ML19256G363
| ML19256G363 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 12/12/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Ahearne J, Gilinsky V, Kennedy R NRC COMMISSION (OCM) |
| References | |
| NUDOCS 7912310171 | |
| Download: ML19256G363 (2) | |
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UNITED STATES uq y h p,( 3 g NUCLEAR REGULATORY COMMISSION
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DEC 121979 MEMORANDUM FOR:
Chaiman Ahearne Comissioner Gilinsky Comissioner Kennedy Commissioner Hendrie Comissioner Bradford FROM:
H. R. Denton, Director, Office of Nuclear Reactor Regulation L. V. Gossick, Executive Director for Operations < signed) T A W THRU:
SUBJECT:
POINT BEACH UNIT 1 - PLANT SHUTDOWN DUE TO STEAM GENERATOR TUBE LEAK On Wednesday November 28, the staff briefed the Comission on the steam generator tube degradation problems at Point Beach Unit 1.
Steam gener-ator tube inspections conducted in August and October 1979 indicated that the Point Beach Unit 1 steam generators are experiencing extensive degradation due to a phenomenon called " deep crevice corrisior " Deep crevice corrosion is characterized by general intergranular attack and stress corrosion cracking of the steam generator tubes in the crevice between the unexpanded portion of the tubes and the tubesheet.
On November 30, 1979, after thorough examinations and preventative actions had been performed by the utility, the NRC issued an Order imposing additional conservative operating restrictions and granting an operating period of two effective full power months. The unit returned to power on November 30, 1979.
Upon returning to power the plant reported low activity levels in the secondary coolant, indicative of a 40 to 50 gpd leak. These leaks had been " background" or " fantom" leaks, had existed for a number of years, and had escaped all detection.
On December 11, 1979 at approximately 5:00 p.m. CST, the plant infomed the Region III Office of Inspection and Enforcement that the unit had experienced a rapid increase in leak rate, exceeding the limitations imposed by the November 30 Order. The increase in leakage was first noticed at 4:13 p.m. CST by a step increase in the activity level in the steam jet air ejector. No significant loss of primary coolant inventory was noted. At 4:35 p.m. CST, the plant's chemical department quantified the leak rate at approximately 260 gpd. At 5:05 p.m. CST, the leak rate was holding steady at approximately 260 gpd with the greatest leakage coming 1661 339 7912310[7/
from steam generator B.
At 5:10 p.m. CST, the unit reduced load and began a 6-hour ramp down leading to taking the unit off line at approximately 11:00 p.m. CST.
(At 7:09 p.m. CST, the unit was at approximately 52% power and the leak rate was stable at 260 gpd.)
The incident resulted in no offsite releases of radiation.
Both NRR and IE staff closely monitored the plant throughout the event. The plant operators will continue to keep the IE Region III Office informed of any abnormal changes in plant conditions. The
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unit should be in a cold shutdown, Mode V condition by late Wednesday afternoon.
The utility has informed Westinghouse of the plant condition and steam generator inspections are scheduled to begin late Thursday.
In addition, the NRR staff is making arrangements to send a team of steam generator experts to the plant to closely review theateam generator inspections.
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/ H. R. Denton, DYrector Office of Nuclear Reactor Regulation cc: SECY OGC OPE I661 340