Nuclear Power

Control Room Simulator for Cook Nuclear Power Plant, Michigan

One aspect of nuclear power that I find interesting is that there are people who love nuclear because they believe that this source is environmentally friendly and practical, and there are those who are vehemently opposed to nuclear because they feel very strongly that nuclear is dangerous to local communities and the waste is excessively harmful to the environment.  To be fair, I should share my personal bias; I like nuclear power for a few reasons; its safer than people know, it does not produce any air pollution, its relatively in-expensive to operate, the fuel is plentiful, and most importantly its proven technology that we are taking advantage of now.  Fusion may be the holy grail of electrical generation, but it won't be viable for decades, if ever, and we have to address our energy needs now while balancing national security, public health and environmental concerns.  As I have said before, nuclear has benefits and drawbacks, and the huge drawback with nuclear is the management of very dangerous waste products.  Since I am not terribly concerned with a reactor going critical and exploding, or otherwise causing a catastrophe, the real question is does the prospect of having to manage highly radioactive waste for a very long period of time out weight the drawbacks of fossil fuel burning plants?  Depending on how a community, country, or the world answers that question will determine how the future of nuclear power.

How Nuclear Reactor Works
As strange as this may sound, a nuclear power plant is fundamentally a cousin of the coal, or natural gas plant in that the water is heated to create steam, which turns a turbine that spins a generator that produces electricity.  A radioactive substance, in commercial reactors that fuel is uranium, creates heat as the atoms break down, and vast amounts of heat is generated.  So the operation of a nuclear reactor is basic in concept since all that is required is to gather a sufficient quantity of nuclear fuel, submerge it in water, and use the steam to produce power.  Of course, in practice it is not that simple for when nuclear fuel is amassed, the radioactivity feeds off itself and starts a chain reaction that has the potential to perpetuate it self uncontrollably and that is when the reactor has the potential to explode or melt down.  However, a reactor works more efficiently if the reaction does not have to be stimulated

Let me explain, in a little more detail how the reactor actually works.  Uranium is radioactive, which means that it is inherently unstable.  Eventually, given its instability, a uranium will decay or break apart.  In nuclear reactors, the fuel is enriched with an isotope of uranium that will decay when struck with a neutron, and in turn throws off two or three more neutrons.  Now what makes a nuclear reactor work is that those two or three neutrons will likely trike two or three uranium atoms, which will in turn each decay releasing heat and two or three neutrons each potentially releasing up to 9 neutrons.  If those 9 neutrons hit 9 uranium atoms, then 27 neutrons could be released, and so on and so on.  Or, in other words, this is the start of a chain reaction.  If this reaction continues without abatement, then the fuel will start to get very hot, melt, and the the reactor could melt down.

Chain Reaction Video:




Uranium fuel is formed into pellets that are about the size of the end of a grown mans pinky finger.  These pellets are arranged in long stacks within a metal tube called fuel rods.  A fuel rod may be as long as 12 feet, and they batched together to form an assembly.  A typical fuel assembly is arranged into 8x8, 14x14, 17x17 blocks of fuel rod.  These assemblies are placed into the reactor core in a manner that balances safety and efficiency, and intermixed with the fuel are control rods that can slow or even stop the reaction. Control rods are made up of a material, such as cadmium, that is very good at capturing neutrons, and if you remember the sequence of atoms decaying, releasing neutrons that strike other uranium atoms causing them to decay and release more neutrons.  If those free neutrons are stopped, then the chain reaction is slowed or stopped. 

Reactor design does vary from plant to plant or country to country, but the basic design for capturing the heat energy released as a uranium atom decays is for the whole reactor core to be contained within a large stainless steel vessel filled with water similar in many respects to a large boiler.  This water is able to circulate through the fuel assemblies where is gets heated.  The heated water either its self becomes steam (see Boiling Water Reactor, abbreviated BWR) or is used to make steam (see Pressurized Water Reactor, abbreviated PWR).  Like a coal or natural gas plant, the steam then turns a turbine that turns a generator.

Picture of the reactor vessel from EIA (Energy Information Administration).  This is from a PWR (Pressurized Water Reactor)

Water is circulated through the reactor vessel and used to generate steam.  One safety feature of a nuclear reactor is the water that is passed through the reactor and nuclear fuel is isolated from the water that becomes steam and passes through the turbine.  Often, a power plant will have three separate water loops, a primary that cools the reactor, a secondary that is heated by the primary loop to become steam, and a tertiary loop that is used to convert the steam back into water.  Typically the tertiary loop is drawn from an environmental source such as a river, lake, or ocean.  The diagram below from the Tennessee Valley Authority (TVA) illustrates the multiple loops, the primary loop is pinkish, the secondary is blue and goes to the turbine, and the tertiary loop (in this diagram) goes to the cooling tower.

http://www.ocrwm.doe.gov/factsheets/doeymp0010.shtml

Fusion – A Look at the Future

The picture to the left is of the University of Michigan's Laser Chamber - considered to be one of the most intense lasers in the world. The red beam is NOT the laser it's self, its a sighting laser used to aim the main laser. This is an infrared laser that is being illuminated by a phosphorescent card. It may be hard to see, but the reason the laser seems to be tapering toward the left is because it is being focused at a specific point.

For many decades the promise of fusion power has been dangling like a carrot and vowing endless, safe, clean power. Each year it seems like the day that we will actually realize this dream keeps getting pushed back further and further. But, honestly, I don’t really know anything about how a fusion reactor might operate, what waste, if any, it may produce, or when we might see these plants in operation. However, I do know someone who can answer some of these questions and so I sat down with my friend Chris McGuffey to discuss the future of fusion. Chris is working toward a PhD in Nuclear Engineering at the University of Michigan, in Ann Arbor.  Michigan has one of the best nuclear engineering graduate programs in the US (here), and the laser my friend is working with as part of his research is lauded to be the most intense laser in the world (2008). His research is focused on the physics of lasers and particle beams, or as he puts it; “Specifically I work to create electron beams and x-ray beams which may be substantially cheaper than those produced by conventional accelerators. Additionally the same physical mechanisms are important in the "fast ignition" and "direct drive" schemes of inertial confinement fusion.”

Through my discussion with Chris, I can present you a vision of the future:
Let me transport you 50 years into the future (assuming the world doesn’t end in 2012) to the opening of one of the first commercial fusion reactors. Imagine a thick walled stainless steel chamber that is spherical in shape and ten meters (or think 10 yards for the metric challenged) in diameter. Pointed at the center of this sphere, where the fusion reaction is taking place, are a number of instruments, and lasers. The reaction is fed by a steady stream of fuel pellets that are about as large as the head of a pin and are being fired into the center of the reactor at 5-10 times per second. As each pellet is zipping into the chamber, lasers lock onto the pellet applying light pressure and heat to initiate a burn.  When the pellet reaches the center of the chamber, an extremely powerful and amazingly short burst from the lasers will have heated it enough that the fusion reaction will begin. What is being termed a “burn” is not the traditional burn, like how wood burns; this burn is two isotopes of hydrogen being fused together to form an alpha particle (a helium atom without any electrons) and one neutron, and then perpetuating this reaction throughout the fuel pellet. The heat that is produced when the atoms fuse is not what will be used to produce electricity.  Instead you have one fast neutron that will shoot off into a fluid that is laced with the isotope lithium-7. When the neutron interacts with the lithium, another reaction occurs. In this reaction, the fast neutron combines with the lithium and causes it to split into one tritium, one helium, and a slow neutron as well as creating heat (Nave, 2006). The heat will be used to create steam to turn a turbine that will be used to generate electricity.

Portals to view into the laser chamber.

However, this vision of the future makes a few assumptions; one, we have developed materials or processes that will be able to survive the constant bombardment of high energy neutrons for a reasonable, and economical amount of time; two, we will be able to capture the energy efficiently. Lastly, can we capture more energy than it takes to ignite the reaction. Probably, one question that should be asked and some people may not be asking is: is this worth it? I, for one, have been led to believe that fusion is this holy grail for the power industry, and promises to be clean, safe and to have unlimited power potential since the fuel is the most abundant element in the universe: hydrogen. Call me a cynic, but I want to know what the catch is. Nothing is free, and nothing is so easy, so I have been wondering if fusion is as clean and safe as I have been led to believe.  Well, I thought it was a good question and that is what I hoped to glean from my discussion with Chris.  His answer was a little unexpected; fusion is safe, is clean and has the potential to be everything that is promises.  Since the process is not like a chain reaction in a fission reaction where we have to be constantly reigning it in, there is no possibility of a catastrophic event; like a nuclear explosion or melt down.  Also, since the fuel is hydrogen, and all the necessary containment is relatively light material - lighter than uranium, so any radioactivity produced will be short lived.  When Chris was referring to short lived, he did not mean short on a geological time scale, he meant short on the human scale. So the waste, can be managed in our life times, and in a hundred years or less the waste will be safe.  Also, it will not be as "hot" as the waste produced by current fission reactors that is also very long lived.  Think tens if not hundreds of thousands of years.  As for environmental impact, the fusion reactor will produce as many green house gases as a conventional nuclear power plant.  What I mean by that, is that the reactors largest contribution of green house gases will likely have to do with its construction and not its operation.  The heavy equipment to forge, move, and build the reactor will burn fossil fuels (presumably) that would otherwise not be burned.  So then if this is so great what is the hold up?  Research.  The technology required to commission the first reactor is so daunting, and expensive.  The impression I got from Chris was that 50 years may be a some what optimistic time line.  Specifically, we will need to have some vast improvements in materials to make this dream a reality.

There are two main reactor designs emerging from research and development programs, one is the Inertial Confinement Fusion (ICF) design that I had illustrated above. High power lasers are used to initiate the fusion reaction by applying intense amounts of heat and pressure. When I say pressure, the pressure is indirectly applied by the lasers.  They heat a little vessel that the fuel pellet will be contained in.  As the vessel is heated to incredible temperatures in extremely small fractions of a second (think 1x10^-9 to 1x10^-14 seconds) the vessel will explode inward, and compress the fuel.  The second design uses magnetic force to squeeze the atoms together to initiate the fusion reaction, and is referred to as Magnetic Confinement Fusion (MCF). The International Thermonuclear Experimental Reactor (ITER) project is building a MCF test reactor in Cadarache, France that is expected to run for 30 years. Construction is beginning and is expected to be finished in 2018, followed by 20 years of experimentation.

Above is some of the gear used in the laser lab.

In regards to ICF, there are two major projects in the world. One is the National Ignition Facility (NIF) located at the Lawrence Livermore National Lab in Livermore California. This facility is expected to be the first to achieve “ignition” – meaning that the reaction will produce more power than it consumes. France has also started a project called the Laser Megajoule that will deliver 1.8 million joules of power to the targets and will help to study the physics of the heat and pressures that exist in the center of the sun. 

Currently, the biggest hurdle to building a successful commercial reactor is developing materials that will survive the harsh environment in the reactor chamber. High energy neutrons are shooting out and smashing into the walls of the reactor. As the neutrons strike the walls of the reactor they are damaging the micro structure of the material and will eventually fatigue the steel to such a degree that the reactor vessel will have to be retired. Even though neutrons are very penetrating, and damaging they can be stopped with lead shielding fairly easily.

To the right is a gray wall of duct tape wrapped lead bricks used to shield the lab from powerful X-ray radiation emitted when the particle beam created by the laser passes through the stainless steel walls of the laser chamber.

This is just an introductory article on fusion, I expect to write many more that will delve into more detail as this blog evolves over time.  But just a recap, below are some of the advantages and disadvantages of fusion as far as can be determined at this time.

Disadvantages:
-Not currently a working option
-Very expensive R&D required to have functioning reactor design
-Likely to be very expensive to build the reactors
-Many unknowns

Advantages:
- Cheap, abundant fuel
- No greenhouse gases are produced
- Short-lived, manageable radioactive waste
- No chance of catastrophic explosion or melt-down

I would like to say thank you to Chris McGuffey for taking the time to sit down with me and talk about lasers, fusion and for letting me take the above pictures in the lab.

Energy 101: 01 - Types of Energy Sources

I plan to organize this blog around the various types of energy sources, so it might be best to define and describe how we produce energy and transmit that power to the consumers.  Firstly the sources are broken into two major categories; nonrenewable and renewable.

The image to the left is the Trenton Power plant in Detroit Michigan.  A 776 Mega Watt (MW) capacity power plant that has three units, the first of which was built in 1949.

Nonrenewable Energy Sources:  These are created by slow geological process and/or have a finite quantity on the earth.  For instance, oil or coal is created in such a slow process, it will take millions of years to create more.  Uranium is a nonrenewable source because there is only a finite amount of this element on the earth, and there is no natural process on the earth that will replenish this source.  In the US coal is the most common fuel source for generating electricity(49.8% according to the DOE), this is mainly because there are extremely large coal deposits in the US and this is a cheap fuel source. 

List of Nonrenewable resources:
Oil
Coal
Natural Gas
Propane
Other Fossil Fuels
Nuclear (Uranium)

To the right are five wind turbines located near the town of Elkton Michigan.  There are a total of 32 wind turbines with a combined capacity of 53 MW.  


Renewable Energy Sources:  Renewable energy is replenished at the same rate or faster than they are used, so they are effectively limitless.  Most all of these sources derive their energy from the sun in some way or another, the only exception to this is geothermal.  For electrical power generation, hydro power is by far the most common.  When considering all types of energy (heat energy for instance) biomass is the most common renewable energy source.

List of Renewable Energy Sources:
Wind
Solar
Biomass
Bio-Fuels
Hydro (water, such as from dams)
Geothermal
Tidal


My future articles will explain how these various sources are utilized to generate electrical energy and how it is distributed via "the grid."