ML19210A126

Event Rept 76-22/3L:on 760526,interlock Circuit Between Effluent Monitor RM-L6 & Discharge Valve WDL-V257 Failed, Causing Degradation of Sys Containing Radioactive Matl. Caused by Personnel Error & Interlock Failure

ML19210A126
Person / Time
Site:	Three Mile Island
Issue date:	06/29/1976
From:	Arnold R METROPOLITAN EDISON CO.
To:
References
GQL-0904, GQL-904, NUDOCS 7910240843
Download: ML19210A126 (4)

Text

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Dear Sir:

p , Qg.-f Docket No. 50-289 Ill l OV Operation Licer.se Us. DPR-50 In accordance with the Technical Specifications of our Three Mile Island Nuclear Station Unit 1 (TMI-1), we are reporting the following reportable occurrence. This submitta' is being made h dayc late in accordance with the June 25, 1976 telephone conversation between our Mr. D. Grace and your Mr. R. McClintock.

(1) Report Number: ER 76-22/3L (2a) Report Date: June 25, 1976 (2b) Event Date: May 26, 1976 (3) Facility: Three Mile Island Nuclear Station Unit 1 (h) Identification of Event:

Title:

Failure of the interlock circuit between Effluent Monitor RM-L6 and the Effluent Discharge Valve WDL-7257 to function.

Type: A reportable occurrence as defined by Technical Specification 6.9.2.B. (h) in that the failure of the interlock circuit between Effluent Monitor RM-L6 and the Effluent Discharge Valve WDL-V257 to function constituted an abnormal degradation of a system designed to contain radioactive material resulting from the fission process.

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Mr. J. P. O'Reilly, Director June 29, 1976 GQL 090b (5) Conditions Prior to Event:

Power Core: Ten (10%) Percent Elec. O RC Flow: 142 x 106 lb/hr RC Pressure: 2155 psi EC Temp: 563 F PRZR Level: 220 inches PRZR Temp: 6h8 F (6) Description of Event:

On 26 May 1976, at approximately lh00 hours, during a controlled release of radioactive liquid from the "B" Waste Evaporator Condensate Storage Tank (WDL-T-llB), a high alarm was received on the Liquid Effluent Radiation Monitor, RM-L6. In responding to the alarm, Control Room personnel checked to insure that the discharge had been terminated by the high alarm, but discovered that the hi6h alarm had failed to close the Liquid Release Valve, WDL-V-257 The discharge was manually terminated by s Control Room personnel at that time.

(T) Designation of Apparent Cause of Event:

Material failure is the apparent cause of the occurrence in that the relay in the interlock circuit between the Effluent Monitor, RM-L6, and the Effluent Discharge Valve, WDL-V-257, failed to operate. Personnel error also contributed to the situation in that personnel did not inmediately recognize the situstion and check to ensure that the discharge valve was shut.

(8) Analysis of Event:

Analysis of the radioactive liquid prior to release indicates that the tank contained 91.6 Ci of mixed fission and activation products. Based on available dilution flow, a discharge rate of 29 GPM from the tank would have resulted in concentrations of one-one hundredth of 10 CFR 20, Appendix "B", Table II concentrations released to the river. An actual release rate of 26 GPM was used to release the contents of the tank.

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ES curies C,'37 were released. The concentration of radioactive liquid in the tank was calculated to produce a response on EM-L6 of 356 cpm above background, and by procedure the high alarm setpoint was set at 2512 (two times the expected response above background). However, due to an operator misreading and reporting the monitor background as 1800 cpm rather than the actual background of 2500 cym, the RM-L6 high alarm occurred as soon as the release was started.

Based on the above, neither 10 CFR 20 nor the Technical Specification limits were exceeded and no threat to the health and safety of the public nor adverse impact to the environment resulted from this incident.

Mr. J. P. O'Reilly, Director June 28, 1976 GQLC904 (9) Corrective Action:

Lnmediate: The discharge of radioactive liquid to the river was manually terminated i==ediately upon realization that the autc=atic interlock had failed. Upon determination that a defective relay had caused the occurrence, the relay was replaced and the controlled discharge was resumed.

Long Term: The shift supervisor i= mediately counseled the operator at the time of the incident. Operators on other shifts were also briefedwith regard to the i=portance of these types of alarms and the need for corrective action.

(10a) Failure Data Relay Manufacturer: Deltral Controls Corp.

Model: Milwaukee Relay Series 105 Type: 3-Pole double-throv 10 a=p 115 volt AC (10b) Similar Events None Sincerel' ,

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