NAME OR DESIGNATION OF PROGRAM, COMPUTER, NATURE OF PHYSICAL PROBLEM SOLVED, 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 OR MONITOR UNDER WHICH PROGRAM IS EXECUTED, ANY OTHER PROGRAMMING OR OPERATING INFORMATION OR RESTRICTIONS, NAME AND ESTABLISHMENT OF AUTHOR, MATERIAL, CATEGORIES

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Program name | Package id | Status | Status date |
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REFLOS | NEA-0262/01 | Tested | 01-MAR-1969 |

Machines used:

Package ID | Orig. computer | Test computer |
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NEA-0262/01 | IBM 360 series | IBM 360 series |

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3. NATURE OF PHYSICAL PROBLEM SOLVED

REFLOS is a programme for the evaluation of fuel-loading schemes in heavy water moderated reactors. The problems involved in this study are:

a) Burn-up calculation for the reactor cell.

b) Determination of reactivity behaviour, power distribution, attainable burn-up for both the running-in period and the equilibrium of a 3-dimensional heterogeneous reactor model; investigation of radial fuel movement schemes.

c) Evaluation of mass flows of heavy atoms through the reactor and fuel cycle costs for the running-in, the equilibrium, and the shut down of a power reactor.

If the subroutine for treating the reactor cell were replaced by a suitable routine, other reactors with weakly absorbing moderators could be analyzed.

REFLOS is a programme for the evaluation of fuel-loading schemes in heavy water moderated reactors. The problems involved in this study are:

a) Burn-up calculation for the reactor cell.

b) Determination of reactivity behaviour, power distribution, attainable burn-up for both the running-in period and the equilibrium of a 3-dimensional heterogeneous reactor model; investigation of radial fuel movement schemes.

c) Evaluation of mass flows of heavy atoms through the reactor and fuel cycle costs for the running-in, the equilibrium, and the shut down of a power reactor.

If the subroutine for treating the reactor cell were replaced by a suitable routine, other reactors with weakly absorbing moderators could be analyzed.

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4. METHOD OF SOLUTION

Nuclear constants and isotopic compositions of the different fuels in the reactor are calculated by the cell-burn-up programme and tabulated as functions of the burn-up rate (MWD/T). Starting from a known state of the reactor, the 3-dimensional heterogeneous reactor programme (applying an extension of the technique of Feinberg and Galanin) calculates reactivity and neutron flux distribution using one thermal and one or two fast neutron groups. After a given irradiation time, the new state of the reactor is determined, and new nuclear constants are assigned to the various defined locations in the reactor.

Reloading of fuel may occur if the prescribed life of the reactor is reached or if the effective multiplication factor or the power form factor falls below a specified level. The scheme of reloading to be carried out is specified by a load vector, giving the number of channels to be discharged, the kind of movement from one to another channel and the type of fresh fuel to be charged for each single reloading event. After having determined the core states characterizing the equilibrium period, and having decided the fuel reloading scheme for the running-in period of the reactor life, the fuel cycle costs are evaluated following proposals of the EURATOM Economic Handbook.

Nuclear constants and isotopic compositions of the different fuels in the reactor are calculated by the cell-burn-up programme and tabulated as functions of the burn-up rate (MWD/T). Starting from a known state of the reactor, the 3-dimensional heterogeneous reactor programme (applying an extension of the technique of Feinberg and Galanin) calculates reactivity and neutron flux distribution using one thermal and one or two fast neutron groups. After a given irradiation time, the new state of the reactor is determined, and new nuclear constants are assigned to the various defined locations in the reactor.

Reloading of fuel may occur if the prescribed life of the reactor is reached or if the effective multiplication factor or the power form factor falls below a specified level. The scheme of reloading to be carried out is specified by a load vector, giving the number of channels to be discharged, the kind of movement from one to another channel and the type of fresh fuel to be charged for each single reloading event. After having determined the core states characterizing the equilibrium period, and having decided the fuel reloading scheme for the running-in period of the reactor life, the fuel cycle costs are evaluated following proposals of the EURATOM Economic Handbook.

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5. RESTRICTIONS ON THE COMPLEXITY OF THE PROBLEM

Maximum number of groups of channels having rotation symmetry is 60.

Maximum number of groups of channels having specular symmetry is 120.

Maximum number of harmonics for the approximation of the axial flux distribution is 19.

Highest order of Bessel functions for the approximation of the radial flux distribution is 12.

Maximum number of axial pieces of a channel with possibly different neutronic properties is 20.

Maximum number of neutron groups: two fast, one thermal.

Maximum number of different types of channels in the reactor is 10. Maximum number of burn-up steps characterizing one type of channel is 50.

Maximum number of groups of channels having rotation symmetry is 60.

Maximum number of groups of channels having specular symmetry is 120.

Maximum number of harmonics for the approximation of the axial flux distribution is 19.

Highest order of Bessel functions for the approximation of the radial flux distribution is 12.

Maximum number of axial pieces of a channel with possibly different neutronic properties is 20.

Maximum number of neutron groups: two fast, one thermal.

Maximum number of different types of channels in the reactor is 10. Maximum number of burn-up steps characterizing one type of channel is 50.

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7. UNUSUAL FEATURES OF THE PROGRAM

The only moderator considered is heavy water.

Xenon is assumed to be in equilibrium during the burn-up process.

Reflector and moderator are assumed to have the same macroscopic neutron cross-sections.

Spatial Xenon and temperature distributions within the reactor core are not considered.

The channels of the reactor are treated as line sources and line sinks for neutrons. Thus, their finite size is not taken into account. As a consequence, the channels must not be too large nor too closely packed within the moderator.

The programme does not take into account the condition that the fast flux vanishes at the extrapolated boundary of the radial reflector.The error thereby introduced is negligible if the radial reflector is greater or equal to 4*SQRT(tau), where tau is the slowing down area of the moderator.

The slowing down properties of the materials within the channel are not treated separately but must be included in a suitable way by modifying the slowing down properties of the moderator.

The only moderator considered is heavy water.

Xenon is assumed to be in equilibrium during the burn-up process.

Reflector and moderator are assumed to have the same macroscopic neutron cross-sections.

Spatial Xenon and temperature distributions within the reactor core are not considered.

The channels of the reactor are treated as line sources and line sinks for neutrons. Thus, their finite size is not taken into account. As a consequence, the channels must not be too large nor too closely packed within the moderator.

The programme does not take into account the condition that the fast flux vanishes at the extrapolated boundary of the radial reflector.The error thereby introduced is negligible if the radial reflector is greater or equal to 4*SQRT(tau), where tau is the slowing down area of the moderator.

The slowing down properties of the materials within the channel are not treated separately but must be included in a suitable way by modifying the slowing down properties of the moderator.

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NEA-0262/01

File name | File description | Records |
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NEA0262_01.001 | SOURCE IBM 360/65 | 7023 |

NEA0262_01.002 | OVERLAY CARDS & INPUT DATA | 220 |

NEA0262_01.003 | PROGRAM TO PREPARE THE LIBRARY | 56 |

NEA0262_01.004 | INPUT DATA FOR LIBRARY PROGRAM | 1050 |

NEA0262_01.005 | REFLOS OUTPUT | 1205 |

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- B. Spectrum Calculations, Generation of Group Constants and Cell Problems
- C. Static Design Studies
- D. Depletion, Fuel Management, Cost Analysis, and Power Plant Economics

Keywords: burnup, cost, distribution, fuel cycle, fuel management, heavy water moderated reactors, heterogeneous reactors, neutron flux, power distribution, reactivity, three-dimensional.