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As a science writer, I’ve written about a lot of things I’ve never expected to see up close. The outer planets of the solar system, for example. The bottom of the ocean.

Nuclear reactors.

I still haven’t reached Neptune, and I’ve never been to the bottom of the sea, unless you count the Captain Nemo ride at Disneyland. But as of this summer, I can say I’ve been inside a reactor.

In August, my wife (an engineer) and I toured the Bruce A Restart Project on the eastern shore of Lake Huron, just north of Kincardine, Ontario, at the Bruce Power nuclear power plant.

There are eight CANDU reactors there, four known as Bruce B and four known as Bruce A. The Bruce A reactors were brought into service in the late 1970s, but were laid up by Ontario Hydro in the mid-to-late ‘90s. In 2001 Bruce Power took over operation of the reactors, and in 2003 and 2004 brought Bruce A Units 3 and 4 back into service.

Now Bruce Power is in the process of bringing Units 1 and 2 into service, refurbishing them so they can operate for an additional 25 years. Once Units 1 and 2 are back in operation, Units 3 and 4 will be shut down for their own refurbishment.

The project involves replacing fuel channels and steam generators and upgrading all the 1970s-era electronics and electrical components to modern standards. It’s the first time anywhere in the world anyone has attempted to completely refurbish a mothballed CANDU reactor. Which means the people at Bruce Power are literally writing the book on how to do it.

So, what’s one of the largest engineering projects Ontario has seen since the plants were first built like, up close and personal?

Well, we covered almost every aspect of it during our three-hour tour (yes, the Gilligan’s Island theme song did run through my head a couple of times). In no particular order, here’s what impressed met.

First…it’s big. It’s really, really big. The reactor is big (though remarkably small when you consider the amount of energy it produces). The building is big. The steam generators are big. The crane being used to lift them in and out through the roof is extremely big. The turbines that spin steam into electricity are big.

For most people, nuclear energy has a high-tech sheen to it. They picture a clean, quiet control room somewhere and people dressed in white lab coats speaking in hushed tones. But in fact, a nuclear-powered generating station is a massive industrial facility, a place of steel and cables and concrete and vents and pipes. Intellectually, I knew that, but it was still eye-opening to see it up close.

A second thing that made an impression: the focus on safety and security. I’ve never gone through a bomb-sniffing machine before, and I’ve certainly never gone through a radiation detector before. I found the steps taken to ensure the safety of workers and the public and the security of the plant comprehensive and reassuring.

Third…well, third, I was impressed by the heat. The vault of the reactor was hot. Not in the sense of being radioactive, I hasten to add. It was thoroughly decontaminated before work began and remaining spots with high radioactivity are monitored and clearly marked. The detectors we wore registered a dose, in the 45 minutes we were in the vault, equivalent to one-10th of a dental X-ray.

No, the vault is simply very, very warm. Especially when you’re wearing three layers of clothes, a hard-hat, goggles, and rubber gloves.

When Units 1 and 2 come back online over the next couple of years, Bruce Power’s eight reactors will produce more than 6,200 megawatts, making it the source of about 25 percent of Ontario’s electricity on a typical day…all produced, emission-free, thanks to the simple fact that when you split an atom of uranium, a small portion of its mass turns into energy.

We’re impressed by the pyramids of Egypt, but really, piling a bunch of rocks on each other is nothing compared to the modern engineering marvels we take for granted every day.

Considering that everybody living in the northern hemisphere 13 years ago was the unwilling recipient of at least a few radioactive particles from Chernobyl, we all have good reason to hope they’re correct.

Nuclear reactors split uranium atoms by bombarding them with neutrons. A small portion of the atoms’ mass becomes energy, and they release more neutrons, which in turn bombard other nearby atoms, splitting them and beginning a chain reaction. If the material is packed together tightly enough, this chain reaction is uncontrolled, and you get an atomic explosion. In nuclear reactors, a material called the moderator controls the chain reaction by slowing the nuetrons.

In Chernobyl-style reactors, the reaction is moderated by graphite. Ordinary water is piped through the core of the reactor and heated into steam. This both cools the reactor core and drives the power turbines. Chernobyl-style reactors don’t have a containment vessel–the steel-and-concrete tower familiar from North American reactors–and become unstable at low power, liable to sudden surges of power.

On April 25, 1986, the Number 4 reactor at Chernobyl was to be shut down for routine maintenance, and it was decided to take advantage of that to run a test of emergency power systems. Due to poor communication, a series of actions was taken that led to a dangerous situation: the reactor’s power output fell to the point where it became unstable, certain safety systems were disabled, and most of the control rods, used to damp neutron output and thus shut down the reactor in a hurry, had been withdrawn.

At 1:23 a.m. on Saturday, April 26, 1986, the unstable reactor suffered a power surge estimated to be 100 times greater than normal. The fuel ruptured. Hot fuel particles hit the water system, causing a steam explosion that destroyed the reactor core. A second explosion ripped the roof off the reactor building, exposing the reactor core and sending a shower of hot, highly radioactive debris into the air.

The building caught fire, giving rise to more clouds of radioactive steam and dust. More than 100 fire-fighters fought the blaze, many of them suffering fatal radiation doses; the building fires were extinguished within a few hours, but by then the reactor’s graphite had caught fire. It burned for 10 days, hurling a constant stream of radioactive material high into the atmosphere. Radioactive emissions continued in total for 20 days.

After the accident, the reactor was encased in a steel-and-concrete sarcophagus that is currently being re-fortified. Two of the other four reactors were permanently shut down. Ukraine was supposed to close all of them by 2000, but because the government can’t afford to build the two new reactors it needs to replace the power it draws from Chernobyl, reactor Number 3 is now up and running again.

Immediately after the accident, 134 people showed signs of acute radiation sickness, of whom 28 died. 135,000 people were evacuated from the area; most received significant doses of radiation. Approximately 800,000 workers were brought in to try to decontaminate the area, and received varying doses of radiation. Around 270,000 people continue to live in contaminated areas.

Large portions of agricultural land were contaminated, including almost a quarter of the agricultural land in Belarus. A swath of forest near the site received so much radiation the trees died and had to be destroyed as radioactive waste. Interestingly, wildlife now abounds in the area, and although rodents are so contaminated you wouldn’t want to handle them, researchers have yet to find any malformed individuals.

There has been a substantial increase in reported cases of thyroid cancer in Belarus, Ukraine and some parts of Russia. An increase in leukemia was expected, but hasn’t shown up yet. Nor have there been perceived increases in other cancers–but that could be simply because enough time has not yet elapsed. Nevertheless, it’s estimated that, when all the health consequences are taken into account, 3,756 people have now died from the accident.

Harder to measure have been the psychosocial effects, caused by the fear of disease, the stress of being exiled from their homes, a distrust of authorities, and economic and social hardship.

Not to mention insomnia. With a nuclear reactor once again operating at Chernobyl, it’s a safe bet a lot of people aren’t sleeping well these days.

There’s not much in the way of interesting scientific anniversaries on my list for this month, which suits me fine, because it means I can focus on the one that interests me most:  the 40th anniversary of the launch of the world’s first nuclear submarine, the USS Nautilus, on January 21, 1954.

I don’t know why, but submarines have always fascinated me.  Maybe it’s because I’ve lived my whole life on the prairies, as far as you can get from an ocean, which lends the sheen of the exotic to anything to do with the seas.  Maybe it’s from early exposure to the old television series Voyage to the Bottom of the Sea (recently reincarnated, for all intents an purposes, as Sea Quest DSV) and Jules Verne’s novel 20,000 Leagues Beneath the Sea.  Whatever, the 40th anniversary of the launching of the Nautilus seems an excellent opportunity to pursue my submarine interest.

Submarines have been around a surprisingly long time.  Cornelius Drebbel, court engineer to James I of England, demonstrated an underwater vessel on the Thames way back in 1620.  It was propelled by oars sealed at the locks by leather gaskets, and submerged (as far as we can tell) by letting water into the hull, then surfaced by pumping it out again (and crewed, one hopes, by volunteers!).

That’s still the way submarines do it today, although with greater sophistication.  Submarines consists of two hulls, an inner one containing air, called the pressure hull, and an outer one.  The space between the two is filled with ballast tanks, which are flooded with water to make the sub sink and pumped full of air to make the sub rise.

A submarine is thus a perfect example of Archimedes’ Principle, which states that an object in a fluid will rise if the amount of fluid it displaces weighs more than it does, and sink if the amount of fluid it displaces weighs less than it does.  It stabilizes at a point at which the amount of fluid it displaces weighs exactly the same as it does.  Submarines control their depth by matching their weight to the weight of the water they displace

The second submarine of note, the Turtle, added another innovation:  propellers.  Designed by David Bushnell while he was a student at Yale (those crazy engineering students!) and launched during the American Revolution, it was a one-man craft shaped sort of like a fat barrel.  A complex system of valves, air vents and pumps controlled its rising and sinking, and propulsion came from two sets of hand- and foot-cranked propellers:  one set to drive it forward and one to move it up and down.  On September 6, 1776, Sgt. Ezra Lee piloted the Turtle out to the British flagship Eagle off New York and attempted to attach a mine to it with an auger.  Unfortunately (or fortunately, depending where your sympathies lie), the auger couldn’t penetrate the Eagle‘s copper sheathing.  Lee jettisoned the mine and no damage was done.

The nuclear Nautilus was named that for a good reason:  the first practical submarine was also named Nautilus.  Robert Fulton (of steamboat fame) demonstrated it to the French navy in 1800 and 1801.  Compared to the crude Turtle of just 25 years before, it was a modern marvel.  Made of metal, it carried four men, could stay underwater for six hours, had a streamlined fish shape to reduce water resistance, used water ballast tanks to raise or lower the craft, and was propeller-driven–although, there being no practical underwater power source yet, the propeller, like the Turtle‘s, had to be cranked by hand.  However, for surface travel, it carried a collapsible mast and sail.

The Nautilus added one more important innovation:  horizontal rudders, or diving planes, to control the angle of the sub’s ascent or descent.  With that addition, the elements of the modern submarine were all present.  However, none of the governments Fulton demonstrated the Nautilus for were convinced, and so he dropped the project.

The Nautilus was designed to tow a mine that could be brushed up against an enemy ship:  from the beginning, submarines have been seen primarily as military vessels.  To the Confederates in the U.S. Civil War went the dubious honor of being the first to actually sink a ship via submarine:  the hand-cranked sub Hunley carried a “spar torpedo”–an explosive charge on the end of a six-metre pole.  It succeeded in sinking the USS Housatonic off Charleston on February 17, 1864, but destroyed itself in the process.

World Wars I and II brought fleets of more-and-more-advanced submarines into the world’s oceans.  Electric motors finally provided a suitable underwater power source, although batteries had to be recharged frequently by extended surface travel using diesel engines.  That’s why submarines of the two world wars still had the shape of surface vessels, with sharp prows and long, slender hulls.

The nuclear Nautilus had those features, too, because that’s how the U.S. Navy knew how to build submarines:  but the nuclear Nautilus spelled the end of the days of extensive surface running.

A nuclear-powered sub contains a small, well-shielded nuclear reactor that creates intense heat, which is used to generate steam to turn propulsion turbines and supply electricity for all the subsidiary systems.  Because nuclear power does not require oxygen and produces no noxious fumes, it puts no strain on the submarines’ air supply.  In fact, it powers devices which turn seawater into fresh water and oxygen.

That means that a nuclear submarine’s range is practically limitless.  The Nautilus sailed 170,000 kilometres, 146,000 of them submerged, before refueling, and on August 3, 1958, even sailed under the Arctic ice and the North Pole.  In 1960, a second-generation nuclear sub, the USS Triton, sailed around the world, entirely underwater, in just 84 days.

Without the need for frequent surface running, modern nuclear submarines have teardrop-shaped hulls that provide the maximum streamlining for underwater travel:  and allow speeds of up to 30 knots, fast even for most surface ships.

The Nautilus pointed the way, for good or bad, to today’s world where fleets of submarines carrying enough nuclear missiles to destroy entire countries are continually at sea, but with its trip under the Arctic ice, it also showed how submarines could be used for scientific research.

Here’s hoping the future focus is on submarines more for the latter purpose than the former.

Actually, that’s not a very fair comparison, because nuclear fusion really does seem to be on the way, while most people will never get rich in a lottery. On the other hand, a lot of lottery winners will have come and gone before fusion finally becomes a viable energy source.

However, on still another hand (hmm, that makes three), almost all of our present energy sources are ultimately derived from nuclear fusion, because nuclear fusion is, literally, the power of the sun.

Fission, as you may recall from last week’s column, is the splitting of a very large atomic nucleus into two smaller nuclei. The two smaller nuclei mass less, even put together, than the large nucleus did. That missing mass turns into energy–lots of

energy.

Fusion is the opposite process. In nuclear fusion, two small nuclei are combined to form one larger nucleus. Oddly enough, when you’re dealing with very light elements like hydrogen and helium, two small nuclei actually have more mass than a single nucleus of twice the size. Once again, after fusion, there’s a missing mass, and it’s that mass that turns into energy.

How much energy? Well, ever hear of the hydrogen bomb?

Fusion is a lot harder to achieve than fission, because, as a little experimentation with magnets will show you, like charges repel. If you try to shove two hydrogen nuclei together–each consisting of a single positively charged proton–they’re not going to like it. The sun overcomes this mutual distaste by the simple procedure of cramming everything together to a density 100 times that of water, then heating it up to 15 or 20 million degrees. At that temperature the particles get quite excited, rush around frantically and run into each other with great force. But even in the centre of the sun, it’s estimated that a proton will exist on the average for 10 billion years before it’s finally fused with another. (And I thought I’ve been single a long time…)

So in order to initiate fusion on Earth, physicists have to not only match conditions at the centre of the sun, they have to improve on them. One way is to use deuterium or tritium, both isotopes of hydrogen–that is, they both have a single proton in their nucleus, like hydrogen, but they have one and two extra neutrons, respectively. Fusion of these nuclei occurs millions of times faster than the Sun’s basic proton-proton reaction.

In order to create the high temperatures required for fusion, physicists must turn the deuterium and tritium into a plasma. This is the fourth state of matter, above the familiar three of solid, liquid and gas; it’s a “soup” in which electrons and nuclei are completely separated from each other. Trouble is, this plasma is at a temperature of 100 million degrees Celsius. Obviously you can’t let this touch the walls of the container you’re trying to keep it in.

One solution to keep the plasma from vaporizing the machinery that created it is to contain it in a magnetic field, or “bottle,” shaped like a doughnut. (Well, scientists call it a “torus,” but it looks like a doughnut to me.) This kind of fusion reactor is called a tokamak, and it’s been the most popular over the years.

A newer kind of fusion reactor uses what is called “inertial confinement.” Basically this relies on the inertia of the fuel to keep it together after it has been compressed to the high density necessary to achieve fusion, which is accomplished by focusing extremely powerful lasers on glass-walled pellets containing the fuel. The beams evaporate the outer layers of the pellets and cause the rest to implode, compressing the fuel.

Still, it’s the tokamak that has had the most support, and the tokamak which has so far had the most success. In fact, just a year or so ago physicists at Princeton University announced they have developed a fusion reactor capable of producing as much energy as it consumes. This point, called “break-even” is an important stepping stone toward the development of a commercial fusion reactor.

Fusion is an immensely attractive energy source for a number of reasons. For one thing, its basic fuel can be obtained from one of the most plentiful substances on earth, ordinary seawater. (Deuterium exists naturally in seawater; although tritium does not, it can be produced from relatively common lithium during normal operation of the reactor.)

For another, fusion would be a very clean form of energy, producing far fewer and far less dangerous wastes than fission. (Fission reactors produce plutonium; fusion reactors produce helium. Which would you rather have in your back yard?)

The trouble is, energy-producing fusion is proving to be an immensely tough technology to develop. The Princeton project has been underway for 15 years and has cost $1 billion, and scientists caution fusion could still be decades away from commercial use. That was why the flap a couple of years back over so-called “cold fusion” was so great.

It would certainly be convenient if fusion could be induced in a test-tube instead of requiring duplication of conditions at the centre of the sun, wouldn’t it? Unfortunately, while something may have been happening in that test tube, fusion apparently wasn’t it–at least not in any exploitable form.

Still, the race is on, and it really does appear that it will only be a matter of time before fusion is the energy choice of a “new generation.”

Considering the environmental and economic costs of our present methods of energy production, it can’t come a moment too soon.

About 1.78 billion years ago (give or take a few million years) there was enough uranium trapped in the rock near Gabon, West Africa, for a chain reaction to begin on its own. For a million years, Gabon was home to the world’s first nuclear reactor.

Still, we egotistical humans don’t really pay much attention to things that happened before we were around to appreciate them. We generally consider the Nuclear Age to have been born on December 2, 1942, under the squash courts at the University of Chicago, when the “nuclear pile” built by Italian physicist Enrico Fermi (and the rest of the Manhattan Project scientists) started producing heat from the process of nuclear fission.

Fission was discovered in 1938 by the German physicists Otto Hahn and Fritz Strassmann. They were bombarding uranium with neutrons–uncharged particles that make up atomic nuclei along with the positively charged protons–when they identified barium nuclei among the fragments from the collisions. The barium nucleus has 56 protons, far fewer than uranium’s 92.

Two colleagues of Hahn and Strassmann, Lise Meitner and her nephew Otto Frisch, who had fled to Copenhagen to escape the Nazis, suggested that a neutron could break a uranium atom into two pieces, a process they named fission. They went on to prove their idea experimentally.

Danish theorist Niels Bohr, together with American John Wheeler, explained this with the “liquid drop” analogy. Think of the heavy uranium nucleus as a drop of liquid. If a drop of liquid is distorted enough from its original spherical shape, it will split into two drops, because two spherical drops require less energy to maintain than one distorted large drop. The nucleus behaves the same way, splitting into two pieces if it’s distorted enough.

This can happen spontaneously in some atomic nuclei. Uranium-238, for example, the most common form of uranium, exhibits this spontaneous fission (not to be confused with ordinary radioactivity, in which the nucleus sheds particles a few at a time). But this happens so slowly that the spontaneous fission half-life of uranium-238–the time in which it would take half of all uranium-238 nuclei to spontaneous split into smaller nuclei–is 8,000 trillion years. (In other words, don’t wait up.)

However, fission can also be induced by bombarding certain nuclei with neutrons, as Meitner and Frisch proved. A nucleus of uranium-238 will capture an energetic neutron and form an energized nucleus of uranium-239 (the numbers are the total number of protons and neutrons in the nucleus). However, the uranium-239 nucleus distorts much more easily, and within a tiny fraction of a second, it splits into two smaller fragments.

The two new nuclei aren’t the only thing produced, however. There are usually some smaller bits left over, including neutrons, because a large nucleus contains a larger proportion of neutrons than a small one. These neutrons may then bombard other large nuclei nearby, which will split and send out neutrons to bombard other nuclei, producing a self-sustaining “chain reaction.”

The total mass of two medium-sized nuclei is less than the mass of a large nucleus twice their size. Thus whenever a large nucleus is split, a certain amount of mass disappears–and reappears as energy. A lot of energy, as Einstein’s equation points out.

If the chain reaction is controlled, it produces energy in a nice steady flow that can be harnessed to heat water to make steam to turn turbines to create electricity to run your hair dryer. If the chain reaction is uncontrolled, and the uranium is tightly packed enough (“critical mass”) it can lead quickly to an extremely large and sudden release of energy and spoil your day in a hurry. (This did not go unnoticed during the Second World War, which is why on July 16, 1945, there was a rather impressive explosion in the desert near Alamogordo, New Mexico.)

Since an uncontrolled nuclear chain reaction is obviously not desirable under most circumstances, especially not if you’re standing nearby, some way has to be found to “moderate” the process. This is done by surrounding the fuel with some substance that slows down the neutrons set free by fission. In the CANDU (CANadian Deuterium Uranium) reactor, this moderator is “heavy” water, water in which the ordinary hydrogen atoms have been replaced with deuterium, a form of hydrogen containing a neutron in its nucleus in addition to the usual single proton. The CANDU reactor also uses heavy water as a coolant. Ordinary water can also be used as a moderator and coolant, while the infamous Chernobyl reactor used graphite as a moderator.

The uranium oxide that fuels reactors is contained in “fuel rods.” There are also “control rods”; these are made of boron or cadmium or some other material that absorbs neutrons and can therefore slow down or stop the reaction.

Nuclear fission has the advantage, as an energy source, of producing no noxious fumes or greenhouse-effect-enhancing gases and of making extremely efficient use of its fuel supply (one gram of uranium yields roughly the same amount of power as one tonne of coal).

Its disadvantages include problems of waste disposal and transport, high capital costs and public fears about safety. What’s really needed is a way to harness nuclear power that does not involve messy fissionable material like uranium and does not produce unpleasant side-effects like waste plutonium.

Which brings me to the topic of nuclear fusion–and next week’s column.