The Discontinuous Asymptotic Telegrapher’s Equation (P1) Approximation

Avner P. Cohen, Roy Perry, Shay I. Heizler*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Modeling the propagation of radiative heat waves in optically thick material using a diffusive approximation is a well-known problem. In optically thin material, classic methods, such as classic diffusion or classic P1, yield the wrong heat wave propagation behavior, and higher-order approximation might be required, making the solution more difficult to obtain. The asymptotic P1 approximation [Heizler, Nucl. Sci. Eng., Vol. 166, p. 17 (2010)] yields the correct particle velocity but fails to model the correct behavior in highly anisotropic media, such as problems that involve a sharp boundary between media or strong sources. However, the solution for the two-region Milne problem of two adjacent half-spaces divided by a sharp boundary yields a discontinuity in the asymptotic solutions that makes it possible to solve steady-state problems, especially in neutronics. In this work we expand the time-dependent asymptotic P1 approximation to a highly anisotropic medium using the discontinuity jump conditions of the energy density, yielding a modified discontinuous P1 equation in general geometry. We introduce numerical solutions for two fundamental benchmarks in plane symmetry. The results thus obtained are more accurate than those attained by other methods, such as Flux Limiters or Variable Eddington Factors.

Original languageAmerican English
Pages (from-to)189-207
Number of pages19
JournalNuclear Science and Engineering
Issue number2
StatePublished - 2 Nov 2018
Externally publishedYes

Bibliographical note

Publisher Copyright:
©, © 2018 American Nuclear Society.


  • Radiative transfer
  • Su-Olson benchmark
  • asymptotic P approximation


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