Do you step control rods to the end-of-travel to verify rod position for a Rod Position Indication outside of limits? If not, what method is used to verify rod position prior to adjusting indication?
Background:
Point Beach has two control rods that exhibit unusual rod position indication variations. We have shown rod position indication takes step change swings (+/- 20 steps) following control rod shroud fan temperature changes. We have moved the control rod drive shaft of these two rods from bank D control banks to shutdown banks, and the problem has followed the drive shaft. Most other rod position indications vary by +/- 5 steps, with no large "swings." Research into why these two drive shafts exhibit different properties has not been successful. It is believed that these drive shafts have some residual magnetism causing the Rod Position Detectors to indicate erroneously. These jack shafts were replaced in 1998.