ML20056B728
| ML20056B728 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 09/18/1970 |
| From: | Anthony D, Duncanson R NORTHERN STATES POWER CO. |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102080445 | |
| Download: ML20056B728 (10) | |
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NSF NORTHERN 5TATES POWER COMPANY M f NNE A Pou s. MI QT&q t
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Dr. Peter A. Morris, Director
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United States Atomic Energy Comissic a
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Dear Mr. Morris:
MONTICELLO NUCLEAR GENERATING PLANT E-5979 ba*'"YY i Docket No. 50-263 License No. DPR-22
.j Reporting of Abnormal Occurrences Three conditions have occurred at the Monticello Nuclear Generating Plo.. ; recently which require reporting to your office in accordance with provisions of Appendix A, Technical Specification, of the Provisional Operating i
License DPR-22.
Two of the occurrences are classified as Abnormal Occurrences as defined in Section I. A.4 of the Technical Specifications and require report-l ing in accordance with Section 6.6.B.2 'f the Specifications. The third oc-currence was considered reportable in accordance with Set tion 6.6.B.2 of the Technical Specifications.
The Region III Compliance Office has been notified i
l in accordance with the requirements of Section 6.6.A of the Technical Specifi-cations.
The three occurrences involved failures of system components in the Standby 1
Gas Treatment System.
The failures were detected during operational testing a
periods when secondary containment integrity, including an operable Standby Gas Treatment System, was not reouired.
Secondary containment integrity has 9102080445 70091Es CF ADDCK 05000263 CF
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N O R*..ERN STATES POWER Co. ?ANY Dr. Peter A. Morris September 18, 1970 been maintained at all times as required by Sections 3.7.B and 3.7.C of the Technical Specifications.
The attached Abnomal Occurrence Reports No,1 and No. 2 report the details of the first two occurrences. The attached Unusual Occurrence Report No. 2 reports the details of the third occurrence. As explained in the attached reports, the Standby Gas Treatment System component failures have been correctrd and both circuits of the system are operable.
Yours ver truly, I
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R. O. Duncanson, Jr., P.E.
Gen. Supt. of Power Plants-Mechanical ROD /jma
September 17 1970 9
f.10iRICELLO TJUCLEAR GENERATING PLANT ~
Abnormal Occurrence Report IJo. 1 k~/I70 0
1.
Sum,arv Descrintien of Occurrence At approximately 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br />, September 8,1970,- an abnormal occurrence consisting of a failure in the current limiting circuitry for the air heater in Standby Gas Treatment System filter train A rendered the unit inoperable.
An investigation of the occurrence was conducted on Sept-ember 9,1970.
2.
Detailed Darerintion of the Occurrence a.
Summarv of Condi tions At the time of the occurrence, no fuel was in the reactor and secondary containment was not required.
Final plant testing was in progress in anticipation cf starting fuel loading operations during the evening of September 8th.
b.
Account and Ana' vsis of tha Occu r rence Each of the two Standby Gas Treatment System filter trains was orig-inally provided with a 20 KW air heater to reduce the relative humidity of the air passing through the train.
With one 20 KW heater in a SGTS filter train, the regaired flow rate through the train was unobtainable i
due in part to the large pressure drop across the heater. To correct this deficiency, the 20 KW heaters were removed and three 12 KW heaters (each having a flow area approximately ecpivalent to the 20 KW heater) were installed in each filter ' rain.
The power control ci r-cuitry for a filter train heater was designed for 20 KW.
I nstallati on of the new heaters (36 KW in each filter train) reouired recalibration j
of the current limiting circuitry for the heaters.
At approximately i
2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />, September 7,1970, a fuse to the filter train A air heaters was blown during the recalibration of the current limiting circuitry.
Recalibration was being performed in accordance with vendor's recommended procedures which reg; ired an initial momentary 36 KW output to the heaters.
Calibration work was immediately sus-pended until the cause of the blown fuse could be determined.
At approximately 0900 hours0.0104 days <br />0.25 hours <br />0.00149 weeks <br />3.4245e-4 months <br />, September 8,1970, it was discovered that i
one of the three 12 KW heaters installed in filter train A was
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shorted ou t.
This heater was then disconnected from the circuitry.
At approximately 1420 hours0.0164 days <br />0.394 hours <br />0.00235 weeks <br />5.4031e-4 months <br />, September 8,1970, the blow fuse for filter train A ai r heaters was replaced, the control panel door was closed and the control panel was energized.
At approximately 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br />, September 8,1970, the control panel door was opened for calibration of the curreni 1:miting circuit to the two operational heaters in filter train A.
When the control panel door was opened,
, smoke was detected in the panel and component failure in the air heater power control circuitry was detected.
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c Investigation of this occurrence indicated that a short in the defective air heater combined with the momentary 36 Kfl output re-1 commended for calibration, resulted in high current flow causing damage to one of the silicon controlled rectifiers, to the current limiting transformer and to other components in the power control circuitry for the filter tr2in A air heaters.
On September 10, 1970, a CVI Corporation Project Engineer arrived on site with the necessary SGTS filter train A power control circuit i
J replacement components.
The damaged components were replaced and the defective 12 KW heater section was meggared and reinstalled.
The circuit was recalibrated for a maximum 20 KW output to the train 4
A air heater. Subsequent testing revealed that the heater and heater j
controls are operating properly. This work was completed by 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br />, September 10, 1970.
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Significance or Consecuenms of the Occurrence c.
i Section 4.7.8 of the Technical Specification requires the demo.;-
stration that the output of the inlet heater of each SGTS train be at
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1 east 15 KW.
When it was determined that the heater on SGTS train i
A was not operable, train A was considered to be inoperable end fuel loading operations were scheduled with plant condi tions es-l
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tablished in accordance with Section 3.7.B.2 of the Technical i
Speci ficati ons.
As previously stated the Abnormal Occurrence conditions were corrected and train A,of the SGTS was operable as 1
i of 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> on September 10th.
4 3.
Recomendatione for the Prevention of Similar Future Occurrences Investigation of this occurrence has revealed that the air heaters were not megEared prior to energizing the control panel for calibration.
It i
is recommended that any repaired heater be meggared to detect a short, if one exists, subsequent to installation and prior to energizing the control circuitry.
It is also recommended that procedures for calibrating the current limiting circuit be revised to incorporat~e use of a watimeter and adjustment of the current limiter from the low limit setting to the desired j
setpoint without exceeding 20 KW output.
1 i
Prepared by:
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.f Y" IL D. / Antony, Enginee Occurrence Investigator DDA/caf i
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September 17, 1970 MONTICELLO NUCLEAR GENERATING PLANT Abnormal Occurrence Report No. 2
(. 3 1.
Sumarv Dascriotion of Occurrenca At approximately 1735 hours0.0201 days <br />0.482 hours <br />0.00287 weeks <br />6.601675e-4 months <br />, September 10, 1970, an abnormal occurrence occurred when Standby Gas Treatment System filter train B failed to provide a flow rate sufficient to maintain a 0.25 inch of water vacuum in the reactor building under calm wind conditions.
An investigation of the occurrence was conducted on September 14, 1970.
2.
Detailed Descriotion of the Occurrence a.
Summarv of Conditions At the time of the occurrence there were 36 fuel elements in the core and conditions were in accordance with Technical Specification 3.7.C such that Secondary Containment Integrity was not recpired.
Surveillance testing was being performed on Standby Gas Treatment S stem filter train B.
y b.
Account and Analvsis of the Occurrenca At approximately 1735 hours0.0201 days <br />0.482 hours <br />0.00287 weeks <br />6.601675e-4 months <br />, September 10, 1970, Standby Gas Treatment S stem filter train B was started for verification of operability y
(this verification was required to comply with Technical Specification 3.7.B.2 because SGTS filter train A had been declared inoperable on Sep. ember 8,1970, due to a failure in its air heater current limiting circuitry).
A low flow condition (2800 CFM) throuph train B was observed at this time.
Exhaust fans V-EF-26 and VZEF-18A were operating at the time of the SGTS train B low flow.
Exhaust fan V-EF-26 f akes suction from the turbine building air ejector room and normally exhausts to the off-gas stack providing dilution air for either of the two 100 percent capacity dilution fans, V-EF-18A or i
V-EF-18B.
After the low flow condition through train B was observed, train B was shutdown and SGTS train A was started.
Low flow through train A was also observed.. Stack dilution fan operation was then I
t r ans fe r re d f rom V-E F-1 SA to V-E F-188.
The flow through SGTS train A then increased to 3900 CFM. SGTS operation was then transferred from train A to train B at which time the SGTS flow decreased to 3300 CFM.
Investigation at this time revealed that a backdraft damper on exhaust fan V-EF-18B failed to close properly when operation was transferred from V-EF-18B to V-EF-18A. Tbe backdrafi damper for V-EF-188 was 4
then manually closed.
With V-EF-18A operating and the backdraft j
damper for V-EF-1SB closed, flow through SGTS train A was observed i
to be 4000 CFM and flow through SGTS train B was observed to be I
approximately 3300 CFM. SGTS filter train B was then considered inoperable because it was questionable whether train B could provide a flow rate sufficient to maintain a 0.25 inch of water vacuum in the reactor building under calm wind conditions.
l
. On September 11, 1970, the off-gas dilution fan backdraft damper problem was investigated.
The backdraf t damper for V-EF-1SB was found to be hanging up on the ductwork and flexible connection between the fan discharge and the off-gas dilution air piping due to end play on the damper shaft. This problem was corrected by putting a collar on the shaf t to center the damper and eliminate the end play.
Although no problems had been experienced with the backdraft damper for V-EF-18A, a collar was also added to its shaft to eliminate end play.
It is to be noted that the backdraft damper problem was inconsequential to the low flow problem experienced with SGTS filter train B.
I Exhaust fan V-EF-26 was operating when the low flow condition through SGTS filter train B was discovered.
This fan was also operating 4
during the subsequent attempts to obtain prcper flow through the B train on September 10, 1970. There is another exhaust fan, V-EF-11, which will automatically provide dilution air to the off-gas dilution fans if V-EF-26 should fail. The normal operation fo r these two fans is such that V-EF-26 will provide dilution air for the dilution fans and V-EF-11 will exhaust directly to the reactor building plenum.
On SGTS initiation both V-EF-11 and V-EF-26 should l
exhaust directly to the reactor building plenum and the SGTS should provide dilution air for the off-cas dilution fans.
V-EF-11 was i
not operating at the time of the abnormal occurrence.
On September 11,1970, V EF-11 was started and i t was discovered that the operation of this fan reduced the flow through SGTS filter train A from 4000 CFf3 with the train A discharge damper throttled to 74 percent open to 3S50 CFM with the discharge damper full open.
Investigation by a Bechtel Field Engineer, on September 12, 1970, revealed a design error in the logic circuitry for the plenum exhaust dampers for V-EF-11 and V-EF-26.
The ci reuitry was designed such that the plenum exhaust damper for V-EF-26 would open only on SGTS filter train A operation and the plenum exhaust damper for V-EF-11 would open only cn SGTS filter train B operation.
At the time of the abnormal occur rence, exhaust fan V-EF-26 was operating.
When SGTS filter train B was started, the plenum exhaust damper for V-EF-26 did not open. This resulted in reduced flow through SGTS filter train B due to the additional amount of dilution air being supplied by V-EF-26.
A wiring change was made (Bechtel FC0 559) to provide for opening of the plenum exhaust dampers for V-Ef-11 and V-EF-26 independent of which SGTS filter train is operating.
A procedure was written for testing the logic changes made. The test was performed on September 12, 1970, and proper operation was verified.
Further testing requiring three successive runs of each SGTS filter train was initiated at approximately 1740 hours0.0201 days <br />0.483 hours <br />0.00288 weeks <br />6.6207e-4 months <br />, September 12, 1970.
Both filter trains operated properly for the first two test runs.
During the third test run, SGTS train A was manually tripped and train B automatically started.
The unit operated properly for approximately 30 seconds at which time train B momentarily tripped ana restarted.
it was then discovered that a GE CR120 seal-in relay for train B had a cracked
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_y pole piece cover.
It was also noticed that the relay was chattering lou dl y.
The pole piece cover was re. aced and the chattering noise di sappeare d.
Proper operation of both SGTS units was then verified by performing three additional successful runs on each filter train.
Flow through SGTS filter train A was found to be 4000 CFM with its discharge dan.r throttled to approximately 70 percent open.
Flow y
through SGTS filter train B was found to be 4000 CFM with its discharge damper throttled to approximately 81 percent open.
Both Standby Gas Treatment System filter trains were then esasidered to be operationt1.
Signi ficance or Consecuences of the Occurrence c.
t Section 4.7.C.1 (c) of the Technical Specifications requires
~~h surveillance testing to demonstrate the secondary containment cap-ability of maintaining at least a 0.25 inch of water vacuum under calm wind condi tions.
Br. sed on pre-operational testing, it was questionable whether a flow rate of 3300 cfm in train B was sufficient to meet this recpirement.
As a result, train B was considered inoperable and plant activities, fuel loading, were resumed during the evening of September 10th in accordance with the provisions of Section 3.7.B.2 of the Technical Specifications.
As discussed in Abnormal Occurrence Report No. 1, the train A air heater current limiting circuitry had been repaired and train A was operable as i
of 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br />, September 10, 1970, 3.
Recomndations for the Prevention of Similar Future Occurrences investigation of this occurrence has revealed that a design error in the logic circuitry for the plenum discharge damper for exhaust fan V-EF-26 prevented Standby Gas Treatment System filter train B from providing the proper flow.
Corrections were made to the logic circuitry and testing was performed to verify proper operation. These logic corrections are considered adecpate, by the investigator, to prevent future occurrences i
of this problem, it was noted in this report that a problem had been discovered with the off-gas dilution fan backdraft dampers.
The solution to this problem, as discussed in the report, is also considered adequate to prevent future occurrence.
Also noted in this report is the momentary tripping of SGTS train B due to a cracked pole piece cover on a GE CR120 relay.
The operation of noisy relays will be watched to verify continued reliable operation until the program for the replacement of these relays has been accomplished.
Prepared by:
Iew$u 0- 0$y y D.D. ' Antony, Engineer Occurrence Investigator DDA/ car
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September 17, 1970 MONTICELLO NUCLEAR GENERATil!G PLANT Unusual Occurrence Report No. 2 rue.u mur cat.a 9-If"7f 1.
Summarv Descriotion of Condi tion At 1737 hours0.0201 days <br />0.483 hours <br />0.00287 weeks <br />6.609285e-4 months <br />, September 11_, 1970, an abnormal condition occurred with a failure of the Standby Gas Treatment System train A flow controller. An investigation of the condition was conducted on September 15, 1970.
2.
Daiailed Descriotion of the Condition Surrnary of Condi tions a.
At the time the condition occurred, there were 58 fuel elements in the core and conditions were in accordance with Technical Specification 3.7.C such that Secondary Containment Integrity was not required.
Secondary Containment integrity was not required at any time that this condition existed, b.
A. mount and Anal ysis of the Condi tion
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At approximately 1730 hours0.02 days <br />0.481 hours <br />0.00286 weeks <br />6.58265e-4 months <br />, September 11, 1970, the first of three Standby Gas Treatment System train A operability tests was initiated.
The flow controller (FIC 2943) for train A operated properly during the first test and maintained 4000 CFM flow.
SGTS train A was then shutdown and restarted for the second operability test. T he flow through the train increased to 3950 CFM and stayed at that flow with the discharge damper adjusted to approximately 80 percent open.
A control deviation was indicated on the controller, however the controller failed to respond. The controller was then placed in a manual mode of operation and an attempt was made to manually open the discharge damper. The damper position could not be adjusted as the controller output was fixed at a constant value. The controller in question is a Leeds and Northrup Model 420 C. A.T. Controller.
On September 12, 1970, it was determined that there was a bad field effect transistor (FET) in the controller.
At approximately 1330 hours0.0154 days <br />0.369 hours <br />0.0022 weeks <br />5.06065e-4 months <br />, September 12, 1970, a Leeds and Northrup Field Repre entative arrived on site wi th spare FET's. The FET was replaced on in. in-operable controller.
A capacitor was installed on the output side of the FET in the flow controller for each SGTS train. The capacitors, which were connected directly to ground, were installed to protect the FET's be suppressing feedback noise spikes.
It is noted that the SGTS filter train air heater temperature controllers are of the same type as the flow controllers. During the pre-operational testing of the SGTS, a similar problem existed with these con-trollers. The solution to the problem was the installation of capacitors to protect the FET's.
There have been no subsequent problems with the temperature controllers. Testing of both Standby Gas Treatment System trains c,n September 12, 1970, indicated that their respective con. trollers are operating properly.
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Si rin i fi canca nr Consecuences of the Occurrenea Abnormal Occurrence No.1 involved train A of the SGTS.
As a result, train A was inoperable from September 8th until approxi-mately 1630 hours0.0189 days <br />0.453 hours <br />0.0027 weeks <br />6.20215e-4 months <br /> on September 10th.
During this period of time, plant operations continued in accordance with Section 3.7.B.2 of the Technical Specifications.
Abnormal Occurrence No. 2 involved train B of the SGTS.
As a result train B was inoperable from aoproximately 1735 hours0.0201 days <br />0.482 hours <br />0.00287 weeks <br />6.601675e-4 months <br /> September 10th until the afternoon of Septem'ber 12th.
Plant operations were conducted on September 10'th after 1735 hours0.0201 days <br />0.482 hours <br />0.00287 weeks <br />6.601675e-4 months <br /> until approximately 070C hours on September 11th in accordance with Section 3.7.B.2 of the 'lechnical S ecifications.
Fuel loading operations are not p
i conducted during the daytime so secondary containment integrity was not recpired during the day on September 11th.
Testing of the SGTS was being conducted on September 11 in accordance with Section 3.7.B.2 of the Technical Specifications (prior to resuming fuel loading cctivities) when the failure of the train A flow controller occurred.
Although the installation of the flow controller from train B into train A made train A operable it was decided to suspend fuel loading activities until the SGTS l
was made reliably operable.
Corrections to 'the SGTS system were made on September 12 as described in Abnormal Occurrence ~ Report No. 2 and after a series of successful tests, both trains of the SGTS were considered to be reliably operable.
Fuel loading activities were resumed during the evening of September 12th.
Daily tests of the SGTS have been conducted since September 12th and no additional system failures
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have occurred.
3.
Recommendations for the Prevention of Similar Future Condi tions i
I investigation of this condition indicates ~ that the SGTS train A flow con-troller failure was caused by a field effect transistor which apparently became defective due to feedback voltage spikes.
The FET was replaced and a capacitor was added to the output of the FET to suppress these spikes.
Although it is difficult to predict the failure of an electronic component, the solution to this problem seems to be adequate to prevent re trrence of this condi tion.
It is noted that the controller failure would not have prevented annunciation of' a low flow (3500 CFM) alarm and a transfer of operation to SGTS train B on low flow (3300 CFM).
Prepared by:
l/
,4 k D.D. Antony, Engineerd Occurrence Investigator DDA/ car
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