Posts Tagged ‘CP-1’


Herb Anderson’s “Live Block” of the Chicago Pile

June 4, 2016


They don’t give out spent nuclear fuel as a memento anymore.  But on the tenth anniversary of the first nuclear reactor (the Chicago Pile) going critical, pile physicist Herbert L. Anderson was presented with this handsome “live block” of graphite and uranium metal fuel, piping hot and right out of the reactor core.  With an estimated two millicuries of Cs-137 then distinguishing it from the natural uranium whence it was made, the unique artifact spent the next sixty years as part of Anderson’s home decor, a reminder of his pivotal role in one of the 20th century’s greatest triumphs in physics.  Herb’s wife Betsy kindly gave it to me in 2014 with the hope that new understanding and appreciation would follow.

Now, having had nearly two years to get to know this artifact, I can share some preliminary findings about it–and a few lingering questions as well.  I am grateful for ongoing partnerships with the University of Missouri and the Vinca Institute of Nuclear Sciences that are bringing new details to light about its metallurgy and history, and I am grateful for past assistance from the University of New Mexico here in Albuquerque.  I am actively searching for ways to bring this piece of the first reactor to an appreciative public audience.  So, dear reader, if you have suggestions or information that will help with either the technical understanding of the artifact, or its accommodation in a museum for the upcoming 75th anniversary of the Manhattan Project, please get in touch.

Part I: Basic physical description


This is a “live block” (meaning a piece of graphite with nuclear fuel installed in it), distinguished from the “dead blocks” of pure graphite that were interspersed or used as reflectors in the Chicago Pile.  Several museums possess “dead blocks”; to my knowledge, these include the American Museum of Science and Energy (Oak Ridge), the Bradbury Science Museum (Los Alamos), the National Atomic Testing Museum (Las Vegas), and the National Museum of Nuclear Science and History (Albuquerque).  My friend Kelly Michaels has an excellent photo set of these artifacts.  Pieces of Chicago Pile fuel also survive independently;  most notably, this piece once belonging to Alvin Weinberg.  However, the Herb Anderson “live block” is unique, to my knowledge, in that it contains fuel and moderator together.  The block’s measured dimensions, including fuel dimensions and those of the decorative housing, are available in a SolidWorks model to interested parties (please contact me).

The “T01” lot stamp appearing on the right face of the graphite block indicates that the graphite is AGOT made by the National Carbon Company, one of at least six types of graphite used to build the Pile.  AGOT had the lowest neutron absorption of all of these types, so was preferred for the pile’s core region.  About 2/3 of the CP-1 pile consisted of AGOT.  This grade of nuclear graphite went on to be used in the Graphite Reactor at Oak Ridge and the plutonium production reactors at Hanford.

The fuel is unclad uranium metal in cylindrical elements that bear identifying stamp marks on the front faces.  When I replaced the original cracked acrylic housing around the artifact, I was able to weigh the fuel elements directly.  The left element weighed 2.564 kg, and the right one, 2.553 kg.  The left element stamp reads “M230/L101/P2” while the right one reads “M170/L79/P1”.  The significance of these marks remains unknown to me.  I believe that if someone is able to assist in their interpretation, we might learn which of the three recorded contributing manufacturers of U metal produced this fuel.  It should be noted that metal fuel was a small minority of the Chicago Pile fuel, amounting to just 5.4 metric tons; the vast majority of the fuel was pressed-oxide “pseudosphere” elements.  Metal was made variously by Westinghouse, Metal Hydrides Corp., or the Ames Process.

Another question raised by this artifact is that it contains cylindrical metal fuel placed into chamfered recesses in the graphite designed for receiving “pseudosphere” oxide fuel.  As such, the cylinders cannot remain centered or upright in the recesses without the assistance of some acrylic supports that may be seen in the x-ray image.  I am quite sure that acrylic was not part of the original pile construction!  One is tempted to question, then, whether this fuel-and-stringer combination is original.  It could be that most graphite live blocks were machined for pseudosphere fuel, but when metal became available, the pseudosphere live blocks were used anyway (perhaps with graphite inserts serving the mechanical function of the acrylic supports, which begs the question of why the artifact contains acrylic instead; or perhaps without any supports, the fuel cylinders simply being dropped awkwardly into the recesses).  A lack of detailed photos from the construction of CP-1 makes the question hard to answer.

Part II: Gamma spectrometric estimate of fuel burnup


Mentioned earlier is the fact that this fuel contains cesium-137.  In fact, the external radiation signatures are dominated by this long-lived fission product.  Without a doubt, then, the fuel has been significantly exposed to reactor operation.  By comparing count rates in the Pa-234m gamma peaks to that in the Cs-137 peak at 662 keV, we can determine the quantity of Cs-137 remaining in the fuel under the assumption that the Pa-234m is in equilibrium with its U-238 parent.  This will motivate the estimation of fuel burnup range under various assumptions about the artifact’s history.  I performed the requisite experiments with my PGT germanium detector and obtained the spectrum shown above, leading to an estimated activity of 540 microcuries of Cs-137 distributed throughout the total fuel at the time of measurement.  Here are a few historical scenarios and the fuel burnup roughly corresponding to them:

  • The fuel operates in CP-1 only (December 1942-February 1943):  163 kWd/MTU
  • The fuel operates in CP-1 and its reconstruction in the Red Gate Woods (CP-2), and is removed from the operating reactor before being presented to Herb Anderson in November 1952 at the Tenth Anniversary celebration in Chicago: 132 kWd/MTU
  • The fuel was removed from the pile (CP-2) when it was decommissioned in 1954, and somehow was then integrated into the artifact: 127 kWd/MTU

There are challenges with all three potential histories.  The first is very unrealistic, given the known operating conditions of CP-1 in the brief months it was in use.  Intermittently critical, with a peak power of ~200 W achieved on one day only, the burnup in the fuel attested by these calculations is many thousands of times greater than what is possible according to the conventional history of that Pile.  The second scenario is supported by both the burnup calculation (even though I am aware of no formal operating records from CP-2) and the description given by Mrs. Anderson of how Herb got the item, but it leads to two big puzzles, firstly concerning how the fuel was removed from the reactor while the reactor was still in service, as the pile was not designed to be easily disassembled in the CP-2 instantiation; and secondly concerning the high activity levels of the discharged fuel when it must have been released from government custody to Anderson.  The third explanation avoids the issue of taking apart the reactor just to obtain a souvenir as the reactor was disassembled during decommissioning; however, it is historically inconsistent with the story told by Mrs. Anderson.  So what this gamma spectrometry measurement allows us to say with certainty is that the fuel was used in CP-2 (as well as the original pile, presumably).  Beyond that, plenty of thought-provoking questions remain.

Part III: Neutron multiplication properties

It would seem there is no greater aspiration for a piece of the world’s first nuclear reactor than to return, momentarily, to the task originally undertaken with so much fanfare: multiplying neutrons in fission chain reactions.  These three photos above show some multichannel-scaling apparatus to look at fission in the CP-1 block (set up in my kitchen, because this is a “cooking” project of sorts).  We are going to examine the time correlation between neutron counts in a bank of two He-3 proportional counters next to our specimen.  Both counter tubes and the specimen are reflected by polyethylene blocks to trap neutrons in the system as best we can.  Highly-correlated counts point to fission “chains”, in which a fission event causatively leads to successive ones on a time scale controlled by the neutron transport properties of the specimen and surroundings.  I’ll measure correlation by way of excess variance, or the Feynman Y-statistic: the difference between the measured variance-to-mean ratio of counts accumulated in a certain time window interval and unity (which corresponds to idealized, uncorrelated, Poisson-distributed counts).  We’ll look at the CP-1 live block by itself and with a small additional neutron source present.  We will also look at the neutron source alone, a lead brick, and the empty polyethylene cavity.  Results and commentary below.

So what the fuck does this mean?  Firstly, the CP-1 block by itself produces strongly time-correlated neutrons (purple data) on a measurement scale of about a millisecond or greater, while the little homemade AmBe neutron source is pretty much stochastic (red data).  (Note, though, that the AmBe source is about five times stronger a neutron source than the block.)  Putting the block in with the AmBe source slightly reduces the neutron count (~12%) versus the source alone, but produces excess correlation of nearly 30% of the block by itself, indicating the presence of induced fission.  The high correlation in the block itself may be attributed to spontaneous fission (SF) as a minor decay mode of U-238, as well as a smaller contribution of spallation and fission induced by secondary cosmic rays.  These neutron sources each produce a burst of neutrons, and are also closely coupled to successive induced fissions.  The AmBe source, by contrast, is driven by radioactive decay: alpha particles slam into beryllium.  Notice the curvature of the data in all cases: it rises as we lengthen the counting window.  That is to say, there is more neutron correlation as the window gets longer.  Neutrons take their time moving through materials, scattering, slowing down, and finally reaching the detector, and neutrons produced in coincidence will not register as such unless the window is long enough to account for their random meanderings through material.  Finally, just to illustrate fission and other fission-like reactions in something other than uranium, I put a 20-pound lead brick in the counter.  Now you may believe that lead is not a fissionable material, but under the right conditions–such as when a 500-MeV electron in the secondary cosmic ray spectrum hits it–the lead nucleus can split up by fission or by a somewhat similar process called spallation, cooking off a distribution of neutrons.  And that is why we see highly-correlated neutrons (green data) being emitted by lead.  Again note the upper right graph, though: lead is a very weak source of neutrons even though the ones that are emitted are highly time-correlated.


Nuclear Collection (Part VI)

March 13, 2011

Click any thumbnail image to view in full size. And, as always, if you have something radioactive and in need of a good home, contact me: I buy and trade all the time. Enjoy!

Lithograph by Leo Vartanian commemorating the CP-1 nuclear reactor.  In what has to be the winningest art idea ever,  moderator graphite from the historic reactor was actually ground up to make the ink in which the portraits of physicists Leo Szilard, Arthur Compton, Enrico Fermi, and Eugene Wigner were rendered.  Prints were distributed by Argonne National Laboratory to honor long and illustrious careers.  The ink is not detectably radioactive.  See my other mementos of CP-1 here. Size is 17″ by 22″(framed).

Though it is in many ways a modern and progressive nation, Japan steadfastly clings to certain curious anachronisms.  From the land of whaling and sailor-suit school uniforms come these examples of radioactive “quack cures”, modern instances of a fad phenomenon that, half a century ago, had largely been driven into extinction in the US and Europe.  Both items pictured—the Wellrich Co. Ltd. “Health Card” (top) and the “Mainasu ION” plaque (bottom)—contain natural thorium as verified by gamma spectrometry.    The “Health Card” claims to offer benefits that include denaturing nicotine in cigarettes.  The health benefits of the negative ion disk aren’t mentioned on it, but surely have no basis in sound science.  It is equipped with an adhesive surface on the back for mounting.  Dozens of varieties of negative ion quack products are peddled by Asian eBay sellers, and I have no idea how many of these items might be radioactive.  The Wellrich card and the ion disk measure 1400 CPM and 550 CPM respectively on a Ludlum 44-9 pancake Geiger tube.  (Donated to my collection by Bill Kolb.)




More radioactive vacuum tubes. All the specimens in this batch were kindly donated anonymously, and all are receiver protection tubes for military radar sets.  In this application, gas breakdown, aided by deliberately-included radioactivity, dissipates any high-power RF energy that finds its way into the receiver waveguide.  From left to right in the top photo: Varian MA37002X with Co-60 (originally “0.7 microcuries max.”), date code 1995; Omni-Wave MPT-24 with (originally) 25.0 microcuries of Kr-85, date code 1984; Omni-Wave MPT-47-B with (originally) 25.0 microcuries Kr-85, date code 1976.  The gamma spectra of the two Kr-85 tubes clearly shows the residual 514-keV gamma activity of the 10.8-year fission product and even permits a coarse estimate of the quantity remaining (about 3 microcuries in the MPT-24, 0.2 microcuries in the MPT-47-B).  More radioactive tubes are described here and here.

Large receiver protection tube with tritium. The application is the same as the tubes mentioned above, but this one is a monster, measuring almost 16 inches in length.  The part number is MA3948L-12, the manufacturer is Varian, and the contents are mostly argon and a small amount of radioactive tritium (H-3), 10 mCi.  The second photo shows an electrodeless RF discharge established in the tube.
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Contaminated Geiger counter strap from Chernobyl trip. Last summer’s trip to Pripyat resulted in detectable radioactive contamination of my shoes (see description) as well as this shoulder strap.  Gamma spectrometry easily identifies Cs-137, one of the handful of long-lived fission products, in a hot spot on the strap.  The activity in the spot is small, only about one nanocurie (~35 Bq).  Some possible contribution from the synthetic transuranic americium-241 is also noted.


Nuclear Collection (Part I)

May 5, 2008

Here are some relatively recent additions to my collection of radioactive and nuclear-related items. Some of them I don’t know nearly enough about! Take a look, and if you have some information to add, please contact me. I will post other galleries as I get the chance. Also: I collect this kind of stuff (obviously), so if you have something radioactive and you’re not a big fan of radioactive stuff, let’s make a deal: send it to me. You get rid of the hot stuff that’s gonna harelip your kids and give you leukemia and whatnot, and I’ll pay you money for it.

Click on a photo for large size. Descriptions are at bottom of post.

graphite from CP1Graphite from CP-1, the world’s first nuclear reactor, built under the stands of Stagg Field at the University of Chicago in 1942. This 25th Anniversary memento popped up on eBay not long ago and I paid dearly for it. However, there’s not much of this stuff left; all but a couple bars of this famously pure graphite went on to be incorporated in CP-2 and thereafter entombed in concrete under a nondescript field in Illinois. The eBay seller would only say “I do know that my grandfather worked on the building of the atomic bomb but other than that I don’t know much else.” I have a feeling that the human story could be interesting, but on account of the seller’s reluctance to share so much as her grandfather’s name and other “personal information,” there’s nothing more to say right now. Tips appreciated…

graphite from CP1More Graphite from CP-1. This example was also obtained on eBay, but bears slightly different markings (the additional Argonne National Laboratory label on the side of the graphite piece) and different dimensions. Also, no notecard or box came with this one.

worker\'s badge from ChernobylWorker’s badge from the Chernobyl Nuclear Power Plant, dating from 1987 (the year after the catastrophe at Unit 4). Anyone able to read Russian shorthand? The back of the badge contains addresses and perhaps a description of what this man did at the plant. This badge is not discernibly radioactive.

Uranium glassUranium glass memento from the “Conference Nucleaire Europeenne” of 1975, held in Paris. The box also came with a slip of paper informing the recipient that “Ce verre est colore par un sel d’uranium” (“This glass is colored by a salt of uranium”). A present from a good friend, James Thiel. Shown at right under light from a mercury vapor discharge.

ionium“Ionium thorium nitrate” from Marie Curie’s lab. At least that’s the provenance claimed by the previous curator of this fascinating and rather radioactive vial. Ionium was a name for Th-230, the naturally-occurring parent of radium (Ra-226). Today, the vial contains 8.6 +/- 10% microcuries of radium as determined by careful gamma radiation measurements. If it’s indeed as old as the Curie lab, then there should be a couple hundred microcuries of alpha-emitting Th-230 present, in addition to a rather inconsequential activity of Th-232 carrier. The vial is contained in a test tube that has some rather cryptic markings on it. Take a look at the full-size pic and let me know if this means anything to you…

Walkie recordallThis late-model Walkie-Recordall contains a 4.8 microcurie radium source. An expensive dictation recorder in its day (ca. 1950s and ’60s), the battery-operated apparatus came in a discreet suitcase with hidden microphone—perfect for industrial espionage. Radium was used to discharge static on the “sonoband” embossing medium. This specimen was found by scintillation detector in a flea market in Ohio. The included sonoband, containing a medical lecture, was heavily damaged by radiation in the place where it sat in front of the radium source for years. The band still plays (video coming shortly). I pay $50 per Walkie radium source; taking out this radioactive strip does not impact operability of the recorder.

back in the good ol\' daysBack in the good ol’ days of 2004, an average joe could still buy uranium oxide from MV Laboratories in New Jersey, with nary a question asked. Those days are history! This 30-gram quantity of greenish-black U3O8 remains sealed in its bottle, an emblem of American freedom that has been eroded by the drumbeat of irrational fear. Something about “islamofascists” I think.

alpha sourceThis is an interesting alpha check source kindly given to me by Taylor Wilson. On the backside is a bare surface deposit of black UO2, evidently reading 700 CPM on the Nuclear Chicago Model R6 survey meter. Perhaps the UO2 was electrodeposited?


radium calibration sourceAnother interesting check source from Taylor, this one an “ionotron” type radium foil (probably about 0.1 microcurie) on a card that was last calibrated in 1955 at the height of the golden age of nuclear. It’s hard to see on the photo, but radiation damage has denatured and cracked the plastic right over the source strip in the lower right-hand corner.

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