PCTR Integral Measurements of ²³⁹Pu Α($$^{-}_{α}$$) in Fast Spectra

Technical Report · Mon Apr 15 04:00:00 EST 1968

DOI:https://doi.org/10.2172/4521426· OSTI ID:4521426

Lanning, D. D. ^[1]; Busselman, G. J. ^[1]; Bennett, C. L. ^[1]; Newman, D. F. ^[1]; Bierman, S. R. ^[1]

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1. Battelle Pacific Northwest Labs., Richland, WA (United States)

Accurate integral values of the capture-to-fission cross section ratio ($$^{-}_{α}$$) for ²³⁹Pu can be measured in the Physical Constants Test Reactor (PCTR) as a function of the carbon-to-uranium ratio in plutonium oxide-uranium oxide carbon mixtures. These mixtures are to be prepared with plutonium-to-uranium ratios such that the neutron multiplication factor of an infinite system (k_∞) is very close to unity. The range of carbon-to-uranium (C/U) atom ratios to be studied will vary the neutron spectrum from a mostly fast reactor system, where $$^{-}_{α}$$ is believed to be well known, down into the intermediate spectrum where $$^{-}_{α}$$ is believed to be more uncertain. Calculations indicate that this can be accomplished by making measurements in the C/U range of zero to about 25. The percent of plutonium in the UO₂ plus PuO₂ mixtures varies from about 8% to approximately 14% over this range of C/U for mixtures with k_∞ equal to unity. A total of four to six measurements are required, together with differential perturbation measurements at each point to enhance the accuracy. The expected results include the derived values of $$^{-}_{α}$$ and $$^{-}_{η}$$ for ²³⁹Pu, where $$^{-}_{η}$$ is the integral value of the number of neutrons produced per neutron absorbed in²³⁹Pu. Values of reaction rate ratios (²³⁸U absorption, ²³⁸U fission, ²³⁵U fission, and ²³⁹Pu fission) will be measured, together with the standard PCTR measurements of k_∞ and the breeding ratio. Available techniques for neutron spectral indices such as integral foil measurements will also be used. These initial PCTR experiments can be extended to greater C/U atom ratios if there is a gap between the present BNL exponential studies on η of ²³⁹Pu in D₂0 systems and these proposed CIU experiments. The calculated values of the fraction of plutonium in uranium to keep k_∞ equal to unity for the C/U range of 0 to 25 increased with increasing C/U. Obviously, as the system becomes more thermal, this fraction of plutonium will begin to decrease. A study of the region of inflection between mostly fast and mostly thermal systems will add greatly to the reactor physics information and will be of value for theory-experiment correlations. Such systems are a simple extension of the initial experiments described above.

• Research Organization: Battelle Pacific Northwest Labs., Richland, WA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA), Nuclear Criticality Safety Program (NCSP); US Atomic Energy Commission (AEC)
• DOE Contract Number: AT(45-1)-1830
• NSA Number: NSA-22-035288
• OSTI ID: 4521426
• Report Number(s): BNWL-774
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
Breeding Ratio
CAPTURE
CROSS SECTIONS
Criticality
FAST NEUTRONS
FISSION
Integral Measurements
MEASUREMENT
N36550* --Physics (Nuclear)--Nuclear Properties & Reactions
A >= 90--Nuclear Reactions & Scattering
NEUTRON BEAMS
NUCLEAR REACTIONS
Nuclear Criticality Safety Program (NCSP)
PCTR
PILE NEUTRONS
PLUTONIUM 239
Plutonium Oxide
RESEARCH REACTORS
SPECTRA
Safety
Uranium Oxide