Patent Number: 
Section: claims

1. A radiation-monitoring diagnostic hodoscope system for producing an approximate image of radiation-producing components within and below a pressure vessel of shutdown nuclear plant, said system comprising:A) at least one gamma-radiation-monitoring hodoscope unit adapted to detect gamma radiation in a limited substantially-straight narrow radiation beam of less than 50 degrees and in at least one specific gamma-energy range, said at least one hodoscope unit comprising:1) a collimating means adapted to produce said narrow radiation beam and2) at least one radiation detector adapted to produce electrical signals corresponding to intensities of gamma radiation in said at least one specific gamma energy range;B) a positioning means for positioning said at least one hodoscope unit so as to accumulate sufficient radiation data representing radiation intensity and gamma energies in a sufficiently large number of narrow radiation beams to create said approximate image of said gamma radiation-producing sources within and below said pressure vessel; andC) a computer processor programmed with an algorithm adapted to associate said gamma or neutron radiation data so as to produce said approximate image of said radiation-producing components. 2. The system as in claim 1 wherein the at least one specific gamma energy range is at least two specific gamma energy ranges. 3. The system as in claim 1 wherein the processor is programmed to produce an approximate one-dimensional image. 4. The system as in claim 1 wherein the processor is programmed to produce an approximate two-dimensional image. 5. The system as in claim 1 wherein the processor is programmed to produce an approximate three-dimensional reconstructed image. 6. The system as in claim 1 wherein said system also comprises at least one neutron-radiation monitoring hodoscope. 7. The system as in claim 1 wherein said systems comprises at least one neutron- and gamma-radiation-monitoring hodoscope. 8. The system as in claim 1 wherein the nuclear plant is a boiling-water nuclear plant. 9. The system as in claim 1 wherein the nuclear plant is a pressurized-water-cooled nuclear plant. 10. The system as in claim 1 wherein the nuclear plant is a single nuclear plant of a group of nuclear plants consisting of: gas-cooled nuclear plants, liquid-metal-cooled nuclear plants, and heavy-water-cooled nuclear plants. 11. The system as in claim 1 wherein the at least one radiation detector is at least one scintillator detector. 12. The system as in claim 11 wherein the at least one scintillator detector is a sodium-iodide detector comprising a NaI scintillator. 13. The system as in claim 11 wherein each of the at least one scintillator detector includes a photomultiplier tube and a preamplifier. 14. The system as in claim 11 wherein each of the at least one scintillator detector includes a single photomultiplier for detecting light photons. 15. The system as in claim 1 wherein the at least one radiation detector is a bismuth-germanate-oxide (BGO) detector. 16. The system as in claim 1 wherein the at least one radiation-monitoring hodoscope unit is a plurality of such hodoscope units mounted external to the pressure vessel and adapted to function as plant-operation-monitoring instruments, as well as a real-time monitoring function of a shutdown nuclear plant, as well as monitoring such a plant while undergoing damaging or potentially damaging transients. 17. The system as in claim 16, wherein the damaging or potentially damaging transient includes one of a group of transients consisting of an accidental or uncontrolled loss-of-coolant condition, including melting of the reactor fuel, and melt-through of nuclear fuel through the bottom of the pressure vessel. 18. The system as in claim 16 wherein a biological shield surrounds the pressure vessel and at least a portion of the plurality of hodoscope units are mounted in or within the biological shield and pointed toward the pressure vessel so as to monitor gamma radiation produced within the pressure vessel. 19. The system as in claim 18 wherein the at least one hodoscope unit mounted within the biological shield is pointed to a region below the pressure vessel so as to monitor radiation originating in the region below the pressure vessel. 20. The system as in claim 18 wherein the at least one hodoscope unit is pointed to the region below the pressure vessel. 21. The system as in claim 16 wherein data obtained from at least some of the hodoscopes units is stored for later analysis.