Computer Programs

NESC0432 COBRA-4I.

NESC0432 COBRA-4I.

COBRA-4I, Transient Thermohydraulics Fuel Elements Clusters, Subchannel Analysis Method

NAME OR DESIGNATION OF PROGRAM, COMPUTER, DESCRIPTION OF PROBLEM OR FUNCTION, METHOD OF SOLUTION, RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM, TYPICAL RUNNING TIME, UNUSUAL FEATURES OF THE PROGRAM, RELATED AND AUXILIARY PROGRAMS, STATUS, REFERENCES, MACHINE REQUIREMENTS, LANGUAGE, OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED, OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS, NAME AND ESTABLISHMENT OF AUTHOR, MATERIAL, CATEGORIES

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1. NAME OR DESIGNATION OF PROGRAM: COBRA-4I.

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2. COMPUTERS

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Program name	Package id	Status	Status date
COBRA-4I	NESC0432/12	Tested	22-OCT-1997

Machines used:

Package ID	Orig. computer	Test computer
NESC0432/12	DEC VAX series	DEC VAX 8810

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3. DESCRIPTION OF PROBLEM OR FUNCTION

COBRA4I performs steady-state and transient thermal-hydraulic analysis of rod bundle nuclear fuel elements and cores via the subchannel analysis method.

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4. METHOD OF SOLUTION

The conservation equations of flow and energy are solved for interconnected subchannel control volumes via conventional finite differencing techniques. The steady-state calculations are solved by implicit finite differencing whereas the transient calculations are performed by either an implicit or explicit finite difference scheme. Internal rod temperatures are calculated by an orthogonal collocation approximation to the heat conduction equation.

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5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

Using the COBRA4I code option to store variables on peripheral storage devices eliminates any practical limit as to maximum problem size. However, computer core requirements and code execution time is always a consideration when determining the complexity of the problem to be solved.

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6. TYPICAL RUNNING TIME

On a CDC 7600 running time is 0.004 seconds per cell-iteration using the implicit solution scheme and 0.00006 seconds per cell-iteration using the explicit scheme. The number of cells is determined as the number of subchannels times the number of axials nodes. The number of iterations required per time-step varies according to convergence criteria and complexity of physics; however, typical values are from 10 to 20 iterations for the implicit scheme and 10 to 50 iterations for the explicit scheme. The three sample problems run in less than 30 seconds on the CRAY1. The U-tube and fuel thermal sample problems each run in less than 2 minutes and the 7-pin sample problem in less than 1 minute on an IBM3033.

NESC0432/12

NEA-DB executed the two test cases included in this package on a VAX 8810 computer. The following CPU times were required: 45 seconds (thermal model problem); 45 seconds (U-tube problem).

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7. UNUSUAL FEATURES OF THE PROGRAM

The improved capabilities of COBRA4I over its predecessor COBRA3C include:
(a) A new explicit solution scheme to calculate severe transients  involving flow reversals, recirculations and expulsion and  reentry flows with either a flow or pressure boundary       condition specified.
(b) Improved storage allocation to reduce central memory       requirements and improved running time.
(c) Improved fuel rod heat conduction model to calculate interior-   rod temperatures with axial conduction and variable thermal  conductivity included. Each rod may now consist of axially-       varying materials.
(d) Addition of a set of correlations to calculate the properties  of superheated steam and a set of heat transfer correlations  covering the complete range of heat transfer from subcooled       through boiling.
(e) Problem "Dump and Restart" capabilities which allow the  solution to be saved for subsequent use either to continue  calculations or to be used as an initial guess for a different  problem which can result in significant time savings for       similar problems.
(f) Auxiliary program to re-dimension COBRA based on user  specified input defining problem size and code options       desired, thus minimizing storage requirements.
(g) Auxiliary program to generate COBRA input for hexagonal rod-  bundle geometry. Input for card groups 4, 7, and 8 can be  generated, thus greatly reducing the amount of input required.  (h) Line-printer plotting capability to display pressure drop,  mass flux, enthalpy and crossflow versus axial position for       all or a specified number of gaps and channels.
(i) A thermally-conducting wall model which can conduct heat       between two channels on opposite sides of a wall.

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8. RELATED AND AUXILIARY PROGRAMS

COBRA4I is an extended version of the COBRA3C computer program. The auxiliary program SPECSET re- dimensions COBRA4I according to user-specified problem size, and the auxiliary program GEOM calculates COBRA input for data groups 4, 7, and 8 for hexagonal rod bundles. The IBM version also contains auxiliary program CSPECS which replaces pseudostatements of the form *CALL SPECx in COBRA4I with the correctly sized set of FORTRAN declarative statements comprising COMDECKx.

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9. STATUS

Package ID	Status date	Status
NESC0432/12	22-OCT-1997	Tested at NEADB

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10. REFERENCES

- C.L. Wheeler, C.W. Stewart, R.J. Cena, D.S. Rowe, and A.M. Sutey,
  COBRA-IV-I: An Interim Version of COBRA for Thermal-hydraulic
  Analysis of Rod Bundle Nuclear Fuel Elements and Cores,
  BNWL-1962, March 1976.
- C.W. Stewart, C.L. Wheeler, R.J. Cena, C.A. McMonagle, J.M. Cuta,
  and D.S. Trent,
  COBRA-IV: The Model and the Method,
  BNWL-2214, July 1977.
- C.W. Stewart, C.A. McMonagle, M.J. Thurgood, T.L. George, D.S.
  Trent, J.M. Cuta, and G.D. Seybold:
  Core Thermal Model: COBRA-IV Development and Applications,
  BNWL-2212, January 1977.
- D.M. Lister and P.A. Jallouk,
  COBRA IV-I An IBM Compatible Version,
  NUREG/CR-0519 (ORNL/NUREG/CSD-9), December 1978.
- COBRA4I, NESC No. 432.7600G, Tape Contents Description,
  National Energy Software Center Note 77-37, Revised May 23, 1981.
- COBRA4I, NESC No.432.CRA1, COBRA4I Tape Description,
  National Energy Software Center Note 82-108, August 20, 1982.
- COBRA4I, NESC No. 432.3033, COBRA4I Tape Description and
  Implementation Information,
  National Energy Softawre Center Note 86-05, October 25, 1985.

NESC0432/12, included references:

- C.L. Wheeler et al.:
  COBRA-IV-I: An Interim Version of COBRA for Thermal-Hydraulic
  Analysis of Rod Bundle Nuclear Fuel Elements and Cores.
  BNWL-1962, UC-32  (March 1976)
- C.W. Stewart et al.:
  Core Thermal Model: COBRA-IV Development and Applications.
  BNWL-2212, NRC-4  (January 1977)
- C.W. Stewart et al.:
  COBRA-IV: The Model and the Method
  BNWL-2214, NRC-4  (July 1977)
- D.M. Lister and P.A. Jallouk:
  COBRA-IV-I - An IBM-Compatible Version
  NUREG/CR-0519  (December 1978)
- M. Birgersson:
  COBRA4I Tape Description and Implementation Information
  NESC Note 86-05  (October 25, 1985)

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11. MACHINE REQUIREMENTS

202,000 (octal) words and 4 scratch units besides the standard input/output units (CDC7600), 450K bytes and 6
units besides the standard input/output units (IBM3033).

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12. PROGRAMMING LANGUAGE(S) USED

Package ID	Computer language
NESC0432/12	FORTRAN

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13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED

SCOPE (CDC6600,7600), NOS (CDC CYBER175), COS (CRAY1), MVS (IBM3033), VM/CMS (IBM4331).

NESC0432/12

VMX V5.0-1 (VAX 8810).

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14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:

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15. NAME AND ESTABLISHMENT OF AUTHOR

  7600     C.L. Wheeler, C.W. Stewart*, J.F. Cena,
           D.S. Rowe, and A.M. Sutey
           Pacific Northwest Laboratories
           Battelle
           P.O. Box 999
           Richland, Washington 99352

  CRAY1    T. Hosokawa
           Century Research Center Corporation
           No. 2, 3-Chome, Hon-cho
           Nihonbashi, Chuo-Ku
           Tokyo, Japan

  IBM      D.M. Lister and P.A. Jallouk
           Oak Ridge National Laboratory
           P.O. Box X
           Oak Ridge Tennessee 37831

           Elba Pezzoni
           Comision Nacional de Energia Atomica
           Buenos Aires, Argentina
* Contact

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16. MATERIAL AVAILABLE

NESC0432/12

File name	File description	Records
NESC0432_12.001	Information file	127
NESC0432_12.002	Changes made in VAX conversion	1148
NESC0432_12.003	COBRA-4I FORTRAN Source	6788
NESC0432_12.004	VAX FORTRAN Include file	9
NESC0432_12.005	VAX FORTRAN Include file	13
NESC0432_12.006	VAX FORTRAN Include file	26
NESC0432_12.007	VAX FORTRAN Include file	53
NESC0432_12.008	VAX FORTRAN Include file	32
NESC0432_12.009	VAX FORTRAN Include file	30
NESC0432_12.010	VAX FORTRAN Include file	13
NESC0432_12.011	VAX FORTRAN Include file	7
NESC0432_12.012	VAX FORTRAN Include file	5
NESC0432_12.013	VAX FORTRAN Include file	8
NESC0432_12.014	VAX FORTRAN Include file	5
NESC0432_12.015	VAX FORTRAN Include file	3
NESC0432_12.016	VAX FORTRAN Include file	10
NESC0432_12.017	VAX FORTRAN Include file	4
NESC0432_12.018	VAX FORTRAN Include file	15
NESC0432_12.019	VAX FORTRAN Include file	13
NESC0432_12.020	VAX FORTRAN Include file	6
NESC0432_12.021	VAX FORTRAN Include file	16
NESC0432_12.022	VAX FORTRAN Include file	8
NESC0432_12.023	VAX FORTRAN Include file	26
NESC0432_12.024	VAX FORTRAN Include file	3
NESC0432_12.025	VAX FORTRAN Include file	4
NESC0432_12.026	VAX FORTRAN Include file	2
NESC0432_12.027	VAX FORTRAN Include file	3
NESC0432_12.028	VAX FORTRAN Include file	2
NESC0432_12.029	VAX FORTRAN Include file	2
NESC0432_12.030	VAX FORTRAN Include file	2
NESC0432_12.031	VAX FORTRAN Include file	2
NESC0432_12.032	VAX FORTRAN Include file	77
NESC0432_12.033	Command file for compilation	14
NESC0432_12.034	Command file for linking	13
NESC0432_12.035	Command file for running (brief)	58
NESC0432_12.036	Command file for running (complete)	226
NESC0432_12.037	Test case 1 input data Utube problem	44
NESC0432_12.038	Test case 2 input data thermal model problem	118
NESC0432_12.039	Test case 1 output	1744
NESC0432_12.040	Test case 2 output (original)	1791
NESC0432_12.041	Test case 2 output (NEADB)	1791
NESC0432_12.042	Command file to rename file names	42

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17. CATEGORIES

G. Radiological Safety, Hazard and Accident Analysis
H. Heat Transfer and Fluid Flow

Keywords: LMFBR reactors, blowdown, enthalpy, fluid flow, heat transfer, hydraulics, reactor cores, reactor safety, rod bundles, transients, water cooled reactors.