United States Nuclear Regulatory Commission - Protecting People and the Environment

Morning Report for September 10, 2007

Headquarters Daily Report

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REGION IV

EXCESSIVE REACTOR COOLANT SYSTEM LEAKAGE

Licensee/Facility:

UNION ELECTRIC CO.
Callaway
FULTON, Missouri
Dockets: 05000483
[1] W-4-LP
License No:
Notification:

MR Number: 4-2007-0004
Date: 09/06/2007

Call from SRI

Discussion:

This Morning Report supplements information provided in NRC Event Notification Report for September 7, 2007, (Event Number 43622), in which the licensee for Callaway Plant declared a Notice of an Unusual Event (NOUE) because of leakage greater than 25 gpm from the reactor coolant system. The plant remained at full power throughout the event. The following provides additional detail regarding the event.

At approximately 9:00 p.m., operators responding to control room annunciators identified a loss of letdown flow. Operators determined that a chemical and volume control system letdown relief valve, located inside containment, had lifted. Leakage through the valve was estimated to be 120 gpm and approximately 650 gallons of primary water entered the pressurizer relief tank before plant operators terminated the relief valve leakage by isolating the letdown system. The emergency declaration was made because leakage exceeded 25 gpm. The licensee exited the NOUE at 12:20 a.m., on September 7, 2007, when plant conditions stabilized. Subsequent investigation by the licensee indicated that a pressure perturbation in the system caused the relief valve to lift.

The NRC resident inspector responded to the site and verified plant conditions. The licensee subsequently identified a failed letdown pressure control transmitter and a failed letdown pressure control valve, both of which have been repaired. The licensee's investigation of the cause of the damaged components is ongoing. The NRC continues to monitor the licensee's actions.












Contacts:

Name Office Abbrev Phone No E-Mail
GADDY, VINCENT G R4 (817) 860-8141 VGG@nrc.gov
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