**RSICC CODE PACKAGE PSR-464**

**1. NAME AND TITLE**

SOLA-LOOP: Nonequilibrium, Drift-Flux Code System for Two-Phase Flow Network Analysis.

**2. CONTRIBUTORS**

Los Alamos National Laboratory, NM, through the Energy Science and Technology Software Center, Oak Ridge, TN.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; CDC7600 (P00464760000).

**4. NATURE OF PROBLEM SOLVED**

SOLA-LOOP is designed for the solution of transient two-phase flow in networks composed of one-dimensional components. The fluid dynamics is described by a nonequilibrium, drift-flux formulation of the fluid conservation laws. Although developed for nuclear reactor safety analysis, SOLA-LOOP may be used as the basis for other types of special-purpose network codes. The program can accommodate almost any set of constitutive relations, property tables, or other special features required for different applications.

**5. METHOD OF SOLUTION**

The drift-flux equations are formulated as continuity equations, the momentum equation, and the internal energy equation. The mixture density, the macroscopic vapor density, the center of mass velocity, and the mixture specific internal energy are chosen as dependent variables, and time and axial position are the independent variables. Constitutive relations and exchange rates are determined by the intended use of the code. The calculation cycle used to solve by point relaxation methods the finite difference formulation of the flow equations in a single one-dimensional component is made up of four tasks. First, the momentum equation is advanced explicitly using the values from the previous cycle for all contributions. Next, an iteration is made to replace the pressure with advanced time values. This pressure iteration scheme is a variant of the Implicit Continuous fluid Eulerian (ICE) technique. Then, all other dependent variables are updated, and in the fourth task data output, time-step control, and housekeeping operations are performed. Various boundary conditions may be applied at the ends of the one-dimensional component meshes to represent inlet and exit conditions including prescribed velocities or pressures, uniform or gradient-free outflow, and periodic boundaries in which the bottom and top of a component are joined. Where two or more components are coupled, special coupling equations are solved to obtain the appropriate boundary conditions for each. Different time-steps can be used in various components. The time-steps are determined by numerical stability requirements and other user-specified conditions.

**6. RESTRICTIONS OR LIMITATIONS**

Current dimensioning in the SOLA-LOOP program allows maxima of 10 components, 8 segments per component, 200 junctions, 6 time levels, pressure groups, and vapor production rates per cell and 5 boundary data sets.

**7. TYPICAL RUNNING TIME**

The time required is highly problem-dependent. NESC executed the sample problem in less than 3 CP minutes on a CDC7600.

**8. COMPUTER HARDWARE REQUIREMENTS**

SOLA-LOOP was developed on a CDC 7600 computer.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A Fortran IV compiler is required to compile the code which ran under the SCOPE operating system.

**10. REFERENCES**

a) included in documentation:

C.W. Hirt, T.A. Oliphant, W.C. Rivard, N.C. Romero, and M.D. Torrey, "SOLA-LOOP: A Nonequilibrium, Drift-Flux Code for Two-Phase Flow in Networks," NUREG/CR-0626, LA-7659 (June 1979).

NESC No. 859.7600, "SOLA-LOOP Title Input, NESC Note 80-29," (December 17, 1979).

Sample problem output from CDC.

b) background information:

C.W. Hirt, N.C. Romero, M.D. Torrey, and J.R. Travis, "SOLA-DF: A Solution Algorithm for Nonequilibrium Two-Phase Flow," NUREG/CR-0690, LA-7725-MS (June 1979).

C.W. Hirt, B.D. Nichols, and N.C. Romero, "SOLA, A Numerical Solution Algorithm for Transient Fluid Flow," LA-5852 (April 1975).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced documents in (10.a) and one DS/HD diskette which includes the Fortran source and sample problem input.

**12. DATE OF ABSTRACT**

August 2000.

** KEYWORD:** REACTOR SAFETY