A lumped parameter method of characteristics approach and multigroup kernels applied to the subgroup selfshielding calculation in MPACT
Abstract
An essential component of the neutron transport solver is the resonance selfshielding calculation used to determine equivalence cross sections. The neutron transport code, MPACT, is currently using the subgroup selfshielding method, in which the method of characteristics (MOC) is used to solve purely absorbing fixedsource problems. Recent efforts incorporating multigroup kernels to the MOC solvers in MPACT have reduced runtime by roughly 2×. Applying the same concepts for selfshielding and developing a novel lumped parameter approach to MOC, substantial improvements have also been made to the selfshielding computational efficiency without sacrificing any accuracy. These new multigroup and lumped parameter capabilities have been demonstrated on two test cases: (1) a single lattice with quarter symmetry known as VERA (Virtual Environment for Reactor Applications) Progression Problem 2a and (2) a twodimensional quartercore slice known as Problem 5a2D. From these cases, selfshielding computational time was reduced by roughly 3–4×, with a corresponding 15–20% increase in overall memory burden. An azimuthal angle sensitivity study also shows that only half as many angles are needed, yielding an additional speedup of 2×. In total, the improvements yield roughly a 7–8× speedup. Furthermore given these performance benefits, these approaches have been adopted as the default in MPACT.
 Authors:
 Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
 Univ. of Michigan, Ann Arbor, MI (United States)
 Publication Date:
 Research Org.:
 Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
 Sponsoring Org.:
 USDOE
 OSTI Identifier:
 1373334
 Alternate Identifier(s):
 OSTI ID: 1407807
 Grant/Contract Number:
 AC0500OR22725
 Resource Type:
 Journal Article: Published Article
 Journal Name:
 Nuclear Engineering and Technology
 Additional Journal Information:
 Journal Volume: 49; Journal Issue: 6; Journal ID: ISSN 17385733
 Publisher:
 Korean Nuclear Society
 Country of Publication:
 United States
 Language:
 English
 Subject:
 21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS; CASL; Lumped Parameter; M&C 2017; MOC; MPACT; Subgroup SelfShielding
Citation Formats
Stimpson, Shane G., Liu, Yuxuan, Collins, Benjamin S., and Clarno, Kevin T. A lumped parameter method of characteristics approach and multigroup kernels applied to the subgroup selfshielding calculation in MPACT. United States: N. p., 2017.
Web. doi:10.1016/j.net.2017.07.006.
Stimpson, Shane G., Liu, Yuxuan, Collins, Benjamin S., & Clarno, Kevin T. A lumped parameter method of characteristics approach and multigroup kernels applied to the subgroup selfshielding calculation in MPACT. United States. doi:10.1016/j.net.2017.07.006.
Stimpson, Shane G., Liu, Yuxuan, Collins, Benjamin S., and Clarno, Kevin T. 2017.
"A lumped parameter method of characteristics approach and multigroup kernels applied to the subgroup selfshielding calculation in MPACT". United States.
doi:10.1016/j.net.2017.07.006.
@article{osti_1373334,
title = {A lumped parameter method of characteristics approach and multigroup kernels applied to the subgroup selfshielding calculation in MPACT},
author = {Stimpson, Shane G. and Liu, Yuxuan and Collins, Benjamin S. and Clarno, Kevin T.},
abstractNote = {An essential component of the neutron transport solver is the resonance selfshielding calculation used to determine equivalence cross sections. The neutron transport code, MPACT, is currently using the subgroup selfshielding method, in which the method of characteristics (MOC) is used to solve purely absorbing fixedsource problems. Recent efforts incorporating multigroup kernels to the MOC solvers in MPACT have reduced runtime by roughly 2×. Applying the same concepts for selfshielding and developing a novel lumped parameter approach to MOC, substantial improvements have also been made to the selfshielding computational efficiency without sacrificing any accuracy. These new multigroup and lumped parameter capabilities have been demonstrated on two test cases: (1) a single lattice with quarter symmetry known as VERA (Virtual Environment for Reactor Applications) Progression Problem 2a and (2) a twodimensional quartercore slice known as Problem 5a2D. From these cases, selfshielding computational time was reduced by roughly 3–4×, with a corresponding 15–20% increase in overall memory burden. An azimuthal angle sensitivity study also shows that only half as many angles are needed, yielding an additional speedup of 2×. In total, the improvements yield roughly a 7–8× speedup. Furthermore given these performance benefits, these approaches have been adopted as the default in MPACT.},
doi = {10.1016/j.net.2017.07.006},
journal = {Nuclear Engineering and Technology},
number = 6,
volume = 49,
place = {United States},
year = 2017,
month = 7
}

An essential component of the neutron transport solver is the resonance selfshielding calculation used to determine equivalence cross sections. The neutron transport code, MPACT, is currently using the subgroup selfshielding method, in which the method of characteristics (MOC) is used to solve purely absorbing fixedsource problems. Recent efforts incorporating multigroup kernels to the MOC solvers in MPACT have reduced runtime by roughly 2×. Applying the same concepts for selfshielding and developing a novel lumped parameter approach to MOC, substantial improvements have also been made to the selfshielding computational efficiency without sacrificing any accuracy. These new multigroup and lumped parameter capabilitiesmore »

Advances in the development of a subgroup method for the selfshielding of resonant isotopes in arbitrary geometries
The subgroup method is used to compute selfshielded cross sections defined over coarse energy groups in the resolved energy domain. The validity of the subgroup approach was extended beyond the unresolved energy domain by partially taking into account correlation effects between the slowingdown source with the collision probability terms of the transport equation. This approach enables one to obtain a pure subgroup solution of the selfshielding problem without relying on any form of equivalence in dilution. Specific improvements are presented on existing subgroup methods: an Nterm rational approximation for the fueltofuel collision probability, a new Pade deflation technique for computingmore »