05000255/LER-2005-003
| Docket Number04 13 2005 2005 -- 003 -000 05 24 2005 | |
| Event date: | 04-13-2005 |
|---|---|
| Report date: | 05-24-2005 |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(B), Prohibited by Technical Specifications |
| 2552005003R00 - NRC Website | |
FACIUTY NAME (1)� DOCKET NUMBER (2) LER NUMBER (6� PAGE (3) Palisades Nuclear Plant 05000-255 2005 -- 03 — 00
EVENT DESCRIPTION
On April 13, 2005, with the plant operating at approximately 100% power, a review of test data determined that, contrary to Technical Specification (TS) SR 3.7.10.4, a positive differential pressure of >/= 0.125 inches water gauge was not being maintained between the control room envelope (CRE) and the adjacent electrical equipment room (EER), when the control room ventilation system (CRV) [VI] was operating in emergency mode. Additionally, review of the surveillance procedure that is periodically performed to demonstrate compliance with the 18-month frequency of TS SR 3.7.10.4, revealed that the differential pressure between the CRE and the EER is not specifically measured.
Consequently, for greater than the past three years, TS SR 3.7.10.4 has not been fully met with regard to demonstrating that the CRV can maintain a positive pressure of >1= 0.125 inches water gauge relative to the EER.
This is reportable in accordance with 10 CFR 50.73(a)(2)(i)(B) as a condition prohibited by the plant's Technical Specifications.
CAUSE OF THE EVENT
During the week ending April 9, 2005, special testing of the CRV was performed using a tracer gas to directly measure unfiltered in-leakage into the CRE. Additionally, static pressure was measured within the CRE, and adjacent ventilated spaces. A high static pressure condition was identified in the EER. An inspection of the EER was performed, which determined that the elevated static pressure was caused by the lack of a return air flow path.
A review of plant design documents was performed to determine the intended configuration of the EER ventilation. The EER is supplied with ducted air from the switchgear and cable spreading room ventilation system. Return air from the EER was designed as non-ducted through the open doorway to the 1-D switchgear room. The door was originally.restrained in the open position with a fusible link.
An unrecognized change in the design configuration occurred in 1989, when the door between the EER and the 1-D switchgear room was closed. With air being supplied to the EER, but with no path for return air, a high static pressure condition was created, which could not be overcome by the CRV to maintain the TS required positive pressure of >1= 0.125 inches water gauge relative to the EER.
A surveillance procedure confirms that the differential pressure between the CRE and the 1-D switchgear room is >1= 0.125 inches water gauge, but does not specifically measure the differential pressure between the CRE and the EER, due to the assumption that there is no differential pressure between the 1-D switchgear room and the EER. This assumption would only be valid with the door between the 1-D switchgear room and the EER open.
r FACILITY NAME (1) DOCKET NUMBER (2) LER NUMBER (6 PAGE (3) Palisades Nuclear Plant 05000-255 2005 -- 03 — 00
SAFETY SIGNIFICANCE
The tracer gas testing that was performed during the week ending April 9, 2005, verified that the unfiltered in-leakage to the CRE was within acceptable limits, despite the CRE not being maintained at a positive differential pressure of >1= 0.125 inches water gauge relative to the EER. Therefore, the occurrence has minimal safety significance.
CORRECTIVE ACTIONS
Upon discovery, both CRV filtration trains were considered inoperable, and TS LCO Condition 3.7.10.F was determined to be applicable. TS LCO 3.0.3 was entered and immediate action was taken to reduce the high static pressure condition in the EER, by blocking open the door between the EER and the 1-D switchgear room, to allow a return air flow path from the EER to the 1D switchgear MOM.
Subsequent to this action, the CRV was operated in emergency mode and measurements were performed that verified that the differential pressure between the EER and the 1-D switchgear room was neutral. Therefore, the CRE was determined to be at a positive pressure of >1= 0.125 inches water gauge relative to each of these rooms. TS LCO 3.0.3 was then exited.
A work order has been initiated to restore the door to its original design configuration.
PREVIOUS SIMILAR EVENTS
None