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NESC9597 FLODIS.

FLODIS, Thermal Response of FSV HTGR Core

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1. NAME OR DESIGNATION OF PROGRAM:  FLODIS.
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2. COMPUTERS
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Program name Package id Status Status date
FLODIS NESC9597/01 Arrived 27-APR-2001

Machines used:

Package ID Orig. computer Test computer
NESC9597/01 IBM 360 series
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3. DESCRIPTION OF PROGRAM OR FUNCTION

FLODIS was developed to analyse shutdown transients for the Fort St. Vrain high-temperature gas- cooled reactor (HTGR) core. The program is a lumped node representation for the 37 refueling regions in the active core, the  side reflector blocks, the gas annulus between the core barrel and the prestressed concrete reactor vessel (PCRV) liner, and the PCRV cooling system. Heat conduction in all three coordinate directions and to the coolant is modeled. The calculation uses the specified operating conditions for the reactor at power to determine appropriate loss coefficients for the variable orifices in each refueling region. Iterative techniques are used to determine the distribution of coolant flow as a function of time during the transient. Both forced and natural convection flows can be calculated. FLODIS can be adapted to other HTGR systems with minor modifications.
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4. METHOD OF SOLUTION

The mathematical model consists of two parts -
the flow distribution and the temperature distribution. Navier- Stokes equations are applied to the flow problem. The temperature distribution differential equations are integrated using a Crank- Nickolson technique. The resulting algebraic equations are solved with a Gauss-Seidel iterative procedure.
A rectangular grid is superimposed on the reactor to define the mesh spaces. There are 142 mesh spaces in the active core, 146 in the side reflector, and 52 in the gas annulus between the core barrel and PCRV liner. Axially, there are 20 mesh spaces for a total of 6800 representing the entire system.
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5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

The orifice loss coefficients are assumed to remain constant throughout the transient. The effect of conduction between refueling regions is not included.
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6. TYPICAL RUNNING TIME:  40 minutes of CPU time are required on an IBM 360/91.
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7. UNUSUAL FEATURES OF THE PROGRAM

A typical refueling region is represented by four rectangular mesh spaces. The flow is allowed to  distribute within a refueling region according to the temperature variations between the four mesh spaces.
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8. RELATED AND AUXILIARY PROGRAMS:
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9. STATUS
Package ID Status date Status
NESC9597/01 27-APR-2001 Masterfiled Arrived
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10. REFERENCES

- D.D. Paul
Depressurization Accident Analysis for the Fort St. Vrain Reactor,    ORNL/NUREG/TM-58, December 1976.
NESC9597/01, included references:
- D.D. Paul:
  FLODIS: A Computer Model to Determine the Flow Distribution and
  Thermal Response of the Fort St. Vrain Reactor
  ORNL/TM-5365 (June 1976).
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11. MACHINE REQUIREMENTS:  540K bytes of memory are required on an IBM 360/91.
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12. PROGRAMMING LANGUAGE(S) USED
Package ID Computer language
NESC9597/01 FORTRAN
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13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  OS/360.
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14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:
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15. NAME AND ESTABLISHMENT OF AUTHORS

           D.D. Paul
           Oak Ridge National Laboratory
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16. MATERIAL AVAILABLE
NESC9597/01
source program   mag tapeFLODIS PSource program                     SRCTP
test-case data   mag tapeSample problem                             DATTP
test-case data   mag tapeControl information                        DATTP
report                   ORNL/TM-5365 (June 1976)                   REPPT
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17. CATEGORIES
  • G. Radiological Safety, Hazard and Accident Analysis
  • H. Heat Transfer and Fluid Flow

Keywords: convection, reactor cores, thermal conduction.