NESC0511 VENUS-2.

1. NAME OR DESIGNATION OF PROGRAM:  VENUS-2.

3. DESCRIPTION OF PROBLEM OR FUNCTION

VENUS-2 is an improved edition  of the VENUS fast-reactor disassembly program. It is a two- dimensional (r-z) coupled neutronics-hydrodynamics code that calculates the dynamic behavior of an LMFBR during a prompt-critical disassembly excursion. It calculates the power history and fission energy release as well as the space-time histories of the fuel temperatures, core material pressures, and core material motions. Reactivity feedback effects due to Doppler broadening and reactor material motion are taken into account.

4. METHOD OF SOLUTION

The power and energy release are calculated using a point-kinetics formulation with up to six delayed neutron groups. The reactivity is a combination of an input driving function and feedback effects due to Doppler broadening and material motion.  An adiabatic model is used to calculate the temperature increase throughout the reactor based on an initial temperature distribution  and power profile provided as input data. These temperatures are, in turn, converted to fuel pressures through one of several equation of state options provided. The material motion that results from the pressure buildup is calculated by a direct finite difference solution of a set of two-dimensional (r-z) hydrodynamics equations.  This is done in Lagrangian coordinates. The reactivity change associated with this motion is calculated by first-order perturbation theory. The displacements are also used to adjust the fuel densities as required for the density dependent equation-of- state option. An automatic time-step-size selection scheme is provided.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

VENUS-2 is written so that the dimensions of the storage arrays can be readily changed  to accomodate a broad range of problem sizes. In the base version, the total number of mesh intervals is restricted such that (NR+3)*(NZ+3) is less than 700, where NR and NZ are the total number of mesh intervals in the r and z directions, respectively. The total number of spatial regions used in the mockup must be no greater than 20. The number of spatial grid points in the input material- reactivity-worth distribution cannot exceed 26 by 26 in any region.  The program requires about 380K bytes of central storage with these  restrictions. If the available storage is increased, these restrictions can be relaxed accordingly.

6. TYPICAL RUNNING TIME

Typical problems require from 2 to 15 minutes of IBM 360/75 CPU time, with some cases taking up to 45 minutes.
Rather mild excursions in reactors that have little initial void space usually require the longer running times. The sample problem requires about 2 minutes on an IBM 3033 and less than a minute on a CDC 7600.

7. UNUSUAL FEATURES OF THE PROGRAM

Several special subroutines were developed for VENUS-2 that partially alleviate some of the basic modeling restrictions in the code. These include approximate treatment of the following effects: a) fuel-sodium interaction (heat transfer), b) fission gas pressures, and c) nonhomogeneous material  motion due to preferential axial sodium expulsion. Although these were not included as standard options in the code, the models are discussed in ANL-7951.

8. RELATED AND AUXILIARY PROGRAMS

VENUS-2 offers a number of improvements and refinements over the original VENUS code. In particular, the ANL density-dependent equation-of-state option was substantially improved. In addition, an option was added that greatly improves the accuracy of calculations where sodium is present in the core. Other areas of improvement include time-step control, accounting for the heat-of-fusion of the fuel in the energy balance, calculating the energy in molten fuel, and improved data edits.

VENUS-2 will optionally plot the Lagrangian mesh grid at specified time intervals during the excursion and create a three- dimensional isometric plot displaying the pressure as a function of  two space variables. The CalComp plotter is used.

10. REFERENCES

- J.F. Jackson, R.B. Nicholson:
  VENUS-II: An LMFBR Disassembly Program
  ANL-7951, September 1972
- W.T. Sha, T.H. Hughes:
  VENUS-A, Two-Dimensional Coupled Neutronics-hydrodynamics Com-
  puter Program for Fast Reactor Power Excursions
  ANL-7701, October 1970
- VENUS2, NESC No. 511.360, Tape Description, Implementation
  Information, Sample Output, and ANL-7951 Erratum,
  National Energy Software Center Note 80-53, August 12, 1980.
-  VENUS2, NESC No. 511.7600, Sample Problem Output,
  National Energy Software Center Note 80-52, August 12, 1980.

11. MACHINE REQUIREMENTS

440k bytes are used for the IBM version when  storing the data in double-precision. Single-precision storage is adequate for the converted CDC 7600 version which requires 160,000 (octal) words of memory for execution. One peripheral storage device is needed if the graphical output option is used.

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:
OS/360 (IBM360) and SCOPE 2.1 (CDC7600).

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:

15. NAME AND ESTABLISHMENT OF AUTHOR

J.F. Jackson
NRC Programs
Los Alamos Scientific Laboratory
P. O. Box 1663
Los Alamos, New Mexico 87545, U. S. A.

R.B. Nicholson
Research and Technology Center
Exxon Nuclear Company
2955 George Washington Way
Richland, Washington 99352, U. S. A.

D.P. Weber
Reactor Analysis and Safety Division
Argonne National Laboratory
9700 South Cass Avenue
Argonne, Illinois 60439, U. S. A.

File name	File description	Records
NESC0511_03.001	INFORMATION	42
NESC0511_03.002	JOB CONTROL	64
NESC0511_03.003	OVERLAY CARDS	6
NESC0511_03.004	VENUS FOTRAN SOURCE	3343
NESC0511_03.005	DUMMY PLOTTING ROUTINES	11
NESC0511_03.006	PLOTTING ROUTINES	296
NESC0511_03.007	SAMPLE PROBLEM INPUT	291
NESC0511_03.008	SAMPLE PROBLEM OUTPUT	5161

File name	File description	Records
NESC0511_04.001	SOURCE	3011
NESC0511_04.002	S.P. INPUT	291
NESC0511_04.003	S.P. OUTPUT	5161
NESC0511_04.004	SOURCE	3340
NESC0511_04.005	PLOTTING ROUTINES	296
NESC0511_04.006	S.P. INPUT	291
NESC0511_04.007	OVERLAY CARDS	6
NESC0511_04.008	S.P. OUTPUT	5161