ML19317F508

RO 270/76-10:on 760909,radioactivity Level Increased in Component Cooling Sys.Caused by Letdown Cooler a Leakage. Letdown Cooler Isolated for Future Repair

ML19317F508
Person / Time
Site:	Oconee
Issue date:	09/20/1976
From:	DUKE POWER CO.
To:
Shared Package
ML19317F505	List: ML19317F504 ML19317F508
References
RO-270-76-10, NUDOCS 8001140737
Download: ML19317F508 (2)

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d DUKE POWER COMPANY-OCONEE UNIT 1 i:

I Report No.,: R0-270/76 Report Date: September 20, 1976 Occurrence'Date: September 9,:1976 Facility: Oconee Unit 2, Seneca, South Carolina Identification of Occurrence: Increased activity in the Component Cooling

-System resulting from letdown cooler leakage Conditions Prior'to Occurrence: Unit at 90 percent full power Description of Occurrence:

On September 9,1976, routine ra/tochemistry monitoring revealed an increasing level of radioactivity in the Oconee Unit 2 Component Cooling System. By isolating letdown coolers singly and observing the resulting change in activity in the CCS, the source of the radioactivity was identified as letdown cooler "B" from which primary coolant was leaking into the Component Cooling System.

Letdown cooler "B" was isolated to prevent further leakage and increase in CCS activity.. Analysis of I-131 activity in the CCS verified the leakage to be approximately 133cc/ day.

Ayparent Cause of Occurrence _:

As stated above, the apparent.:cause of this occurrence was a leak in letdown cooler "B", allowing leakage of primary coolant into the Component Cooling System.

Analysis of Occurrence:

Isolation.of letdown cooler "B" prevented further increase of activity in the Component Cooling System. The CCS is a closed system; therefore, any activity present:will remain within the system. The level of activity in the system does not adversely affect the operation of the unit or its components. Activity in the system will be reduced through normal makeup to the system and decay of the isotopes. 'Also, since the CCS liquid is chemically buffered to a high pH value, primary coolant that has leaked into the system is quickly neutra-lized and its possible corrosive effects minimized. From these considerations it is concluded that this occurrence did not adversely affect the health and safety of the~public. -

Corrective Action:

Letdown cooler!"B" has been isolated terminating further contamination of the Component" Cooling System. During the next refueling outage or maintenance outage 'of sufficient duration, Lthe cooler will be either repaired or replaced.

• This occurrence is similar to Reportable' Occurrence 269/76-12 submitted by our b letter of' July. 21, 1976,. in which leakage from Oconee Unit 1 letdown cooler "A"

.was reported. .A follow-up letter of September 1, 1976, provided guidelines for

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e continued operation of the unit with limited use of letdown cooler "A". In a similar manner, Oconee Unit 2 will be operated within those guidelines until letdown cooler "B" is repaired or replaced.

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