**1. NAME AND TITLE**

DASH-FP: A One-Dimensional Analytic-Numerical Solution to the Problem of Multicomponent Time-Dependent Diffusion of Fission Products.

**2. CONTRIBUTOR**

Los Alamos National Laboratory, Los Alamos, New Mexico.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV, COMPASS; CDC.

**4. NATURE OF PROBLEM SOLVED**

DASH-FP solves the multicomponent time-dependent diffusion with radioactive decay problem which arises in the study of high-temperature gas-cooled reactors' fission product migration.

**5. METHOD OF SOLUTION**

DASH-FP provides a one-dimensional analytic-numerical solution of the diffusion problem. The diffusion operator is numerically approximated by a spatial finite-difference representation. The resulting time-dependent problem is solved analytically using a matrix operator method. Comparisons to a number of known one-dimensional analytic solutions have been made. These comparison problems include the one species and two species, two material slab, cylinder, and sphere cases.

The method used produces a correct analytic solution of the equations for isotopes of any possible decay constants. For a given geometry, the error varies inversely as the square of the number of calculational cells.

**6. RESTRICTIONS OR LIMITATIONS**

None noted.

**7. TYPICAL RUNNING TIME**

no. of no. of no. of no. of running

isotopes cells materials time steps time

DATA1DM 1 24 4 1 2.6 sec

DATA2DM 2 24 4 1 14.4 sec

DATA3DM 3 24 4 1 46.9 sec

DATAESY 2 4 2 1 1.0 sec

DATA 2 24 3 5 6.4 sec.

**8. COMPUTER HARDWARE REQUIREMENTS**

The code is operable on the CDC computers. It requires approximately 60 K words of small core storage and 400 K words of large core storage.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A Fortran IV compiler is required. Subroutine SEARCH is coded in COMPASS. There is an option for plotting, set up for the DISSPLA plot routines. The plotting is done as a postprocessor.

**10. REFERENCES**

L. M. Carruthers, "DASH Abstract" (April 1981).

C. E. Apperson, Jr., C. E. Lee, and L. M. Carruthers, "DASH: A Multicomponent Time-Dependent Concentration Diffusion with Radioactive Decay Program," NUREG/CR-0776, LA-7793-MS (April 1979).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document and one (1.2MB) DOS diskette which contains the source codes and sample problem input and output.

**12. DATE OF ABSTRACT**

February 1982.

**KEYWORDS: ** FISSION PRODUCTS; DIFFUSION THEORY; NUCLIDE TRANSPORT; ONE-DIMENSION; TIME-DEPENDENT