Implicit Monte Carlo with a linear discontinuous finite element material solution and piecewise non-constant opacity

Journal Article · Tue Feb 23 00:00:00 EST 2016 · Journal of Computational and Theoretical Transport

DOI:https://doi.org/10.1080/23324309.2016.1157491· OSTI ID:1255243

Wollaeger, Ryan T. ^[1]; Wollaber, Allan B. ^[1]; Urbatsch, Todd J. ^[1]; Densmore, Jeffery D. ^[2]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
2. Bettis Atomic Power Lab., West Mifflin, PA (United States)

Here, the non-linear thermal radiative-transfer equations can be solved in various ways. One popular way is the Fleck and Cummings Implicit Monte Carlo (IMC) method. The IMC method was originally formulated with piecewise-constant material properties. For domains with a coarse spatial grid and large temperature gradients, an error known as numerical teleportation may cause artificially non-causal energy propagation and consequently an inaccurate material temperature. Source tilting is a technique to reduce teleportation error by constructing sub-spatial-cell (or sub-cell) emission profiles from which IMC particles are sampled. Several source tilting schemes exist, but some allow teleportation error to persist. We examine the effect of source tilting in problems with a temperature-dependent opacity. Within each cell, the opacity is evaluated continuously from a temperature profile implied by the source tilt. For IMC, this is a new approach to modeling the opacity. We find that applying both source tilting along with a source tilt-dependent opacity can introduce another dominant error that overly inhibits thermal wavefronts. We show that we can mitigate both teleportation and under-propagation errors if we discretize the temperature equation with a linear discontinuous (LD) trial space. Our method is for opacities ~ 1/T³, but we formulate and test a slight extension for opacities ~ 1/T^3.5, where T is temperature. We find our method avoids errors that can be incurred by IMC with continuous source tilt constructions and piecewise-constant material temperature updates.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: AC52-06NA25396
• OSTI ID: 1255243
• Report Number(s): LA-UR-15-24303
• Journal Information: Journal of Computational and Theoretical Transport, Vol. 141, Issue C; ISSN 2332-4309
• Publisher: Taylor and Francis
• Country of Publication: United States
• Language: English

Related Subjects

97 MATHEMATICS AND COMPUTING
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
radiation
transport
methods