Patent Number: 051715163
Section: claims

1. A reactor core monitoring system, comprising: a reactor core having a plurality of fuel segments, each fuel segment comprising a plurality of fuel rods;  monitoring and controlling means for monitoring core state parameters of said reactor core and controlling operation of said reactor core;  memory means for storing nuclear constants in infinite lattice, a local power distribution in infinite lattice, and a R factor in infinite lattice obtained beforehand by a heterogeneous neutron flux diffusion calculation in infinite lattice;  reactor core performance determining means for determining a global power distribution on the basis of said core state parameters of said reactor core input from said monitoring means;  core neutron diffusion determining means for determining a deviation of a thermal neutron flux at a fuel rod position in a selected fuel segment and a thermal neutron flux in infinite lattice for said selected fuel segment on the basis of said nuclear constants stored in said memory means and said global power distribution determined by said reactor core performance determining means;  local power distribution determining means for determining a local power distribution in said selected fuel segment, on the basis of said thermal neutron flux deviation determined by said core neutron diffusion determining means and said local power distribution in infinite lattice stored in said memory means;  R factor correction means for determining a corrected R factor based on the R factor in infinite lattice stored in said memory means and the local power distribution in said selected fuel segment determined by said local power distribution determining means; and  critical power ratio determining means for determining a critical power ratio on the basis of the corrected R factor determined by said R factor correction means.  a first memory for storing said nuclear constants in infinite lattice;  a second memory for storing said local power distribution in infinite lattice; and  a third memory for storing said R factor in infinite lattice.  a reactor core status indicator for providing a status of said reactor core on the basis of said critical power ratio.  storing beforehand nuclear constants in infinite lattice, a local power distribution in infinite lattice and a R factor in infinite lattice obtained by calculating a heterogeneous neutron flux diffusion in infinite lattice;  monitoring core state parameters of said reactor core;  determining a global power distribution on the basis of said core state parameters from said reactor core;  determining a deviation between a thermal neutron flux at a fuel rod position in a selected fuel segment and a thermal neutron flux in infinite lattice for said selected fuel segment based on said stored nuclear constants and said global power distribution;  determining a local power distribution in said selected fuel segment based on said thermal neutron flux deviation and on said stored local power distribution in infinite lattice;  determining a corrected R factor based on said stored R factor in infinite lattice and the local power distribution in said selected fuel segment;  determining a critical power ratio based on the corrected R factor; and  controlling positions of control rods of said reactor core when said critical power ratio falls below a predetermined threshold.  producing a representation of a status of said fuel segments in said reactor core. 2. A reactor core monitoring system as recited in claim 1, wherein said memory means comprises: 3. A reactor core monitoring system as recited in claim 2, wherein said second memory stores the local power of all of said fuel rods in said selected fuel segment. 4. A reactor core monitoring system as recited in claim 2, wherein said second memory stores the local power of a representative fuel rod of largest local power in the fuel segments. 5. A reactor core monitoring system as recited in claim 3, wherein said R factor correction means determines said corrected R factor directly from the local power distribution obtained by said local power distribution calculating means. 6. A reactor core monitoring system as recited in claim 4, wherein said R factor correction means finds a corrected R factor based on the R factor in infinite lattice stored in said R factor storage area and on the local power of said selected fuel rod. 7. A reactor core monitoring system as recited in claim 1, further comprising: 8. A reactor core monitoring system as recited in claim 7, wherein said reactor core status indicator includes means for producing a display of said fuel assemblies in said reactor core on the basis of said critical power ratio. 9. A reactor core monitoring system as recited in claim 1, wherein said monitoring and controlling means comprises means for inserting a control rod into said reactor core when said critical power ratio falls below a predetermined threshold, thereby avoiding a boiling transition. 10. A reactor core monitoring method, said reactor core having a plurality of fuel assemblies each having a plurality of fuel segments, and each fuel segment having a plurality of fuel rods, comprising: 11. A reactor core monitoring method as recited in claim 10, further comprising: 12. A reactor core monitoring method as recited in claim 11, wherein said step of producing a representation of a status of said fuel segments in said reactor core includes producing a core map where said fuel segments are displayed based upon said critical power ratio. 13. A reactor core monitoring method as recited in claim 10, wherein said step of determining said corrected R factor comprises determining said R factor directly from said local power distribution. 14. A reactor core monitoring method as recited in claim 10, comprising storing said local power of all of said fuel rods in said selected fuel segment. 15. A reactor core monitoring method as recited in claim 10, comprising storing said local power of a representative fuel rod of largest local power in said fuel segment.