Waterford: Something Is Slowing Down Their Control Rods

Apr 25: Look what popped up it my e-mail? 

NUREG/CR-5783 BNLrNUREG-52299(1993)

Aging Assessment of the Combustion Engineering and Babcock & Wilcox

Control Rod Drives

Feb 22 meeting:

Significant increase in fuel damage in DBA...well, cladding damage without fuel melt. 

ANO ask and got the drop time change before they got all the equipment changes while Waterford did not? 

The below with seals, crud and filters are non applicable to PWR according to the NRC. This is about BWRs. WaterFord is a PWR. 

My Apologizes... 

???

Leaking seals leaking, maybe from a "crud bust" thru CRD Hydraulic. 

If they had good 1 micron filters in CRDH installed but did not clean / flush them periodically, then they filled up caused a high DP, then broke. 

Or the filters could be just plugged, causing hi dp, low flow. 

The seals on the drives themselves need to be replaced on a regular interval.

This is what I hate about the new NRC...they don't have to know what is causing the slower scram times. If they don't know what is causing it, how can they predict how it will behave. 

CEO Drop T.S. Change Request.

Most logical is the CEA replacement

Potential Cause 

Plant Primary Side Modifications 

• Steam Generator replacemen 

• Reactor Vessel Head replacement
• CEA replacement 

• Transition to Next Generation Fuel Product

In the below graph, I brought this out in the pre LAR meeting. Basically:

1) Check it out, as the core ages, the rod drop speeds become more erratic. 

2) How do you explain the stability cycle 1 thru 10. 

3) How do you explain the erratic drop timing between cycle 11 thru 18? 

4) Say the drop timing for the element or a rod is noisy on cycle. The timing for a rod is changes from one test to another. There is a lot of variability of the timing. If you have a lot of variability of the rod drop group timing, the average could jump all around. As a example, say you do do one testing (like they do), the average could be 2.8. If the actually rod drop group timings were highly erratic, changed from one test to another, then the average say on three test could come out to say 2.6, 3.2 and 3.9. How then would we know we are safe? 

Background for LAR 

• CEA Drop Times have challenged the Technical Specification (TS) limit in the last two surveillance performances 

– Waterford 3 TS 3.1.3.4 requires: 

• the arithmetic average of all CEA Drop Times be ≤ 3.0 seconds 

• Individual CEA drop times ≤ 3.2 seconds 

• Insertion time is measured from fully withdrawn position to 90% inserted