New reader Dave asks,
…I apologize if it’s stupid, but I had always been under the impression there were suits that were designed to shield people from radioactivity…?
Nothing wrong with that question! Except I have to haul out more acronyms. We routinely use PPE (personal protective equipment) to protect us from contamination.
(Crappy explanation of contamination versus radiation here.)
We wear lots of different things to avoid contamination. But the only radiation shielding we wear is for β−, beta particles. Generally it’s plastic shields over the eyes.
In theory I guess you could shield for β+ , positron radiation. I’ve never heard of it and doubt it’s used. Positrons are basically anti-matter, so after a fast life each enters a mutual suicide pact with an electron. Their offspring are two powerful photons of .511 MeV (mega electron-volts) each. And those photon concerns will swamp the particle concerns.
Those heroic operators are being irradiated with gamma radiation, high-energy photons.
We can stop 100% of charged particles (alphas, betas, even protons) with certainty. But chargeless high-energy photons, like gammas and x-rays, penetrate. For them we use HVLs (half-value layers) and TVLs (tenth-value layers). A given TVL of any material will eliminate 9/10′s of the radiation. You need another to reduce it another 10x, and so on.
Long story short (too late?) the human frame cannot support meaningful gamma shielding. I know they did it in the Gilligan’s Island episode with the radioactive meteorite, but that technology is beyond us.
There are movable shielding options like shielded frames and lead blankets. I’ve never known a nuke plant that didn’t have lead blankets. But their utility isn’t what you’d like. With a widespread source, you can pick up more dose putting up the shielding than you save once it’s in place.
What I don’t know is why you couldn’t set up cameras, toss some water hoses over the pool’s side, then clear out of the area, let the water flow, and monitor from afar. Maybe they’re doing that.
Thank you for sharing your expertise on the issue. It helps some of us figure out what is happening.
What sort of heat production is there in the spent fuel? Reactor fuel in full operation was supposed to be something like 50 W/cm^3 – I imagine when it is shut down it is some percentage of this (1%? 5%). What about when it has been sitting in the fuel pond for months? It speaks to the level of effort necessary to keep the pool filled (it seems to me that if it boils, that is fine, as long as it is not allowed to boil off completely).
PS – where is all this hydrogen coming from? It seems you could almost put the pumps in place and abandon the site if not for all the hydrogen explosions every time they try to vent steam. Why don’t they just open the reactor vents and allow the core pressure to drop to atmospheric pressure? They can pump water in and allow it to boil off (it seems like they’ll have to do this anyway) rather than letting the temperature and pressure build.
If spent rods aren’t cooled, the residual radioactive decay can raise the temperature enough to “crack” water–separate it into free hydrogen and free oxygen. As it accumulates, you just need a combustable mixture and a spark.
I’d held out some early hope that maybe they had some stored hydrogen in there–why anyone would, I’ve no idea–but my rose-tints fell off. If they can’t keep the spent fuel covered it could happen over and over.
I always thought it was amazing that you need 25 radiation lengths to stop serious gammas and, lo and behold, the atmosphere is about 25 radiation lengths deep.
Ah, brings me back to my days of playing with lead slurry to build calorimeters for the SSC.
I never did shielding calculations in the field, only in study.
Our technician “calculations” were along the lines of, “Can we hang lead blankets on this? Yeah? How many?”
Ams, I might be able to answer part of your question. The H2 comes from the Zirconium (Zr) and water at 2000F to produce ZirconiumOxide ZrO2 and H2 plus some heat.
Yes, the residual heat in the control rods is comparatively low, but we’re always hypersensitive to any possible release of fission products from the fuel rods. It shouldn’t take much water to keep the spent rods cool, but the safety systems for the pools are just not to the same level as for the reactors.
Sparkey,
Thanks for coming in and keeping me from getting my knee into my mouth. Now to extricate my foot…
Yeah, but as long as there is any water in the pool at all, why would the Zr be at 2000F? This is at atmospheric pressure, right?
Okay, stipulating that this is speculation,
Humidity? I know the heat would expand everything away from it, but possibly atmospheric water vapor?
No doubt that occurs in some degree, but it doesn’t feel like it would scale up to a massive explosion. Hopefully all will be made clear…
I thought that most of the H2 seen at these plants was coming from Units 1, 2, & 3 where they’re having trouble removing the residual heat from the reactors that were running when the quake happened. Those are the units that blew their tops, right? From the articles I’ve seen the Japanese don’t know why the fire started in Unit 4, and I don’t recall seeing any mention of H2 associated with it.
Here is an that states:
“TEPCO, which operates the Fukushima power plant, is still considering the use of high-pressure fire hoses to spray cooling water into the spent fuel pool.
Radiation levels are far too high to permit workers to bring hoses anywhere near the pool’s edge to re-flood it manually.”
Pretty much explains the difficulty in getting water into the pools.
There are a couple of other articles that say two workers are missing…
Crap, forgot to close the HTML. You gotta ad an “edit post” capability wormme.
I’ll try to remember and edit it. Tomorrow. And if you know how I can empower you, let me know!
That’s what I was guessing. Didn’t know about the missing workers.
And I’m not trying to be snide, but I was wishing the Japanese mania for robotics might have yielded timely fruit. Of course they’re looking for automated delivery now. Maybe some mad tinkerer is being approached even now…
Appreciate the explanation, that makes a lot more sense now…
You’re very welcome!
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