**1. NAME AND TITLE**

MOMENT I: Moments Method Neutron Transport Code System.

**2. CONTRIBUTOR**

National Bureau of Standards, Washington, D. C.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; UNIVAC 1108.

**4. NATURE OF PROBLEM SOLVED**

MOMENT I calculates spatial moments of the Legendre harmonic coefficients of neutron fluence. Other codes or procedures must be used to construct spatial or angular distributions of fluence for these moments.

**5. METHOD OF SOLUTION**

Each moments equation is an integral equation involving a function phi_{nk}(E) of energy for a
particular spatial index n and angular index k. The equation is solved by numerical procedures.
The source term is completely specified for n equal to 0. For n not equal to 0, it may be regarded
as known if the equations are solved in an appropriate succession of increasing n. Gaussian
integration is used over part of the scattering integral term.

MOMENT I requires the processing of neutron cross section data from a form such as ENDF/B to a form suitable for input to this code. A processing code will be provided but, for the present, the processing must be done by the user. Processed data for several elements are included in this package. This code produces data similar to the Nuclear Development Associates RENUPAK code. Details of the solution of the moments equations differ considerably from those used in RENUPAK.

**6. RESTRICTIONS OR LIMITATIONS**

For the UNIVAC 1108 version of this code, the number of energies for which moments are calculated is limited to 400 and the number of (n,k) combinations is limited to 80. Solutions at 600 energies and 130 (n,k) combinations are said to be possible on the IBM 360/91. The composition of the medium is limited to 10 elements with a total of 150 partial interactions.

**7. TYPICAL RUNNING TIME**

On the UNIVAC 1108, 76 energies, 76 (n,k) combinations, and 35 integration intervals for each of 2 partial interactions took 4 minutes and 20 seconds run time. The running time is roughly proportional to the number of energies, integration intervals, and types of interactions. It is approximately proportional to the square root of the number of (n,k) combinations.

**8. COMPUTER HARDWARE REQUIREMENTS**

MOMENT I is operable on the UNIVAC 1108 computer.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A FORTRAN IV compiler is required. A library of cross sections which is required input is included in the package.

**10. REFERENCE**

C. M. Eisenhauer, B. L. Simmons, L. V. Spencer, "A Neutron Moments Computer Code, Moment I," NBS Technical Note 725 (May 1972).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document and one (1.2MB) DOS diskette which contains the source code, a library of data and sample problem input.

**12. DATE OF ABSTRACT**

August 1975.

**KEYWORDS:** NEUTRON; MOMENTS METHOD; INFINITE MEDIUM