Nuclear Reactors - How they work (part 2)

Previously (part 1) we had a Pressurized Water Reactor (PWR) which was critical and adding heat to the coolant/moderator.  After the reactor reaches the point where it is generating heat, and the moderator becomes less effective, it becomes neccessary to withdraw the control rods again to increase power output.

Since this is a PWR, we are not supposed to have large-scale boiling in the core.  Steam doesn't transfer heat as readily as water does, and in a PWR, in-core boiling is a bad, bad thing.  For this reason the pressure in the primary coolant loop must be kept well above the boiling point of water for the temperature found in the core.  How do we do that?  We have a pressurizer!

The pressurizer does three things:  First, it acts as a surge volume for the primary coolant system by maintaining a compressible steam-filled void space.  Secondly, it keeps the system pressure high enough that boiling cannot occur in the core.  This is accomplished by keeping the pressurizer vessel half full of water, and adding enough electrical heaters that the temperature in the pressurizer is kept higher than that of the core.  All boiling will occur in the pressurizer, not in the core.

Lastly, the pressurizer controls the primary coolant system pressure.  As more electric heaters are energized in the  pressurizer vessel, saturation conditions increase, causing pressure to rise.  To reduce primary pressure, a shower spray head at the top of the vessel can spray slightly cooler water into the steam, condensing a portion of the steam and reducing pressure.  It's quite a simple and elegant process.

Below is a simplified diagram of the primary and secondary systems of a PWR.  The radioactive primary coolant (Red) is contained in a closed loop.  The reactor core is the heat source, the control rod drive mechanism positions the control rods to increase/decrease reactor power, the primary pump circulates the primary coolant, and pressurizer serves as a static surge volume.

The steam generator segregates the radioactive primary coolant from the steam/water system, but  allows heat to be transferred out of the primary coolant loop and generate steam for the turbine.  

Pressure in the primary system is increased by energizing submerged electrical heaters in the pressurizer, and reduced by spraying a small slip-stream of primary coolant from the reactor coolant pump through a spray head at the top of the pressurizer. This cools and condenses some of the steam in the pressurizer, reducing system pressure.

Temperature is gradually increased by withdrawing the control rods.  Remember in the previous post that the neutron population would increase with no control rod movement if the reactor were slightly supercritical?  That is no longer the case when power level is high enough for the reactor to generate heat.  After the core begins heating and the "negative temperature coefficient of reactivity" kicks in, withdrawing the control rods increases power, followed by a smaller drop in power as the primary coolant heats up.  So control rods are withdrawn in a series bumps, and the coolant temperature is slowly increased.

The primary coolant pump circulates primary coolant (very pure water) between the reactor core and the steam generator.  The reactor core adds heat created by fission.  The steam generator removes heat by boiling secondary water in a heat exchanger.  Thus, primary coolant is radioactive, but does not boil.  Secondary water is non-radioactive, and does boil.

In a PWR, excess fuel is loaded, more than what is required to bring the reactor up to power.  This is done so that the reactor can continue to run as the U-235 is expended, and fission products build up.  Many of the atoms that are created by fission are strong neutron absorbers (poisons), and eventually result in the inability of the reactor to maintain full power.  This is in spite of excess U-235 added at during refueling.  Only about 3% of the U-235 is used up before the accumulation of poison halts reactor operation.  This is why fuel recycling is so desirable from an industry standpoint.

Commercial PWRs are unique in that they add boric acid to the primary coolant.  Boron is a neutron absorber.  With the addition of boron to the coolant, the control rods may be entirely withdrawn from the core, using only boron to control neutron population.  This is desirable because in the vicinity of control rods, neutron population, and fissions will be depressed.  This forces other regions of the core to run hotter for a given power level.  With control rods out of the core, neutron distribution is more consistent and hot spots due to uneven neutron flux are less likely to develop.

At a certain point, on the secondary side of the steam generator, steam is at an adequate pressure to begin warming up the steam turbine.  This also has an interesting impact on reactor power.  As we create steam on the secondary side of the steam generator, we are also removing heat from the primary coolant.  This slightly cooler primary coolant returns to the reactor.  Since it is now more dense, it is a better moderator, and more neutrons stay in the core to cause fissions.  Reactor power now increases along with steam demand.  This is a very desirable feedback loop, because now there is little need to adjust the control rods.  We allow the steam turbine load to determine what power level the reactor will operate at.

The remainder of the steam plant operates in a very similar manner to a fossil-fueled plant.  One difference:  Since it is not possible to superheat the steam with this process, steam dryers are added between different stages on the steam turbine, to prevent mist from damaging the lower pressure sections.

Nuclear Reactors - How they work (part 1)

I've always been fascinated by nuclear reactors.  Even as a child, I was mystified by the blue glowing water I would see in the National Geographic Magazine.  The whole notion of releasing enormous amounts of energy by gathering certain materials together in a small area is a bit mind-boggling.

So how does a reactor work?  First, a little chemistry, then a little physics. 

As an example of how nuclear energy is created, we can look at an atom of Helium-4, which contains 2 protons, 2 neutrons, and 2 electrons. 
Neutrons (blue) have no electrical charge.  Protons (red) have a +1 charge.  Electrons (yellow) orbit the atom at a pretty far distance and have a -1 charge.  Electrons and protons (and therefore charge) are balanced in typical atoms.

Because protons have a +1 charge, they repel each other. The repulsive electrostatic force is squared every time the distance is cut in half.  The closer these protons get to each other, the more they want to fly apart!  This is similar to pushing powerful magnets together with both north poles together.  However nature provides a way to hold these repelling protons together in spite of themselves :)

Back now to our physics...

The atomic mass of each component:

proton = 1.007766612
neutron = 1.00864160
electron = .000548892490

OK, funky numbers with lots of decimal places.  Bear with me here.  This is important.

Mass of all these individual components added together in a Helium Atom = 4.03391420898
Yet the actual measured mass of a Helium Atom is only = 4.002602  What the HECK!!!!???  
These numbers should be the same!

There is a difference in the atomic mass of 0.03131220898 between the individal components and the assembled atom.

This difference in the calculated mass and the actual mass is called the "mass defect".   Holding two positively-charged protons very close together requires a great deal of energy.  It also requires an incredibly powerful short-range force, called the nuclear force.  The nuclear force is so strong that it can overcome the repulsion of particles with like charges.  However, it requires so much energy to bind a nucleus together against the repulsive electrostatic force that there is a noticable change in the mass of the atom and its components.

Here is where we get to Einstein's awesome realization: Mass and energy are equivalent and interchangeble.

The difference in mass of an assembled Helium atom and its components is due to the large amount of energy required to hold that atom's nucleus together against the repulsive force of those positively charge protons that are trying to repel each other.  E=mc^2 is the equation that explains how much energy was needed to assemble the Helium atom from its components.  It's also how much energy would be released if they were taken apart again.  This energy is called Binding Energy.

Binding energy is the same exact thing as the mass defect, only from the viewpoint of energy, rather than mass.  E=mc^2 is the mathematical conversion between the two states (matter and energy).

To better understand how much energy, E we are talking about, we need to look on the right side of the equation.  The m (or mass) is a very tiny number, 0.03131220898.  However c is the speed of light, and that number is squared.  So the speed of light times the speed of light is a very, very, large number.  The energy that would be released if we break apart one helium nucleus into its components would be 28.3 Million Electron Volts.  To put this in perspective, an X-ray has energy at 40-60 thousand Electron volts, while visible light has energy at 2-6 electron volts. 

Unfortunately for our energy needs, Helium atoms are notoriously stable, and almost impossible to break apart.  However, nature has provided us with certain atoms that will split apart quite readily under the correct conditions. 

It turns out that certain high-mass atomic nuclei will split into two smaller fragments after absorbing (or capturing) a neutron.  More importantly, when these atoms split, they release many more neutrons, allowing a continuous reaction (or chain reaction) to be sustained.  Neutrons are the best subatomic particle to create large numbers of fissions, because they have no charge, and readily interact with the nucleus of an atom.  Protons have a positive charge, and therefore are repelled by the positively charged nuclei of atoms.

Below to the left, a neutron is absorbed by a fissionable nucleus. The nucleus splits into two smaller fragments, three additional neutrons, and a gamma ray. This is a pretty typical result of fission.

Atoms that will split (or fission) after capturing a neutron are called "fissionable".  There are a large number of atoms that will fission.   However not just any fissionable material will work in a reactor. 

To assemble a reactor core we need to find fissionable material with some specific properties: 

• Some atoms which are fissionable don't readily absorb neutrons, so they won't work.  
• There needs to be a sufficient supply.  If the fissionable material is rare, it cannot be used.
• The fissionable atom must produce 2 neutrons when spit, or a reaction cannot be maintained. 
• The fissionable atoms must have a long half-life, and not decay to some other element while in the reactor.

There is one other property that has to be met in our fissionable material.  It must also be "fissile". 

To understand the difference between fissionable and fissile, we need to understand about neutron temperature.  When a neutron is ejected from a split atom, it has enormous energy, about 2 Million Electron Volts (or 2 MeV). 

Physically, this is the speed of the neutron.  A 2 MeV neutron is traveling at about 45 million miles/hr.  Neutrons moving this fast don't often linger to induce fission in other atoms.  Statistically they are likely to leave the reactor core before an interaction occurs.  For this reason it is desirable to slow them down.  Neutrons are slowed by allowing them to bounce off lighter atoms and transfer their kinetic energy to the atoms.  This process is called "moderation", and slows the neutrons down to what is called "thermal" energy, .025 eV, or about 4900 miles/hr.  Depending on the mass of the moderating material, it may take from 10-2500 impacts to reduce the speed of a fast neutron from fission to thermal equillibrium.

Below is a table showing neutron energy (or straight line speed) of a neutron with its description.

Neutron energy	Energy range
0.0 eV-0.025 eV	Cold neutrons
0.025 eV	Thermal neutrons
0.025 eV-0.4 eV	Epithermal neutrons
0.4 eV-0.6 eV	Cadmium neutrons
0.6 eV-1 eV	EpiCadmium neutrons
1 eV-10 eV	Slow neutrons
10 eV-300 eV	Resonance neutrons
300 eV-1 MeV	Intermediate neutrons
1 MeV-20 MeV	Fast neutrons
> 20 MeV	Relativistic neutrons

It is at thermal energy, speed, or temperature (pick one), that neutrons will more readily be absorbed by a nucleus and lead to another fission.

Now that we understand the process of neutron moderation, we can return to our need for Fissile atoms.  Fissile atoms are a small subset of fissionable atoms, that will readily split after absorbing a thermal neutron.  The list of candidates of fissile materials is small.  Uranium 233 and 235, Plutonium 239, and 241.  Only Uranium 235 is naturally occuring, while the others must be produced by excess neutrons from other materials inside a breeder reactor.

In another post I will describe other types of reactors, but for now we will stay with the basic thermal reactor, which is fueled with 5% U-235, both cooled and moderated by normal (light) water.

When an atom splits, it creates two highly radioactive atoms that must be contained, and not allowed to get into the coolant/moderator.  Otherwise that water will become very contaminated with radwaste.  For this reason, the uranium fuel is surrounded by zircaloy cladding.  Below is a photo of people inspecting new fuel assemblies for defects in the cladding.

The energy released by splitting or fission of a single U-235 atom is about 200 MeV, most of which is in the form of kinetic energy of the two new atoms.  They are moving at high speed, but due to their mass and charge, they quickly come to rest among other atoms of fuel.  The energy these atom fragments lose as they come to rest is converted to heat.

Back to the reactor core.  Water surrounds an array of these fuel assemblies, which is called the "core".  It takes a certain amount of fissile U-235 packed closely together, and moderated  neurtons for a continuous reaction to take place.  Below is a top-down view of a generic reactor core.

The reaction is started by withdrawing control rods.  Control rods contain strong absorbers of thermal neutrons.  These neutron absorbers are also known as "poisons", in that they slow or stop the nuclear fission process.  Typically a control rod contains cadmium, boron (or a borated alloy) for neutron control.

"Keff" is the number reactor physicists use to determine whether the reactor core is shutdown, steady-state, or starting up.  It's the neutron multiplier.  Keff is the likelihood that a single neutron will make it from birth to cause a fission in another Uranium atom.  Some of the other possibilities are that a neutron will escape from the reactor core, be absorbed in some material other than Uranium, or be absorbed by a Uranium atom, but not cause a fission.

If Keff is < 1.0 the reactor is "subcritical".  If Keff is = 1.0 the reactor is "critical", and if the Keff is >1.0 the reactor is "supercritical".  Nothing in any of these terms should be fear-inducing, they just describe a core reactivity condition for sustaining (or changing) the neutron population.

So... what happens when the control rods are removed?  I will skip the mathematics this time and give a simple description.  Neutrons are always present in U-235, because one of the natural decay modes for U-235 is spontaneous fission.  However reactors contain a strong artificial neutron source to ensure there are plenty of neutrons to get things going.  Think of the installed neutron source as sort of a pilot light for a gas furnace.

When the control rods are removed partially, neutron population begins to increase for two reasons.  The neutrons are no longer being absorbed in the poison, and so they begin splitting U-235 atoms, which generates even more neutrons.  The neutron population increases, even if Keff is less than 1, for the above reasons. 

Eventually though, if the control rods have been removed far enough, neutrons from new fissions will equal the losses, and Keff will be 1.  The reactor will then be critical.  However it won't be generating any heat.  Reactors typically are critical at an output of about 5 watts.  About the power required by a single "night light" bulb.  Power must be increased by a factor of 10^8 to get to 500 Megawatts.

After the reactor is critical, the neutron population must increase a great deal before any noticeable heat is generated.  So the rods are pulled out a little more, and each generation of neutrons has a few million more than the previous generation.  With this small increase in reactivity, there is no further need to withdraw the control rods.  Neutron multiplication will increase on its own.

Eventually the reactor reaches a point at which heat is generated, and this is where things get interesting.  The moderator (cooling water surrounding the fuel assemblies) heats up, and becomes less dense.  It is therefore less effective at slowing down neutrons. 

Because the moderator is less effective as temperature increases, more neutrons escape the core, which reduces neutron population, and reactor power stops rising.  We therefore have a heat-induced dampening effect on reactor power.  Its technical term is "negative temperature coefficient of reactivity".  Basically, more heating tends to reduce reactor power.  This is a desirable thing, because it prevents a runaway nuclear reaction.  Unfortunately not all reactors have this characteristic :(

So far, so good.  We have a critical nuclear reactor (Keff = 1.0) which is adding heat to the coolant!

I think that now is a good place to stop and think about the next post.  My brain hurts :)

Part 2 is here.

The steam cycle

I have been meaning to do a post on the steam cycle, otherwise known as the Rankine Cycle. It's pretty simple to describe the four-step process. The complicated part is designing, maintaining, and operating the machinery that makes it happen continuously, year after year.

The water/steam cycle is the most practical and commonly used means of converting heat energy into electrical energy.  The process works like this:  Fuel is burned for heat.  The heat vaporizes a liquid (typically very pure water), which is then expanded through a steam turbine.  Lastly it is condensed at very low pressure to extract all possible thermal energy and also to re-use the pure water. 

Summer Vacation

The family just returned from summer vacation.  It was an exhausting whirlwind of a trip, and I don't intend to repeat that sort of vacation again.  It took 3 days of driving to get to SoCal, and 3 days to return, with a lot of side trips while we were there.  Disneyland, the Ringling Circus, Bakersfield, and Morro Bay.

Although we saw some really cool things and got to visit old friends, we didn't go anywhere that was nicer than where I live.  Hmmm.  Maybe that's why this is a vacation spot...

That said, I did get some really cool pictures of places that we visited.  One of those places was Bodie, California, a turn of the century ghost town.  There is a lot more there than the pictures posted here.  I just wanted to share the cool old steam and electric power stuff :)

Below, a skid-mounted boiler

A steam piston engine for running the mine elevator.  Note the journal for the shaft at the far end.

The flywheel and shaft that were attached to the steam engine.  This wheel is enormous.  The shaft is a foot across.



A small AC generator.  This is about 3 ft across.

We also went to Twin Lakes at Mammoth Village.  A very pretty place, although after a year of living in northern Idaho, the forests in California looked pretty sparse and dry.

 

On the way home, we drove over White's Pass, between Mt. Ranier to the north and Mt. St. Helens to the south.  Below is a photo of St. Helens.  Unfortunately, there was a lot of moisture haze in the air, so I didn't get a clear shot.  This is the northwest side of the mountain that blew out in 1980.

Mt. Ranier, another dangerous volcano.  The forest here is quite lush.

Upper Clear Creek Falls.  The water spreads way out, maybe 20 ft across and maybe an inch deep, before pooling together again at the bottom.

Lower Clear Creek Falls.



While we were at Morro Bay I happened to see DSRV-2, the "Avalon", on display.  This is a little electric deep-diving submarine.  "DSRV" stands for "Deep Submergence Rescue Vehicle". 

During the cold war, the Navy had a DSRV stationed on each coast.   In the event a military submarine sunk, the Navy had the ability to load these into a cargo aircraft and quickly get it to the sunken boat, to hopefully rescue survivors.

Unfortunately for the crew of the submarine Kursk, this DSRV hatch would not have mated to the Russian submarine hatch.  Also if I recall correctly, the hatch was too damaged to open, probably due to hull flexing and deforming after impacting the bottom.

Here are the specs for DSRV-2.

Builder:	Lockheed Missiles and Space, Co., Sunnyvale, California, USA
Power Plant:	Electric motors, silver/zinc batteries, one shaft, 15 shaft horsepower (11 kW), four thrusters, 7.5 horsepower (6 kW).
Length:	49 ft (15 m)
Beam:	8 ft (2.4 m)
Displacement:	38 tons (39 metric tons)
Speed	4 knots (7 km/h)
Maximum depth:	5,000 ft (1500 m)
Sonar:	Search and navigation
Ships:	Mystic (DSRV 1)
	Avalon (DSRV 2)
Crew:	Two pilots, two rescue personnel and the capacity for 24 passengers

Side note:  A shipmate of mine transferred to this little guy back in the 1980's.  He said that he finally got a chance to look out at the ocean while submerged (military subs have no windows, for obvious reasons).  For his first dive, they took Avalon clear to the bottom off the coast of San Diego, put him in front of a window, then turned on the lights.  He said there was nothing to see but sand and a few empty beer cans.  Hahaha!

Pokey LaFarge - another very cool musical sound

Years ago, I was in Atlanta for a training class. An old navy buddy recommended that I try "Fat Matt's Rib Shack", for some good southern cooking. I enjoyed the meal, but I enjoyed the band even more. The band was Pokey LaFarge and the South City Three.

I don't know how you would classify the music; It seems to vary between early Amerian Blues and Dixieland. It's a distinctly early 20th century American sound, and I really like it. There can't be many bands playing this kind of music anymore.  I have a couple of their albums on order from Amazon right now. As far as I know, their music is original, not covers.  Every one of these guys is a kickass musician.  Check em out!

New musical discovery - Jonathon Wilson

Taking a quick break from power plants...

I was reading Boing Boing today.  One of the articles was a rave review about musician Jonathon Wilson, and how under-appreciated he is.

The review was *SO* over the top in praise that I decided to have a listen to some of his tunes on SoundCloud.  The dude is damn good.  You have to like the late 60's acid rock style like Pink Floyd & The Moody Blues to appreciate the cool retro sound he's creating.  He sounds a lot like Floyd when they were at the top of their game. 

It took some adjustment on my part to give these songs enough time to get flowing.  Most of the music I listen to these days starts thrashing immediately :)  I really like this first song. 

Nearby Corliss Steam Engine

After putting together a series of blog posts about the history of steam engines, I ran across one in my own backyard!  Being new to the area, we were playing tourist, and poking around in the nearby town of Newport, Washington.  Imagine my surprise when we rolled up on this monster!  Yep, that's a standard bus stop bench in front of it. 

According to the sign, it put out 478 horsepower and the big wheel turned 100 RPM. 

This got me thinking about what it must have been at the turn of the 20th century to see one of these beasts in operation... So I checked Youtube, and guess what?  They have a few videos of Corliss steam engines running.  Check them out!

Below is a 500 Horsepower Corliss engine that was once used to power looms in a textile factory.  It's a little freaky watching that massive connecting rod move back and forth so quickly.  Most impressive in fullscreen mode!


Unfortunately the above video doesn't clearly show the steam valve train.   But happily, I found another video that does.  You can easily see how the eccentric wheel operates the wrist-plate, which in turn drives the entire valve train.  I spent a little time trying to understand the purpose of the vertical rods dangling from the upper steam inlet valves and learned something. 

The inlet valves do not shut when the wrist-plate rocks back.  Instead they are closed by the governor tripping them each cycle.  The vertical rods, which are attached to dashpots, allow the steam valves to close more slowly than if they were shut by the wrist-plate, admitting more steam to the cylinder.  An early (and succesful!) type of variable valve timing.


Once again I will turn the valve train explanation over to Wiki, who does a far better explanation than I ever could:

"The inlet valves are pulled open with an eccentric-driven pawl; when the pawl trips, the rapid closure is damped using a dashpot. In many engines, the same dashpot acts as a vacuum spring to pull the valves closed, but Corliss's early engines were slow enough that it was the weight of the dashpot piston and rod that closed the valve.

The speed of a Corliss engine is controlled by varying the cutoff of steam during each power stroke, while leaving the throttle wide open at all times. To accomplish this, the centriugal governor is linked to a pair of cams, one for each admission valve. These cams determine the point during the piston stroke that the pawl will release, allowing that valve to close.

As with all steam engines where the cutoff can be regulated, the virtue of doing so lies in the fact that most of the power stroke is powered by the expansion of steam in the cylinder after the admission valve has closed. This comes far closer to the ideal Carnot cycle than is possible with an engine where the admission valve is open for the length of the power stroke and speed is regulated by a throttle valve."

And lastly, a drawing of this complex arrangement, showing the pawls that open the inlets, and the vertical rods with attached weights.

AC vs. DC Power

At the end of the 19th century, an epic battle was shaping up.  On one side were Thomas Edison and Lord Kelvin, who advocated using Direct Current (DC) power distribution systems.  On the Alternating Current side of the battle were George Westinghouse and Nikolai Tesla (and nature). 

The battle was known as the "War of the Currents".  DC power systems had already been developed and in use in the United States for several years, and were the standard in use in the 1880s.  From Wiki:

"During the initial years of electricity distribution, Edison's direct current was the standard for the United States, and Edison did not want to lose all his patent royalties.  Direct current worked well with incandescent lamps, which were the principal load of the day, and with motors. Direct-current systems could be directly used with storage batteries, providing valuable load-leveling and backup power during interruptions of generator operation. Direct-current generators could be easily paralleled, allowing economical operation by using smaller machines during periods of light load and improving reliability. At the introduction of Edison's system, no practical AC motor was available. Edison had invented a meter to allow customers to be billed for energy proportional to consumption, but this meter worked only with direct current. The transformation efficiency of the early open-core bipolar transformers was very low. Early AC systems used series-connected power distribution systems, with the inherent flaw that turning off a single lamp (or the disconnection of other electric device) affected the voltage supplied to all others on the same circuit.  The direct current system did not have these drawbacks as of 1882, giving it significant advantages."

Innovation would shortly end most of the advantages held by Direct Current however, and by 1896 the war would be over.  The first innovation was a high-efficiency transformer.  This allowed conversion of AC power to very high voltage for transmission with low losses, and conversion to low voltage near the end user.  DC power was generated at 110 volts, and due to line losses at this voltage, there had to be a power plant within a mile or so of the end-user.  This arrangement would require a power plant to be installed every mile or so!  A great arrangement for Thomas Edison, but not so great for everyone else.

What actually caused DC to lose the Battle of the Currents is an electrical relationship, stated in  Ohm's Law.  Ohm's law says that Power is equal to Voltage times Current, or P = V x C.  A corollary of that law is that Power is equal to the square of current times resistance, or P = I^2 x R.  This corollary is what killed Direct Current as a means of using electrical power.

In any electrical system, transmission lines will have a certain resistance to current flow.  This resistance causes heating, and reduces the ability of the transmission line to carry full load.   This is the P - I^2 x R portion of Ohm's Law.  Doubling current increases resistive heating by 4 times, and this power that is wasted heating up the power line is lost to the end user.

Therefore, with a semi-understanding of Ohm's law, P = V x C, we can see we need to minimize current if for a given Power to transmit power over any kind of distance.  This is done by raising voltage as high as practical.  With a transformer we can adjust AC voltage at will, whereas DC has to be generated at the desired end-user voltage, and the entire system must run at that voltage.

There is another reason AC power won the battle:  It is simpler to work with at the generator.  With a DC machine, the power is produced on the rotor, and must be removed using carbon brushes from the commutator.  There are limits to how much current can pass through these brushes, so a typical power plant would have several small machines, each producing a small amount of power.

With an AC generator, the electromagnetic field rotates, and power is produced in the stationary windings of the machine.  Because there is no need to pull power from a rotating member, the AC generator can make a great deal more power than its DC counterpart.  The largest Dynamo ever built could convert 500 horsepower to DC power.  An equivalent physical-size AC machine would be able to convert 10,000 horsepower, with far less complexity and maintenance.

Looking at the small machine below, we can guess a few things: 

• The commutator segments would require regular care to ensure they remained insulated from each other. 
• Maintenance of brushes and tension would be an ongoing affair.
• Due to low voltage, the output current would be large.  You can see how fat the output leads are. 
• With such high currents, moving this electricity would require vast amounts of copper.  

 In the end, AC (rightfully) won the battle, and so now we live in an Alternating Current world.  The Wiki version of this fascinating story is here.

 And here is a video describing the battle!

https://www.youtube.com/watch?v=xyQfrzBfnDU

Steam Power and Electricity - Dynamos

Steam engines were invented around 1700 AD.  Using a steam engine to turn a generator in order to make electricity would have to wait for another 130 years.  Electricity was not understood, and the earliest generators used electrostatic principles to push electrons around.  Surviving examples of these static-electricity type generators include the Wimshurst generator and the Van de Graaf generator.

Old Mission State Park - Cataldo Mission

Recently we were asked to chaperone on a field trip for our daugher's class.  The field trip was to the Cataldo Mission, now called "Old Mission State Park".

I've forgotten a lot of the Idaho history that they taught in Boise grade school, and Northern Idaho always seemed such a long way from where I grew up...

Long story short, I learned a lot about the mission and the interesting story behind it. 

In the early 1800's, the Coeur d'Alene Indian Tribe had heard about certain powerful white medicine men who wore black robes and had great magic.  The "medicine men" were actually Catholic Jesuit Priests, a sect devoted to spreading the word of God through evangelism. 

The Indians sent several chiefs all the way to St. Louis to request their own priest.  In 1842 The Jesuits responded to the request and sent three priests to the area. Their first activity was to choose a location for a mission.  The first was along the St. Joe River, but the site was subject to flooding. In 1846 they chose the current location.

In 1850 the church was taken over by Father Antonio Ravalli, who began designing the new mission building.  He was Italian, had traveled Europe, and seen many of the great Cathedrals there.

He made sure that the building was constructed by the Indians themselves, so that they could feel part of the church. The frame of the building was built using only broad-axes and wood augers.  There were no lumber mills (or even roads) in the area at that time, so each board was made flat by hand from a log using only an axe.  The boards are held together by wooden pegs driven through holes.  Amazingly, even with this primitive construction, this is Idaho's oldest standing building! 

After framing, the walls were filled in with "wattle and daub", which is a blend of creek willows and mud.  The ceiling was initially white, but the indians wanted the ceiling color to more accurately represent the sky, so they created a stain from huckleberries and stained the center three ceiling panels blue.

Unfortunately in the 1920s, the indians were forced to move to a reservation, and the unique building of worship that they had created with their own hands was taken from them.  It was abandoned then, and fell into disrepair, until the Idaho Centennial commision decided to restore it in 1976.  Following the restoration, the mission building is still about 90% original.  On a happier note, the building has since been returned to the Coeur d'Alene Tribe.

Below are the two primitive tools used in the construction of this entire building.  Augur and broadaxe.

Beautiful handmade floor planks



Below is a statue carved by Father Antonio Ravalli.  It is not marble, but local pine.  Near the bottom is a photo of Father Ravalli.

 Father Ravalli made this elaborate candle holder from used cans.



 

A photo of the altar.  Everything is made from pine trees, and finished to look like marble and hardwoods.  The "wallpaper" is made from bits of fabric and old newspapers.

An overview from the back of the mission.  It's an awe-inspiring, hand-made frontier cathedral.