ML20086L115

Ao:On 731224,increase in Reactor Bldg Ventilation Radiation Monitor Noted.Caused by Combination of Misadjustment of Operating Mechanism & Small Air Leak Causing Intermittent Deflating of Disc Seal.Proper Mechanism Adjustment Verified

ML20086L115
Person / Time
Site:	Peach Bottom
Issue date:	01/08/1974
From:	Cooney M PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC
To:	Giambusso A US ATOMIC ENERGY COMMISSION (AEC)
References
NUDOCS 8402070400
Download: ML20086L115 (3)

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PHILADELPHIA ELECTRIC COMPANY lr?

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2301 MARKET STREET 1 PHILADELPHI A. PA.19101 6. ~ ~

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January 8,1974 Mr. A. Giambusso Deputy Director of Reactor Projects Uni ted States Atomic Energy Corxnission Directorate of Licensing Washington, D. C. 20545

Reference:

Peach Bottom Atomic Power Station - Unit 2 Facility Operating License DPR-44 Docket No. 50-277

' Subjec t: Abnormal Occurrence On December 31, 1973, a primary containment penetration Icak was reported ~

to Mr. R. T. Carlson, A.E.C. Region I Regulatory Operations Of fice.

In accordance with Section 6 7.2.A of the Technical Specifications, Appendix A of DPR-44 for Unit #2 Peach Bottom Atomic Power Station, this event is being reported to the Directorate of Licensing as an Abnormal Occurrence.

Description of Event On December 24, 1973, at 6:05 a.m. during a reactor pressure vessel re-lief valve test, an increase in the Unit #2 reactor building ventilation radiation monitor was noted. The total plant release rate peaked at approximately 9.2% of MPC for a maximum of 2 minutes. The release then decreased sharply to approximately 2% of MPC where it remained for a maximum of 3 hours3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br />. The reactor was operating, at approximately 15% of rated pnwer at the time of. the release. A scheduled reactor scram was initiated at 9:10 a.m. on December 24, 1973 Investigation and Corrective Action A program was subsequently developed to determine the source of leakage from the. primary containment to the reactor building. This program consisted of inspections of penetrations, 1 psig hold tests on the drywell and torus. volumes, and Icak rate testing of some containment atmosphere control valves.

Initially, all penetration valve positions were checked and low pressure leak tests were performed on the torus vacuum breaker penetrations between the i

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. . U (V butterfly and swing check valves. All penetration valves were found in the proper position. The results of these Icak tests disclosed that tne "A" torus vacuum breaker penetration Icak rate was approximately 1200 cc/ min with a i psig test pressure. The "B" vacuum breaker penetration leak test also identified a smaller leak rate.

Inspection of the butterfly valve in the "A" ponctration disclosed dirt on the seating surface and a slight misadjustment of the operating mechanism which actuates the disc scaling feature. A small air leak on the air piping on the valve controls was also noted. The combination of the slight misadjustment and small air leak caused intermittent deflating of the disc seal. Inspection of the swing check valve in this penetration also indicated dirt on the scaling surface. These two probicms are believed to have permitted the release to the reactor building. Both valves were cleaned, readjusted and Icak tested at 49.1 psig. The measured Icak rate was 27 cc/ min.

A similar inspection was performed en the "B" toru; vacuum breaker penetration valves. The scating surfaces were found to be dirty on both valves and a leak noted on the swing check valve. After verifying proper mechanism adjustment and c leaning, a test et 49.1 psig indicated a leak rate of 154 cc/ min.

An additional qualitative 1 psig hold test was performed on both the drywell and torus. Internal inspection of the drywell and external inspection of the torus did not identify any leaks.

As a follow-up, leak rate test at 49.1 psig were performed on each penetration containing similar butterfly valves as well as the air lock, and N 2

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make-up penetr ation. The measured leak rates on all these penetrations except the torus exhaust were found to be acceptabic. After a manual adjustment of the torus exhaust valve, this leak rate was also reduced to an acceptable level.

Until an opportunity for an internal examination of the torus exhaust penetration valves is presented, the butterfly valves in the containment atmospheric control system torus exhaust line shall be blocked closed. The vacuum breaker penetrations shall be leak tested at quarterly intervals until' satisfactory performance is established.

The'present total penetration leakage as determined by a review of the present penetration leak rates and a comparison of recorded ILRT values is 8618 cc/ min at 49.1 psig. This cortpares with 16390 cc/ min (60% of allowable) at 49 1 psig.

. Safety Implications The release rate indicated and total activity released as a result of '

this occurrence was well within established A.E.C. limits. Since there were no l personnel in the vicinity of the vacuum breakers at the time of release, no personnel exposure was possibic. The maximum. release rate during the 2 minutes

' was aoproximately 600 Ci/sec with a concentration of spproximately 6 x 10-0 Ci/cc.

The total activity release over the ent' ire 3 hour3.472222e-5 days <br />8.333333e-4 hours <br />4.960317e-6 weeks <br />1.1415e-6 months <br /> period was approximately 0.6 Ci of activation and noble gases. The #2 reactor building ventilation stack filter 3

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l showed only naturally occurring radionuclides. Since the total release and release ra tes were well wi thin A.E.C. limits, and no personnel exposure resulted, there are no safety implications associated with this release.

The primary containment low pressure Icak identified as a result of this occurrence was relatively small. A higher torus pressure would have pro-vided additional force to reduce the leakage of the torus vacuum breaker penc-tration swing check valve, thereby limi ting the release. The penetration tests performe.d af ter the identified Icaks were corrected, resulted in an acceptable primary containment penetration Icak rate. The small Icak identified as a result of the occurrence has inconsequential safety implications.

Very truly yours,

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H. J. Cooney &

As's' t Gen' t Superintendent Generation Division HJC:kam cc: Mr. J. P. O'Reilly Director, Region 1 Uni ted States Atomic Energy Commission 631 Park Avenue King of Prussia, PA 19406 O

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