**1. NAME AND TITLE**

URR: Calculates Resonance Neutron Cross-Section Probability Tables, Bondarenko Self-Shielding Factors and Self- Indication Ratios for Fissile and Fertile Nuclides.

**2. CONTRIBUTOR**

Oak Ridge National Laboratory, Oak Ridge, Tennessee.

**3. CODING LANGUAGE AND COMPUTER**

Fortran 77; VAX family.

**4. NATURE OF PROBLEM SOLVED**

URR was developed to calculate cross-section probability tables, Bondarenko self-shielding factors,
and self-indication ratios for fertile and fissile isotopes in the unresolved resonance region.

**5. METHOD OF SOLUTION**

URR uses Monte Carlo techniques to select appropriate resonance parameters and to compute the
cross sections at the desired reference energy. The neutron cross sections are calculated by the single-level Breit-Wigner formalism with s-, p-, and d-wave contributions. The cross-section probability
tables are constructed by sampling the Doppler broadened cross-section. The various self-shielded
factors are computed numerically as Lebesgue integrals over the cross-section probability tables.

**6. RESTRICTIONS OR LIMITATIONS**

None noted.

**7. TYPICAL RUNNING TIME**

URR is interactive and executes in a few seconds.

**8. COMPUTER HARDWARE REQUIREMENTS**

The code runs on any VAX computer.

**9. COMPUTER SOFTWARE REQUIREMENTS**

The code was written in Fortran 77 and was tested on the VAX 6000 under the VMS operating
system.

**10. REFERENCE**

L. C. Leal, G. de Saussure and R. B. Perez, "URR Computer Code: A Code to Calculate
Resonance Neutron Cross-Section Probability Tables, Bondarenko Self-Shielding Factors and Self-Indication Ratios for Fissile and Fertile Nuclides," ORNL/TM-11297 (August 1989).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document and one (360 K) DOS diskette including the source and
sample case.

**12. DATE OF ABSTRACT**

June 1990.

**KEYWORDS: ** MONTE CARLO; INTERACTIVE, ON-LINE; NEUTRON CROSS SECTION
PROCESSING