ML20084K298
| ML20084K298 | |
| Person / Time | |
|---|---|
| Site: | Quad Cities  |
| Issue date: | 07/18/1974 |
| From: | COMMONWEALTH EDISON CO. |
| To: | US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20084K292 | List: |
| References | |
| AO-50-254-74-8C, NUDOCS 8305190262 | |
| Download: ML20084K298 (2) | |
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REPORT NUMBER: A0 254/74-8c REPORT DATE: July 18, 1974 OCCURRENCE DATE: April 12, 1974 FACILITY: Quad-Cities Nuclear Power Station Cordova, Illinois 61242 IDENTIFICATION CF OCCURRENCE:
Drywell equipment drain sump discharge isolation valves, A0-1-2001-15 and A0 2001-16 excessive leakage.
CONDITIONS PRIOR TO OCCURRENCE:
Reactor in cold-shutdown condition for refueling outage drywell equipment drain sump pumped out and piping drained, sump discharge isolation valves closed.
DESCRIPTION OF OCCURRENCE:
Local leak rate testing of the Unit One drywell equipment drain sump discharge valves was initially conducted during the current refueling outage on April 12, 1974. Valves A0-I-2001-15 and A0-1-2001-16 had been placed in the closed position via control room switch operation.
In the upstream direction valve A0-1-2001-14 remained in the open position in order to facilitate a removal path for possible air leakage through A0-1-2001-15.
In the downstream direction, valve -2001-826 to the waste collector tank remained open for the same purpose.
The leak rate test was performed by pressurizing the pipe volume located between valves A0-1-2001-15 and 16 through a pressure test tap installed for the purpose i
of leak testing these valves (Modification M-4-1-73-82). The absence of pressure test taps upstream or downstream of these valves resulted in the necessity to test both valves simultaneously. Excessive leakage through this valve set resulted in an inability to attain the required 48 psig test valve. After cycling valves A0-1-2001-15 and 16 three times each, the second pressurization attempt also re-l suited in an inability to attain the required test pressure.
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' Af ter taking valves A0-1-2001-15 and 16 out of service, repairs were initiated.
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DESIGNATION OF APPARENT CAUSE OF OCCURRENCE:
Although there existed satisfactory valve stem movement and control room valve position Indication, it appeared that the valves were not fully seating themselves.
Upon examination of the valves' seating surfaces after dismantling, excessive dirt and corrosion products were noticed. This was the apparent reason for the valves not seating properly.
Therefore, the apparent cause of the valve leakages was the fact that the valves were not fully closed during the pressurization, and were therefore unable to sustain the 12 psig test pressure. The leakage paths were to the drywell equipment drain sump pumps through valve A0-1-2001-15, and to the waste collector tank through valve A0-1-2001-16.
0305190262 740718 PDRADOCK05000g S
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A0-50-254/74-8c July 18, ly?4 ANALYSi$ 0F OCCURRENCE:
Although the leakage through the valve series A0-1-2001-15 and A0-1-2001-16 did exceed Technical Specification limits for Individual primary containment' isolation valves, valve operability was satisfactory. Further isolation of these normally water-filled lines could have been accomplished in actual operation through closure of valve A0-1-2001-14 located upstream of valve A0-1-2001-15 inside of the drywell, and closure of valve i-2001-826 downstream of valve A0-1-2001-16 at the waste collector tank.
In this case, no safety-related systems or components would have been rendered inoperable; furthermore, under accident conditions, the pipe sections upstream of these valves would be filled with water, thus not allowing the drywell pressure atmosphere to be directly exposed to these valves, and not allowing the weste collector tank to be exposed to the drywell atmosphere.
Therefera, equipment damage and excessive personnel exposure would not have re-suited toe to the excessive leakage through these valves.
CORRECYlVE ACTION:
Maintenance personnel dismantled valves A0-1-2001-15 and 16 and thoroughly cleaned the valvo seating surfacas and plugs. Each valve w1s cycled three times in order to assure proper valve operability and seating after repairs were completed.
Following repair of the above valves, a local leak rate test was conducted on May 3, 1974, on the valve ' combination which resulted in a measured leakage rate of 1.34 SCFH at a test pressure of 48 psig. This value is within the Technical Speci-fication limit of 18.36 SCFH leakage for any single isolation valve. Since the 1.34 SCFH valve was obtained as a result of dual valve leakage simultaneously in opposite directions, the actual single valve leakage rates would be justifiably lower.
FAILURE DATA:
Valves A0-1-2001-15 and 16 were initially leak tested on November 17, 1970, during pre-operational testing of Unit One. The leakage values for each valve were as follows:
A0 2001 -15 0.0075 SCFH i
l A0-1-2001-16 0.331 SCFM l
l These values were within the Technical Specification Isakage limit of 18.36 SCFH per valve.
These valves were not tested for leakage at any time between pre-operational test-ing and the current refueling outage. Therefore, no leakage failure data exists l
for these valves.
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