Composition and depletion measurements on a nuclear fuel artifact from the Chicago Pile

Transcription

1 Composition and depletion measurements on a nuclear fuel artifact from the Chicago Pile Carl Willis, 3/26/2018

2 Herbert L. Anderson : Anderson performs first US experiment with fission 1942: Physics team of Fermi, Szilard, Zinn, Anderson operate first nuclear reactor

3 December 2, 1942: Physics team of Fermi, Szilard, Zinn, and Anderson successfully operate Chicago Pile (CP-1) at Stagg Field, University of Chicago.

4 CP-1 Fuel: natural U, 5.4 t metal and 45 t pressed U oxide Moderator: graphite, 360 t; dead blocks interspersed with live blocks. 6 types, 4 companies, at least 2 block designs. Operated Dec. 2, 1942 Feb. 28, 1943 at maximum power of ~200 W(t)

5 CP-2 CP-1 relocated and rebuilt in Red Gate Woods. Improved shielding. Operated March 20, 1943 May 15, 1954 at reported maximum power of ~10 kw(t)

6 Anderson given live block in Dec (?)

7 Undated photo of Herb Anderson with CP-1 live block. From Herbert L. Anderson archives, University of Chicago. Kindly retrieved by David Wargowski

8 X-ray view

9 Nuclear fuel Fuel elements are uranium metal cylinders 50.8mm dia. and 68mm long. Only 5.4 t used in CP-1 LEFT ELEMENT RIGHT ELEMENT Mass kg Mass kg Stamp mark M230 / L101 / P2 Stamp mark M170 / L79 / P1

10 -Original acrylic cracked, replaced -Fuel removed and measured Fuel sampling -Fuel sample sent to Dr. John Brockman, University of Missouri, for elemental and isotopic analysis

11 Fuel elemental / isotopic analysis Courtesy of Dr. John Brockman, University Of Missouri Element Abundance (µg / g) Ca 1082 Na 1024 Fe 481 Mg 195 Ni 116 Specimen U-235/U-238 ratio CP-1 live block Standard (nat. U)

12 SolidWorks models are available

13 MCNP models are available

14 Gamma spectrometry setup 2 types of fuel (various manufacturers), 4 graphite products, at least two block designs

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17 Activity calculations Nuclide Activity (MBq) Method & assumptions U ± Mass/specific activity, assume all mass is natural uranium metal (insignificant burnup) Pa-234m ± Assume secular equilibrium of Pa-234m with U-238 in natural U Cs ± 1.8 Calculated from Pa-234m detection efficiencies using linear efficiency fit, assume no peak interferences, assume uniform distribution in volume U-238 & Pa-234m assumptions probably OK: measured fuel density not significantly different from theoretical U-nat metal. Cs-137 assumptions not so reliable, particularly the volumetric uniformity assumption.

18 Cs-137/U-238 burnup estimate Date of decay correction Burnup, kwd/mtu 1943 (CP-1 shut down) (10 th Anniversary of CP-1) (CP-2 shut down, 1954) 133 Burnup E f A Cs 137 a Cs 137 M Y Cs 137 E f is energy released in fission A Cs 137 is activity of Cs-137, decay-corrected to date of interest a Cs 137 is specific activity of Cs-137 M is mass of fuel Y Cs 137 is cumulative thermal fission yield of Cs-137

19 Cs-137 uniformity Fission not uniform in fuel, so Cs-137 not uniformly distributed. Results in overestimate of Cs-137 concentration and burnup MWO2 (MCNP-5 with ORIGEN-22) calculation for fuel burnup of 0.17MWd/t Space distribution of 137 Cs activity Radius [cm] Model: Dragana Nikolic, Vinca Institute of Nuclear Sciences

20 Improved detector efficiency model Model detector and source geometry in MCNP: 4.0x10 3.5x Measured Simulated with the MCNP-5 code 3.0x x10-6 Efficiency 2.0x10 1.5x x10 5.0x Model: Dragana Nikolic, Vinca Institute of Nuclear Sciences Energy [kev]

21 Detailed model vs. simple assumptions Net difference is a few percent lower burnup 3.5x10-6 Measurement Simulated with the MCNP-5 code (1 zone) 3.0x10-6 Simulated with the MCNP-5 code (10 zones) Efficiency 2.5x10 2.0x Model: Dragana Nikolic, Vinca Institute of Nuclear Sciences kev ( 137 Cs) 1.5x Energy [kev]

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23 Conclusions This is the world s first irradiated nuclear fuel, attested by presence of fission products. The manufacturer of the fuel is unknown, but there are legible stamp marks that may help answer this question. Calcium is dominant contaminant at ~1000 ppm, suggesting production by Spedding ( Ames process ) metallothermic technique.

24 More conclusions! Cs-137 activity calculations using a model that accounts for radial burnup nonuniformity and radiation transport to the detector are within a few percent of a simple model of the source and detector. Cs-137 activity is three orders of magnitude too high for irradiation in JUST CP-1, so that scenario can be ruled out as implausible. Calculations are consistent with irradiation in CP-1 and CP-2. However, burnup still seems rather high, suggesting this fuel was centrally located in the pile and that CP-2 had high usage. Unfortunately, I am not aware of any operations logs for this reactor. The CP-2 chronology is not consistent with Anderson being given the block in 1952 at the 10 th Anniversary celebration as Betsy Anderson believes. CP-2 was still in service then and was not built for easy unloading of fuel. I suspect Anderson was given the block much later than 1952.

25 Acknowledgements Betsy Anderson, of Santa Fe, for making her husband s artifact available for measurements and display Dr. Dragana Nikolic, Vinca Institute of Nuclear Sciences, Republic of Serbia, for MCNP models of CP-1, the HPGe detector, and the artifact Dr. John Brockman, University of Missouri, for trace metals analysis on fuel samples Dr. Robert Busch and Ken Carpenter, University of New Mexico, for use of an alternate HPGe detector

26 Other mementos made from irradiated CP-1 fuel University of Chicago Archives Left: piece of CP-1 fuel presented to President Kennedy by Glenn Seaborg in 1962 Below: piece of fuel given to Alvin Weinberg in 1952 Paul Frame, ORAU

27 and, my favorite: Ceremonial trowel fashioned from irradiated CP-1 uranium metal, for use by President Eisenhower in dedicating new AEC headquarters, Photo: National Museum of American History