ENS 44723
ENS Event | |
|---|---|
22:16 Dec 15, 2008 | |
| Title | Unanalyzed Condition Due to Steam Chase Temperature Greater than 165F |
| Event Description | At 1616 on 12/15/08, a plant heating boiler trip resulted in a loss of a reactor building ventilation. The loss of reactor building ventilation resulted in maximum average main steam chase temperatures greater than or equal to 165F. High energy line break (HELB) analysis of piping in the steam chase assumes an initial average temperature prior to the break of 165F. Temperature greater than or equal to 165F in the steam chase challenges EQ qualification of the piping analysis. Abnormal procedures for loss heating boiler and ventilation system failure were entered. C.3 (Shutdown) and C.5-1300 (secondary containment control) were also entered. The plant heating boiler was restarted and ventilation restored prior to power reduction. All systems have been returned to normal.
The licensee notified the NRC Resident Inspector.
The licensee is retracting this report based on the following: Monticello is retracting the event reported based on further evaluation, which found that the issue was not an unanalyzed condition that seriously degraded plant safety. The investigation of the event found the peak temperature achieved was 167.2 degrees F and the condition lasted for approximately 11 minutes. Engineering review of Safety System Components found no impact on the equipment for the temperature reached, Additionally, revised High Energy Line Break (HELB) calculations performed with an initial average Steam Chase Room temperature of 180 degrees F before a HELB determined that Safety System components could perform their safety functions. The station has identified the cause for the event and corrective actions will be tracked in the station's corrective action program. Since there was no impact on the equipment in either Environmental Qualification (EQ) or safety function, the temperature of the event was less than the revised calculation temperature, and the unanalyzed condition that existed in the initial event notification report no longer exists and did not result in a condition that seriously degraded plant safety, this event can be retracted. The licensee informed the NRC Resident Inspector. Notified R3DO (Ring). |
| Where | |
|---|---|
Monticello  Minnesota (NRC Region 3) | |
| Reporting | |
| 10 CFR 50.72(b)(3)(ii)(B), Unanalyzed Condition | |
| Time - Person (Reporting Time:+0.52 h0.0217 days <br />0.0031 weeks <br />7.12296e-4 months <br />) | |
| Opened: | William Stang 22:47 Dec 15, 2008 |
| NRC Officer: | Jason Kozal |
| Last Updated: | Feb 6, 2009 |
| 44723 - NRC Website
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Unit 1 | |
|---|---|
| Reactor critical | Critical |
| Scram | No |
| Before | Power Operation (100 %) |
| After | Power Operation (100 %) |