Monte Carlo surface flux tallies
Abstract
Particle fluxes on surfaces are difficult to calculate with Monte Carlo codes because the score requires a division by the surfacecrossing angle cosine, and grazing angles lead to inaccuracies. We revisit the standard practice of dividing by half of a cosine 'cutoff' for particles whose surfacecrossing cosines are below the cutoff. The theory behind this approximation is sound, but the application of the theory to all possible situations does not account for two implicit assumptions: (1) the grazing band must be symmetric about 0, and (2) a single linear expansion for the angular flux must be applied in the entire grazing band. These assumptions are violated in common circumstances; for example, for separate ingoing and outgoing flux tallies on internal surfaces, and for outgoing flux tallies on external surfaces. In some situations, dividing by twothirds of the cosine cutoff is more appropriate. If users were able to control both the cosine cutoff and the substitute value, they could use these parameters to make accurate surface flux tallies. The procedure is demonstrated in a test problem in which Monte Carlo surface fluxes in cosine bins are converted to angular fluxes and compared with the results of a discrete ordinates calculation.
 Authors:

 Los Alamos National Laboratory
 Publication Date:
 Research Org.:
 Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
 Sponsoring Org.:
 USDOE
 OSTI Identifier:
 1041199
 Report Number(s):
 LAUR1007815; LAUR107815
TRN: US1202621
 DOE Contract Number:
 AC5206NA25396
 Resource Type:
 Conference
 Resource Relation:
 Conference: Intl. Conf. on Math. & Com. Applied to Nuclear Eng. (M&C 2011) ; May 8, 2011 ; Rio de Janeiro, Brazil
 Country of Publication:
 United States
 Language:
 English
 Subject:
 73 NUCLEAR PHYSICS AND RADIATION PHYSICS; 97 MATHEMATICAL METHODS AND COMPUTING; APPROXIMATIONS; DISCRETE ORDINATE METHOD; LANL
Citation Formats
Favorite, Jeffrey A. Monte Carlo surface flux tallies. United States: N. p., 2010.
Web.
Favorite, Jeffrey A. Monte Carlo surface flux tallies. United States.
Favorite, Jeffrey A. Fri .
"Monte Carlo surface flux tallies". United States. https://www.osti.gov/servlets/purl/1041199.
@article{osti_1041199,
title = {Monte Carlo surface flux tallies},
author = {Favorite, Jeffrey A},
abstractNote = {Particle fluxes on surfaces are difficult to calculate with Monte Carlo codes because the score requires a division by the surfacecrossing angle cosine, and grazing angles lead to inaccuracies. We revisit the standard practice of dividing by half of a cosine 'cutoff' for particles whose surfacecrossing cosines are below the cutoff. The theory behind this approximation is sound, but the application of the theory to all possible situations does not account for two implicit assumptions: (1) the grazing band must be symmetric about 0, and (2) a single linear expansion for the angular flux must be applied in the entire grazing band. These assumptions are violated in common circumstances; for example, for separate ingoing and outgoing flux tallies on internal surfaces, and for outgoing flux tallies on external surfaces. In some situations, dividing by twothirds of the cosine cutoff is more appropriate. If users were able to control both the cosine cutoff and the substitute value, they could use these parameters to make accurate surface flux tallies. The procedure is demonstrated in a test problem in which Monte Carlo surface fluxes in cosine bins are converted to angular fluxes and compared with the results of a discrete ordinates calculation.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {2010},
month = {11}
}