NESC0658 FRAP-T6/MOD1.

1. NAME OR DESIGNATION OF PROGRAM:  FRAP-T6/MOD1

3. DESCRIPTION OF PROBLEM OR FUNCTION

FRAP-T6 is the most recent in the FRAP-T (Fuel Rod Analysis Program - Transient) series of progams for calculating the transient behavior of light water reactor fuel rods during reactor transients and hypothetical accidents, such as loss-of-coolant and reactivity-initiated accidents. The program calculates the temperature and deformation histories of fuel rods as functions of time-dependent fuel rod power and coolant boundary conditions. FRAP-T6 can be used as a "stand-alone" code or, using steady state fuel rod conditions supplied by FRAPCON2 (NESC NO. 694), can perform a transient analysis. In either case, the phenomena modeled by FRAP-T6 include:  heat conduction, heat transfer from cladding to coolant, elastic- plastic fuel and cladding deformation, cladding oxidation, fission gas release, fuel rod gas pressure, and pellet cladding mechanical interaction. Licensing audit models have been added, also. The program includes a user's option that automatically provides a detailed uncertainty analysis of the calculated fuel rod variables due to uncertainties in fuel rod fabrication, material properties, power and cooling.

4. METHOD OF SOLUTION

The models in FRAP-T6 use finite difference techniques to calculate the variables which influence fuel rod performance. The variables are calculated at user-specified slices of the fuel rod. Each slice is at a different elevation and is defined to be an axial node. At each axial node, the variables are calculated at user-specified locations. Each location is at a different radius and is defined to be a radial node. The variables at any given axial node are assumed to be independent of the variables at all other axial nodes. The solution for the fuel rod variables begins with the calculation of the fuel and cladding temperatures. Then, the temperature of the gases in the plenum of the fuel rod is calculated. Next, the stresses and strains in the fuel and cladding and the pressure of the gas inside the rod are computed. This calculation sequence is repeated until essentially the same temperature distribution is calculated for two successive cycles. The cladding oxidation and fission gas release are then calculated, and the time is advanced, after which the complete sequence of calculation is repeated to obtain the fuel rod variables at the advanced time.

The models interact in several ways. The fuel temperature calculated by the thermal model is dependent upon the size of the fuel-cladding gap calculated by the deformation model, and the diameter of the fuel pellet depends upon the temperature distribution in the pellet. Mechanical properties of the cladding vary significantly with temperature. The internal pressure varies with the temperature of the fuel rod gases and the strains of fuel and cladding. The stresses and strains in the cladding are dependent upon internal gas pressure. Variables calculated in one model are treated as independent variables by the other models. Two nested calculational loops are cycled until convergence occurs. Convergence is accelerated by the Newton method. The optional uncertainly analysis is based on the response surface method.

5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

Since FRAP-T6 is dynamically-dimensioned, the only constraint on the number of axial  and radial nodes is the size of the available computer memory. The amount of memory required is a function of the number of axial and radial nodes and the selected models given by the equation: S = LB + 1710 + 11NR + 257NZ + 8NR*NZ + I2D (7NA*NZA*NR + 24NA*NZA)  + IB (6NCH*NZCH + NCH + 2) + IF2 (4 + 117NR + 2NZ + 20NR*NZ) + IG (7 + 4NRF + 8NZ + 26NRF*NZ) + IBAL (10,000) where S is the required  number of words of central memory; LB is the memory required to load FRAP-T6 exclusive of array storage (98,000 words); NR is the number  of radial nodes and NZ, the number of axial nodes. I2D=1, if two- dimensional r-theta heat conduction is modeled, 0 otherwise; NA is the number of azimuthal sectors and NZA, the number of axial nodes at which two-dimensional r-theta heat conduction is modeled. IB=1, if the fuel rod is in contact with more than one coolant channel, 0
otherwise; NCH is the number of coolant channels surrounding the fuel rod, and NZCH, the number of vertically-stacked zones in a coolant channel. IF2=1, if the FRACAS2 subcode (deformable pellet deformation model) is used, 0 otherwise. IG=1, if the FASTGRASS sub- code (fission gas production and release model) is used, 0 other- wise; NRF is the number of radial nodes in the fuel. IBAL=1, if the  BALON2 subcode (cladding ballooning model) is used, 0 otherwise. The LB variable can be reduced to a value of about 65,000 by overlaying.

6. TYPICAL RUNNING TIME

The running time varies with the size of the  time-step, the number of nodes specified, and the models chosen.

7. UNUSUAL FEATURES OF THE PROGRAM

The FRAP-T series of programs is designed in a modular manner with each type of calculation and analytical model in a separate module, or subcode. This configuration makes substitution of models and algorithms a straightforward procedure.

8. RELATED AND AUXILIARY PROGRAMS

The series makes use of the INEL (formerly NRTS) Environmental Subroutines (NESC Abstract 613), which are included in the package. The steady-state fuel rod analysis program FRAPCON2 is designed to supply realistic input conditions to FRAP-T6 for transient analysis. The MATPRO11 Rev. 1 materials properties package is linked with FRAP-T6 to provide the necessary materials properties. FRAP-T6 is designed to calculate fuel rod response for reactor system thermal- hydraulic analysis codes, such  as TRAC and RELAP4, or, as an alter- native, a condensed version of  FRAP-T6 can be incorporated in the system's thermal-hydraulic analysis code so that the systems analysis and detailed fuel rod response  can  be  determined  in  a  single  computer  analysis. A
condensed version of FRAP-T6 has been incorporated in the TRAC-PD3 code.

10. REFERENCES

- FRAP-T6/MOD1, NESC No. 658, FRAP-T6/MOD1 Tape Description and Im-
  plementation Information, National Energy Software Center Note
  83-87, September 2, 1983.
- Donald L. Hagrman and Gregory A. Reymann,
  ED., Matpro-Version 11, (Revision 1): A Handbook of Materials
Properties for Use in the Analysis of Light Water Reactor Fuel Rod    Behavior,
  NUREG/CR-0497 (TREE-1280) Rev. 1, February 1980.
- G.A. Berna, M.P. Bohn, W.N. Rausch, R.E. Williford, and D.D.
  Lanning,
  FRAPCON-2: A Computer Code for the Calculation of Steady State
  Thermal-Mechanical Behavior of Oxide Fuel rods,
  NUREG/CR-1845, January 1981.
- NTRS Environmental Subroutine Manual, Aeroject Nuclear Company,
  December 1972.
- R.J. Wagner,
STH20, A Subroutine Package to Compute the Thermodynamic Poperties    of Water,
  ANC Note, 1975.

- L.J. Siefken, Ch.M. Allison, M.P. Bohn, and S.O. Peck:
  FRAP-T6: A Computer Code for Transient Analysis of Oxide Fuel Rods
  NUREG/CR-2148 (EGG-2104), (May 1981).
- L.J. Siefken, V.N. Shah, G.A. Berna, and J.K. Hohorst:
  FRAP-T6: A Computer code for the Transient Analysis of Oxide fuel
  Rods,
  NUREG/CR-2148 (EGG-NSMD-2104) Addendum (June 1983).

11. MACHINE REQUIREMENTS

260,000 (octal) words of SCM and 63,000 (octal words of LCM are required for FRAP-T6.

13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:  NOS/BE  1.4

14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

The FRAP-T6 souce is available only in CDC UPDATE utility format, not suited for use on other computer systems. The INEL Graphics Library  routines: CATGEN, CATID, CATKEY, COMCLS, COMIN, COMOUT, EXTEND, FINDID, FINDKEY, and GFI were not supplied. If the user does not specify the plotting option and removes the *DEFINE CWAF directive from the FRAP-T6 OLDPL the Graphics Library is not required.
However, to obtain graphic output, alternative routines suited to the local computing environment should be provided.

15. NAME AND ESTABLISHMENT OF AUTHOR

             L.J. Siefken*, V.N. Shah, G.A. Berna,
             and J.K. Hohorst
             EG&G Idaho, Inc.
             P.O. Box 1625
             Idaho Falls, Idaho 83415
* Contact

File name	File description	Records
NESC0658_04.003	FRAP-T6/MOD1 INFORMATION FILE	35
NESC0658_04.004	FRAP-T6/MOD1 SOURCE AND SEGLOAD DIRECTIVES	45732
NESC0658_04.005	AUXILIARY ROUTINES AND INPUT DATA	6255
NESC0658_04.006	INEL SUBROUTINES SOURCE (FORTRAN)	1144
NESC0658_04.007	WAGNER STEAM TABLES	2544
NESC0658_04.008	CONTROL INFORMATION AND COMMENTS	45