ML19224D554

LER 79-020/01T-0 on 790621:radioactive Release Rate at Main Stack During Plant Startup Exceeded Tech Specs.Caused by Deficiency in Procedure for Depressurization Following Shutdown.Investigation Underway to Improve Procedure

ML19224D554
Person / Time
Site:	Peach Bottom
Issue date:	07/06/1979
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
Shared Package
ML19224D552	List: ML19224D551 ML19224D554
References
LER-79-020-01T, LER-79-20-1T, NUDOCS 7907120597
Download: ML19224D554 (1)

Text

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Mr. Boyce H. Grier Page 2 July 6, 1979 LER 3-79-20/Ir shutdown immediately. Main stack release, however, continued to increase due to transport time between the vacuum pump and the main stack. This release continued over approxinately 50 minutes. The maximum release rate was 106 % of Technical Specification limits. Technical Specification release limits were exceeded for less than 10 minutes during this transient.

Simultaneoualy with this release, the two reactor building roof vents were releasing at a.value of 11 % of Technical Specification limits. The maximum site gaseous release rate was therefore approximately 117 % of the Technical Specification limit.

Approximately 1000 Ci of m ,od noble gases were released during this event.

Consequences of Event:

Analysis of the roof vent iodine and particulate samples indicated no significant increase in the iodine or particulate release rates during the period of high gaseous activity releases. Analysis of the main stack effluent, sampled 14 hours1.62037e-4 days <br />0.00389 hours <br />2.314815e-5 weeks <br />5.327e-6 months <br /> later when the startup vacuum pump was placed back in service, indicated that the majority of the activity was XE-133 and XE-135 (long lived noble gases). The release was terminated as soon as the increase in radiation levels on the off-gas stack radiation monitor was observed. For these reasons, no environmental impact is anticipated. Plant personnel received no radiation exposure as a result of this event.

Cause of Event:

Depressurization of the p rima ry coolant system following reactor shutdcwn introduced non-condensible fission product gases into the condenser. Transfer of this inventory to the main stack in accordance with normal startup procedures resulted in a gaseous release rate in excess of Technical Specification linits.

The appropriate procedures were deficient in that they did not .

adequately address the special case of significant fission product inventory in the main condenser with respect to operation of the startup vacuum pump.

Corrective Action:

When the increase in the radiation monitor reac ~ ng was noticed, the startup vacuum pump was tripped to terminate the rele se.

Following the initial high release rate, air was pulled through the condenser to provide dilution flow to the vacuum pump during the evacuation of the condenser air space. This eventually get .dtted establishing a condenser vacuum sufficient to permit return of the unit to service. No additional releases scc s JJ L')

79071267

Mr. Boyce 11 . Grier Page 3 July 6, 1973 LER 3-79-20/IT in excess of T'chnical Specification limits occurred during the condenser evacuation operation.

An investigation of tnis occurrence is being performed by the Electric Production Department and the Mechanical Engince-ing Division to determine acceptable procedural or equipment modifications to prevent a recurrence.

Yours truly,

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cf . .

/Cooney f

St erintende t Generation Division-Nucle '

Attachment ec: Director, NRC - Office cf Inspection and Enforcement Mr. Norman M. Haller, NRC - Office of Management &

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.O 6 l site consecuences of this release were cinical since the majority of I io i i the activity released was in the fona of mixed noble gases. I to 8 l 1

7 8 9 SYS'E M 80 CAUSE CAUSE C O Y P.

CODE V ALV E CCCE SUBCOCE COVPONENT CCDs SUBCCOE SLSCODE io P

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40 43 44 47 CAUSE CESCRIPTION AND CORRECTIVE ACTIONS j i o l Reactor depressurization introd2ced fission gas into condenser. This ans l i j was released via main :ack when vacuum pump was started. Vacuum purn I

, , L was i==ediately tripped. Dilutien air was supplied to reduce release I j 3 i, } rate when vacuum pump operation resumed. Engineering invectigation is I p 3 l being conducted to provide cethods or mods to t>revent recurrence.  !

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