How Can Steam From A Nuclear Plant Be Radioactive?

My understanding is the Fukushima reactor was releasing steam from the low pressure coolant water in order to reduce pressure. This would also release heat which helps.

However coolant water surrounds and is completely separated from the inside sealed reactor system itself. That system is closed and has its own cooling water (under high pressure) which transfers heat by conduction to the surrounding cooling water.

They do not mix.

So why is some steam released in an emergency, radioactive?

those are boiling-water reactors (BWRs) which circulate the working fluid water directly into the core and through the turbines. then there is a condensing heat exchanger after the turbines which is a separate cooling loop.

Out of curiosity, what’s radioactive about the steam? Is the water deuterated (or tritiated), or are there other volatile components that evaporate along with the steam?

I’d be interested in knowing also. I tried Googling, and there are tons of sites talking about radioactive steam, but I couldn’t find anything saying what actually makes it radioactive.

My guesses would be Oxygen nuclei absorbing neutrons, or radioactive materials dissolving into water in low concentrations.

ETA: I think it’s hard to get Hydrogen to absorb a neutron. I’m not certain why I think that, however.

This NY Times article says:

“In normal operations, some radioactivity in the cooling water is inevitable, because neutrons, the sub-atomic particles that carry on the chain reaction, hit hydrogen and oxygen atoms in the water and make those radioactive.”

A neutron hitting a hydrogen nucleus (i.e., a single proton) is similar to one billiard ball hitting another: The collision is elastic, and they bounce off each other. With larger nuclei, you can get an effect more like a bullet hitting a sandbag: There are so many particles to spread the energy around to that none of the individual particles ends up doing much of anything, and the whole collection holds together.

Deuterium is not radioactive (though tritium is).

As someone who has taken Nuclear Engineering and Nuclear Chemistry classes, I am embarassed to admit that I did not know that.

Initially, you have tritium from neutron activation of the water.

If any of the fuel elements have ruptured, you can have volatile radioactive fission byproducts (xenon and cesium and such) being vented as well. This appears to have happened.

Fox News just had Paul Gunter (Director of Reactor Oversight, Beyond Nuclear) on, and he said the explosion was a result of hydrogen detonating in the structure around the reactor. And that the hydrogen is produced in the damaged core from the metals and fuel there reacting with the water. IOW, the core did melt and it is exposed. The hot fuel cladding generates hydrogen and oxygen, and they leaked out of the vessel and then accumulated in the structure then and exploded.

He expects a tremendous amount of radioactivity to be released.

Everything I’ve read says that the cores have not been exposed in any of the troubled reactors. The fuel rods were exposed from the core water briefly at the No. 1 Fukushima #3 reactor, but that the injected sea-water/boron mixture had since topped up levels.

I’m disappointed, but not surprised, that an anti-nuclear organization like Beyond Nuclear is spreading speculation (at best) or misinformation (at worst). It’s important to consider the source.

fuel rods in 1 and 3 have been exposed. hydrogen has been produced in both. hydrogen caused the explosion in reactor one building. in understatment by some, ‘it damaged the roof’. seems to me the top half of the building is gone.

Josef Oemen’s article is spreading across the internet, and he indicates that the steam is activated by neutron impact with oxygen, creating a short-lived nitrogen isotope.

http://morgsatlarge.wordpress.com/2011/03/13/why-i-am-not-worried-about-japans-nuclear-reactors/

It’s difficult to confirm online, but the background info to this patent backs it up.
http://www.freepatentsonline.com/5572559.html

it seems like reactor 3 has exploded.

I bet he’ll be proven completely wrong. The reactors have been shut down since Friday, probably shut down automatically in the first few seconds of the quake. Decay heat levels have been subsiding all the time since, requiring less and less cooling. At worst, a limited amount of steam venting may be required over the next week or so to control pressure.

Absolutely, the reactor #1 building is confetti, and also reactor #3 building now. But those buildings surround the reactor containment domes, and a hydrogen explosion isn’t going to touch them.

excuse my hasty posting. that should be

it seems like reactor 3 building has exploded.

which is what i intended to mean.

Not to derail the thread, but what in the blue blazes was Fox doing with Gunter on?

My apologies for posting his analysis.

Agreed. The reactors would have scrammed (control rods pushed in) in about 7 seconds. That still leaves a huge amount of residual heat plus ongoing nuclear reactions which remain after the shutdown which is why it normally takes about 3 days to cool a reactor. When everything goes well.

No apologies necessary. I saw him and in fairness he was accurate up to a point. Plus exaggerated risk makes the media salivate. Note how the talking heads jump quickly with faux concern to worst case questions.

Thankyou everyone, I have learned a great deal over the past 48 hours.

So, if Gunter’s analysis is wrong (can you really heat up water so hot that it rips apart the hydrogen and oxygen – that doesn’t sound right to me), then how is the hydrogen getting generated? Is it a byproduct of the fission reaction?

That’s not what’s happening. At temperatures above 1000 deg C, the hot water (or steam) reacts with the zirconium alloy cladding on the fuel elements and produces hydrogen gas and zirconium oxide in an exothermic reaction.

The reaction is:

H[sub]2[/sub]O + Zr ------> 2H[sub]2[/sub] + ZrO[sub]2[/sub] + heat

The heat produced is about 6,500 kJ per kg of zirconium that reacts.

Cite (pdf).