ML19312C471

AO-269/74-13:on 740816,inadvertent Radwaste Gas Release Occurred During Routine Drainage of Waste Gas Decay Tank B.Caused by Operator Error.Operating Procedure Being Revised

ML19312C471
Person / Time
Site:	Oconee
Issue date:	08/30/1974
From:	DUKE POWER CO.
To:
Shared Package
ML19312C469	List: ML19312C468 ML19312C471
References
NUDOCS 7912130998
Download: ML19312C471 (2)

Text

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A O .

DUKE POWER COMPAhT OCONEE UNIT 1

_ Report No.: A0-269/74-13 Report Date: August 30, 1974 Occurrence Date: August 16, 1974 Facility: Oconee Unit 1 Seneca, South Carolina ,'

Identification of Occurrence: Inadvertent Radioactive Waste Gas Release Conditions Prior to Occurrence: Unit 1 at 100 Percent Full Power Description of Occurrence:

On August 15, 1974, a small quantity of radioactive gaseous vaste was released during the performance of a routine procedure to drain accumulated moisture from Waste Gas Decay Tank B. The Utility Operator opened drain valves LWD-241, 355, 353 and 354 at 2040 to align the Waste Gas Tank to  !

the High Activity Waste Tank in accordance with the approved procedure '

l OP/1&2/A/1104/18, Gaseous Waste Disposal System. Between 2047 and 2123, radiation alarms were received in the spent fuel building and several locations throughout the Auxiliary Building. A Control Operator noticed that the pressure in the Waste Gas Decay Tank B had decreased from 73 to 13 psig indicating that the Waste Gas Decay Tank was being vented. The Control Room operator ordered the Waste Gas Decay Tank drain valves closed at 2055.

The Auxiliary Building was evacuated and exhaust fans were shut down at 2100.

At 2130, after health physics surveys, the Auxiliary Building was re-occupied and the exhaust fans were reenergized.

Designation of Apparent Cause of Occurrence:

The procedure to drain accumulated moisture from the Waste Gas Decay Tank has a caution note to shut the drain valves as soon as water is clear of the sight glass. The operator failed to realize that the sight glass was free of liquid, however, and this resulted in venting the Waste Gas Decay Tank to the High Activity Waste Tank. The initial pressure in the tank (73 psig) contributed to the rate of release from the Waste Gas Decay Tank.

Analysis of Occurrence:

The volume of radioactive gas released to the atmosphere was calculated based upon the change in pressure of the Waste Gas Decay Tank and assuming that all of the gas which left the tank was released to the atmosphere. A total of 4300 cubic feet of gas was released during a 15 minute time period. A sample of the gas in the tank revealed the following activity levels:

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Iodine 131 - 1.29 x 10 pC1/m1, Ienon 13.3 - 0.619 pC1/m1, Xenon 133m -

6.9 x 10-4 pC1/ml and Xenon 135 - 1 x 10-3 pCi/ml.

The objective presented in Technical Specification 3.10 is to limit the average yearly release rate. The instantaneous release rate of Iodine 131 exceeded the average yearly release rate by a small amount; however, this contribution was insignificant when compared to the amount which may be released during the year. Also, since personnel exposure was less than occupational limits, it is concluded that this occurrence did not affect the health and safety of the public.

Corrective Action:

. The operating procedure for the Waste Gas System is being revised to preclude a recurrence of this incident. The procedural step to drain moisture from the Waste Gas Decay Tank is being relocated to the end of the procedure, after a normal gas release has been performed. This will allow the draining of moisture after the tank has been depressurized and will prevent inadvertent venting of the tank through its drain valves.

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