# Impact of the 235U Covariance Data in Benchmark Calculations

## Abstract

The error estimation for calculated quantities relies on nuclear data uncertainty information available in the basic nuclear data libraries such as the U.S. Evaluated Nuclear Data File (ENDF/B). The uncertainty files (covariance matrices) in the ENDF/B library are generally obtained from analysis of experimental data. In the resonance region, the computer code SAMMY is used for analyses of experimental data and generation of resonance parameters. In addition to resonance parameters evaluation, SAMMY also generates resonance parameter covariance matrices (RPCM). SAMMY uses the generalized least-squares formalism (Bayes method) together with the resonance formalism (R-matrix theory) for analysis of experimental data. Two approaches are available for creation of resonance-parameter covariance data. (1) During the data-evaluation process, SAMMY generates both a set of resonance parameters that fit the experimental data and the associated resonance-parameter covariance matrix. (2) For existing resonance-parameter evaluations for which no resonance-parameter covariance data are available, SAMMY can retroactively create a resonance-parameter covariance matrix. The retroactive method was used to generate covariance data for 235U. The resulting 235U covariance matrix was then used as input to the PUFF-IV code, which processed the covariance data into multigroup form, and to the TSUNAMI code, which calculated the uncertainty in the multiplication factormore »

- Authors:

- ORNL

- Publication Date:

- Research Org.:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

- Sponsoring Org.:
- USDOE National Nuclear Security Administration (NNSA)

- OSTI Identifier:
- 962609

- DOE Contract Number:
- DE-AC05-00OR22725

- Resource Type:
- Conference

- Resource Relation:
- Conference: International Conference on the Physics of Reactors - Nuclear Power: A Sustainable Resource Cassino, Interlaken, Switzerland, 20080914, 20080919

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 29 ENERGY PLANNING, POLICY AND ECONOMY; BENCHMARKS; COMPUTER CODES; CROSS SECTIONS; EVALUATION; MATRICES; MULTIPLICATION FACTORS; NUCLEAR DATA COLLECTIONS; NUCLEAR POWER; PHYSICS; R MATRIX; RESONANCE; covariance; SAMMY; ENDF/B; nuclear data; TSUNAMI

### Citation Formats

```
Leal, Luiz C, Mueller, Don, Arbanas, Goran, Wiarda, Dorothea, and Derrien, Herve.
```*Impact of the 235U Covariance Data in Benchmark Calculations*. United States: N. p., 2008.
Web.

```
Leal, Luiz C, Mueller, Don, Arbanas, Goran, Wiarda, Dorothea, & Derrien, Herve.
```*Impact of the 235U Covariance Data in Benchmark Calculations*. United States.

```
Leal, Luiz C, Mueller, Don, Arbanas, Goran, Wiarda, Dorothea, and Derrien, Herve. Tue .
"Impact of the 235U Covariance Data in Benchmark Calculations". United States.
doi:.
```

```
@article{osti_962609,
```

title = {Impact of the 235U Covariance Data in Benchmark Calculations},

author = {Leal, Luiz C and Mueller, Don and Arbanas, Goran and Wiarda, Dorothea and Derrien, Herve},

abstractNote = {The error estimation for calculated quantities relies on nuclear data uncertainty information available in the basic nuclear data libraries such as the U.S. Evaluated Nuclear Data File (ENDF/B). The uncertainty files (covariance matrices) in the ENDF/B library are generally obtained from analysis of experimental data. In the resonance region, the computer code SAMMY is used for analyses of experimental data and generation of resonance parameters. In addition to resonance parameters evaluation, SAMMY also generates resonance parameter covariance matrices (RPCM). SAMMY uses the generalized least-squares formalism (Bayes method) together with the resonance formalism (R-matrix theory) for analysis of experimental data. Two approaches are available for creation of resonance-parameter covariance data. (1) During the data-evaluation process, SAMMY generates both a set of resonance parameters that fit the experimental data and the associated resonance-parameter covariance matrix. (2) For existing resonance-parameter evaluations for which no resonance-parameter covariance data are available, SAMMY can retroactively create a resonance-parameter covariance matrix. The retroactive method was used to generate covariance data for 235U. The resulting 235U covariance matrix was then used as input to the PUFF-IV code, which processed the covariance data into multigroup form, and to the TSUNAMI code, which calculated the uncertainty in the multiplication factor due to uncertainty in the experimental cross sections. The objective of this work is to demonstrate the use of the 235U covariance data in calculations of critical benchmark systems.},

doi = {},

journal = {},

number = ,

volume = ,

place = {United States},

year = {Tue Jan 01 00:00:00 EST 2008},

month = {Tue Jan 01 00:00:00 EST 2008}

}