On-the-fly generation of differential resonance scattering probability distribution functions for Monte Carlo codes

Conference · Mon Jul 01 00:00:00 EDT 2013

OSTI ID:22212811

Sunny, E. E.; Martin, W. R. ^[1]

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1. University of Michigan, 2355 Bonisteel Boulevard, Ann Arbor MI 48109 (United States)

Current Monte Carlo codes use one of three models to model neutron scattering in the epithermal energy range: (1) the asymptotic scattering model, (2) the free gas scattering model, or (3) the S({alpha},{beta}) model, depending on the neutron energy and the specific Monte Carlo code. The free gas scattering model assumes the scattering cross section is constant over the neutron energy range, which is usually a good approximation for light nuclei, but not for heavy nuclei where the scattering cross section may have several resonances in the epithermal region. Several researchers in the field have shown that using the free gas scattering model in the vicinity of the resonances in the lower epithermal range can under-predict resonance absorption due to the up-scattering phenomenon. Existing methods all involve performing the collision analysis in the center-of-mass frame, followed by a conversion back to the laboratory frame. In this paper, we will present a new sampling methodology that (1) accounts for the energy-dependent scattering cross sections in the collision analysis and (2) acts in the laboratory frame, avoiding the conversion to the center-of-mass frame. The energy dependence of the scattering cross section was modeled with even-ordered polynomials to approximate the scattering cross section in Blackshaw's equations for the moments of the differential scattering PDFs. These moments were used to sample the outgoing neutron speed and angle in the laboratory frame on-the-fly during the random walk of the neutron. Results for criticality studies on fuel pin and fuel assembly calculations using these methods showed very close comparison to results using the reference Doppler-broadened rejection correction (DBRC) scheme. (authors)

• Research Organization: American Nuclear Society, 555 North Kensington Avenue, La Grange Park, IL 60526 (United States)
• OSTI ID: 22212811
• Resource Relation: Conference: M and C 2013: 2013 International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering, Sun Valley, ID (United States), 5-9 May 2013; Other Information: Country of input: France; 11 refs.; Related Information: In: Proceedings of the 2013 International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering - M and C 2013| 3016 p.
• Country of Publication: United States
• Language: English

Related Subjects

97 MATHEMATICAL METHODS AND COMPUTING
APPROXIMATIONS
ASYMPTOTIC SOLUTIONS
COMPARATIVE EVALUATIONS
CRITICALITY
CROSS SECTIONS
DISTRIBUTION FUNCTIONS
ELASTIC SCATTERING
ENERGY DEPENDENCE
FUEL ASSEMBLIES
FUEL PINS
GRAPH THEORY
HEAVY NUCLEI
LIGHT NUCLEI
MONTE CARLO METHOD
NEUTRON DIFFRACTION
PROBABILITY
RESONANCE
RESONANCE ABSORPTION
SAMPLING