# A lumped parameter method of characteristics approach and multigroup kernels applied to the subgroup self-shielding calculation in MPACT

## Abstract

An essential component of the neutron transport solver is the resonance self-shielding calculation used to determine equivalence cross sections. The neutron transport code, MPACT, is currently using the subgroup self-shielding method, in which the method of characteristics (MOC) is used to solve purely absorbing fixed-source problems. Recent efforts incorporating multigroup kernels to the MOC solvers in MPACT have reduced runtime by roughly 2×. Applying the same concepts for self-shielding and developing a novel lumped parameter approach to MOC, substantial improvements have also been made to the self-shielding 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 two-dimensional quarter-core slice known as Problem 5a-2D. From these cases, self-shielding 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:
- AC05-00OR22725

- Resource Type:
- Journal Article: Published Article

- Journal Name:
- Nuclear Engineering and Technology

- Additional Journal Information:
- Journal Volume: 49; Journal Issue: 6; Journal ID: ISSN 1738-5733

- 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 Self-Shielding

### 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 self-shielding 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 self-shielding 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.. Mon .
"A lumped parameter method of characteristics approach and multigroup kernels applied to the subgroup self-shielding 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 self-shielding 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 self-shielding calculation used to determine equivalence cross sections. The neutron transport code, MPACT, is currently using the subgroup self-shielding method, in which the method of characteristics (MOC) is used to solve purely absorbing fixed-source problems. Recent efforts incorporating multigroup kernels to the MOC solvers in MPACT have reduced runtime by roughly 2×. Applying the same concepts for self-shielding and developing a novel lumped parameter approach to MOC, substantial improvements have also been made to the self-shielding 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 two-dimensional quarter-core slice known as Problem 5a-2D. From these cases, self-shielding 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},

issn = {1738-5733},

number = 6,

volume = 49,

place = {United States},

year = {2017},

month = {7}

}