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NEA-0591 BEVE.

BEVE, Isotope Buildup in LWR Fuel Pin with Self-Shielding in Pellet

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1. NAME OR DESIGNATION OF PROGRAM:  BEVE. (Burnup Eterogeneo dei VEleni - Heterogeneous burnup of poisons.)
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2. COMPUTERS
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Program name Package id Status Status date
BEVE NEA-0591/01 Tested 17-JUL-1987

Machines used:

Package ID Orig. computer Test computer
NEA-0591/01 IBM 370 series IBM 3084
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3. DESCRIPTION OF PROBLEM OR FUNCTION

The BEVE code calculates the isotopic evolution of a LWR fuel pin taking into account inter- related space and energy self-shielding effects within the pellet.
The code is in particular devoted to calculate Gadolinium depletion  in burnable poison cells. BEVE is part of the BURNY-BEVE code system for fuel/poison depletion.
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4. METHOD OF SOLUTION

Multigroup integral transport theory has been chosen as the best tool to handle the evaluation of Gd behaviour in  LWRs. Use is made of a modified version of the THERMOS code to ob- tain all the necessary spectral and geometrical detail, taking into  account also the radial dependence of the poison concentration due to the radial dependence of spectrum and flux level within the pin (a different spectrum is evaluated in each mesh point). At each ir-  radiation step, the space and energy neutron distribution is calcu-  lated, the burnup of the isotopes in the fuel is consequently calcu- lated and the procedure is automatically repeated for the following  time step and so on. The computer time is reduced since at each irradiation step the neutron distribution of the previous step is used as a guess for the convergence procedure.



In the transport calculations at each irradiation step the conver- gence is checked with respect to the mesh where the absorption rate  as evaluated at the previous irradiation step is maximum; while at beginning of life this mesh is obviously the outermost one; as irradiation proceeds this most significant mesh moves toward the center.



The main output of the BEVE routine consists of the thermal macro- scopic cross sections of the poisoned cell versus burnup to be used  for the computation of the fuel element in x,y geometry.



One BEVE run must be performed for each type of poisoned cell in the element. Each BEVE run supplies for each irradiation step the following information:



-  The value of the fluence in the coupling region.

-  The equivalent natural Gd concentration.

- The cell macroscopic constants for both energy schemes in BURNY    (i.e. one or two thermal groups).



When calculating the fuel element in x,y geometry, if a poisoned cell is present, BURNY identifies what poison cell type it belongs to and then reads in the associated constants from the correspond- ing table supplied by BEVE.



In the thermal range two different cross section libraries are available, set up by the BELIB code and including Gd-155 and 157 and Gd-Nat. One uses a 22 group scheme and the other 30 groups with the standard THERMOS group structure.



In the epithermal and fast range the FORM code was used to cal- culate the group constants.



The two isotopes Gd-155 and 157 are assumed to burn independently (i.e. Gd-156 absorption neglected).



It should be stressed that BEVE provides information on the be- haviour of highly absorbing burnable poison in the thermal range.

Although some epithermal and fast effects are accounted for in the depletion by BEVE, the epithermal constants of the poisoned cell are not calculated by BEVE, but by BURNY.
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5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

Up to 22 mesh inter- vals may be used in the geometrical description of the poisoned cell and of the surrounding coupling region representing the standard fuel cells.

A maximum of 30 thermal energy groups may be used.
3 fissile isotopes may be considered in the depletion - U235, Pu239     and 241.
Max. number of isotopes that may be burnt is 12.
Max. number of regions in which burnup is calculated is 13.
Max. number of isotopes included in the evaluation of the transport     cross section is 16.
Max. number of mixtures is 20.
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6. TYPICAL RUNNING TIME

A typical running time is about 6 secs. for each time step on the 370/168 computer.
NEA-0591/01
NEA-DB ran the test case included in this package on an IBM 3081 computer in 48 seconds of CPU time.
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7. UNUSUAL FEATURES OF THE PROGRAM:  Detailed treatment of poison depletion.
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8. RELATED AND AUXILIARY PROGRAMS

BEVE is part of the BURNY/BEVE code system. The routines that make up BURNY are: RIBOT, STRIF, ROCCE, CRUCOR, EXTERMINATOR and MEDIA. The collision probability method used by BEVE as well as some of the input is based on the THERMOS code. The BELIB code is used to set up the cross section libraries for the thermal energy region. The FORM code is used to calculate the epithermal and fast group constants.

Each run of the BURNY/BEVE system supplies the local power distribu- tions (pin by pin) and the isotopic fuel composition and nuclear constants of each element as a function of burn-up. These constants  are given as input to the three-dimensional core simulator code, BACONE.
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9. STATUS
Package ID Status date Status
NEA-0591/01 17-JUL-1987 Tested at NEADB
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10. REFERENCES

- F. Pistella:
  "The CNEN Calculation Method for Neutronic Design of LWR Cores:
  Reactivity and Power Distributions on x,y Geometry Versus Burnup"
  CNEN RT/FI(75)14 (1975).
NEA-0591/01, included references:
- G.P. Cali (Editor):
  The BEVE Code - How to Use
  NDB/102/06 (November 1979).
- F. Pistella:
  The CNEN Calculation Method for Neutronic Design of LWR Cores
  Reactivity and Power Distributions on x,y Geometry Vs. Burnup.
  Part 1: The Physical Model of the BURNY-BEVE Code System
  Extract from CNEN RT/FI(75)14, pp. 71-94 (1975).
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11. MACHINE REQUIREMENTS

Only the basic system configuration is requested and a region of about 30 K bytes is utilised.
NEA-0591/01
316K bytes of main storage are required on IBM 3081 to  run the test case.
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12. PROGRAMMING LANGUAGE(S) USED
Package ID Computer language
NEA-0591/01 FORTRAN-IV
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13. OPERATING SYSTEM UNDER WHICH PROGRAM IS EXECUTED

The standard configuration of the IBM OS VS1 or VS2 is sufficient but one addi- tional input library is necessary.
NEA-0591/01
MVS (IBM 3081).
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14. OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS:
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15. NAME AND ESTABLISHMENT OF AUTHOR

          F. Pistella
          CNEN (Dipartimento Reattori Termici)
          C.S.N. Casaccia
          Via Anguillarese Km 1 + 300
          00100 Rome
          Italy.
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16. MATERIAL AVAILABLE
NEA-0591/01
File name File description Records
NEA0591_01.001 BEVE Information File 48
NEA0591_01.002 BEVE Source Fortran 1832
NEA0591_01.003 BEVE Sample case input data 71
NEA0591_01.004 BEVE Sample case printed output 2880
NEA0591_01.005 BEVE Cross Section binary library 23
NEA0591_01.006 BEVE Job control 6
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17. CATEGORIES
  • D. Depletion, Fuel Management, Cost Analysis, and Power Plant Economics

Keywords: LWR reactors, burnup, cross sections, depletion, fuel elements, geometry, isotopes, multigroup, poisoning, self-shielding, transport theory, x-y.