Preliminary Precursor Analysis Encl 1 & Encl 2 (Gudana)

In early February 2000, primary-to-secondary tube leakage ranging from one to four gallons per day (gpd) was detected in steam generator (SG) No. 24. On February 15, 2000, while the unit was operating at 99% power, SG leakage rapidly increased from 4 gpd to greater than 75 gallons per minute (gpm). The reactor was manually tripped 13 minutes later, and the faulted steam generator was isolated one hour after the reactor trip. In addition to shutting down the reactor and isolating the affected steam generator, the plant operators also took appropriate action to cool down and depressurize the reactor coolant system to prevent leakage into the faulted steam generator. The highest leak rate which was observed during the event (about 146 gpm) occurred prior to the reactor trip. This maximum flow rate exceeded the capacity of two positive displacement charging pumps (98 gpm/pump).