1. NAME AND TITLE

NAP: Multigroup Time-Dependent Neutron Activation Prediction Code.

2. CONTRIBUTORS

IIT Research Institute, Chicago, Illinois.

NASA George C. Marshall Space Flight Center, Huntsville, Alabama.

3. CODING LANGUAGE AND COMPUTER

FORTRAN IV; IBM 7090 and 7094.

4. NATURE OF PROBLEM SOLVED

Neutron induced gamma-ray activities are computed for use in transport codes. Activation calculations can be made for structural materials, reactor coolants, or any material exposed to a neutron flux. Results are given in terms of neutron flux, decay chain atom densities, photon emission rates, and energy. The code may also be used in the interpretation of activation data such as neutron spectra measurements or isotopic analysis.

5. METHOD OF SOLUTION

The neutron flux is evaluated by an optional one-dimensional multigroup discrete ordinates calculation which should be performed for problems of significant spatial variation. Isotropic scattering and scattering to the next lower group only are assumed. The incident neutron flux as a function of group is a function of time through a time-dependent power level.

Decay chains for (n,gamma), (n,p), (n,alpha), and (n,2n) reactions are determined in succession. The NAP Gamma Radiation Library supplies the data of the radioisotope decay chains and modes of decay. Data for more than 800 isotopes are present.

Resonance self-shielding is accounted for by computation of effective resonance integrals using the NR or NRIA approximations.

Cross sections are obtained from the NAP Library, supplied by the user or calculated, if desired, by known systematics for the thermal region, by statistical resonance theory for the epithermal region, and by compound nucleus formation theory for (n,p), (n,alpha), and (n,2n) reactions.

6. RESTRICTIONS OR LIMITATIONS

Time steps of power 50

Time steps of activities 200

Decay chain steps, maximum of 4

(or until stable)

Energy groups 43

Spatial regions 20

Quadrature 10

Mesh points 100

Number of resolved resonances treated 9

7. TYPICAL RUNNING TIME

Estimated running time of packaged sample problem: 1.5 minutes each.

8. COMPUTER HARDWARE REQUIREMENTS

The code was designed for the 32 K IBM 7094 with standard I-O and 4 tape units.

9. COMPUTER SOFTWARE REQUIREMENTS

The code is operable on the IBM 7090/7094 IBSYS Operating System using IBJOB Processor. The cross sections and gamma radiation libraries are input as binary files.

10. REFERENCES

D. A. Klopp, "Prediction of Neutron Induced Activation - Volume I - NAP Code Manual," IITRI-A6088-21 (January 1966).

D. A. Klopp, "Prediction of Neutron Induced Activation - Volume II - NAP: Physical Models and Experimental Validation," IITRI-A6088-22.

D. A. Klopp, "Prediction of Neutron Induced Activation - Volume III - NAP Cross Section Library," IITRI-A6088-23.

D. A. Klopp, "Prediction of Neutron Induced Activation - Volume IV - NAP Gamma Radiation Library," IITRI-A6088-24.

11. CONTENTS OF CODE PACKAGE

Included are the referenced documents and one (1.2MB) DOS diskette which contains the source code, neutron and gamma-ray cross section libraries, and input and output for two sample problems.

12. DATE OF ABSTRACT

May 1969; updated July 1981, October 1991.

KEYWORDS: ACTIVATION; NEUTRON; DISCRETE ORDINATES; TIME-DEPENDENT; ISOTOPE INVENTORY; ONE-DIMENSION; MULTIGROUP