Nuclear fuel rod questions

jimdana1942 · Mar 18, 2011

okay, the reactor fuel rods need to be kept cool with circulating water.

My questions are:

1. Where did the fuel rods come from?
2. How were they kept cool during transport?
3. Why can't the rods be removed the same way as they were brought to the site?
4. Just wondering, I haven't heard any explanations regarding this.

Probably stupid questions but I am curious.

Kraut · Mar 18, 2011

IANANP (I Am Not A Nuclear Physicist), but I believe in summary, it goes like this: The rods are the fuel for the controlled reaction, and they heat up severely during the reaction, but they are not inherently hot in their natural state. The reaction can be stopped in proper order, but sudden disruption of the process or destruction/loss of components will result in loss of control of the reaction and eventual meltdown if the reaction is not brought back under control.

Emperor · Mar 18, 2011

Google Search: How does a nuclear reactor work? :thumbsup:

Baldrik78 · Mar 18, 2011

jimdana1942 said:
okay, the reactor fuel rods need to be kept cool with circulating water.

My questions are:

1. Where did the fuel rods come from?
2. How were they kept cool during transport?
3. Why can't the rods be removed the same way as they were brought to the site?
4. Just wondering, I haven't heard any explanations regarding this.

Probably stupid questions but I am curious.

1. It was probably mined in Canada. Up until a year or 2 ago, they were the largest exporter. I think some eastern european country is now though.
2. It didn't need cooling because the chain reaction had not been started yet.
3. The chain reaction, once started, is not something you can just flip a switch and stop. To my knowledge, once a the chain reaction has started, it cannot be completely stopped until there is no more fuel. Spent fuel rods can sit in a pool for a year or more before they get moved to a dry cask.

JadeRaven · Mar 18, 2011

Go watch "the world is not enough"
:mamoru:

TomTerrific · Mar 18, 2011

jimdana1942 said:
okay, the reactor fuel rods need to be kept cool with circulating water.

My questions are:

1. Where did the fuel rods come from?
2. How were they kept cool during transport?
3. Why can't the rods be removed the same way as they were brought to the site?
4. Just wondering, I haven't heard any explanations regarding this.

Probably stupid questions but I am curious.

Good questions. The uranium comes from a number of sources. We had uranium extraction facilities at both of our plants in St. James Parish. It occurs naturally in the phosphate rock we used to manufacture fertilizer intermediates. Our product was yellowcake, uranium oxide mix. It was shipped to either a plant near Tulsa or Cairo, Ill., where it was processed into uranium hexafluoride, which was enriched to about 4% U-235, the fissionable stuff.

This in turn is converted to UO2, made into pellets, and fabricated into fuel rods.

When U-235 fissions, it breaks down into different isotopes of various elements, most of which are radioactive. The fission is prompted by neutrons given off by the fission process. When critical mass is attained, the fission is self-perpetuating. Control rods take the neutrons out of the equation, but this isn't an immediate on/off. Residual radionuclides in the used fuel rods give off radiation and heat. Water cools the rods and absorbs some of the radiation. Zirconium is used as the cladding in fuel rods due to its nuclear cross section. It will react with water at elevated temperatures, as any active metal will, with water to produce hydrogen.

Question 3 addresses radioactive waste. American politicians have been dragging their feet in addressing this for decades. They can't ship it out as no one wants it in their back yard, for good reasons.

As someone suggested, this info is available out there but it's a pain to find it. Many agenda driven organizations will tell you all sorts of things and don't expect to get it on TV.
:squint:

dantheman · Mar 18, 2011

We have a member here that works in a Nuclear plant .

brfd557 · Mar 18, 2011

TomTerrific said:
Good questions. The uranium comes from a number of sources. We had uranium extraction facilities at both of our plants in St. James Parish. It occurs naturally in the phosphate rock we used to manufacture fertilizer intermediates. Our product was yellowcake, uranium oxide mix. It was shipped to either a plant near Tulsa or Cairo, Ill., where it was processed into uranium hexafluoride, which was enriched to about 4% U-235, the fissionable stuff.

This in turn is converted to UO2, made into pellets, and fabricated into fuel rods.

When U-235 fissions, it breaks down into different isotopes of various elements, most of which are radioactive. The fission is prompted by neutrons given off by the fission process. When critical mass is attained, the fission is self-perpetuating. Control rods take the neutrons out of the equation, but this isn't an immediate on/off. Residual radionuclides in the used fuel rods give off radiation and heat. Water cools the rods and absorbs some of the radiation. Zirconium is used as the cladding in fuel rods due to its nuclear cross section. It will react with water at elevated temperatures, as any active metal will, with water to produce hydrogen.

Question 3 addresses radioactive waste. American politicians have been dragging their feet in addressing this for decades. They can't ship it out as no one wants it in their back yard, for good reasons.

As someone suggested, this info is available out there but it's a pain to find it. Many agenda driven organizations will tell you all sorts of things and don't expect to get it on TV.

I thought U 235 was weapons grade and U 238 was reactor grade?

TomTerrific · Mar 18, 2011

brfd557 said:
I thought U 235 was weapons grade and U 238 was reactor grade?

No. Practically speaking, naturally occurring U is made up of two isotopes: 99.3% U-238 and 0.7% U-235. There is a decent article on U isotopes on Wiki http://en.wikipedia.org/wiki/Uranium_Isotopes

The mostly U-238 remaining after the U-235 is extracted is called depleted U and is used in ordnance and counterweights in large aircraft like the 747. I don't know if it's still used for the latter.

Weapons grade is 90% U-235 or greater. It is my understanding that Pu is usually used in weapons as its critical mass is about half that of U-235. I'm also told a nuclear shell for the 155mm howitzer was developed. That's pretty small.

There's a potassium iodide thread. I would point out that there were roughly 500 or so atmospheric tests in the 1940s, '50s, and '60s, including thermonuclear devices. These put a lot more s**t in the air than the reactors in Japan have or will.
:squint:

headshot · Mar 18, 2011

Originally Posted by TomTerrific

WOW! Great explanation, thanks

jimdana1942 · Mar 18, 2011

Really good info, Tom. What initiates the chain reaction that causes the fuel rods to become "active"?

jmcrawf1 · Mar 18, 2011

jimdana1942 said:
Really good info, Tom. What initiates the chain reaction that causes the fuel rods to become "active"?

Reaction starter fluid duhhhhhh

flamatrix99 · Mar 18, 2011

jimdana1942 said:
Really good info, Tom. What initiates the chain reaction that causes the fuel rods to become "active"?

Source neutrons.. Material that gives off neutrons is installed in the reactor for the purpose of startup.

flamatrix99 · Mar 18, 2011

TomTerrific said:
No. Practically speaking, naturally occurring U is made up of two isotopes: 99.3% U-238 and 0.7% U-235. There is a decent article on U isotopes on Wiki http://en.wikipedia.org/wiki/Uranium_Isotopes

The mostly U-238 remaining after the U-235 is extracted is called depleted U and is used in ordnance and counterweights in large aircraft like the 747. I don't know if it's still used for the latter.

Weapons grade is 90% U-235 or greater. It is my understanding that Pu is usually used in weapons as its critical mass is about half that of U-235. I'm also told a nuclear shell for the 155mm howitzer was developed. That's pretty small.

There's a potassium iodide thread. I would point out that there were roughly 500 or so atmospheric tests in the 1940s, '50s, and '60s, including thermonuclear devices. These put a lot more s**t in the air than the reactors in Japan have or will.

U-238 aborbs a neutron and becomes U-239 and eventually ends up as Pu-239.

flamatrix99 · Mar 18, 2011

TomTerrific said:
This in turn is converted to UO2, made into pellets, and fabricated into fuel rods.

Here is a picture of what the fuel assemblies look like. When I worked at a different nuc power plant I was qualified as a fuel handler. You can walk right up to it. Like tom said at that point it is just a bunch of metal tubes.

http://me1065.wikidot.com/fuel-assemblies-in-nuclear-reactors

TomTerrific · Mar 18, 2011

jimdana1942 said:
Really good info, Tom. What initiates the chain reaction that causes the fuel rods to become "active"?

Check here http://en.wikipedia.org/wiki/Chain_reaction#Nuclear_chain_reactions

Behind it is the idea of a critical mass, IOW enough that the neutrons zapping other U-235 atoms produce, say double or triple the number of neutrons, which hit other U-235 atoms, etc, etc, etc. Get the picture?

The art/engineering is to keep the chain reaction controlled.

LACamper · Mar 18, 2011

So this could go on as is for quite a while- years even. Or could they encourage it to go faster? A small yield nuke to use up the uranium faster? (yes, the UN would freak, as would much of the Japanese population) Its not like anyone is going to be moving back into the area anytime soon...

I remember reading somewhere that red wine had some limited positive effects for those that had been mildly exposed. Somewhere else I read about drinking lots of beer (the intent was to flush the radiation out IIRC). Any truth at all to either of these?

brfd557 · Mar 18, 2011

Good info thanks Tom!

jimdana1942 · Mar 19, 2011

flamatrix99 said:
Here is a picture of what the fuel assemblies look like. When I worked at a different nuc power plant I was qualified as a fuel handler. You can walk right up to it. Like tom said at that point it is just a bunch of metal tubes.

http://me1065.wikidot.com/fuel-assemblies-in-nuclear-reactors

Really interesting article.

why couldn't the control rods be fully inserted to stop the reaction in a crisis situation or would that not work without water flow?

TomTerrific · Mar 19, 2011

jimdana1942 said:
Really interesting article.

why couldn't the control rods be fully inserted to stop the reaction in a crisis situation or would that not work without water flow?

It's not an on/off situation like turning off a light bulb.

There is still residual heat being produced. Look at the problems they are having with storage of used fuel rods from the reactors on turn-around.

I came across this article this morning. It's from Bob Parks' "What's New," always an interesting read:
HORMESIS: THE LINEAR NO-THRESHOLD MODEL MUST BE WRONG.
Airline crews experience a high total-radiation exposure. But the exposure
of airline crews is spread over many years, while Chernobyl survivors got a
concentrated dose. Statistically they are not distinguished. Do the
derivatives matter? According to a story in the news this week, Chernobyl
survivors today suffer cancer at about the same rate as others their age.
The same is true of Hiroshima survivors. If true, it would seem to support
the radiation-hormesis thesis. "Hormesis" refers to things that are toxic
in large doses, but harmless or even beneficial in small doses. Trace
amounts of selenium, for example, are essential for cell function of
animals. But selenium salts in larger doses, are highly toxic. Airline
pilots or not, we are all exposed to background levels of ionizing
radiation every day of our lives. We do not all succumb to cancer. It
seems there is a repair mechanism that compares neighboring strands of DNA
and patches up damage. The comparison can work only if damaged strands are
isolated. If the damage rate is very high, the same repair mechanism could
multiply the damage.

The site allows copying.
:squint:

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