# The COMET method in 3-D hexagonal geometry

## Abstract

The hybrid stochastic-deterministic coarse mesh radiation transport (COMET) method developed at Georgia Tech now solves reactor core problems in 3-D hexagonal geometry. In this paper, the method is used to solve three preliminary test problems designed to challenge the method with steep flux gradients, high leakage, and strong asymmetry and heterogeneity in the core. The test problems are composed of blocks taken from a high temperature test reactor benchmark problem. As the method is still in development, these problems and their results are strictly preliminary. Results are compared to whole core Monte Carlo reference solutions in order to verify the method. Relative errors are on the order of 50 pcm in core eigenvalue, and mean relative error in pin fission density calculations is less than 1% in these difficult test cores. The method requires the one-time pre-computation of a response expansion coefficient library, which may be compiled in a comparable amount of time to a single whole core Monte Carlo calculation. After the library has been computed, COMET may solve any number of core configurations on the order of an hour, representing a significant gain in efficiency over other methods for whole core transport calculations. (authors)

- Authors:

- Nuclear and Radiological Engineering and Medical Physics Programs, George W. Woodruff School, Georgia Inst. of Technology, Atlanta, GA (United States)

- Publication Date:

- Research Org.:
- American Nuclear Society, Inc., 555 N. Kensington Avenue, La Grange Park, Illinois 60526 (United States)

- OSTI Identifier:
- 22105847

- Resource Type:
- Conference

- Resource Relation:
- Conference: PHYSOR 2012: Conference on Advances in Reactor Physics - Linking Research, Industry, and Education, Knoxville, TN (United States), 15-20 Apr 2012; Other Information: Country of input: France; 6 refs.

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 22 GENERAL STUDIES OF NUCLEAR REACTORS; DENSITY; EIGENFUNCTIONS; EIGENVALUES; ERRORS; FINITE DIFFERENCE METHOD; FISSION; GEOMETRY; HTTR REACTOR; MONTE CARLO METHOD; RADIATION TRANSPORT; REACTOR CORES; STOCHASTIC PROCESSES; THREE-DIMENSIONAL CALCULATIONS; TRANSPORT THEORY

### Citation Formats

```
Connolly, K. J., and Rahnema, F.
```*The COMET method in 3-D hexagonal geometry*. United States: N. p., 2012.
Web.

```
Connolly, K. J., & Rahnema, F.
```*The COMET method in 3-D hexagonal geometry*. United States.

```
Connolly, K. J., and Rahnema, F. Sun .
"The COMET method in 3-D hexagonal geometry". United States.
```

```
@article{osti_22105847,
```

title = {The COMET method in 3-D hexagonal geometry},

author = {Connolly, K. J. and Rahnema, F.},

abstractNote = {The hybrid stochastic-deterministic coarse mesh radiation transport (COMET) method developed at Georgia Tech now solves reactor core problems in 3-D hexagonal geometry. In this paper, the method is used to solve three preliminary test problems designed to challenge the method with steep flux gradients, high leakage, and strong asymmetry and heterogeneity in the core. The test problems are composed of blocks taken from a high temperature test reactor benchmark problem. As the method is still in development, these problems and their results are strictly preliminary. Results are compared to whole core Monte Carlo reference solutions in order to verify the method. Relative errors are on the order of 50 pcm in core eigenvalue, and mean relative error in pin fission density calculations is less than 1% in these difficult test cores. The method requires the one-time pre-computation of a response expansion coefficient library, which may be compiled in a comparable amount of time to a single whole core Monte Carlo calculation. After the library has been computed, COMET may solve any number of core configurations on the order of an hour, representing a significant gain in efficiency over other methods for whole core transport calculations. (authors)},

doi = {},

journal = {},

number = ,

volume = ,

place = {United States},

year = {2012},

month = {7}

}