Patent Number: 
Section: claims

1. A method of controlling a nuclear reactor shutdown system, the method comprising:detecting a fission rate within a core of a nuclear reactor with a sensor, the sensor providing an output signal corresponding to the fission rate;determining a measured flux signal from the output signal with a signal conditioning module, the measured flux signal corresponding to a percentage of a reactor power;calculating a first derivative of the measured flux signal with a rate module, the rate module outputting a rate signal corresponding to a percentage of reactor power per unit of time;calculating a flux rate difference signal based on the rate signal and a bias value;applying a gain to the flux rate difference signal to produce a rate-based signal component;summing the rate-based signal component and the measured flux signal to produce a rate-assisted flux signal corresponding to a percentage of a reactor power;comparing the rate-assisted flux signal to a trip setpoint with a comparator module, the comparator module generating a trip signal if the rate-assisted flux signal is greater than the trip setpoint; andintroducing one selected from a group consisting of a neutron-absorbing solution and neutron-absorbing rods into the core of the reactor in response to the trip signal being generated,wherein determining the measured flux signal includes determining a linear measured flux single from the linear output signal with the signal conditioning module, the linear measured flux signal corresponding to a linear percentage of a reactor power. 2. The method of claim 1, wherein the sensor includes an in-core flux detector. 3. The method of claim 1, further comprising filtering the rate signal with a noise filter module prior to biasing the rate signal. 4. The method of claim 3, wherein the act of filtering the rate signal is performed with a second order low pass noise filter. 5. The method of claim 1, wherein the trip signal is a first trip signal associated with a first shutdown system logic channel, and wherein introducing the neutron-absorbing rods into the core of the reactor occurs in response to at least the first trip signal and a second trip signal associated with a second shutdown system logic channel. 6. The method of claim 1, wherein the act of calculating a flux rate difference signal includes comparing the rate signal with a bias value. 7. The method of claim 1, wherein applying the gain to the flux rate difference signal includes applying the gain to the flux rate difference signal when the flux rate difference has a positive value. 8. The method of claim 1, wherein the gain is not applied when the flux rate difference signal has a negative value. 9. A shutdown system for a nuclear reactor having a reactor core, the system comprising:a sensor associated with the reactor core and operable to detect a fission rate within the core and generate an output signal related to the fission rate;a signal conditioning module operable to generate a measured flux signal based on the output signal, the measured flux signal corresponding to a percentage of a reactor power of the nuclear reactor;a shutdown system trip controller includinga rate module operable to generate a rate signal from the measured flux signal, the rate signal corresponding to a percentage of the reactor power of the nuclear reactor per unit of time;a comparator module operable to compare the rate signal with a bias value, the comparator module generating a flux rate difference signal based on the comparison;an amplifier module operable to apply a gain to the flux rate difference signal to produce a rate-based signal component, anda summing module operable to apply the rate-based signal component to the measured flux signal to produce a rate-assisted flux signal,wherein the comparator module is further operable to compare the rate-assisted flux signal to a trip setpoint, the comparator module generating a trip signal if the rate-assisted flux signal is greater than the trip setpoint; anda shutdown apparatus operable to absorb neutrons within the reactor core upon receipt of the trip signal,wherein the measured flux signal is a linear measured flux signal based on a linear output signal, the linear measured flux signal corresponding to linear percentage of reactor power of the nuclear reactor. 10. The shutdown system of claim 9, wherein the shutdown apparatus includes neutron-absorbing rods. 11. The shutdown system of claim 9, wherein the shutdown apparatus includes a neutron-absorbing solution. 12. The shutdown system of claim 9, wherein the sensor includes an in-core flux detector. 13. The shutdown system of claim 9, wherein the comparator module operable is further configured to determine whether the flux rate difference signal is positive. 14. The shutdown system of claim 9, wherein the rate module is operable to generate the rate signal by calculating a first derivative of the measured flux signal and wherein the shutdown system trip controller further includes a second-order, low pass filter for filtering noise in the rate signal. 15. A controller for producing a nuclear reactor shutdown system trip signal in response to a sensor signal, the controller comprising:a signal conditioning module receiving the sensor signal and outputting a measured flux signal;a rate module operable to generate a rate signal from the measured flux signal, the rate signal corresponding to a percentage of reactor power of the nuclear reactor per unit of time;a comparator module operable to compare the rate signal with a bias value, the comparator module generating a flux rate difference signal;an amplifier module operable to apply a gain to the flux rate difference signal to produce a rate-based signal component; anda summing module operable to apply the rate-based signal component to the measured flux signal to produce a rate-assisted flux signal;wherein the comparator module is further operable to compare the rate-assisted flux signal to a trip setpoint and generate a trip signal, andwherein one selected from a group consisting of a neutron-absorbing solution and neutron-absorbing rods is inserted into the core of the reactor in response to the trip signal being generated,wherein the measured flux signal is a linear measured flux signal. 16. The controller of claim 15, wherein the controller includes a micro-processor. 17. The controller of claim 15, wherein the controller includes a second-order, low pass filter operable to filter noise in the rate signal.