ML12229A315
| ML12229A315 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 08/16/2012 |
| From: | Nirodh Shah NRC/RGN-III |
| To: | |
| References | |
| PNO-III-12-009 | |
| Download: ML12229A315 (2) | |
Text
PRELIMINARY NOTIFICATION - REGION III August 16, 2012 PRELIMINARY NOTIFICATION OF EVENT OR UNUSUAL OCCURRENCE - PNO-III-12-009 This preliminary notification constitutes EARLY notice of events of POSSIBLE safety or public interest significance. Some of the information may not yet be fully verified or evaluated by the Region III staff.
Facility Monticello Nuclear Generating Plant Northern States Power Co.
Monticello, MN Docket: 50-263 License: DPR-22 Licensee Emergency Classification Notification of Unusual Event Alert Site Area Emergency General Emergency X Not Applicable
SUBJECT:
MONTICELLO SHUTDOWN DUE TO DRYWELL UNIDENTIFIED LEAKAGE ABOVE TECHNICAL SPECIFICATION LIMITS DESCRIPTION:
On August 10, 2012, the licensee noted that the drywell unidentified leakage rate had increased from a nominal 0.2 gallons per minute to 8.4 gallons per minute, exceeding the Technical Specification limit of 5 gallons per minute. The leakage rate then dropped to < 0.5 gallons per minute after about 15 minutes. The licensee reduced reactor power to 10 percent and remained at this power while workers entered the drywell to identify the source of the leakage. The leakage was coming from a mechanical bolted connection on a section of piping associated with the residual heat removal system. Subsequently, on August 14, 2012, at 12:00 p.m. CDT, the plant was shutdown to commence repairs.
The Technical Specification limit for unidentified leakage allows time for early detection of a problem that could indicate a failure of the reactor pressure boundary. The limit requires that the plant be shutdown if the unidentified leakage rate exceeds 5 gallons per minute and cannot be reduced to below the limit within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> or if there is any indication of pressure boundary leakage. As stated above, the unidentified leakage rate dropped below the Technical Specification limit within 15 minutes. Additionally, the identified leak was not considered pressure boundary leakage.
The NRC resident inspectors were aware of the increase in the unidentified leakage rate and observed the initial power reduction and the subsequent plant shutdown. The resident inspectors were also monitoring the licensees investigation and repair activities.
This preliminary notification is issued for information only. State and local officials have been informed. The site issued a press release on August 14, 2012, describing the event.
The information presented herein has been discussed with the licensee, and is current as of 9:00 a.m. CDT, on August 16, 2012.
ADAMS Accession Number: ML12229A315 CONTACT:
Nirodh Shah 630-829-9821 Nirodh.Shah@nrc.gov