Resonance Self-shielding Impact on Neutron Spectrum Determination for Missouri S and T Reactor
- Missouri University of Science and Technology, Nuclear Engineering Department, 226 Fulton Hall, Rolla, Missouri 65409 (United States)
Neutron Activation Analysis is a useful technique for characterizing the neutron flux at nuclear facilities. It involves irradiating samples to produce unstable isotopes, which enables qualitative and quantitative analyses of unknown samples. In the process, samples are bombarded with neutrons; new elements then become radioactive isotopes due to absorption of neutrons. These emit different amounts of gamma energy during the decay process, and gamma rays are counted using HPGe. Each reaction product has a known half-life and cross-section, and by measuring the amount of gamma radiation energy emitted from a radioactive isotope, it is possible to identify the isotope and activity. However, the neutron spectrum is not precise or representative of the actual neutron environment because of the self-shielding effect. This occurs with large samples that have large cross-sections or thicknesses in the resonance range of the neutron flux spectrum. Several methods have been used to mitigate this problem, such as thinning or diluting alloys samples, calculating the self-shielding factor for each material, and generating a corrected library for the unfolding procedure code. The Missouri University of Science and Technology Reactor (MSTR) is a pool-type research reactor that operates up to 200 kW. It uses light-water for both moderation and natural convective heat removal. The reactor core consists of 15 fuel elements positioned in a 9 x 6 aluminum grid plate, with four elements used for reactor power control. The fuel element is 19.75% low enriched uranium in 18 curved fuel plates. The reactor has seen various configurations starting with configuration designation 101W and subsequent reconfiguration increases the numeric designation by 1. The current configuration, 120W, was implemented in 2010. The new configuration provides more in-core locations for activation experiments and uses more fuel elements than previous ones. One of the irradiation locations in the MSTR core is the source holder. It is desired to improve the documentation of neutronic characteristics of the MSTR which are cardinal to experiments supported by the facility. One of these characteristics is the neutron spectrum at various locations in the reactor. Successful efforts yielded the neutron spectrum at a known location through the unfolding of the activity of irradiated foils. The purpose of this current study is to investigate the impact of resonance self-shielding of some of the activated foils on the determined spectrum.
- OSTI ID:
- 23047417
- Journal Information:
- Transactions of the American Nuclear Society, Vol. 116; Conference: 2017 Annual Meeting of the American Nuclear Society, San Francisco, CA (United States), 11-15 Jun 2017; Other Information: Country of input: France; 7 refs.; available from American Nuclear Society - ANS, 555 North Kensington Avenue, La Grange Park, IL 60526 (US); ISSN 0003-018X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ABSORPTION
ALUMINIUM
CROSS SECTIONS
DILUTE ALLOYS
ENRICHED URANIUM
FOILS
FUEL PLATES
GAMMA RADIATION
IRRADIATION
NEUTRON ACTIVATION ANALYSIS
NEUTRON FLUX
NEUTRON SPECTRA
NEUTRONS
RADIOISOTOPES
REACTOR CORES
RESEARCH REACTORS
RESONANCE
SELF-SHIELDING