Do you not find it somewhat curious .. with all this talk of meltdown in Japan .. that just last month I posted an article (about the use of Visual Metaphor in web design) .. which contained a photo of a fuel cell, pulled from a nuclear reactor (.. glowing beautifully with Cherenkov radiation)? Cuz I do.
Uh, actually there were two pictures.
Moreover, you might recall, how (in that post) I included a story .. about a Japanese Nuclear engineer, who died due to radiation exposure ..
.. when he stuck a pipe in the water (.. while trying to spy the serial number on the ID tag attached to a spent fuel cell).
You must admit » it does seem a little trippy .. given the TIMING of that post. Cuz shortly thereafter we have reports of nuclear fuel cells melting down in Japan, and people dying there.
And consider how the story of the engineer was not at all germane to the topic of discussion that day (i.e. web design). It seemed to stick out. No?
Afterwards, I asked myself why I added it, since it had nothing to do with web design. I normally try to stay on-topic .. unless there's a compelling reason to digress. And that particular digression was a BIG one (consisting of several paragraphs).
In fact, you can still find those photos posted at the bottom of the home page (.. at least, until I transfer them to the February archive).
Reactors are one of those things with which I have plenty of first-hand experience.
In the Navy, for example, I literally *lived* with a reactor .. while stationed aboard a nuclear-powered ballistic-missile submarine, home-ported in Pearl Harbor, Hawaii (.. with the Dog) for a few years.
In commercial nuclear power, I might as well have lived there. I've worked at a handful of different plants around the country .. as a migrant nuclear worker of sorts.
I've worked at both pressurized and boiling water reactor plants. (I prefer PWRs, as I think do most rad ho's.) On both the East & West coasts.
I have been to the nasty-of-nasties (highest dose areas) .. in both PWR & BWR plants. Which is why I have a lifetime occupational exposure record with respectable numbers (.. selling my body for $Rad dollars).
[ Dont think I wasnt a little concerned when the Bug was born .. but he came out "perfect." Whew. ]
Meanwhile, military/Navy plants have no really nasty places (.. radiation-wise). You could literally eat lunch sitting on the reactor in your street clothes. (If they would let you. Which they dont.)
» Ceramic Pellets Inside Long Metal Pins (Rods)
Yeah, I know a little about reactor fuel cell construction. Tho that was never my focus. (Rather » plant operations & radiation protection.)
The military doesnt teach you how to build a reactor, just how to operate one.
They do however, teach enough so you know what kind of animal you're dealing with. From an operational perspective, you dont really need to know from-whence-the-beast-cometh. Only what it looks-like here-n-now.
But I picked up bits here & there .. along the way. Plus I ask lotsa questions.
A fuel cell is comprised of little pellets (dark gray), similar in size and shape to that of a thin cigarette filter .. like a long stick cut into small pieces, tho a little smaller and stubbier than a cigarette filter.
A bucket-load of these ceramic (uranium-containing) fuel pellets are fed into long pins (called "rods" by some) .. that are maybe 12-feet tall.
These pins are made of an exotic (metal) alloy .. specifically design to withstand the enormous heat and pressure that is generated when a reactor is operating at power (.. a truly beautiful thing, technologically speaking).
[ Uranium is classified as a METAL, but they (somehow) convert it into a GAS (Uranium hexafloride) .. during the production process .. in order to enrich it .. using centrifuges that spin at superfast speeds. More about enrichment later.
I'm no chemist, but the technology required to turn a super-heavy metal such as uranium into a gas .. seems very sophisticated. No? Modern alchemy. ]
All of the fuel cells that I saw came in grids of 8-pins by 8-pins, for a total of 64 pins (i.e. "rods") per fuel assembly. (I hear there exist other configurations than the 8x8 variety.)
[ Many of the news articles that I read used the term 'fuel rods'. I have never heard that term used before. Rods were always control rods (discussed below).
So maybe they use a different reactor core construction in Japan. And I guess you could call these pins (that make up a fuel cell) 'rods'. But I wouldnt.
Intuitively, to me, a rod is round and a cell is square. Either way, melting nuclear fuel is very bad, no matter what terminology you use. ]
That glowing shaft pictured above is a single fuel cell. The average reactor core consists of maybe a thousand such assemblies .. tho these smaller, older reactors at Fukushima used half that many. I'm not certain, but I think the life of a fuel cell in a reactor core is ~3 to 5 years. Then it's 'spent'.
New fuel cells are first loaded at the outer edges of a reactor core (.. during a refueling outage, while the reactor is shutdown). During subsequent refueling outages, they are moved toward the inner areas, where the neutron flux is greater. The goal here is to try to provide an 'even' burn (uranium) across the core. No localized hot spots.
I never did find out how much each fuel assembly costs. I'd guess a quarter mil .. but if anybody knows for sure, my curiosity will thank you.
» Decay Heat & Reactor Scram
The problem with the reactors in Japan is » decay heat .. caused by radioactive decay of the fission products.
Newly-fissioned fragments are not 'happy' campers. They undergo radioactive decay vigorously and often, a process which gives off considerable heat (.. tho not nearly as much as the fission process itself).
This process of decay subsides with time, tho never stops (.. at least not for thousands of years).
First sign of a problem, the reactor operators are gonna perform a normal or expedited reactor shutdown.
In the case of a massive earthquake, I guess they would scram the reactor, which is like hitting a kill-switch .. that immediately sends all control rods IN (.. to the reactor core). A scram is the closest thing you get in nuclear power to a get-out-of-jail free card.