ENS 42237
ENS Event | |
|---|---|
20:12 Dec 31, 2005 | |
| Title | |
| Event Description | The EFW actuation occurred when the 'B' MFW pump RPM rose then dropped to ~4000 rpm. The MFW pump then recovered immediately. This transient caused EFIC [Emergency Feedwater Initiation Control] to actuate and both EFW pumps received start signals on invalid low SG level from the EFIC low range level instruments. These instruments measure level based upon a dp [differential pressure] across an orifice and are not considered reliable at 95% power and full MFW flow. All other SG level instruments indicate SG level was above EFIC setpoint during the MFW pump transient. This can be concluded by reviewing the OTSG [Once Through Steam Generator] level prior to and during the transient. Prior to the transient the EFIC low range level instruments indicated a level of ~24 inches. During the transient the EFIC low range level instruments indicated as low as 4 inches. However, the Startup Range level only lowered from ~122 inches prior to the transient to ~120 inches.
Both EFW pumps were immediately overridden and stopped once it was verified this was not an actual under feed condition to the OTSGs. No EFW injection into the OTSGs occurred due to the EFW actuation. There was no ongoing maintenance at the time which would have explained the "B" MFW pump transient. The licensee informed the NRC Resident Inspector.
On 12/31/05, an 8-hour notification (EN 42237) was made by Arkansas Nuclear One reporting an automatic actuation of Emergency Feedwater (EFW). The report was submitted pursuant to the requirements of 10 CFR 50.72 (b)(3)(iv)(A) Valid System Actuation. The actuation of EFW occurred as a result of a "B" Main Feedwater (MFW) pump transient which caused an invalid low Steam Generator (SG) level signal from the Emergency Feedwater Initiation and Control (EFIC) instrumentation. As discussed in the original event report, the low SG level EFIC instruments do not provide valid indication at 95% power and full MFW flow. As a result of the elevated flow rate during this perturbation, an invalid indication below the low SG level setpoint was produced resulting in the system actuation. All other SG level instrumentation indicated that actual SG levels remained within the normal operating band, confirming that no low level condition existed and that this event represented an invalid actuation. Accordingly, this update revises Event Notification 42237 to be submitted pursuant to 10 CFR 50.73 (a)(2)(iv)(A) and the 60-day Optional 10 CFR 50.73 (a)(1) requirement - Invalid Actuation of EFW. EFID and EFW systems functioned as designed in response to the invalid low SG level signal. The original event report stated that there was no EFW injection into the steam generators as a result of the actuation; however, subsequent reviews of historical Safety Parameter Display System (SPDS) data indicated that the electric EFW pump (P-7B) fed the steam generators for approximately 5 seconds during the event. The licensee notified the NRC Resident Inspector. R4DO (Shannon) notified. |
| Where | |
|---|---|
Arkansas Nuclear  Arkansas (NRC Region 4) | |
| Reporting | |
| 10 CFR 50.73(a)(1), Submit an LER, Invalid Actuation | |
| Time - Person (Reporting Time:+-0.93 h-0.0388 days <br />-0.00554 weeks <br />-0.00127 months <br />) | |
| Opened: | Richard Harris 19:16 Dec 31, 2005 |
| NRC Officer: | Steve Sandin |
| Last Updated: | Jan 6, 2006 |
| 42237 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (95 %) |
| After | Power Operation (94 %) |
WEEKMONTHYEARENS 541472019-05-09T17:05:0009 May 2019 17:05:00
[Table view]10 CFR 50.73(a)(1), Submit an LER 60-Day Telephonic Notification of Invalid Engineered Safety Feature Actuation Signal ENS 537772018-10-09T05:00:0009 October 2018 05:00:00 10 CFR 50.73(a)(1), Submit an LER 60-Day Optional Telephonic Notification of Invalid Specified System Actuation ENS 422372005-12-31T20:12:00031 December 2005 20:12:00 10 CFR 50.73(a)(1), Submit an LER Automatic Actuation of the Emergency Feedwater (Efw) Due to a Transient on the "B" Main Feedwater (Mfw) Pump 2019-05-09T17:05:00 | |