05000317/LER-1980-035-01, /01T-0:on 800727,while Operating at 100% Power, Unit Exceeded Tech Specs by 24 Mwth for 4 Days.Caused by Tube Failure in Steam Generator Blowdown Recovery Heat Exchanger 11 Resulting in Power Calculation Error

/01T-0:on 800727,while Operating at 100% Power, Unit Exceeded Tech Specs by 24 Mwth for 4 Days.Caused by Tube Failure in Steam Generator Blowdown Recovery Heat Exchanger 11 Resulting in Power Calculation Error

ML19331C459
Person / Time
Site:	Calvert Cliffs
Issue date:	08/08/1980
From:	Davis S BALTIMORE GAS & ELECTRIC CO.
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19331C454	List: 05000317/LER-1980-035, Forwards LER 80-035/01T-0 05000317/LER-1980-035-01, /01T-0:on 800727,while Operating at 100% Power, Unit Exceeded Tech Specs by 24 Mwth for 4 Days.Caused by Tube Failure in Steam Generator Blowdown Recovery Heat Exchanger 11 Resulting in Power Calculation Error
References
LER-80-035-01T, LER-80-35-1T, NUDOCS 8008180434
Download: ML19331C459 (2)

LER-1980-035, /01T-0:on 800727,while Operating at 100% Power, Unit Exceeded Tech Specs by 24 Mwth for 4 Days.Caused by Tube Failure in Steam Generator Blowdown Recovery Heat Exchanger 11 Resulting in Power Calculation Error

Event date:
Report date:
3171980035R01 - NRC Website

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8 60 61 DOCKET NUMBER 68 69 EVENT DATE 74 75 REPORT C ATE 80 EVENT DESCRIPTloN AND PROSABLE CONSEQUENCES O'o l

ITrrl 1 n 7/27/80, it was confirmed that Unit 1 exceeded 2700 MWth (T.S.1.3) by 0

10 i31124 MWth while the unit was operating at 100% power for approximately four

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10181 Icomputer calorimetric power. The leak was isolated and correct blowdown l

l0,2, jflow was entered into the calculation at 1530 on 7/21/80.

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33 34 35 36 37 40 41 42 43 44 47 CAUSE DESCRIPTION AND CORRECTIVE ACTIONS li 101 IThe cause was due to' tube failure in all SGBDRHX which is cooled by condensate.

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LER NO.

80-35/1T DOCKET HO.

50-317 EVENT DATE 07/27/80 REPORT DATE 08/08/80 ATTACHMENT EVENT DESCRIPTION AND PROBABLE CONSEOUENCES:

On July 27, 1980, it was confirmed that Unit I had exceeded rated thermal power of 2700 M4th (T.S.1.3) for approximately four (4) days when the unit was operating at 100% pcwer.

This event was caused by an undetected leak in ill steam generator blowdown recovery heat exchanger which resulted in an erroneous input to the plant computer's calorimetric power calculation.

On July 26, 1980, #11 steam generator blowdown recovery heat exchanger which is cooled by condensate water was discovered to have an approximately 200 gpm leak from the condensate side to the bicwdown recovery side.

As the.<

leak increased in magnitude, the Operator closed the throttle valve to maintain the required indicated blowdown flow rate.

This action resulted in an error in the nonconservative direction between actual blowdown flow rate and indicated blowdown flow rate.

It has been estimated by conducting a hand calculated heat balance and confirmed by an actual test that the leak caused an error of approximately 24 MWth in calorimetric power.

At 1530 on July 26, 1980, the heat exchanger was isolated and placed out of service after it was confirmed to have failed tubes.

After the heat exchanger was placed out of service and proper response of the bloudcw.1 flow rate meter was verified, the correct blowdown flow rate was entered into the computer calorimetric calculation.

An investigation was conducted in an attempt to verify the actual inception date of the leak so that a best estimate could be made as to the actual length of time the unit exceeded 2700 M4th.

Two parameters were studied.

First a comparison of calorimetric power to incore instrument power was made, however, the results were inconclusive.

The second parameter studied was steam generator chemistry.

This data showed that blowdown became ineffective on 7/22/80..

Therefore, it was concluded that the !11 steam 92nerator blcxdown recovery heat exchanger tubes failed on that date.

Af ter reviesing the unit's power history and assuming that the leak started on 7/22/80, it has been concluded that the unit exceeded power for91 hours.

An assessment of the sienificance of the overpower condition on the Safety Analysis concluded that'the overpower condition was more than offset, since local peaking factors (F t and F.. t remained at least 8% below their Technical Specification limit duriEg the evfn)t. Therefore, an adequate margin of safety remained.

CAUSE DESCRIPTION AND CORRECTIVE ACTIO"S:

The cause of this event was due to tube failure in i11 steam generator blowdown heat exchanger which resulted in an erroneous input to the plant computer calorimetric power calculation. Corrective action to prevent recurrence will be to implement a weekly preventative maintenance functional check to verify proper bloudewn flow rate.