# MPACT Subgroup Self-Shielding Efficiency Improvements

## Abstract

Recent developments to improve the efficiency of the MOC solvers in MPACT have yielded effective kernels that loop over several energy groups at once, rather that looping over one group at a time. These kernels have produced roughly a 2x speedup on the MOC sweeping time during eigenvalue calculation. However, the self-shielding subgroup calculation had not been reevaluated to take advantage of these new kernels, which typically requires substantial solve time. The improvements covered in this report start by integrating the multigroup kernel concepts into the subgroup calculation, which are then used as the basis for further extensions. The next improvement that is covered is what is currently being termed as “Lumped Parameter MOC”. Because the subgroup calculation is a purely fixed source problem and multiple sweeps are performed only to update the boundary angular fluxes, the sweep procedure can be condensed to allow for the instantaneous propagation of the flux across a spatial domain, without the need to sweep along all segments in a ray. Once the boundary angular fluxes are considered to be converged, an additional sweep that will tally the scalar flux is completed. The last improvement that is investigated is the possible reduction of the numbermore »

- 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). Consortium for Advanced Simulation of LWRs (CASL)

- Sponsoring Org.:
- USDOE Office of Nuclear Energy (NE)

- Contributing Org.:
- Univ. of Michigan, Ann Arbor, MI (United States)

- OSTI Identifier:
- 1328310

- Report Number(s):
- ORNL/TM-2016/407; CASL-U-2016-1063-001

NT0304000; NEAF343; CASL-U-2016-1063-001; TRN: US1700303

- DOE Contract Number:
- AC05-00OR22725

- Resource Type:
- Technical Report

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 97 MATHEMATICS AND COMPUTING; 22 GENERAL STUDIES OF NUCLEAR REACTORS; M CODES; EIGENVALUES; COMPUTER CALCULATIONS; SELF-SHIELDING; KERNELS; EFFICIENCY; MULTIGROUP THEORY; NEUTRON FLUX; SCALARS

### Citation Formats

```
Stimpson, Shane, Liu, Yuxuan, Collins, Benjamin S., and Clarno, Kevin T.
```*MPACT Subgroup Self-Shielding Efficiency Improvements*. United States: N. p., 2016.
Web. doi:10.2172/1328310.

```
Stimpson, Shane, Liu, Yuxuan, Collins, Benjamin S., & Clarno, Kevin T.
```*MPACT Subgroup Self-Shielding Efficiency Improvements*. United States. doi:10.2172/1328310.

```
Stimpson, Shane, Liu, Yuxuan, Collins, Benjamin S., and Clarno, Kevin T. Wed .
"MPACT Subgroup Self-Shielding Efficiency Improvements". United States. doi:10.2172/1328310. https://www.osti.gov/servlets/purl/1328310.
```

```
@article{osti_1328310,
```

title = {MPACT Subgroup Self-Shielding Efficiency Improvements},

author = {Stimpson, Shane and Liu, Yuxuan and Collins, Benjamin S. and Clarno, Kevin T.},

abstractNote = {Recent developments to improve the efficiency of the MOC solvers in MPACT have yielded effective kernels that loop over several energy groups at once, rather that looping over one group at a time. These kernels have produced roughly a 2x speedup on the MOC sweeping time during eigenvalue calculation. However, the self-shielding subgroup calculation had not been reevaluated to take advantage of these new kernels, which typically requires substantial solve time. The improvements covered in this report start by integrating the multigroup kernel concepts into the subgroup calculation, which are then used as the basis for further extensions. The next improvement that is covered is what is currently being termed as “Lumped Parameter MOC”. Because the subgroup calculation is a purely fixed source problem and multiple sweeps are performed only to update the boundary angular fluxes, the sweep procedure can be condensed to allow for the instantaneous propagation of the flux across a spatial domain, without the need to sweep along all segments in a ray. Once the boundary angular fluxes are considered to be converged, an additional sweep that will tally the scalar flux is completed. The last improvement that is investigated is the possible reduction of the number of azimuthal angles per octant in the shielding sweep. Typically 16 azimuthal angles per octant are used for self-shielding and eigenvalue calculations, but it is possible that the self-shielding sweeps are less sensitive to the number of angles than the full eigenvalue calculation.},

doi = {10.2172/1328310},

journal = {},

number = ,

volume = ,

place = {United States},

year = {2016},

month = {8}

}