Patent Number: 
Section: claims

1. A method for at least one of operating and building a nuclear reactor core comprising:modelizing a nuclear reactor core by performing the computer implemented steps of:partitioning, by a computer processor, the core in cubes to constitute nodes of a grid for computer implemented calculation,splitting, by the computer processor, the cubes into a first category and a second category, each cube of the first category being adjacent only to cubes from the second category so that the first category and second category of cubes are oriented in a checkerboard pattern with the first category of cubes and the second category of cubes alternating in a two-dimensional representation,ordering, by the computer processor, the cubes of the first category and then the cubes of the second category, andcalculating, by the computer processor, neutron flux and/or thermohydraulics parameters by using an iterative solving procedure of at least one linear system, components of an iterant of the linear system constituting the neutron flux and/or thermohydraulics parameters to be calculated, wherein, during the iterative solving procedure, calculations are conducted on the cubes of the first category then on the cubes of the second category; andat least one of operating and building the nuclear reactor core on the basis of the calculated neutron flux and/or the calculated thermohydraulics parameters,wherein the iterative solving procedure is conducted only on the cubes of the first category thus calculating the components of the iterant corresponding to the cubes of the first category, and then the components of the iterant corresponding to the cubes of the second category are calculated on the basis of the components of the iterant corresponding to cubes of the first category,wherein the linear system to be solved for the first category of cubes is preconditioned to amount to:                    A        _            red        ⁢                  x        _            red        =                    b        _        _            red        ⁢                  ⁢    with    ⁢                  ⁢          {                                                                                    A                  _                                red                            =                              1                -                                  A                  ND                  2                                                                                                                                                              b                    _                    _                                    red                                =                                                                            b                      _                                        red                                    -                                                            A                      ND                                        ⁢                                                                  b                        _                                            black                                                                                  ,                                          wherein xred designates the components of the iterant corresponding to the cubes of the first category,AND designates a non-diagonal matrix coupling cubes of the first category with cubes of the second category, and bred and bblack designates source factors. 2. The method as recited in claim 1 wherein the iteration of the solving procedure amounts to:         {                                                                      x                _                            red                              (                                  n                  +                  1                                )                                      =                                                            b                  _                                red                            -                                                A                  ND                                ⁢                                                      x                    _                                    black                                      (                    n                    )                                                                                                                                                      x                _                            black                              (                                  n                  +                  1                                )                                      =                                                            b                  _                                black                            -                                                A                  ND                                ⁢                                                      x                    _                                    red                                      (                                          n                      +                      1                                        )                                                                                          wherein xblack designates the components of the iterant corresponding to the cubes of the second category. 3. The method as recited in claim 1 where the iteration of the solving procedure amounts to:dred(n+1)={circumflex over (M)}D−1└λ(n){circumflex over (F)}dred(n)−{circumflex over (M)}NDdblack(n)+Qred┘dblack(n+1)={circumflex over (M)}D−1[λ(n){circumflex over (F)}dblack(n)−{circumflex over (M)}NDdred(n+1)+Qblack]wherein dred designates the components of the iterant corresponding to the cubes of the first category,dblack designates the components of the iterant corresponding to the cubes of the second category,{circumflex over (M)}ND and {circumflex over (M)}D are respectively a diagonal part and a non-diagonal part of a loss migration operator. 4. The method as recited in claim 1 wherein a convergence of the solving procedure is monitored through a residual vector of the linear system, the residual vector being defined as:rred= bred−Āredxred. 5. The method as recited in claim 4 wherein the convergence of the solving procedure is monitored through a maximum absolute value of the components of the residual vector, the maximum being defined as:rmax(i)=maxj=1, . . . , N|rj(i)|. 6. The method as recited in claim 1 wherein the iterative solving procedure is a Gauss-Seidel procedure. 7. The method as recited in claim 6 wherein the Gauss-Seidel procedure is combined with a systematic Successive Over-Relaxation measure. 8. The method as recited in claim 1 wherein the iterative solving procedure is a Conjugate Gradient procedure. 9. The method as recited in claim 1 wherein the iterative solving procedure is a Bi-Conjugate Gradient Stabilized procedure. 10. The method as recited in claim 1 wherein the computer processor includes parallel processors, the steps of partitioning, splitting, ordering and calculating being performed by the parallel processors. 11. A method for at least one of operating and building a nuclear reactor core comprising:modelizing a nuclear reactor core by performing the computer implemented steps of:partitioning, by a computer processor, the core in cubes to constitute nodes of a grid for computer implemented calculation,splitting, by the computer processor, the cubes into a first category and a second category, each cube of the first category being adjacent only to cubes from the second category so that the first category and second category of cubes are oriented in a checkerboard pattern with the first category of cubes and the second category of cubes alternating in a two-dimensional representation,ordering, by the computer processor, the cubes of the first category and then the cubes of the second category, andcalculating, by the computer processor, neutron flux and/or thermohydraulics parameters by using an iterative solving procedure of an eigensystem, components of an iterant of the eigensystem constituting the neutron flux and/or thermohydraulics parameters to be calculated, wherein, during the iterative solving procedure, calculations are conducted on the cubes of the first category then on the cubes of the second category; andat least one of operating and building the nuclear reactor core on the basis of the calculated neutron flux and/or the calculated thermohydraulics parameters,wherein the iterative solving procedure is conducted only on the cubes of the first category thus calculating the components of the iterant corresponding to the cubes of the first category, and then the components of the iterant corresponding to the cubes of the second category are calculated on the basis of the components of the iterant corresponding to cubes of the first category,wherein the eigensystem_to be solved for the first category of cubes is preconditioned to amount to:                    Θ        ~            red        ⁢                  d        _            red        =                    s        _        ~            red        ⁢                  ⁢    with    ⁢                  ⁢          {                                                                                    Θ                  ~                                red                            =                                                1                  ^                                -                                                      [                                                                                            (                                                                                                                    M                                ^                                                            D                                                        -                                                          μ                              ⁢                                                              F                                ^                                                                                                              )                                                                          -                          1                                                                    ⁢                                                                        M                          ^                                                ND                                                              ]                                    2                                                                                                                                                              s                    _                    ~                                    red                                =                                                                            s                      _                                        red                                    -                                                                                    (                                                                                                            M                              ^                                                        D                                                    -                                                      μ                            ⁢                                                          F                              ^                                                                                                      )                                                                    -                        1                                                              ⁢                                                                                                                        M                            ^                                                    ND                                                ⁡                                                  (                                                                                                                    M                                ^                                                            D                                                        -                                                          μ                              ⁢                                                              F                                ^                                                                                                              )                                                                                            -                        1                                                              ⁢                                                                  s                        _                                            black                                                                                  ,                                          {circumflex over (M)}ND and {circumflex over (M)}D are respectively a diagonal part and a non-diagonal part of a loss migration operatorμ is a shift, and{circumflex over (F)}^is a production operator. 12. The method as recited in claim 11 wherein the iteration of the solving procedure amounts to:         {                                                                      x                _                            red                              (                                  n                  +                  1                                )                                      =                                                            b                  _                                red                            -                                                A                  ND                                ⁢                                                      x                    _                                    black                                      (                    n                    )                                                                                                                                                      x                _                            black                              (                                  n                  +                  1                                )                                      =                                                            b                  _                                black                            -                                                A                  ND                                ⁢                                                      x                    _                                    red                                      (                                          n                      +                      1                                        )                                                                                          wherein xred designates the components of the iterant corresponding to the cubes of the first category,xblack designates the components of the iterant corresponding to the cubes of the second category,AND designates a non-diagonal matrix coupling cubes of the first category with cubes of the second category, and bred and bblack designates source factors. 13. The method as recited in claim 11 where the iteration of the solving procedure amounts to :dred(n+1)={circumflex over (M)}D−1└λ(n){circumflex over (F)}dred(n)−{circumflex over (M)}NDdblack(n)+Qred┘dblack(n+1)={circumflex over (M)}D−1[λ(n){circumflex over (F)}dblack(n)−{circumflex over (M)}NDdred(n+1)+Qblack]wherein dred designates the components of the iterant corresponding to the cubes of the first category,dblack designates the components of the iterant corresponding to the cubes of the second category,{circumflex over (M)}ND and {circumflex over (M)}D are respectively a diagonal part and a non-diagonal part of a loss migration operator. 14. The method as recited in claim 11 wherein the iterative solving procedure is a Gauss-Seidel procedure. 15. The method as recited in claim 14 wherein the Gauss-Seidel procedure is combined with a systematic Successive Over-Relaxation measure. 16. The method as recited in claim 11 wherein the iterative solving procedure is a Conjugate Gradient procedure. 17. The method as recited in claim 11 wherein the iterative solving procedure is a Bi-Conjugate Gradient Stabilized procedure. 18. The method as recited in claim 11 wherein the computer processor includes parallel processors, the steps of partitioning, splitting, ordering and calculating being performed by the parallel processors.