Patent Number: 054266807
Section: claims

1. A tool for indicating that a control rod drive is coupled to an associated control rod in a nuclear reactor, comprising: first detecting means for detecting the state of a first position switch inside a position indicator probe of said control rod drive during removal of said control rod drive from a control rod drive housing; and  first indicating means for providing an indication in response to a signal from said first detecting means produced when said first position switch has a closed state.  second detecting means for detecting the state of a second position switch inside said position indicator probe during removal of said control rod drive; and  second indicating means for providing an indication in response to a signal from said second detecting means produced when said second position switch has a closed state.  switching means for providing an output signal in response to signals from said first and second detecting means produced when said first and second position switches both have open states during control rod drive removal; and  third indicating means for providing an indication in response to said output signal from said switching means. 2. The tool as defined in claim 1, further comprising a battery voltage source coupled to said first detecting means. 3. The tool as defined in claim 1, wherein said first indicating means is a light-emitting diode. 4. The tool as defined in claim 1, wherein said first position switch corresponds to an overtravel position of an index tube of said control rod drive, said overtravel position being attainable only if said control rod drive is uncoupled from said associated control rod. 5. The tool as defined in claim 5, further comprising: 6. The tool as defined in claim 5, wherein said second position switch corresponds to a "rod full out" position of said index tube, said "rod full out" position being attainable during control rod drive removal only if said control rod drive is coupled to said associated control rod. 7. The tool as defined in claim 5, wherein said first, and second indicating means are light-emitting diodes of different color. 8. The tool as defined in claim 5, further comprising a transparent housing enclosing said first and second indicating means. 9. The tool as defined in claim 5, further comprising: