Andy –

We still have a manual system and always check the top of core values after detector replacement.  Any re-zeroing of the detector position involves opening the resolver in containment and adjusting the position of the detector.

While the nominal turns per inch on the helical wrap are the same, the detectors aren’t identical.  Even a 0 .1% or 0.2% difference between the old and new detector wrap spacing can result in noticeable differences (some of our detector runs are in excess of 1400 inches), so we have seen noticeable differences in indicated position when we replace detectors.  In our system, the resolver counts turns and translates that into a position indication.  Any change in spacing of the turns will result in a small difference in the distance reported by the resolver.  I believe this is what you saw. 

Mark Mayer

Reactor Engineering

Diablo Canyon Power Plant

805-545-4674

Has anyone had to change their top of core values, after resetting the withdrawn limit switch to 0”, on the moveable incore system by several inches following a detector replacement when no physical dimensions have changed (i.e. just a one for one detector replacement)?

If yes, what was the cause of this change?

Any feedback (i.e. yes or no) would be valuable. I’ve included some background at the bottom of this e-mail.

Thank you in advance for your help.

Thanks,

Andy

Andrew Kelliher

Reactor Engineer

R.E. Ginna Nuclear Power Plant

Phone: (585) 771-3457

"I'm just sayin', I don't like fun." - Karl Pilkington

During Ginna’s 2012 Fall Outage the flux mapping system was replaced. This included replacement of the equipment in containment (drive boxes, transfers, etc) and in the control room. During the 75% flux map one of the new detectors failed and was replaced last month.

On the old system replacement included manually lining up the detector in containment with the WLS and rezeroing the encoder. Following this rezeroing, passes were able to be taken using the previous top of core and bottom of core values without issue.

On the new system this is performed by driving the detector forward from the control room and then telling the system to drive to zero position which looks for the WLS and rezeroes the resolver. However, after this detector replacement all of the top of core values were altered by several inches.

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