05000400/LER-2006-002
| Harris Nuclear Plant - Unit 1 | |
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 4002006002R00 - NRC Website | |
I. DESCRIPTION OF EVENT
On April 29, 2006, during Refueling Outage 13 (RFO-13), a rebuilt York Compressor was installed on the 'A' Chiller [CHU] for the 'A' Essential Services Chilled Water (ESCW) system [KM]. This maintenance was performed as part of a periodic maintenance plan to replace aging components, and it was the first time that Harris Nuclear Plant (HNP) had replaced a safety-related chiller compressor since original startup. To properly connect the rebuilt compressor, personnel had to reinstall and reconnect the linkage between the compressor pre-rotation vane (PRV) shaft and the PRV motor. The VMS-1 Switch is internal to the PRV motor and provides a start permissive for the chiller unit.
Following post-maintenance testing, the 'A' Chiller was successfully started and secured eight times between May 4, 2006 and May 25, 2006. On May 25, 2006 at 20:12, the 'A' Chiller was again started. During this startup of the 'A' Chiller, the PRV motor rotated the linkage to the position which fully opened the PRVs. During this operation, differential movement between the linkage and the PRV shaft occurred because the 1/2" cap screw, which connects the PRV internal control shaft and the external lever, was not torqued to 75 ft-lbs as referenced in plant design drawings during the installation on April 29, 2006. This differential movement created a misalignment of the connecting linkage.
When the 'A' Chiller was secured on May 25, 2006 at 21:20, the PRV motor operated to fully shut the PRVs. However, because of the misalignment in the linkage created by the differential movement, the PRVs reached the fully shut position before the VMS-1 switch was closed. Because the VMS-1 switch failed to close on May 25, 2006 at 21:20, the start permissive for the 'A' Chiller was not met, and therefore the 'A' Chiller would not have started on demand.
This condition was discovered on June 1, 2006 at 16:25 when the 'A' ESCW Chiller received a routine start demand from Operations, but the chiller did not start. Immediate trouble shooting determined that the 'A' Chiller did not start because the VMS-1 switch was open. This misaligned linkage was corrected and the VMS-1 switch was closed under a work order. The 'A' ESCW system and chiller were restored to an operable condition on June 3, 2006 at 05:00.
The 'A' ESCW system was inoperable from May 25, 2006 at 21:20 until June 3, 2006 at 05:00 when the linkage was repaired and the VMS-1 switch was closed. This time is longer than allowed by Technical Specification (TS) 3.7.13. During this time, the 100% capacity, redundant 'B' ESCW System was in-service and fully functional.
Energy Industry Identification System (EIIS) codes are identified in the text within brackets [].
II. CAUSE OF EVENT
The root cause of this event was a technically inadequate procedure, CM-10014, "York Essential Services Chilled Water Chiller Temperature Controller Maintenance! The procedure did not include the requirement to torque the %" cap screw, which connects the PRV internal control shaft and the external lever, to 75 ft-lbs as referenced by plant design drawings.
III. SAFETY SIGNIFICANCE
The 'A' chiller was in inoperable for a period of 199 hours0.0023 days <br />0.0553 hours <br />3.290344e-4 weeks <br />7.57195e-5 months <br /> 40 minutes, which is longer than the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed by TS 3.7.13. There were no actual consequences of the inoperability of the 'A' Chiller since there were no conditions which caused a demand for the 'A' Chiller to start between May 25, 2006 and June 3, 2006. During this time, the 'B' ESCW System, which includes the 'B' Chiller, was in-service and fully functioning to supply all required loads.
If a design basis accident had occurred between May 25, 2006 at 21:20 through June 3, 2006 at 05:00, the 'A' ESCW system would not have been capable of performing its safety-related functions.
This consequence is minimized by the existence of the 100% capacity, redundant 'B' ESCW System.
The 'B' ESCW System, which includes the 'B' chiller, was in service and fully functional during this time period.
This condition is reportable as a condition prohibited by Technical Specifications pursuant to 10 CFR 50.73(a)(2)(i)(B) since the condition existed for a time longer than its allowed outage time. This condition was neither recognized nor discovered until after the allowed outage time for this condition
- had elapsed, and was corrected by the realignment of the linkage and the torquing of the W cap screw on June 3, 2006 at 05:00.
IV. CORRECTIVE ACTIONS
As immediate corrective action, the PRV linkage was properly aligned and the %" cap screw on the PRV control shaft was properly torqued to 75 ft-lbs. This corrective action was completed on June 2, 2006 at 01:41. Following the satisfactory completion of all post-maintenance testing, the 'A' ESCW system was restored to operability on June 3, 2006 at 05:00. The corrective action to prevent recurrence is to revise procedure CM-10014, "York Essential Services Chilled Water Chiller Temperature Controller Maintenance," to provide instructions for properly torquing the W cap screw, which connects the PRV internal control shaft and the external lever arm, when required for cam adjustment.
V. PREVIOUS SIMILAR EVENTS
There is one previous event at HNP where the ESCW system was inoperable for a period longer than allowed by TS. As described in LER 2005-004-00, the cause of this period of inoperability was inadequate implementation of operator manual actions. This previous event and associated root cause are unrelated to this event, and as such, the corrective actions to prevent recurrence put in place for the previous LER on the ESCW, would not have been expected to prevent this occurrence.