Patent Number: 
Section: claims

1. A method for measuring the drop time of at least one control or shutdown rod in a nuclear reactor, said method comprising the steps of: (a) releasing a rod from a resting position above a nuclear reactor core;  (b) guiding the rod through a plurality of energized coils;  (c) recording a signal present at the plurality of energized coils, said signal being recorded from said step of releasing a rod from a resting position above a nuclear reactor core until the rod comes to a resting position within the reactor core, said signal including both a coil power measurement and a rod drop trace, said coil power measurement including information about the instantaneous power of the plurality of energized coils, said rod drop trace including information about the electrical signal induced in the plurality of energized coils by the rod; and  (d) filtering said signal to isolate the rod drop trace from coil power measurement to identify the drop time. 2. The method of  claim 1  further comprising the step of calculating a rod drop time from the rod drop trace. claim 1 3. The method of  claim 1  further comprising the step of applying a filter to isolate the rod drop trace from the coil power measurement to identify the drop time. claim 1 4. The method of  claim 1  wherein the step of releasing the rod from a resting position above a nuclear reactor core further includes the step of releasing a plurality of rods simultaneously from a resting position above a nuclear reactor core. claim 1 5. The method of  claim 4  further comprising the step of overlaying one rod drop trace obtained from one of the plurality of rods with another rod drop trace obtained from another of the plurality of rods. claim 4 6. The method of  claim 1  further comprising the step of storing at least the rod drop trace obtained during said step of filtering said signal to isolate the rod drop trace from the coil the power measurement to identify the drop time. claim 1 7. The method of  claim 6  wherein said step of storing at least the rod drop trace obtained during said step of filtering said signal to isolate the rod drop trace from coil power measurement to identify the drop time includes the step of storing said signal obtained during said step of filtering said signal to isolate the rod drop trace from the coil power measurement to identify the drop time. claim 6 8. The method of  claim 6  wherein said step of storing at least the rod drop trace obtained during said step of filtering said signal to isolate the rod drop trace from coil power measurement to identify the drop time includes the step of storing the coil power measurement obtained during said step of filtering said signal to isolate the rod drop trace from the coil power measurement to identify the drop time. claim 6 9. The method of  claim 6  further comprising the step of overlaying one rod drop trace with another rod drop trace from said step of storing at least the rod drop trace obtained during said step of filtering said signal to isolate the rod drop trace from the coil power measurement to identify the drop time. claim 6 10. A method for measuring a drop time of control and shutdown rods in a nuclear reactor having a coil-based rod position indication system, said method comprising the steps of: (a) releasing a rod from a resting position above a nuclear reactor core;  (b) sensing a coil current from a coil-based rod position indication system;  (c) separating an induced current representing a rod drop position trace from said coil current; and  (d) calculating a rod drop time from said induced current. 11. A method for measuring a rod drop time of a rod in a nuclear reactor core having a coil-based rod position indication system, said method comprising the steps of: (a) sensing a coil current from a coil-based rod position indication system;  (b) separating an induced current from said coil current;  (c) determining a start time of a rod drop event from said induced current;  (d) determining a first stop time of the rod drop event from said induced current, said first stop time representing a time at which the control rod initially reaches a fully inserted position within a reactor core; and  (e) determining a second stop time of the rod drop event from said induced current, said first stop time representing a time at which the control rod comes to a resting position within the reactor core. 12. A method for measuring a drop time of a rod in a nuclear reactor core having a coil-based rod position indication system, said method comprising the steps of: (a) sensing a coil current from a coil-based rod position indication system;  (b) separating an induced current representing a rod drop position trace from said coil current;  (c) determining from said induced current a first time period representing a period of time for the rod to travel from a top position in a reactor core to a bottom position in the reactor core; and  (d) determining from said induced current a second time period representing a period of time for the rod to come to rest after reaching the bottom position in the reactor core.