ML19276H316

RO 50-289/74-04 on 750123-24:while Reactor in Hot Standby Condition,Cover Gas Released to Auxiliary Bldg Ventilation Sys.Caused by Valve Stem leak-off.Possible Design Defect. Loop Seal refilled,RC-V1 Shut & RC-V3 Backseated

ML19276H316
Person / Time
Site:	Three Mile Island
Issue date:	02/03/1975
From:	Arnold R METROPOLITAN EDISON CO.
To:
Shared Package
ML19276H306	List: ML19276H316 ML19276H319 ML19276H325 ML19276H328 ML19276H334 ML19276H336 ML19276H341 ML19276H343 ML19276H350 ML19276H358
References
GQL-0717, GQL-717, NUDOCS 7910160657
Download: ML19276H316 (3)

Text

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ST'CFFICE BOX 542 READING, PENNSYLVANI A 19633 TELEPHCNE 2:5 - 903 0601 February 3, 1975 GQL 0717 Director ~

Directorate of Licensing nuclear Regulator-/ Cc ' ~'

k*ashington, D. C. 20555

Dear Sir:

Operating License DPR-50 -

Docket #50-289  :

In accordance with the Technical Specifications for our Three Mile Island nuclear Station, Unit 1, we are reporting the follo, ring abner =al occurrence:

(1) Report number: A0 50-239/75-Ol+

(2a) Report Date:

(2b) Occurrence Date: January 23-214, 1975 (3) Facility: Three Mile Island nuclear Generating Station, Unit 1 (h) Identification of Occurrence: -

Title:

Unplanned Radioactive Release, Caused by an Inadvertent Loss of the Reclaimed 3oric Acid Tank Loop Seal Type: An abnornal occurrence as defined by the Technical Specifi:a-tions, paragraph 1.8c., in that the Unplanned Radioactite Release, Caused by the Inadvertent Loss of the Reclai=ed 3crie Acid Tank Loop Seal, was in an a= cunt which was of signifi:ance with respect to the limits preser.ibed in the Technical Snecifi-cations, Appendix 3, paragraph 2.3.2.a.

(5) Conditions Prior to occurrence: The reactor was in a hot standby condition with major plant parsneters as follows:

Pover: Core: 15 / b Elec: 0 IN (Gross) 7910160 F7 O .

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2 RC Flow: 135 x 106 lb/hr RC Pressure: 2155 : sic-D es RC Te=p.: 53507 WJu}D &goJu W y$nkg PRZR Level: 210 in.

PR23 Te=p. 65007 (6) Description of Occurrence?

The pressuri:er spray valve (2C-71) was backsested to allov repla:e:en cf its '-d r que cp ers;;r. The pressurizer spray block valve (RC-V3) vas, therefore, closed and was to be operated only if required to ec trol reacter coolant system pressure. When the block valve (RC-V3) vas elesed, valve stem leak off to the vent header in the 3eac:cr 3uilding increased to approxi=ately 10 gp=. This increased valve s-=- 'aa> off caused an overpressure condition fn the vent header nitroge cover gas which blankets the R.C. Drain Tank and "A Reclai=ed 3cric Acid Tank, as well as other tarts within the Waste 31spesal Syste=. This overpressure in the reclal=ed 3cric Acid Tath ccver gas caused the water loss fra the tant everflev 1 cop seal and the subsequent release of radioactive cover gas to the Auxiliary Building Ventilation System. The Auxiliary 3 ilding 7entilation Systen subsequently discharged the released radi: active cover gas through the station vent to the atmosphere.

The "A" Reclai=ed 3cric Acid Ta % loop Seal was refilled to tersi-nate the gas release frc: the vent header, the Limitorque operator vas replaced,RC-V1 vas returned to its :or:a1 shut condition, and the motor operated pressurizer spray block valve (RC-V3) was back-seated to stop the valv= e'-- 'a=V off. As a result, the source of the unplanned Sas release vas ter=i=sted.

(7) It is believed that the apparent cause of the inadvertent loss of the Reclai=ed Soric Acid Ta 2 Lecp Seal, e=d resultant unplanned radioactive release, =ay be due to inadcquate desien of the nitrogen cover gas syste= and/or related syste=s , in that if the systen(s) vould have had sufficient capacity to handle the valve stem leak-off, the cecurrence veuld net have happe ed.

(8) Analysis of Occurre:ce:

)ll Analysis of statien va ' - '* -'en effluent recorder charts and local air sa:ples frc: the s:sti: vent indicate that 60 curies of predo:inately Ze-133 (:65) v - 'aa ed with a maxi:nm release rate of 1.26 x 105 M3 /se:. The average release rate ove the three hour and 37 titute durati; of the release was 1.65 x 10{ M3/sec.

The 2h hour avere.se con:entratica in.the affected area of the

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A0 75-Oh -

3 O%)D - dn D frD 1 f n NM l Auxiliary Building vas 1.23 x 10-3 uCi/ml, whi.-h constitutes '

an incident reportable in ecccriance with 10 *CFR 20.LO3 (b) (2);

and additional infor:stion vill be forwarded in accordance with 10 CFR 20.405 (a). The average concentration is based on a measured 1200 CFM air flov thrcush the area of the release.

Calculated' concentrations at the nearest devnvind unrestricted area, based on a dilution facter of X/Q = 7.6 x 10 sec/:.:3 are 2.6 x 10-0 uCi/c1 for the 10 ticute maximum and 3.h4.x 10-7 uC1/1 for the three hour and 37 minute duration of the release.

No station personnel vere in the area of the release, therefore no exposures occurred during the. peak times of the release.

Station personnel utilized to investigate the causes of the release vere dressed in protective clothing and self-contained .

breathing apparatus. Dosi=etric devices vorn by these individuals indicated only slight exposures (< 15 mrem).

Based on the above discussion, it has been determined that the -

- nealth and safety of no individual was endangered as a result of

• this occurrence.

(9) Corrective Action:

As has been described above, i==ediate corrective actions consisted of refilling the affected loop seal, restoring RC-V1 to its nor=al shut condition, and terminating the source of the release by bach-seating RC-V3 open.

The Plant Operations Review Cc =ittee met shortly after the cccurrence, approved the immediate corrective actions, and as a long ter= pre-ventative action reco: .: ended to the Station Superintendent that an evaluation be conducted of the nitrogen cover gas system, and re'.ated systems, to determine if there is a design inadequacy, and/or opera-tional procedural inadequacy, that could have caused this occu rence, and if so, what can be done to prevent it from happenirg again.

The Station Superintendent concurred with PORC's findings, a consultant has been contracted, and the investigation is in progress.

(10) Failure Data: .

Not applicable.

Sincerely, r

Signed-R. C. ARNOLD fIf9 jl}

R. C. Arnold Vice President RCA: DUG:eg