ML19343C347

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AO 72-04:on 721219,cracks Found in 8-inch Containment Purge Exhaust Bypass Isolation Valve Yoke,Causing Containment Air Leakage.Caused by Thermal Stress Due to Frozen Moisture Accumulation within Valve Internals.Valves Heat Traced
ML19343C347
Person / Time
Site: Haddam Neck, 05000216  File:Connecticut Yankee Atomic Power Co icon.png
Issue date: 12/28/1972
From: Hartley F
CONNECTICUT YANKEE ATOMIC POWER CO.
To:
US ATOMIC ENERGY COMMISSION (AEC)
References
AO-72-04, AO-72-4, CYH-2284, NUDOCS 8103100493
Download: ML19343C347 (4)
v • d • e


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CONNECTICUT YANKEE AT C, M I C POWER COMPANY

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HADDAM NECK PLANT

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December 28, 1972

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Director, Directorate of Licensing n._,.

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REFERENCE:

Provisiona! License No. DPR-14

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Dear Sir:

As defined by Technical Specifications for Connecticut Yankee Atomic Power Station, Section 5.3, the following incident invohing containment air leakage is reported as Abnomal Occurrence No. 72-4.

At 1322, December 19, 1972 a plant computer alarm indicated a

" reactor containment air out of range" condition. The control room operator scanned the data logger message trend printout and noted a decreasing trend in weight of containment air. An imediate invest-igation revealed cracks in the 8-inch containment purge exhaust by-pass isolation valve yoke. The cracked yoke pemitted the valve to open approximately 3/4 of an inch. A temporary closure mechanism was applied to the valve at about 1347 and the air leakage stopped.

A blank flange was applied to the 42 inch purge air exhaust penetrat-ion inside tne reactor containment to pemit repair and testing of the 8-inch bypass valve. A pressure test at 50 psig. confirmed the leak tightness of the bypass valve and the blank flange. The data logger trend printout infomation confimed that leakage was halted upon application of the temporary closure mechanism. A plot of containment weight of air vs. time is included as Attachment "A".

Evaluation of the data logger trend printout information revealed a total loss of 1100 lb. air from the time the valve yoke apparently parted, to the time the temporary closure mechanism was applied to the valve. The average air leakage was 282 ft 3/ min over a time span of 52 minutes. A complete radio chemical analysis of the containment air is included as Attachment "B" to this report. The site boundry concentrations of all released radionuclides are several orders of magnitude below pemissable levels.

After the blank flange was installed and tested for leak tightness, the broken valve yoke was removed and a new yoke installed, followed by a successful leakage test. The temporary blank flange was then removed from the 42 inch containment purge exhaust line.

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U. S. Atomic Energy Comission December 28, 1972 A similar incident occurred on January 18, 1972 and was reported as Abnormal Occurrence No. 72-1.

Following that incident an automatic containment weight of air alam function was implemented to provide the control room operator with an earlier warning of increased con-tainment air. leakage. The effectiveness of the alam as an early warning mechanism was clearly demonstrated by the rapid detection of this leak.

The cause of the first valve yoke failure was detemined to be thermal stresses induced by seasonal fluctuations in temperature.

The most recent valve yoke failure appears to have been caused by noisture accu =ulation within the valve internals followed by freezing

. nd expansion of the accumulated water. To prevent a reoccurrence of this condition the bypass valve and the main purge va've have been electrically heat traced and insulated to prevent freezing and a low point drain has been installed imediately downstream of each valve.

Very truly yours

!}.U's c$

F. W. artley /

Plant Superintendent RHG/bn cc: Mr. James P. O'Reilly, Director Region 1, Directorate of Regulatory Operations

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CONTAlllMENT MPC CONCENTRATION IS0 TOPE AIR CONCENTRATION uc/cc AT SITE uc/cc B0UNDRY

  • Xe-133 7.16 x 10-5 3 x 10-7 5.75 x 10-10 Xe-135 2.5 x 10-6 1 x 10-7 2.0 x 10-II H -3 6.93 x 10-6 2 x 10-7 5.55 x 10-II Part (B, y) 1.5 x 10-9 1 x 10-10 1.2 x 10-14
  • Based upon dilution flow of 35000 cfm and a stack meteorological factor of 1000 s.

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