Gamma-ray Spectrum, CP-1 Graphite Memento

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Jon Rosenstiel
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Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jon Rosenstiel »

Earlier this year I acquired (from a fellow nuke-head) a Lucite encased piece of graphite from Chicago Pile-1, the world’s first nuclear reactor. These 25th anniversary mementos were given out (I believe) mainly to those who labored behind the scenes. It hadn’t occurred to me until just recently that this small piece of history may contain, if it is the real thing, a clue or two to its origin. Sure enough, a long term count turned up a weak signature from Eu-152, and an even weaker signature from Cs-137. Eu-152 is a neutron activation product of the naturally occurring Eu contained in the graphite, while Cs-137 is a fission product.

Spectrum: (All unlabeled lines are background)


Memento on detector's face:


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Richard Hull
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Richard Hull »

Great run on your gamma spec! Remnant rads for sure. I wonder how long CP-1 was operated? Not long I think, due to its location. I believe CP-2 was the one used during the war built in a more secure location near or at what became the Argonne lab.

I just did a wikipedia look up. I was right CP-1 was only operated a few months at about 1/2 to1 watt. Moved in 1943 to Argonne as CP-2 which saw active service until 1957 when it was torn down and buried. I assume they dug some up to make the graphite souvenirs.

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
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Jim Kovalchick
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jim Kovalchick »

Thanks for posting this Jon. About six years ago I did a 24 hour count on my CP-1 sample using a Canberra Falcon I borrowed from work. I didn't see the Eu peaks but there was a tiny Cs 137 peak. Others didn't believe my results so I repeated the count with the same results.

When Carl did his study of his CP-1 fuel he wondered if the the results were showing that the fuel also saw duty in CP-2. I wonder if all these graphite souvenir samples out there also were from the reactor after it moved to Argonne.

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Richard Hull
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Richard Hull »

As noted in my post, CP-2 was used actively until 1957 at an unknown power level. Thus, if all the CP-1 graphite blocks were used in CP-2 they saw a much longer neutron exposure time than CP-1.

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Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jim Kovalchick »

Once it's established, as Carl did, that there were enough fission events in the fuel to produce measurable fission products, it's all a matter of product migration not the neutron fluence seen by the graphite itself. The amount of products left in a piece of graphite will be dependent on a couple things, the relative proximity of the graphite to a piece of fuel, circulation within the core, and if the preparation of the sample cut off any contamination. This means that the amount will vary widely. Tim Koeth has measured his sample multiple times and found nothing.
Jon Rosenstiel
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jon Rosenstiel »

Jim,

Re: your 24-hour count, how much shielding did you use?

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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Rex Allers »

Jon,
That's quite an impressive GS measurement tool and shield. Do I interpret correctly that the scan was almost 4 days?
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Richard Hull
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Richard Hull »

As I understood it, there was no core in the classic sense in CP-1. Instead, the fuel was distributed all about and within the moderator in a manner that would allow moderation of purely natural uranium fission over the bulk of the volume. Explains the low power over a huge volume. I do not know how CP-2 was constructed or operated. So fission products could exist all over the fuel laden blocks for sure and migration via what even air cooling system was employed, probably in CP-2. Once enrichment got into the game, piles were just not the thing to do anymore.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jim Kovalchick »

Jon
I did not use much shielding. The Falcon I used had a tungsten ring lined with copper. I'm sure my counts included some background.
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jon Rosenstiel »

Jim,
Ok, one more question, did you do a 24-hr background run also? I ask because my background runs always have a small Cs-137 peak. (Two to three counts/hour with the detector inside of the lead shield) I don't think there is an exact source for the Cs-137 background, it just seems to be pretty-much everywhere.

Rex,
Yes, runtime was nearly 4-days. The memento's Cs-137 activity was very weak, it took that long for the spec software (FitzPeaks) to determine that the peak was real and not background.

Richard,
From what I could find the highest power level that CP-2 ever ran at was 10 kW (thermal), normally it was run at around 1 kW. As I understand it, CP-2 was basically CP-1 with a few improvements plus 5-feet of concrete shielding. I spoke with Carl a couple of days back, asked him to check out this thread when he had a chance. Hopefully he'll weigh in here soon.

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Jim Kovalchick
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jim Kovalchick »

Jon,
My background count was longer than a day and there was no by CS 137.
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Bruce Meagher »

A few years ago our local university demolished a large shielded room with many tons of low background steel acquired from some pre-WWII ship as well as a bunch of virgin lead. It was unfortunate for sure. One of my professors mentioned that steel made post the atomic era contains radionuclides making extreme low counting more challenging (same goes for lead). Jon, could your shielding material (lead/steel) be the source of your low background Cs-137?
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jon Rosenstiel »

Thanks Jim, that's good to know. I've cleaned the inside of the shield multiple times and even tried another detector but I always get the same 2 to 3 counts/hour Cs-137 background, I was beginning to think that was normal. So maybe, as Bruce suggests, the shield's construction materials are the source.

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Richard Hull
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Richard Hull »

Nuc Lead is a company that deals in many lead products. One is "virgin lead" It costs a good bit extra as it is lead that was mined over a hundred years ago and is usually in the form of buried pipe, underground electrical buried covering, ancient ballast culled from old sailing ships, etc.

I may have told this real story here before.

We have a world class scrap yard of some note that HEAS travelers seem to haunt on the Friday morning before HEAS. There are a number of images of some of them in the yearly October spate of photos about HEAS in Images du jour. I am pals with the owner as we have been looting the place for all manner of cool stuff since the mid-eighties.

The yard's proprietor approached me on one of my visits to "the yard" some years back. He was most upset that he lost a bid for about 2 tons of scrap lead offered by the State. He told me that this lead was from the underground pipe that was dug up from underneath the Virginia state capitol and its grounds, then under going a major updating at the time. The capitol building in downtown Richmond was designed by Jefferson and had its water and sewer systems installed in the early 1800's.

The owner noted that his bid was for 50 cents per pound and the winning bid was for $1.25 per pound. He said, "who ever bid that was crazy"! That was about 27 cents beyond the current price on the open market for good clean lead ingots. "Them old pipes is nasty and dirty", he said, "Probably filled with poop from the civil war". (The capitol had a major restoration after the civil war and lead plumbing was no longer used and just left in place.)

I went into a long diatribe on the lead's value to people making "quiet shields" for nuclear trace measurements. I told him that they might get $20.00 or more per pound in a cast shield weighing hundreds of pounds. The cigar he usually had chomped between his teeth nearly fell out. He just shook his head and said..."Well, ya' learn something new everyday."

As lead has been recycled since Roman times, it was used until relatively recently, (50's-60's) in gutter work, roofing, sewage plumbing, etc. During the nuclear testing in the 40's-60's, a lot of nuclear fission products pool in and on roofs, gutters, etc. As much of it was recycled in tear-downs during "the end of lead", melts included a good bit of this fallout. It is still making the rounds, if now in much diluted form. Sr90 and Cs137 are just a few of the long lived goodies that are to be found in trace amounts in recycled lead. Only ancient buried or hidden away lead and absolutely fresh mined, deep buried lead is considered "Virgin Lead". Provenance of origin is usually demanded and given warranting the source in quiet shields.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Jim Kovalchick
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jim Kovalchick »

My shielding was tungsten, not lead. I'm not sure that makes a difference, but what make a difference was my very long background count did not include a Cs spike, but both of my sample counts did.

I did my count about six years ago. I doubt that the little bit I saw then would be seen now. I may have the count data somewhere, and if I find it I will look to see if any Eu peaks were there too.
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Re: Gamma-ray Spectrum, CP-1 Graphite Memento

Post by Jim Kovalchick »

I've been thinking about this a little more, I remain unconvinced that fission products would be uniformly distributed through the reactor to the point that every sample would be expected to have remaining products today if any did. The reactor used two different fuel types, metal and oxide, and I would expect that fission product migration and retention would vary significantly between those two types. Also, HTGR experience shows that fission product diffusion through graphite can vary significantly depending on the manufacturing techniques. For example in the old Peach Bottom HTGR fuel, permeability coefficients for cesium differed by a much as a factor of four between graphite types used. I'm not sure that the permeability of the graphite used in CP-1 varied to that extent, but given that the graphite came from different manufacturers, I think it could vary. Given also, that the flux and therefore fluence and fission products, would vary across the core from fuel distribution and neutron leakage, I don't think it should be a surprise that some samples show significantly more left over radioactive material than others.
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