Patent Number: 
Section: claims

1. A method for monitoring a nuclear reactor for a shutdown condition, the method comprising:detecting gamma radiation within a core of the nuclear reactor utilizing one or more self-powered detectors located within the core of the nuclear reactor;outputting, by the one or more self-powered detectors, a current based on the detected gamma radiation;generating a current value of Keff based on the outputted current in accordance with the following equation;            K      eff        ⁡          (      t      )        =      1    -                                        f            ⁡                          (                              t                Ref                            )                                ⁢                      I            Ref                                                f            ⁡                          (              t              )                                ⁢                      I            ⁡                          (              t              )                                          ⁢              (                  1          -                      K            Ref                          )            wherein tRef is a time after shutdown of the nuclear reactor, t is a time after tRef, wherein a ratio of f(tRef)/f(t) is a fission product correction factor based on a time dependent fission product gamma decay relation, I(t) is an output current of the one or more self-powered detectors at time t, IRef is an output current of the one or more self-powered detectors at time tRef, and KRef is a neutron multiplication factor at time tRef; monitoring the current value of Keff; and based on the monitoring of the current value of Keff, adding Boron to coolant in the nuclear reactor when an undesirable change in Keff is detected. 2. The method of claim 1, wherein the one or more self-powered detectors comprise a neutron detector comprising rhodium. 3. The method of claim 1, wherein the one or more self-powered detectors comprise a gamma radiation detector that is platinum-based. 4. The method of claim 1, wherein monitoring the current value of Keff is performed continuously during a shutdown period of the nuclear reactor. 5. The method of claim 1, further comprising:monitoring fission events within the core in a source range utilizing a source range ex-core detector positioned outside of the core, wherein the current value of Keff is generated without input from the source range ex-core detector. 6. The method of claim 1, wherein the adding boron comprises adding boric acid to the coolant. 7. A method for monitoring a nuclear reactor for a shutdown condition, the method comprising:detecting gamma radiation within a core of the nuclear reactor utilizing one or more self-powered detectors located within the core of the nuclear reactor;outputting, by the one or more self-powered detectors, a current based on the detected gamma radiation; adjusting the outputted current to remove influences of fission product gamma radiation using a time dependent analytical correction factor;monitoring the adjusted current; and based on the monitoring of the adjusted current, adding Boron to coolant in the nuclear reactor when an undesirable change in the adjusted current is detected. 8. The method of claim 7, wherein the one or more self-powered detectors comprise a neutron detector comprising rhodium. 9. The method of claim 7, wherein the one or more self-powered detectors comprise a gamma radiation detector that is platinum-based. 10. The method of claim 7, wherein monitoring the adjusted current is performed continuously during a shutdown period of the nuclear reactor. 11. The method of claim 7, further comprisingmonitoring fission events within the core in a source range utilizing a source range ex-core detector positioned outside of the core, wherein the outputted current is adjusted without input from the source range ex-core detector. 12. The method of claim 7, wherein adding boron comprises adding boric acid to the coolant.