Implementation and testing of the on-the-fly thermal scattering Monte Carlo sampling method for graphite and light water in MCNP6

Journal Article · Sat Jan 23 00:00:00 EST 2016 · Annals of Nuclear Energy (Oxford)

DOI:https://doi.org/10.1016/j.anucene.2016.01.006· OSTI ID:1255160

Pavlou, Andrew T. ^[1]; Ji, Wei ^[1]; Brown, Forrest B. ^[2]

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1. Rensselaer Polytechnic Inst., Troy, NY (United States)
2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Here, a proper treatment of thermal neutron scattering requires accounting for chemical binding through a scattering law S(α,β,T). Monte Carlo codes sample the secondary neutron energy and angle after a thermal scattering event from probability tables generated from S(α,β,T) tables at discrete temperatures, requiring a large amount of data for multiscale and multiphysics problems with detailed temperature gradients. We have previously developed a method to handle this temperature dependence on-the-fly during the Monte Carlo random walk using polynomial expansions in 1/T to directly sample the secondary energy and angle. In this paper, the on-the-fly method is implemented into MCNP6 and tested in both graphite-moderated and light water-moderated systems. The on-the-fly method is compared with the thermal ACE libraries that come standard with MCNP6, yielding good agreement with integral reactor quantities like k-eigenvalue and differential quantities like single-scatter secondary energy and angle distributions. The simulation runtimes are comparable between the two methods (on the order of 5–15% difference for the problems tested) and the on-the-fly fit coefficients only require 5–15 MB of total data storage.

• Research Organization: Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE
• Grant/Contract Number: NRC-HQ-13-G-38-0035; AC52-06NA25396
• OSTI ID: 1255160
• Report Number(s): LA-UR-16-20313; PII: S0306454916300081
• Journal Information: Annals of Nuclear Energy (Oxford), Vol. 91, Issue C; ISSN 0306-4549
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

22 GENERAL STUDIES OF NUCLEAR REACTORS
97 MATHEMATICS AND COMPUTING
neutron transport
nuclear reactors
thermal scattering
simulations
chemical binding
adaptive-in-temperature