ML20056B757
| ML20056B757 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 10/06/1970 |
| From: | Anthony D, Duncanson R NORTHERN STATES POWER CO. |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102110259 | |
| Download: ML20056B757 (5) | |
Text
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NB Y' Regulatory NORTHERN STATES POWER COMPANY Minneapolis, Minnesoi r pip t
S October 6, 1970
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Dr. Peter A. Morris, Director A
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Dear Dr. Morris:
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MONTl CELLO NUCLEAR GENERATING PLANT Docket No. 50-263. License No. DPR-22 Feporting~of Uperating Occurrence A condition has occurred at the Monticello Nuclear Generating Plant recently which we are reporting to your office in accord'.nce with provisions of A pendix p
A, Technical Specifications, of the Provisional Operating License DPE-22.
The condi tion was considered reportable in accordance with Section 6.6.B.2 of the Speci fications. The Fegion ill Compliance office has been notified in accordance with the regai rements of Section 6.6. A of the Technical Speci fications.
The condition occurred when the inlet valve to the A circui t of the Standby
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Gas Treatment System failed to open when a startup of the system was automatically initiated during a planned test. The cause of the problem has been determined and the necessary repai rs have been completed.
The details of the occurrence are described in the attached Unusual Occurrence Fepori Nn. 5.
Yours very,iruly, I;
JLw F.O. Duncanson, Jr. P. Ef Gen. Supt. of Power Plants - Mechanical Chairman - Monticello Safety Audii Conrniitee ROD /caf P
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Unusual Occurrence Report No. 5
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1.
Sum ary Descrinfion of Occurrence At approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, September 28, 19~ [ dur of efgileksk open
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l Standby Gas Treatment System train A, the in
'v An investigation of this occurrence was beg
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i concluded on October 5, 1970.
i 2.
Detailed Descrintion of the Occurrence l
a.
Summary of Condit ions l
1 At the time of the occurrence, the core was @ and conditions l
were in accordance wiih Technical Specificalion 3.7.C such that Secondary l
Coniai nment integri ty was rat requi red.
l 4
i b.
Acenuni and Analysis of the Occurrence At approximately 1400 hours0.0162 days <br />0.389 hours <br />0.00231 weeks <br />5.327e-4 months <br />, Septe-ber 28, 1970, SGTS train A was started by far. R. Kmi tch, NSP Lead Plant Equipment Operator, under the direct ion of f!r. D. Antony, NSP Engineer, for testing purposes.
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When the unit was started, it was noticed that the filter train inlet v31 vq AO ?9A% hvi n s n,emH. Train A mm 9!o wi in mde #v opproximately 15 seconds before it was shutdown.
An attempt was then made to cpen the valve using the manual handswitch, however, the 1
valve would not open. The problem was immediately investigated by far. Antony', f/r. J. Przybys (Bechtel Field Engineer) and f/r. E. Seedorf (NSP instrument Technician).
The following brief description of the valve operating mechanisms (refer to attached diagram) will aid in understandinE the account and findings of the investigation.
When the solennia valve is enercized, air is allowed to pass through the solenoid val vq through the bleed-off valve via the spring loaded poppet and air ports, around the rubber j
diaphram of the diaphram valve and to the air operator, causing the butterfly valve ( A0 2945) to close.
When the solenoid valve is de-energized, the air supply is interrupted and the air above the rubber i
diaphr am is vented via the bleed-off valve and the solenoid valve.
When air is vented from above the rubber diaphram, the diaphram is lifted due to the high pressure below it, allowing the air from.the air operator to vent and causing ih c valve (A0 2945) to open.
It is noted that the air which is vented via the bleed-off valve must ds so by passing between the seat of the adjustable plug and the main seat of the valve.
The rate of venting is therefore dependert on the setting of the adjustable plug.
Following the failure on September 28, adjustments of the bleed-off valve plup were made and the valve was cycled approximately five times by f/r. R. Tigue, NSP l. cad Plant Equipment Operator. The valve operated properly, but was slow on 1
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opening (15 to 20 seconds) during one of the cycles.
The plug was then removed from the bleed-off valve at which time it was discovered that there was a piece of teflon tape approximately l} inches in length i
located near the main seat.
The teflon tape, which was still attached to the copper tubing, was removed and the plug was put back.into the i
bl eed-off valve.
SGTS train A was then started by Mr. Tigue imder the j
direction of Mr. Antony and was shutdown approximately 10 seconds later because A0 2945 had not opened.
Another adjustment of the bleed-off valve was made and A0 2945 was cycled and found to be slow at i
opening (15 seconds). During the course of this testing it was discovered that the filter train discharge valve A0 2979, was also slow at opening (15 seconds).
On September 30, 1970, air operated butterfly valve A0 2945 was removed from the line and disassembled.
Paint found on the bronze bushings was removed and the bushings were lubricated with silicone grease.
The l
valve was reassembled and bench tested. At this time it was discovered ihat ihe butierv1y valve would iravel beyond ihe center point of the rubber valve liner when the valve was closed, thereby making it more difficult to open the valve.
The air-operator was adjusted to eliminate l
the overtravel. The valve was reinstalled on October.lst.
The valve was cycled approximately ien iimes and it operaied proper 1y.
investication of this occurrence indicated that air operated valve, AD 2N5, iciled iv upu. Juc io cdjum bnents n.Ju iv th$ bl c.cd-o f f
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valve en September 26, 1970.
These adjustments were made by Mr.
Seedorf under the direction of Mr. Antony in an attempt to quiet A0 2945 which had been excessively noisy when opening. Both SGTS trains were run on September 26th and 27th and they operated properly.
It is believed that when the bleed-off 31ve was adjusted on September 26, the adjustable plug was fully seated. This would normally prevent A0 2945 from opening, however, ii is also believed ihat ihe ieflon tape which was found in ihe bleed-off valve had prevented ihe spring 1oaded poppet from seating, allowing the valve (A0 $45) to cpen during the i
operability tests on September 26th and 27th. The leflon tape was apparently blown from the seat of the poppet during, operation on September 27th. With the poppet seated and the adjustable plug seated i
Ihere was no means of venting ihe air, iht.s preventing A0 2945 from l
opening on September 28th.
The slowness in openirg during subsequent testing is attributed to the valve overtravel condition and the rate
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of bleed-off.
i c.
Resulis of the Occurrere i
l As a result of the failure of the Standby Gas Treatment System train A inlet valve to open, the train was considered inoperable.
3.
Corrective Action The corrective actions taken on A0 2945 included the removal of the piece of 4
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teflon tape from the bleed-off valve and adjustment of the bleed-off valve to provide for rapid venting.
The air operator was also adjusted
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to prevent over travel of the but terfly valve.
Neolube was applied to the lining of the valve and paint was removed from the valve bushires. The bleed-off valves for A0 2944 (filter train B inlet), A0 2978 (filter train B discharge) and A0 2979 (filter train A discharge)were also disassembled and inspected. A piece of teflon tape was found and removed from the main seat of the bleed-off valve for A0 2978.
Neolube was applied to the valve liners and the valves were inspected for overtravel. Overtravel was dis-covered on A0 2979 and the air operator was adjusted accordingly. The rate of bleed-off for A0 2979 was also increased.
All of the valves (A02944, 2945, 2978 cnd 2979) were tested and found to operate properly.
Prepared By:
m D.D. Antony, Engineer Occurrence Investigator DDA/mmm s
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