Neutrons, Electrons, Electric Current, Nuclear Power, Nuclear Chain Reaction, Residual Decay Heat and Pressurized Water Reactor

Posted by PITHOCRATES - July 18th, 2012

Technology 101

We create about Half of our Electric Power by Burning Coal to Boil Water into Steam

An atom consists of a nucleus made up of protons and neutrons.  And electrons orbiting around the nucleus.  Protons have a positive charge.  Electrons have a negative charge.  Neutrons have a neutral charge.  In chemistry and electricity the electrons are key.  When different atoms come together they form chemical bonds.  By sharing some of those electrons orbiting their nuclei.  In metals free electrons roam around the metal lattice of the crystalline solid they’re in.  If we apply a voltage across this metal these free electrons begin to flow.  Creating an electric current.  The greater the voltage the greater the current.  And the greater the work it can do.  It can power a television set.  Keep your food from spoiling in a refrigerator.  Even make your summers comfortable by running your air conditioner. 

We use electric power to do work for us.  Power is the product of voltage and current.  The higher each is the more work this power can do for us.  In a direct current (DC) system the free electrons have to make a complete path from the power source (an electric generator) through the wiring to the work load and back again to the power source.  But generating the power at the voltage of the workload required high currents.  Thick wires.  And a lot of power plants because you could only make wires so thick before they were too heavy to work with.  Alternating current (AC) solved this problem.  By using transformers at each end of the distribution path to step up and then step down the voltage.  Allowing us to transmit lower currents at higher voltages which required thinner wires.  And AC didn’t need to return to the power plant.  It was more like a steam locomotive that converted the back and forth motion of the steam engine into rotational power.  AC power plants generated a back and forth current in the wires.  And electrical loads are able to take this back and forth motion and convert it into useful electrical power.

Even though AC power allows us to transmit lower currents we still need to move a lot of these free electrons.  And we do this with massive electric generators.  Where another power source spins these generators.  This generator spins an electric field through another set of windings to induce an electrical current.  Sort of how transformers work.  This electrical current goes out to the switchyard.  And on to our homes.  Simple, really.  The difficult part is creating that rotational motion to spin the generator.  We create about half of our electric power by burning coal to boil water into steam.  This steam expands against the vanes of a steam turbine causing it to spin.  But that’s not the only heat engine we use to make steam.

To Shut Down a Nuclear Reactor takes the Full Insertion of the Control Rods and Continuously Pumping Cooling Water through the Core

We use another part of the atom to generate heat.  Which boils water into steam.  That we use to spin a steam turbine.  The neutron.  Nuclear power plants use uranium for fuel.  It is the heaviest naturally occurring element.  The density of its nucleus determines an element’s weight.  The more protons and neutrons in it the heavier it is.  Without getting into too much physics we basically get heat when we bombard these heavy nuclei with neutrons.  When a nucleus splits apart it throws off a few spare neutrons which can split other nuclei.  And so on.  Creating a nuclear chain reaction.  It’s the actual splitting of these nuclei that generates heat.  And from there it’s just boiling water into steam to spin a steam turbine coupled to a generator.

Continuous atom splitting creates a lot of heat.  So much heat that it can melt down the core.  Which would be a bad thing.  So we move an array of neutron absorbers into and out of the core to control this chain reaction.  So in the core of a nuclear reactor we have uranium fuel pellets loaded into vertical fuel rods.  There are spaces in between these fuel rods for control rods (made out of carbon or boron) to move in and out of the core.  When we fully insert the control rods they will shut down the nuclear chain reaction by absorbing those free neutrons.  However there is a lot of residual heat (i.e., decay heat) that can cause the core to melt if we don’t remove it with continuous cooling water pumped through the core. 

So to shut down a nuclear reactor it takes both the full insertion of the control rods.  And continuously pumping cooling water through the core for days after shutting down the reactor.  Even spent fuel rods have to spend a decade or two in a spent fuel pool.  To dissipate this residual decay heat.  (This residual decay heat caused the trouble at Fukushima in Japan after their earthquake/tsunami.  The reactor survived the earthquake.  But the tsunami submerged the electrical gear that powered the cooling pumps.  Preventing them from cooling the core to remove this residual decay heat.  Leading to the partial core meltdowns.)

Nuclear Power is one of the most Reliable and Cleanest Sources of Power that leaves no Carbon Footprint

There is more than one nuclear reactor design.  But more than half in the U.S. are the Pressurized Water Reactor (PWR) type.  It’s also the kind they had at Three Mile Island.  Which saw America’s worst nuclear accident.  The PWR is the classic nuclear power plant that all people fear.  The tall hyperboloid cooling towers.  And the short cylindrical containment buildings with a dome on top housing the reactor.  The reactor itself is inside a humongous steel pressure vessel.  For pressure is key in a PWR.  The cooling water of the reactor is under very high pressure.  Keeping the water from boiling even though it reaches temperatures as high as 600 degrees Fahrenheit (water boils into steam at 212 degrees Fahrenheit under normal atmospheric pressure).  This is the primary loop.

The superheated water in the primary loop then flows through a heat exchanger.  Where it heats water in another loop of pumped water.  The secondary loop.  The hot water in the primary loop boils the water in the secondary loop into steam.  As it boils the water in the secondary loop it loses some of its own heat.  So it can return to the reactor core to remove more of its heat.  To prevent it from overheating.  The steam in the secondary loop drives the steam turbine.  The steam then flows from the turbine to a condenser and changes back into water.  The cooling water for the condenser is what goes to the cooling tower.  Making those scary looking cooling towers the least dangerous part of the power plant.

The PWR is one of the safest nuclear reactors.  The primary cooling loop is the only loop exposed to radiation.  The problem at Three Mile Island resulted from a stuck pressure relief valve.  That opened to vent high pressure during an event that caused the control rods to drop in and shut down the nuclear chain reaction.  So while they stopped the chain reaction the residual decay heat continued to cook the core.  But there was no feedback from the valve to the control room showing that it was still open after everyone thought it was closed.  So as cooling water entered the core it just boiled away.  Uncovering the core.  And causing part of it to melt.  Other problems with valves and gages did not identify this problem.  As some of the fuel melted it reacted with the steam producing hydrogen gas.  Fearing an explosion they vented some of this radioactive gas into the atmosphere.  But not much.  But it was enough to effectively shut down the U.S. nuclear power industry. 

A pity, really.  For if we had pursued nuclear power these past decades we may have found ways to make it safer.  Neither wind power nor solar power is a practical substitution for fossil-fuel generated electricity.  Yet we pour billions into these industries in hopes that we can advance them to a point when they can be more than a novelty.  But we have turned away from one of the most reliable and cleanest sources of power (when things work properly).  Using neutrons to move electrons.  Taking complete control of the atom to our make our lives better.  And to keep our environment clean.  And cool.  For there is no carbon footprint with nuclear power.

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Earthquake and Tsunami Devastate Japan

Posted by PITHOCRATES - March 11th, 2011

Have they no Shame?

It’s started.  Even before the aftershocks stopped.  The global warming crowd is blaming man for Japan’s earthquake (see Some respond to Japan earthquake by pointing to global warming by Amanda Carey posted 3/11/2011 on The Daily Caller).

Hours after a massive earthquake rattled Japan, environmental advocates connected the natural disaster to global warming. The president of the European Economic and Social Committee, Staffan Nilsson, issued a statement calling for solidarity in tackling the global warming problem.

“Some islands affected by climate change have been hit,” said Nilsson. “Has not the time come to demonstrate on solidarity — not least solidarity in combating and adapting to climate change and global warming?”

“Mother Nature has again given us a sign that that is what we need to do,” he added.

Of course, he is counting on that the rest of the world being as ignorant as he is.  Global warming doesn’t cause earthquakesTectonic plates shifting along fault lines do.  It’s a completely different science.  If you can call global warming science.  Which, based on his statements, you can’t.

Shame on these people.  Rubbing their hands together in glee whenever some horrible act of nature occurs that they can politicize.

8.9 Magnitude Earthquake hits Japan

The 8.9 magnitude earthquake is the biggest yet to hit Japan.  Since they’ve been keeping records, at least.  It’s caused some incredible devastation.  And a tsunami.  But it’s something Japan was prepared for.  And she will survive.  Because she has done it before (see Daybreak reveals huge devastation in tsunami-hit Japan by Edwina Gibbs and Chisa Fujioka posted 3/11/2011 on Reuters).

The quake surpasses the Great Kanto quake of September 1, 1923, which had a magnitude of 7.9 and killed more than 140,000 people in the Tokyo area.

The 1995 Kobe quake caused $100 billion in damage and was the most expensive natural disaster in history.

This time the death toll will not be anywhere near what it was in 1923.  Thank God.  The cost will be severe, though.  But it’s better to face that then hundreds of thousands in deaths.  Like they had in Haiti.  With their 7.0 magnitude quake.  Over 300,000 thousand died there.  Why?  Because of their poverty and political corruption.  For poverty is the leading cause of death in the world. 

Japan is an advanced nation.  A nation of laws.  With a strong economy.  Her people are prosperous.  Making life better for everyone.  Because of this, her people worked in buildings designed to withstand the power of earthquakes.  And a lot of them did.

Free-Market Economies are Safer to Live In

In advanced nations with strong, free-market economies, people come first.  These economies, after all, respond to consumer demand.  Safety matters.  So they build things safe.  Because the people matter.  And they demand it.

Contrast that with a command economy.  In National Socialist Germany (i.e., Nazi Germany), the state came first.  And the state didn’t hide that fact.  People were expendable.  Their needs were subordinated to the state’s.  Ditto for their enemy.  The Soviet Union.  In fact, when the Red Army was on the move, the infantry advanced ahead of their tanks.  To protect their tanks from land mines.  You see, with their vast population, it was easier to replace people than tanks.  For their people were an expendable resource.

This mindset no doubt played a role in the Soviet economy.  And their nuclear program.  What happened at Chernobyl could not have happened in the United States.  The Chernobyl nuclear reactor design was flawed.  And there was no containment vessel.  Safety was not a driving design criteria.  That’s why during testing the reactor core heated beyond control.  And exploded.  Without a containment vessel, that explosion threw up radioactive waste into the atmosphere and across Europe.  This did not happen at Three Mile Island.  Because in our free market economy, people come first.  So we build things safe.

Japan’s Nuclear Power Plants Overheating

Some of Japan’s nuclear reactors are having problems.  They’re overheating.  It’s nothing to do with their design.  In fact, it’s their design that has kept them this safe so far after an 8.9 magnitude earthquake and up to 7 (and still counting) aftershocks measuring 5.2 or stronger.  It was the one-two punch of mother nature.  The earthquake took out the primary electrical power.  Then the tsunami washed out their backup generators (see Report: 2 Japanese plants struggling to cool radioactive material by the CNN Wire Staff posted 3/11/2011 on CNN World).

The International Atomic Energy Agency said Friday on its website that the quake and tsunami knocked out the reactor’s off-site power source, which is used to cool down the radioactive material inside. Then, the tsunami waves disabled the backup source — diesel generators — and authorities were working to get these operating.

A double failure of low probability.  In power redundancy, it is common to have two electrical services from two independent electrical grids.  The plant can operate split over both or entirely on one or the other.  That’s one level of redundancy.  Should both of these sources go out (which in itself is a low probability), then there are on-site diesel generators.  Completely independent and self contained.  So no matter what happens with the offsite electrical sources, the generators can provide electrical power.  That is, unless they’re submerged in seawater.  Nuclear power plants may also have a battery backup as well.  Of course, batteries only last so long.  And don’t do well submerged in seawater.

Nuclear reactors boil water to make steam to produce electricity.  The boiling of this water is what cools the reactor core.  Even with the reactors shut down there is still residual heat that will grow unless the cooling pumps keep running to circulate water around the core.  And this is the problem they’re having.  The cooling pumps aren’t running.

This won’t be another Chernobyl

The disaster that hit Japan would have destroyed a lesser nation.  They need help.  And we should give it.  Whatever they need.  But in the end, they will shake this off and go on with life.  Because they are a people who can take pretty much whatever life throws at them.  Let’s just hope they can get those cooling pumps running again.  They have good designs.  Good operating procedures.  Good safety measures in place.   And some of the best nuclear people in the business.  This won’t be another Chernobyl.

Let’s help Japan.  And keep the Japanese in our prayers.

www.PITHOCRATES.com

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