Patent Number: 
Section: description

A method for measuring the drop time of a control and/or a shutdown rod in a nuclear power plant is disclosed. To describe the method of the present invention, it is useful to refer again to FIG. 3 which illustrates a conventional rod position indication system. In the present invention, the drop time of the rod 12 in nuclear reactor 10 is measured with the coils 22 remaining energized. In the preferred embodiment, the drop time is measured for all of the rods 12 simultaneously in a single test. FIG. 4 illustrates the signal generated at the coils 22 which includes both the rod drop trace and the coil power for each rod 12. By applying a filter, the rod drop trace, such as that illustrated in FIG. 5, is separated from the coil power producing the same drop time results as would be obtained using the prior art method. Those skilled in the art will recognize that the filter can be either analog, digital, or a combination of both and be accomplished using either hardware or software. A number of filtering approaches may be used to isolate the rod drop trace from the coil power measurement. The filter may be a fixed filter based upon known characteristics of either the rod drop trace or the coil power or a variable or programmable filter using actual coil power measurements to separate the coil power from the rod drop trace. In the preferred embodiment, the actual coil power is continuously monitored for use by the filter. Using the rod drop trace of FIG. 5, the operator is able to check for the proper and timely insertion of the rods 12 into the reactor core 14. The total rod drop time consists of a first time period 26 which is the time taken for the rod 12 to travel from the top of the reactor core 14 to the bottom and a second time period 28 which is the time taken for the rod 12 to come to rest after bouncing in the dashpot 16 at the bottom of the reactor core 14. Once the rod drop trace has been isolated from the coil power, the drop time is calculated and a report is automatically generated which may include the date and time of the event, the measured signal of FIG. 4, the rod drop trace of FIG. 5, and the calculated drop time. The test data is stored for later use. The reporting capabilities include the ability to overlie one plot upon another. This allows a direct graphical comparison of previous drop time measurements with instant measurements or of one rod 12 with another within a single test. Accordingly, a method for measuring the drop time of the control and shutdown rods in a nuclear power plant has been disclosed. The measurement is taken while the coils encircling the rod housing remain energized and allows the drop time of all control and shutdown rods to be measured together in one test when the rods are dropped together into the reactor simultaneously. The method allows drop time measurements to be taken automatically in the event of an actual mishap or whenever the reactor is automatically shut down or scrammed (tripped). Additionally, unnecessary wear and tear on the switchgears controlling the coil power is avoided by eliminating the need to turn of the coil power. Finally, test results are available in real time providing the operator with an indication of the rod position while the test is in progress. Also, there is no need for a lengthy procedure to turn the power off to the rod position indication coils and the test can be performed on as many rods as desired at one time. This will reduce the test time which is of much interest in nuclear power plants from an economic standpoint. While a preferred embodiment has been shown and described, it will be understood that it is not intended to limit the disclosure, but rather it is intended to cover all modifications and alternate methods falling within the spirit and the scope of the invention as defined in the appended claims