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NEA-0997 THT.

THT, 3-D Coarse Mesh LWR Bundle Fluxes and Power with Discontinuity Factors

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1. NAME OR DESIGNATION OF PROGRAM:  THT.
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2. COMPUTERS
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Program name Package id Status Status date
THT NEA-0997/01 Tested 05-JUN-1985

Machines used:

Package ID Orig. computer Test computer
NEA-0997/01 IBM 370/168 IBM 3081
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3. DESCRIPTION OF PROGRAM OR FUNCTION

THT is a 3-dimensional neutron  coarse mesh program to evaluate average bundle fluxes and power in LWRs. The method employed in THT is aimed at being more precise than current industrial design methods without being too slow. The horizontal meshes in THT correspond exactly to the horizontal sections of the bundle. The vertical mesh size has no equivalent limitations but should usually be chosen near to the horizontal meshes. The approximations involved in the method require in fact the mesh size to be much larger than the thermal and epithermal mean free paths in the bundles. This condition is always met when dealing with standard LWR bundles.
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4. METHOD OF SOLUTION

The basic equations in THT are similar to those of some widely used industrial design methods: they are derived from diffusion theory and use 3-group neutron constants, but only the fast fluxes are explicitly calculated. The THT theory includes, however, two features which both result in a refinement of the system coefficients evaluations with respect to the other methods:

(1) A new spectral model to evaluate the thermal and epithermal average flux inside the assemblies, based on local solutions of the  thermal and epithermal flux equations.

(2) Discontinuity factors, as defined by Henry, are used in the equations to connect the fast, epithermal, and thermal fluxes across the node boundaries.

THT was mainly written to study the new coarse mesh method developed at AGIP Nucleare. The program is therefore particularly suited for comparison with reference data and allows the user to choose different values for some model parameters and different convergence strategies. For the same reason, however, there exists no interface  with other programs.
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5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

The length of the container array is independent of input. At present this array has a length of 100,000 words, which allows THT to treat problems as large as 1600 nodes cases. On the PRIME 750 computer, the dimension  of the container array can be modified, if necessary, by changing the corresponding DIMENSION and COMMON statements throughout the program. On other large computers it may be sufficient to modify only the DIMENSION statement in the main program.
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6. TYPICAL RUNNING TIME

Execution times depend on the number of meshes and the required precision. A problem with 8 * 8 * 12 nodes required 0.283 minutes on a PRIME 750 computer to converge with a precision EPS0 = 10E-5 for the maximum difference between the ratios of the fluxes of the 2 last iterations.
NEA-0997/01
NEA-DB executed the test cases included in the package  on IBM 3081K. The following CPU times were required: 1.8 seconds for test case 1 and 0.4 seconds for test case 2.
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7. UNUSUAL FEATURES OF THE PROGRAM

Flexible dimensioning is used throughout the program so that only the total storage requirement for a given problem is of concern. A choice between different convergence stragegies is allowed. Reference fluxes and powers can be input, and an automatic comparison is performed. The percentage errors for average fluxes and powers for each node and/or for each bundle can be printed.
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8. RELATED AND AUXILIARY PROGRAMS

The code CUBAG is not strictly related to THT, but it can process the same input as for THT. CUBAG  is a neutron coarse mesh code written at AGN but based on a method and a program (PCUB) developed by B. Montagnini et al. at the University of Pisa. It is a 3-group method based on cubic expansion  of the flux inside each coarse mesh. The Montagnini method is a very general 3-dimensional and 3-group coarse mesh method to solve the neutron diffusion equation and can approach as much as required the  exaction diffusion solution. For this reason CUBAG has been very useful to produce reference 3-dimensional cases to test the accuracy of the THT results. At present, CUBAG can only treat homogeneous bundle constants and does not include discontinuity factors. The AGIP version CUBAG of PCUP was largely modified in the input-output  subroutines to accept the THT input, suited to treat LWR cases, and  to print the same output as THT.
THTMR is a small program to evaluate in advance the memory requirements for THT. It requires only 10 integer input parameters out of the first 25 integer input parameters for THT. These 10 parameters show up on the listing of the program.
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9. STATUS
Package ID Status date Status
NEA-0997/01 05-JUN-1985 Tested at NEADB
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10. REFERENCES:
NEA-0997/01, included references:
- E. Biscaretti and O. Chiovato:
  THT - An LWR 3-Dimensional Neutron Coarse Mesh Method Including
  Discontinuity Factors.  (July 1984)  (Unpublished)
- E. Biscaretti and O. Chiovato:
  THT - How to Use.   (September 1984)
- E. Biscaretti and O. Chiovato:
  ADICOM - A New Coarse Mesh Diffusion Method for LWRs.
  (In Italian)  Paper presented at the "Meeting on Reactor Physics"
  at the University of Bologna  (March 1983)
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11. MACHINE REQUIREMENTS

A problem with 768 nodes can be run on PRIME  750 in 200K bytes of main storage.
NEA-0997/01
With a container array of 100000 words, main storage requirements for running the test cases are 524K bytes on IBM 3081K.
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12. PROGRAMMING LANGUAGE(S) USED
Package ID Computer language
NEA-0997/01 FORTRAN-IV
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13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED:
NEA-0997/01
MVS-SP (IBM 3081K).
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14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS

THT is written in standard FORTRAN-IV. It has been developed on a PRIME 750 computer, but should run on any other computer supporting  standard FORTRAN-IV. To run THT on an IBM 370/168, only the time routines had to be replaced. The version that has been submitted to  the NEA Data Bank is ready to be implemented on IBM computers.
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15. NAME AND ESTABLISHMENT OF AUTHORS

     E. Biscaretti and O. Chiovato
     AgipNucleare
     Via Brenta 29
     20139 MILAN (Italy)
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16. MATERIAL AVAILABLE
NEA-0997/01
File name File description Records
NEA0997_01.003 INFORMATION FILE 47
NEA0997_01.004 THT SOURCE PROGRAM (FORTRAN) 2986
NEA0997_01.005 THT JCL TO EXECUTE THE TEST CASES 78
NEA0997_01.006 THT TEST CASE 1 INPUT DATA 25
NEA0997_01.007 THT TEST CASE 1 PRINTED OUTPUT 2558
NEA0997_01.008 THT TEST CASE 2 INPUT DATA 50
NEA0997_01.009 THT TEST CASE 2 PRINTED OUTPUT 1019
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17. CATEGORIES
  • C. Static Design Studies

Keywords: LWR reactors, coarse mesh, diffusion equations, fuel elements, neutron flux, three-dimensional.