NESC0901 PAD.

1. NAME OR DESIGNATION OF PROGRAM:  PAD.

3. DESCRIPTION OF PROBLEM OR FUNCTION

The Pajarito Dynamics (PAD) program models dynamic systems with interactive neutronics, thermo-  dynamics, and hydrodynamics in one-dimensional spherical, cylin- drical, and planar geometries. The program has been applied to prompt critical excursions in various fissioning systems (solution,  metal, LMFBR, etc.) as well as to nonfissioning systems. PAD appli-  cations have included: controlled (nondestructive) and damaging reactor transient experiments, hypothetical LMFBR disassembly and recriticality accidents, hypothetical criticality accidents invol- ving the handling and processing of various forms of fissile mate- rials, and nonneutronic systems employing only the thermodynamic and hydrodynamic aspects of the program.

4. METHOD OF SOLUTION

A system is divided into discrete, contiguous regions, or mass points. The neutronics is comprised of one- dimensional Sn transport calculations for determining the spatial power profile and material motion reactivity feedback and analytic models for input and temperature feedback reactivities. Equation-of- state models in the program describe the thermodynamics of solids, liquids, and vapors and also phase transitions. Heat transfer bet- ween two materials at a mass point is considered. The hydrodynamics  (acceleration, velocity, position) proceeds in a Lagrangian coordi-  nate system. The neutronic-thermodynamic-hydrodynamic cycle is repeated stepwise in space and time until the desired calculational  endpoint is reached.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

Maxima of -
   100 hydrodynamic regions
    40 materials
    16 neutron energy groups

6. TYPICAL RUNNING TIME

A 16-group, S4, 20 mesh-point model of an LMFBR running for 10,000 iterations (time-steps) an including 50 Sn  calculations with a total of 20,000 inner iterations requires about  two minutes of CDC7600 time. The longest running sample problem requires approximately 95 CP seconds on the CDC7600.

7. UNUSUAL FEATURES OF THE PROGRAM:

8. RELATED AND AUXILIARY PROGRAMS

The internal geometric reactivity change is based on DTF4 (NESC Abstract 209). PAD disassembly calcu-  lations for a representative LMFBR model have been compared with those obtained from the FX2-POOL and VENUS2 (NESC Abstract 511) programs.

10. REFERENCES

- T.P. McLaughlin, D.M. Peterson, and W.R. Stratton,
  Energy Release from Molten-Fuel Recriticality Accidents, Transac-
  tions of the American Nuclear Society, Vol. 18, pp. 198-199, June
  23-27, 1974.
- T.P. McLaughlin,
  Prelimanary Topical Report on Comparison Reactor Disassembly
  Calculations,
  LA-6106-MS, November 1975.
- T.P. McLaughlin,
  Effects of Neutron Streaming and Geometric Models on Molten Fuel
  Recriticality Accidents,
  LA-6127-MS, November 1975.

- D.M. Peterson, W.R. Stratton, and T.P. McLaughlin:
  PAD: A One-Dimendional, Coupled Neutronic-Thermodynamic
  Hydrodynamic Computer Code
  LA-6540-MS, (December 1976).
- PAD Tape Description and Implementation Information
  NESC Note 82-21 (October 1, 1981).

11. MACHINE REQUIREMENTS

PAD requires system input and output units and a bulk storage device (e.g., disk or tape) on which four coded files may be defined. Each file should have a 32,000 (octal), 60-bit word capacity. PAD requires approximately 140K (octal) words of storage for execution on a CDC7600.

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  SCOPE 2.1.5
(CDC7600).

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

PAD was developed for the CDC RUN compiler with the rounded arithmetic option. Sample problem 2 terminates abnormally if rounded arithmetic is not used. Memory must be preset to zero prior to execution. Dummy routines are included in the package in place of several LANL com- puting environment routines. The dummy routines and their functions  are: XIT, an error interception routine; XITFIX, a routine to pro- vide the application program with the job status, program counter and program status words; GETHPK, a routine to provide the hardware  exchange package; DMPPK, which prints the exchange package; DMP, a routine to dump small core memory locations; and GETQ, which pro- vides various job parameters such as the job time limit, to the calling program.

15. NAME AND ESTABLISHMENT OF AUTHOR

Authors      D.M. Peterson, W.R. Stratton, and
             T.P. McLaughlin

Contact      H.M. Forehand, Jr.
             Los Alamos National Laboratory
             P.O. Box 1663
             Los Alamos, New Mexico 87545

source program   mag tapePAD Source Program (FTN)                   SRCTP
test-case data   mag tapeInput S. P. 1, Nonphysical Test Case       DATTP
test-case data   mag tapeInput S. P. 2, Nonneutronic Work Calcul.   DATTP
test-case data   mag tapeInput S. P. 3, Sodium Hammer Energetics    DATTP
test-case data   mag tapeInput S. P. 4, Sample Metal System-Cylin.  DATTP
test-case data   mag tapeInput S. P. 5, Sample Metal System Axial   DATTP
source program   mag tapeLISTIT Source Program (FTN)                SRCTP
test-case data   mag tapeGlossary of PAD COMMON Variable Names      DATTP
test-case data   mag tapePAD Input Specifications                   DATTP
source program   mag tapePAD CDC UPDATE Source Program              SRCTP
test-case output listing Sample Output                              OUTLS
test-case output listing Sample Problem Output (5 Microfiches)      OUTLS
report                   LA-6540-MS (1976)                          REPPT
prog. note               NESC Note 82-21 (October 1, 1981)          NOTPT