wiring up of the mills. This is the opposite of a coal-fired plant, where most of the lifetime costs are buying up fuel to run the plant. Once you’ve built and placed your wind farm, so long as there is wind, you’re basically generating electricity for free.

This actually amplifies the uncertainty of investing in wind power. Building a coal power plant costs less (per megawatt) upfront. And the plant will reliably produce a certain amount of energy, so long as you buy coal. If you can’t count on the wind blowing steadily for decades, the much higher starting costs seem scarier and scarier.

Where you build your wind farm really matters. You want some place close to where people want to buy energy and where the wind is totally consistent, where it blows the same speed every day. Here’s where technological advances are really helping: Climate models and detailed records going back decades help us pinpoint where the winds are the best, along with where we think the wind will be the best in the future.

Wind’s energy comes from differences in pressure. Sunlight hits the atmosphere, heating it. Then its gas molecules (mostly nitrogen and oxygen) get jittery from that solar energy, bouncing around more and increasing the local pressure. They start to move en masse, seeking lower pressure points in the atmosphere. Gravity from the sun, the moon, and the earth all tug, deflecting their course. The molecules of gas in the atmosphere also feel the planet turning beneath them. All of this together makes up the wind.

The rub is, all of the pollutants we’ve added to the atmosphere are changing how the atmosphere interacts with sunlight in relatively unpredictable ways. (This is global warming or climate change.) So, where the wind blows now might not be where the wind will blow in a few decades. Our continued belching of greenhouse gases makes building a wind farm riskier, and therefore less attractive, than building a fossil fuel plant.

For now, we could use better transmission lines to connect Midwestern wind farms with major American cities. And we can improve our wind prediction tech–including new systems that account for climate change–to take some of the risk out. But boy, talk about your screwy logic. The things prompting our desire for alternative energy–climate change, pollutants–are what make wind power, by itself, an unlikely candidate to replace fossil fuels as our major energy source.

(For more, here’s a comprehensive technical report on wind power.)

Former Vice President Al Gore, seeking to shake up an energy debate that is focused mostly on drilling, challenged the United States to shift its entire electricity sector to carbon-free wind, solar and geothermal power within 10 years, and use that power to fuel a new fleet of electric vehicles.

Can it be done?

To answer that, let’s get to know our fossil fuels by rewinding to the Carboniferous era. Pangaea has just come together, with the fusing of the Northern and Southern super continents. Dropping sea levels have generated many new swampland real estate opportunities. Enter lignin, a chemical compound that has made wood hard for 350 million years.

These swamps were filled with plants held together by this funny, new substance—a substance too new to be eaten by microbes. Rather than degrade, the remains of lignin-baring plants soon filled swamps (much like how we’ve filled the oceans with plastic grocery bags).

Lignin, like most things in life, is made up of long chains of carbon atoms. All of this carbon-containing waste built up, becoming buried over hundreds of millions of years before bacteria evolved to eat lignin. And free oxygen didn’t reach this material, either, so those untouched hydrocarbon chains entombed deep in rock became coal. Similarly, algae buried under the ocean floor, without oxygen, eventually becomes oil and natural gas.

Convert that story to hard numbers: All of the fossil fuel consumed in 1997 represented over 400 years of the total plant and animal growth on the ancient planet Earth.

Almost all living systems eventually come back to energy from the sun. But that fact has its own astounding ratio: It took a half-millennium of solar energy capture by all of the living things to generate the energy we typically consume in a single year.

Those ratios are alarming, but they also make fossil fuels’ case. The upsides are so attractive: density (huge amounts of energy in small volumes/masses), stability (won’t lose much energy during storage or transport), and usability (fossil-fueled machines are far less complex than virtually any other power source).

All of the alternatives available to humanity are, in some way or another (complexity, initial investments, geography, distribution), inferior to fossil fuels. So when we consider ending our use of fossil fuels, the combination of alternatives we settle upon must match or exceed these properties–or we must adjust our lifestyles to reflect the inherent inferiority of the non-carbon fuel sources.

Now, in the twilight of fossil fuels, we have a shot at building such a combination. We can take the last remaining supplies of carbon fuels and build the networks of solar, wind, geothermal and nuclear power plants neccesary. Or we can accept that in the future–the near future–our lives will be far less rich than they are now.

So starts a new series here on Dear Science, where I’ll be reviewing some of the science behind wind, solar, geothermal and biomass energy. I’ve already covered nuclear power, the unwelcome (by some) member of the carbon-free energy club.

The insanity of shipping even the cheapest goods around the planet, to save a little on labor costs, is finally being recognized as insane:

As the cost of shipping continues to soar along with fuel prices, homegrown manufacturing jobs are making a comeback after decades of decline. While it once cost $3,000 to ship a container from a city like Shanghai to New York, it now costs $8,000, prompting some businesses to look closer to home for manufacturing needs…

The rise in transportation costs are fueling what some economists are calling “reverse globalization.” For instance, DESA, a company that makes heaters to keep football players warm, is moving all its production back to Kentucky after years of having them made in China.

“Cheap labor in China doesn’t help you when you gotta pay so much to bring the goods over,” says economist Jeff Rubin.

Some local manufacturers have suddenly found themselves in the thick of boom times.

(ABC news)

And, according to the New York Times, this spells the end of the exurb:

Suddenly, the economics of American suburban life are under assault as skyrocketing energy prices inflate the costs of reaching, heating and cooling homes on the distant edges of metropolitan areas….
Across the nation, the realization is taking hold that rising energy prices are less a momentary blip than a change with lasting consequences. The shift to costlier fuel is threatening to slow the decades-old migration away from cities, while exacerbating the housing downturn by diminishing the appeal of larger homes set far from urban jobs.

Seattle Bubble disagrees:

Pretty much any way you slice it, the higher cost of housing close-in far outweighs any financial benefits you get by cutting your commute. Run the numbers for any pair of far-flung vs. close-in cities around Seattle and you’ll find the same thing.

By comparison, if that same family stayed in Marysville but sold their 20 MPG car and bought a used Prius that gets 45 MPG, they save nearly $200 a month (at $5/gallon), while the upgrade only cost about $10,000 up front. Heck, they could probably trade straight across for a used Saturn that gets 30 MPG and still save over $115 a month.

The picture is slightly better for first-time home buyers, since they’re comparing both locations at today’s prices, but it’s still not a financial win to go close-in. A potential first-time buyer with a downtown commute looking at putting $20,000 down on an average home in Marysville can expect to spend $2,400 on PITI + commute, vs. $2,850 in Shoreline. With $50,000 down it’s $2,230 vs. $2,780. That’s still $450-$550 a month more to live close-in, with the high cost of housing more than negating their gas savings.

While I like Seattle Bubble’s analysis, I must disagree with conclusion. The relative energy impact of living in an exurb goes far beyond the gas needed to putter out an additional ten or twenty miles each way, each day.

Consider how errands are done in the ‘burbs relative to an urban setting–trips to the bank, the grocery store, the bar, the movie theater, the daycare center and so on. Moving closer to the city center often means moving into a denser, more walkable neighborhood–where these resources are right at hand rather than miles down the road. If you can walk to your bank and your grocery store, you’re piling on the savings far beyond having a shorter commute each day.

Next consider the vastly higher energy costs to heat and cool an isolated structure, the energy and chemicals needed to maintain a vast lawn. Distributing utilities to widely dispersed homes is also costly–requiring more water pumps, more sewers to maintain, more garbage trucks driving more miles and more transmission losses on the sprawling network of electrical wires. Even when the homeowner is shielded from these costs, they still exist.

Driving until you qualify remains a false economy. By focusing on the costs of the commute, we miss the bigger costs of living in low-density sprawl. This is not to say we all must live in the very urban core of the biggest and most expensive cities. Well designed mass transit systems, like Metra in the Chicago area, allow this sort of density to form in smaller communities. All of this makes me want to say “I told you so” to those who killed the monorail and the light rail expansion.

Wilkins Ice Shelf, a broad plate of floating ice south of South America on the Antarctic Peninsula, is connected to two islands, Charcot and Latady. In February 2008, an area of about 400 km² broke off from the ice shelf, narrowing the connection down to a 6 km strip; this latest event in May has further reduced the strip to just 2.7 km.

This animation, comprised of images acquired by Envisat’s Advanced Synthetic Aperture Radar (ASAR) between 30 May and 9 June, highlights the rapidly dwindling strip of ice that is protecting thousands of kilometres of the ice shelf from further break-up…

Wilkins Ice Shelf has experienced further break-up with an area of about 160 km² breaking off from 30 May to 31 May 2008. ESA’s Envisat satellite captured the event – the first ever-documented episode to occur in winter.

Excellent! The jury might be coming back on climate change. Perhaps this would be a good time to remind you of my posts and introduce you to a new podcast on nuclear power .

Nuclear power plants were first proposed at the dawn of the cold war. It was assumed the best fuels–enriched the most for atoms releasing the most neutrons per fissioning–would forever be reserved for military use. We had bombs to build. Hundreds, thousands, millions–enough to scare the Soviets (and the Soviets to scare us.) Military first, commercial power second. So, the plants were designed around using minimally enriched fuels with moderators to keep the scant neutrons around. Hence the collection of plants in operation today, almost all based around mildly enriched Uranium, moderated and cooled by heavily pressurized water. By far not the safest or most efficient design, but doable, particularly if you are limited to mediocre quality fuel.

Two funny things happened along the way.

The development of the hydrogen bomb vastly increased the efficiency of atomic bombs. Effectively limitless amounts of explosive force can be created using relatively small amounts of highly enriched Uranium or Plutonium, some heavy hydrogen and lithium and a whole lotta unenriched Uranium. About the time the US and the Soviets could destroy the entire surface of the planet three times over, interest in building more bombs started to wane.

Then the US won the cold war. While more and more states can field nuclear bombs, most have realized all you need are a few–just enough to pose a solid deterrent. You can’t eat atomic bombs. Nor can you really use them in war. Atomic bombs have always been a sort of military-industrial masturbation, a show of prowess rather than a practical weapon, a solid way of saying “don’t mess with me.”

The result? Our present world is awash in enriched Uranium-235 and plutonium–fine for making bombs or much better nuclear power plants. With this sort of high quality fuel, we have neutrons to spare. Let’s do some interesting things with them.

The first thing we can chuck from our reactor? The moderator. If we have enough neutrons, we can keep the chain reaction going even if most are flying away before meeting another fuel atom–a fast neutron reactor. No more graphite or water. Now we can use something more forgiving as a coolant, like molten metal or an inert gas. Wait, wasn’t one of the safety features of the water-moderated, water-cooled reactor that the loss of water would shut down the chain reaction? Fine. We’ll load the fuel a matrix that physically expands as it gets hotter. If it gets hot enough, the fuel will get too far away to keep the chain reaction going. Great! We’re back to the lose-coolant, lose-chain reaction situation.

What can we do with all those extra neutrons? Why not use them to smash up all those pesky radioactive decay products! Now, instead of having to periodically remove the fuel rods and chemically remove all the neutron-absorbing, non-fissioning, and highly radioactive waste atoms, we’ll just burn them off right in our reactor.

A traditional pressurized water reactor can only fission about 3-5% of the Uranium in it’s fuel before it has to be removed an reprocessed. About 270,000 metric tons of radioactive waste are scattered around the world, predominantly stored in pools or casks right next to the power plants thanks to this inefficiency. If we use the extra neutrons in our fast neutron reactor to burn off the radioactive waste, we can boost this efficiency to above 90%. With some relatively simple fuel-reprocessing on site, we can boost this to 99%.

Nuclear waste is the overwhelmingly major problem with nuclear power plants today. There is no plan, no strategy beyond burying it someplace for at least a million years. No technology exists that matches the problem. Fast neutron plants, that eat their own waste and potentially the waste of others, are an overwhelmingly better solution than Yucca mountain.

Where are these plants? The ideas here aren’t new ones. A pilot project, the Integral Fast Reactor (IFR) was to build a liquid sodium metal cooled, plutonium and U-235 fueled fast neutron reactor with an on-site waste processing center. The project’s budget was cut in 1994 by President Clinton‘s energy secretary and thus languished before the project could be completed. The ideas from this project have been rejuvenated, with plans for a liquid sodium, liquid lead and gas cooled reactor variants based around the same general principles, called generation IV reactors, to be ready for commercial operation in 2030.

The designs are, individually, brilliant. The lead-cooled variant is designed to be modular. The reactor is small, easily installed and removed and works for about fifteen to twenty years without having to be opened or refueled. Perfect for countries or remote areas with no interest in or infrastructure for refining nuclear fuels. The gas-cooled variant can operate safely at huge temperatures and is incredibly efficient at minimizing waste products in a relatively simple manner. The sodium-cooled design is the dreamiest to me. Such a reactor complex could not only operate at tremendous efficiencies, but also eat up the waste of the older pressurized water reactors. Keen!

2030 is too far away. If we were smart, we would throw resources at these fourth generation technologies, pushing to have the pilot reactors and designs finalized within ten years. None of these are perfect. No source of power is without risk or environmental injury. None. Our planet hosts nearly seven billion people. Fossil fuel reserves are dwindling. The atmosphere and oceans are buckling under the carbon strain. Nuclear power, particularly responsibly applied with standardized plant designs and a real plan for dealing with the waste, remains our best hope. The physics and technology is available. We just need to do it. Now.

Let’s talk about Chernobyl. We enter our time machine, and roll ourselves back to the start of the cold war. We’re nuclear engineers in the Soviet Union charged with getting as many reactors operating as soon as possible. Every bit of enriched Uranium is going to bomb manufacturing, as is all the available heavy water. So, all we have is a bunch of unenriched Uranium and regular water to build our reactors. Hmmm.

Let’s think back to our earlier reactor design talk:

Hey, something nifty! Water is both a good coolant and moderator! No moderator, no chain reaction, right? So, if you use water as your coolant and moderator, your reactor has an intrinsic safety feature. If you lose coolant, you lose moderation and the chain reaction stops. We all live! Thus, almost all nuclear reactors in operation today use water as a coolant and moderator….
But what water, and what fuel? Here’s the trade-off: The better the moderator, the crappier your fuel can be… The rarer versions of fuel (U-235 is better than the common U-238) or moderators (heavy water is better than regular water) tend to be the better. Building a reactor typically requires enriching for either the better moderator or the better fuel.

But, we don’t have enriched Uranium or heavy water. Well, we aren’t required to use water as both our moderator and coolant. What if we stick with water as our coolant, but use something else to moderate the neutrons? Graphite will do the job and it’s cheap and plentiful. So, we’ll build our reactor with unenriched Uranium (or even better, depleted Uranium coming out of the atomic bomb plants) as the fuel, regular water as the coolant and graphite as the moderator. What do we have to lose?

In this design, when the water coolant is lost, the graphite moderator stays and the chain reaction continues. In fact, it speeds up, as the regular water isn’t around to absorb some of the neutrons anymore. Added bonuses? The graphite will tend to chemically explode when it heats up enough. So, lose coolant, the chain reaction speeds up, the reactor quickly overheats and explodes with both chemical and nuclear power as energy sources. Neat. Even better? If the fuel is old, and thus filled with all sorts of highly radioactive waste atoms, the massive explosion will be sure to spread all these atoms far and wide–a sort of gigantic dirty bomb. The resulting mess will result in far far far more radioactivity than dropping an atomic bomb. At least in the bomb, most of the radioactive atoms are consumed to produce the explosive force.

I’d like to imagine the following exchange, between a middle manager in the Soviet Union and us, some plucky nuclear engineers, when planning these plants:

Middle manager: “You have my plant design?”
Us: “Yes, but it is incredibly dangerous!”
MM: “But it will work without any Plutonium, enriched Uranium or heavy water?”
Us: “Yes. In fact, it produces Plutonium as a waste product!”
MM: (Claps hands) “Excellent. We shall have such nice dachas when I tell everyone of this plan.”
Us: “It is far to dangerous to build. I refuse to do it!”
MM: (Laughs. Then pauses.) “Oh. You’re serious.”
MM: (Considers his boss, probably some one-eyed, one-armed veteran of Zhukov’s Berlin campaign in the Great Patriotic War, who won’t be sympathetic to concerns about hoards of irradiated civilians after asking why his reactor isn’t operating yet.)
MM: (Points to us.) “Guards, shoot this man.”
Us: (Shot in the head)
MM: (Turns to our assistant) “So, ready to build the reactors?”
Assistant: “Let’s just pick some places in Ukraine, Romania and other shitholes to build ‘em, yes?”

I have no doubt similar disagreements happened in the United States, when faced with similar shortages. American middle managers couldn’t resolve disputes with engineers by the bullet-to-the-head trick, probably tipping the debate outcome.

Chernobyl was this sort of reactor, a reaktor bolshoy moshchnosti kanalniy (aka RBMK, aka insane). The inevitable eventually happened. Coolant was lost. Does it really matter why? Ok, fine. This particular fiasco wasn’t caused by normal operations. They were messing with the plant, trying an “experiment.”

Like most reactors, these must be shut down periodically to swap out the spent fuel rods for fresh ones. So, shutting down the plant, by putting in all the control rods, is pretty typical. During one of these routine shutdowns, the plant operators got an idea. The water pumps, supplying coolant to the reactor, are powered by the reactor’s own turbine. Backup power is available from on-site diesel generators, but these take 40 seconds to power up. The plant operators asked themselves, if we shut off the steam to the reactor’s turbine, will the turbine keep spinning long and fast enough to keep the water pumps operating until the diesel backup gets up to speed?

Great question, guys! I’ll give you a hint to the answer: No. Kaboom!

Why on earth would they think to try something so nuts, to shut off coolant to a reactor that will run out of control upon the loss of coolant? Most were conscripts from coal power plants elsewhere in the empire. They didn’t know better.

What exactly happened? The wikipedia article on the Chernobyl disaster does an admirable job breaking it down clearly. In short, the coolant ran out, the reaction sped even more out of control, melting the reactor and exploding the graphite. Huge amounts of highly radioactive waste was spread all over Europe.

Something to help you sleep at night? Reactors of this design, admittedly modified to be a little safer, are still operating in the former Soviet Union.

When it comes to “disasters” at nuclear power plants, this is only one deserving the title of disaster. Compared to Chernobyl, the Three Mile Island is a pathetic also-ran. In this contest, the US takes a distinct silver to the Soviets’ uncontested gold.

The reactor at Three Mile Island was far more typical, using pressurized light water as both a moderator and coolant, and slightly enriched Uranium as a fuel. What happened? Again, the Wikipedia article on the TMI accident is superb. The short of this one?

Poorly designed controls and displays for a reactor made it virtually impossible for the plant operators to respond properly when a coolant pump failed. There was no reliable way to see how much high-pressure water remained in the reactor, no reliable way to tell if emergency valves were opened or closed, no way to tell when things were running out of control. The operators made poor decisions based on poor information, resulting in the high pressure water eventually all flashing to steam and the reactor core melting. Still, even with all these bad things in a row, only a teeny, tiny amount of radiation escaped into the environment.

Why on earth would such poorly designed reactor controls allowed? Because, brilliantly, almost every reactor in the United States is different from every other one. Thank the lowest-bid culture, in which almost every commercial power plant in the US was guaranteed to be different from any other built before. With such a system, one cannot even train experts to work around shoddy design choices. Each must be discovered individually at a particular plant. Urk!

Not every nuclear power plant system is run this way. The French, in contrast, have almost all of their reactors one of three basic designs. Yes, they have quirks. But at least the quirks are shared among all the reactors of the same type. The net result? The French get about three quarters of their power from these nuclear plants and have had no accident even approaching the severity of Three Mile Island.

The possibility of a nuclear plant accident, however prominent a role it plays in the public imagination, should be a secondary concern to the problem of nuclear waste. Chernobyl, without a doubt, was a fantastic failure. While there will inevitably be future accidents at plants, they are vastly more likely to be more Three Mile Islands rather than Chernobyls.

We’ve got our reactor up and humming. Our fuel is fissioning, splitting into smaller atoms and releasing neutrons. Our moderator is slowing down the neutrons, keeping them around long enough to fission the next fuel molecule. Our control rods are absorbing enough neutrons to keep the chain reaction in check. The coolant is transferring the heat out of the reactor.

Over time we have to pull our neutron-absorbing control rods out farther and farther just to keep the chain reaction going. Why?

When we loaded our reactor, the fuel was chemically fairly pure. Recall, however, that nuclear decay typically results in new chemicals being created–whether by alpha or beta decay or by fissioning. As our reactor operates, these new atoms build up. Most are radioactive themselves, also undergoing various decays. Most of these atoms are neutron hoarders–gleefully absorbing our precious neutrons, while offering up few when they themselves decay. So, as these new atoms build up, we lose more and more neutrons. Eventually there are too few free neutrons left to keep the chain reaction going, even if we completely remove the control rods. Such fuel, still containing a bunch of Uranium but now contaminated various highly radioactive but non-chain reacting atoms, is called spent. It’s hideously radioactive, more radioactive than when we put the fuel in the reactor, but useless as fuel.

Welcome to the trickiest problem of nuclear power, the waste. What can we do?

Pull the spent fuel rods out of the reactor and replace them with fresh ones. We’ve only used a tiny percent of the Uranium up, but on the positive our reactor will start working again. On the negative, we have a whole bunch of really radioactive former-fuel that is useless.

Consider these unwelcome new atoms. The more radioactive the atom–the more often the atom decays–the quicker it uses itself up and becomes something else. So, the most dangerous to health atoms disappear relatively quickly–within years or maybe decades. The problem is, even the less radioactive waste–that will last for hundreds of thousands of years–is still radioactive enough to be a threat to health.

We could just store the spent fuel rods, for millions of years, until it is only minimally radioactive. Water is a pretty fantastic shield against radiation. So, we build a whole bunch of swimming pools in the reactor containment buildings and then sink the radioactive waste to the bottom, waiting for the most radioactive atoms to decay into other more manageable things. That will be fine for a few years at least. When the pools get filled, we’ll next build some metal and concrete casks outside of the reactor building, next to the plant and store the rods there. Finally, we’ll hope that someone, somewhere, finds a suitable mountain to carve out and drop the waste into, just to get it off our property.

But wait, you say. The new atoms, ruining our chain reaction, are only a teeny percentage of the spent rods. We could chemically break down the fuel, purify for Uranium and create new fuel from the old. Great! We’ve now reduced the freakishly radioactive waste we cannot use to a much smaller mass and recycled the fuel. Neat. We stopped doing this in the 1970′s. Why? While the leftover atoms are useless for commercial power plants, they would make great starting material for a dirty bomb. Ouch.

So, we’re back to the pool, cask, prayer plan for the waste. While there are proposals for more clever ways of dealing with the waste, right now nearly three hundred thousand tons of highly radioactive spent fuel rods are scattered all over the world. Typically in casks next to the power plant, they represent by far the biggest environmental and health risk from nuclear power. And we really don’t have anything better planned in the near future, right as we’re embarking upon a plant building binge.

Unlike waste from chemical plants, or carbon pouring out of smokestacks and tailpipes everywhere, this waste is a uniquely human creation. While sitting in a reading of The World Without Us, about what a world after the end of humanity would look like, I realized that radioactive waste would be the longest lasting legacy of humanity.

After all the bridges and towers crumble, after all the seawalls give up, after all the dams burst, after all the plastic garbage is eaten by some newly evolved bug, after our bones are recycled into every imaginable different thing, our radioactive waste–made of atoms not seen on the planet since its birth–will persist.