Posts Tagged waste

“What nuclear waste problem?” (TWiN Podcast 77)

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I have a family member that I love dearly and have an infinite amount of respect for.  She is a fantastic mother, a caring person, respected in her chosen profession, and a good friend.  She would do anything she could to help someone in need.  When we first met she was strongly opposed to nuclear energy.  Over the years we have discussed it from time to time and I’ve had some influence on her perspective.  She’s not totally won over yet, but we’re making progress.  Not too long ago she asked me, “But what about the waste?  That really worries me!”  She really didn’t believe me when I said “There’s no such thing as a nuclear waste problem.  That’s nothing but a myth.”

Let me explain.

Used nuclear fuel is very safely stored in earthquake proof storage pools and dry storage casks at nuclear plants around the USA.  It can stay there until we’re ready to recycle it, and we WILL recycle it eventually because it would be a waste not to do so.  When we remove used fuel from a reactor more than 90% of the potential energy is still in the fuel.  It would be wasteful to even consider putting it in a hole a mile underground!  Also, when we do recycle it, the left over material is much smaller and is much easier to handle, but we’ll talk about that in a few minutes.

First we need to look at the components of used power reactor fuel, and recognize that with recycling each of the components can be separated from one another.  A typical batch of used nuclear reactor fuel is made up of the following materials (not counting the structural materials):

 

% Composition (approx)

Uranium

93%

Plutonium

1.5%

Minor Actinides

0.2%

Fission Products

5.3%

When the fuel is new the concentration of the isotope U-235 is about 4% and U-238 is the rest.  After the fuel is burned in a reactor the uranium is mostly U-238 (very close to the isotopic mix of natural uranium) because most of the U-235 gets burned out by absorbing neutrons and fissioning.  There is also a small but important amount of plutonium that is formed when uranium atoms capture neutrons but do not fission.  This is called “breeding” and in fact at the end of life of a reactor fuel load more than 20% of the heat generated is from the fission of plutonium atoms formed by breeding.  All of this plutonium and uranium can be mixed back together to make new nuclear fuel.  This is what is commonly referred to as mixed oxide fuel, or MOX fuel.   MOX fuel is currently used in commercial reactors in the United Kingdom, France, Germany, Switzerland, and Belgium.

Risk of Diverting Used Power Reactor Fuel for Weapons

This is a good time to discuss a common misperception about reprocessing and the risk that a rogue nation would use commercial nuclear fuel reprocessing as a source for weapons grade plutonium.  It turns out this really is not an issue.  The plutonium from used fuel is a mixture of five isotopes, Pu-238 through Pu-242.

Let’s take a look at how each plutonium isotope would affect a nuclear weapon:

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Lessons from Dr. Evil (Episode 67)

podcastListen to the podcast here. Have you noticed that the numbers we use in daily conversation keep getting bigger and bigger? When I was young my father pointed out to me that a family who had one million dollars could live off the interest alone, and would have a tough time spending it all. While that was certainly true at the time, the value of a million dollars is not what it used to be.

If you listen to the podcast you’ll hear an audio clip of one of my favorite movie villains to help illustrate my point.  Even Dr. Evil had trouble comprehending the size of a billion dollars, but what hundreds of billions or even a trillion? We hear and read those numbers in the news and in conversation, but what do they really mean? It’s easy to understand the number of zeros that make them different, but that still be pretty abstract. I contend that many of us really don’t comprehend how large those numbers are when it comes to measuring things in the real world.  We need visual or mental references to help us understand the scale of such large quantities. Let’s use electrical power as an example. The base unit of measure for electrical power is the Watt, but what is the difference between a watt, a KW, a MW, and a GW? Read the rest of this entry »

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