ENS 41224
ENS Event | |
|---|---|
19:20 Nov 24, 2004 | |
| Title | Eccs Loops Declared Inoperable in Support of Log Term Accident Mitigation |
| Event Description | The following event description is based on information currently available. If through subsequent reviews of this event, additional information is identified that is pertinent to this event or alters the information being provided at this time, a follow-up notification will be made via the ENS or under the reporting requirements of 10CFR50.73.
On November 24, 2004, at approximately 12:20 Mountain Standard Time (MST), Palo Verde Nuclear Generating Station Unit 3 was operating at 0% power at approximately normal operating temperature and pressure when 3 of the 4 ECCS injection check valves were identified to be in a degraded condition. While performing normal torque verifications on the bonnet bolts for these check valves, it was identified that the graphoil seals were degraded in that the seal material had extruded past the retaining ring. Although there was no evidence of actual leakage associated with these valves, the long term integrity of the valves during post accident operation could not be assured. As a result, the Operators conservatively declared both trains of ECCS inoperable per LCO 3.5.3 and 3 of 4 Safety Injection Tanks inoperable per LCO 3.5.1, requiring entry into LCO 3.0.3. Operations also declared both RCS loops inoperable per LCO 3.4.5. A cooldown and depressurization of the RCS is in progress to Mode 5. Unit 3 was preparing for Mode 2 entry following a refueling outage when the degraded check valve seals were identified. Engineering continues to evaluate this condition. There were no RPS/ESF actuations, and none were required. There were no structures, systems or components that were inoperable at the start of event that contributed to the event. This condition did not result in any challenges to the fission product barrier or result in any releases of radioactive materials. There were no adverse safety consequences or implications as a result of this event. This condition did not adversely affect the safe operation of the plant or health and safety of the public. The NRC Resident Inspector has been notified of this condition and this ENS notification.
Engineering has determined that these RCS PIV's (Pressure Isolation Valves) were always capable of performing their safety function. The extrusion of the graphite seal material for the check valves did not affect the capability of the RCS PIV check valves safety function and did not present a danger to the pressure boundary of the RCS. It was estimated that no more than about 5% of the graphite material was extruded. The loss of this small amount of packing material, did not challenge the integrity of the seal. This is based on industry experience and the results of Palo Verde tests. Also, the functionality of the SI check valves disc was not compromised since the internal disc to seat clearances achieved were within the range desired. Nevertheless, the seals for valves SIEV227, 237 & 247 were replaced while in Mode 5 to add additional margin to the joint design. LCO 3.0.3 and the other impacted LCO entries (3.4.5, 3.5.1, 3.5.3) were conservative and were not required. Therefore, this 10CFR50.72(b)(3)(v)(D) notification, ENS ID # 41224 of 11/24/2004, 20:01 ET, is retracted and no followup LER will be submitted for this event. The NRC Resident Inspector has been notified of the retraction and this notification. R4DO (Pick) notified. |
| Where | |
|---|---|
Palo Verde  Arizona (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident | |
| Time - Person (Reporting Time:+0.68 h0.0283 days <br />0.00405 weeks <br />9.31464e-4 months <br />) | |
| Opened: | David Oakes 20:01 Nov 24, 2004 |
| NRC Officer: | Jeff Rotton |
| Last Updated: | Dec 14, 2004 |
| 41224 - NRC Website | |
Unit 3 | |
|---|---|
| Reactor critical | Not Critical |
| Scram | No |
| Before | Hot Standby (0 %) |
| After | Hot Standby (0 %) |