From: Hawes, Mark W [mailto:mwhawes@duke-energy.com] Sent: Wednesday, January 16, 2008 10:22 AM To: pwrrm-bounces@retaqs.com Subject: FW: [Pwrrm] Point Beach Question:
At Catawba (Westinghouse-4 loop) we don't have issues with DRPI (rod position indication) associated with rx vessel head ventilation. We do, however, withdraw each control rod beyond "end of travel" . . . hard stop position is 231 Steps Wd at CNS, so rods are withdrawn to indicated position of 235. The rods are then reinserted to specified fully withdrawn (parked) positions.
This evolution is performed upon reaching full power following any unit shutdown which required reactor trip breakers to be opened. The acknowledged problem being 1 to 2 steps of uncertainty with regard to where drive rods are engaged, and withdrawn from, when breakers are reclosed.
Mark Hawes CNS Reactor Engineering (803) 831-3855
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From: Keller, Lee A Sent: Tuesday, January 15, 2008 1:47 PM To: Hawes, Mark W Subject: FW: [Pwrrm] Point Beach Question:
Pls address
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From: pwrrm-bounces@retaqs.com [mailto:pwrrm-bounces@retaqs.com] On Behalf Of VANCE, KEVIN Sent: Monday, January 14, 2008 4:29 PM To: pwrrm@retaqs.com Subject: [Pwrrm] Point Beach Question:
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.