ML19261F308

Nonroutine 10-Day Rept 74-01 Re 740905,06 & 07 Unplanned Releases of Radioactivity.Caused by Blown Loop Seal Due to Inadequate Design.Loop Seal Plugged.Seal Design Mods Under Way

ML19261F308
Person / Time
Site:	Three Mile Island
Issue date:	10/03/1974
From:	METROPOLITAN EDISON CO.
To:
Shared Package
ML19261F307	List: ML19261F306 ML19261F308
References
NUDOCS 7910250770
Download: ML19261F308 (3)

Text

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Enclosure Metropolitan Edisen Cc=pany Three Mile Island Nuclear Statien, Unit 1 Operating License No. DFE-50 Nonroutine 10-Day Report Th-01 Infernation R2gardine Septenber 5, 6, and L 'fra, Unplanned Releases of Radicactivity

1. Description of Incidents:

a. September 5 Incident On Septenter 5, 197h, the Control Roc = received an alar = from the particulate =enitor which sa,ples the ventilated air frc=

the Auxiliary Building. Health E'.ysics persennel i=nfiately sampled the Auxiliary Building air. Cnly 133X e and 13 Xe, and 85Kr and 88K r in lover cencentraticns, were found to be present.

Operations persennel then tried to locate the source Jf the release, but by the time they were able to begin their search, the radiation level had decreased back to normel.

It was later determined that the cause of the incident was that the lecp seal en the Miscellaneous Waste Evaporator Feed Tank had blevn, thereby alleving radicactive gases to escape frc= the tank and the associated vent header through the blevn Icop seal into the auxiliary building sump. The locp seal was refilled by an auxiliary operster and the evaperater was restarted.

b. Septenber 6 Incident Cn September 6, the same auxiliary building particulate level alarm was received in the Centrol Rect. Health Physics and Operatiens personnel responded as befcre. It was determined that the radicactive release had come thrcugh tht locp seal en the Miscellanecus Waste Evaporator Feed Iank. It was found that the water in the locp seal had been blown cut although the reascn for this was not apnarent. Folleving the second incident, the ceal was ence again refilled.

c. Septe=Ler 7 Incident Prior to the third incident en Septenber 7, a full investiga-tien was begun to deternine the cause of the two previcus icop seal blevouts, but befcre this investigation eculd be ccepleted, the seal was blown cut again. This time the loss 1482 019 792o no 7 7 0

of sealant was attributed to a trip of a Miscellaneous Evaporator Feed Tank pu=p in that when the feed pu=p no longer tock suction en the feed tank, the leve: ircreased at a rate which was sufficient to increase the air pressure above the liquid in the tank to a peint where the 1 cop seal was blevn. The trip of the evaporater feed pump could not, hcvever, te attributed to having caused either cf the first two incidents.

d. General Cc=:ent Regarding All Three Incidents During the course of the three incidents, no perscnnel v<er-exposures cecurred altheuch . total of fcur people were exposed to liquids and gases of higher than ncr al radic-activity levels

2. Designation of Apparent Cause of Incidents:

Folleving censultations with the Architect Engineer, it has been determined that the bleving of the locp seal in the case of all three incidents was due to inadeouate des 13 n, in that the as-built system is not capable of handling cor al operating pressure transients .

3 Safety Analysis:

Fcr the folleving reasons it is celieved that the unplanned releases of radicactivity frc= the locp seal did not endanger the health and safety cf the public:

a. During all three incidents, at no time were the releases significant with respect to the l!=iting ecnditiens of the Technical Specificaticns.

b. A thercugh monitoring of the four station perscnnel directly expcsed to the releases shewed no detectable levels of ingested radicactive material due to these incidents. This, tcgethet with a review of the conditiens to which they were subjected, has resulted in a determination that these fcur individuals were not expcsed to harmful levels of radicactivity; and for all practical purposes, it is impossible for the public te have been expcsed to radiation which was =cre intense than this.

h. Cerrective Actions:

In addition to those ccrrective actions mentiened in part 1. abcVe, the overficv leg of the locp seal was plugged inmediately felleving the Septenber 7 incident; and this plug vill remain in place until design =cdificaticns of the seal have been ec=pleted (described in section 5. belev); and any overpressure in the feed tank vill be relieved to the vent header which is valved to the feed tink during evapcratcr operatien.

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5 Preventative Acticn:

The Plant Operaticns Review Cc=nittee (PCEC) convened after each of the three incidents and, tcgether with the Station Superintendent, approved of all corrective actions previcusly described in this report. In addition, PCEC recc== ended that preventative actica te taken to redesign and =cdify the lecp seal piping and valve syster in such a way that blevcut, siphoning, and backsurge vill be prevented while overflev protection of the evaperater vill still be afforded.

The Station Superintendent concurred with these recen=endatiens and has taken steps to ensure their cc=pletien. It is presently anticipated that =cdification of the lecp seal vill be executed shortly after ec=pletion of the required design studies.

6. Failure Data:

Not applicable.

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