ML20056B681
| ML20056B681 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 02/21/1972 |
| From: | Mayer L NORTHERN STATES POWER CO. |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102080342 | |
| Download: ML20056B681 (4) | |
Text
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4, ygp NORTHERN STATES POWER COMPANY f0TR ICELL O f1JCLEAR GENERAT I f6 PLAf6 Monticello, Vinnesota 55362 4^@x
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February 21, 1972 j
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Dr. Pe te r A. Mo r r i s, Di recto r Division of Peactor Licensine ErGuu ngy
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Dear Dr. Morris:
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UDfRICELLO IJJCLEAR GENERATI!L PLAIH Docket No. 50263 License No. DPR-22 ADDITIONAL I NFORMATION ON I fSTRUMETRAT10N PR3BLEfS This let ter is to inform you of addi tional information obtained concerning several plant inst. unentation problems which were the subject of previously I
submi tted reports.
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l 1.
?!ain Steam line Hioh Flow I nsi rument at ion Problems (See report to l
Dr. Morris dated November 23, 1971) i Sixteen switches with a range of 0-70 psid were installed in the main steam line high flew isolation system on September I, 1971, to replace I
the original 0-200 psi d swi t ches.
The lower range swi tches were installed because of lower than expected differential pressure reasure-nents from the main steam line flew nozzles.
During surveillance testing on November 11 and 12, 1971, three of the switches were found to exhibit signs of high friction or binding in their nechanisms and another swi tch was found to exhibi t non-repeatable trip settings.
T he f our defective swi tches were imrediately replaced by 0-200 psi d wwitches previously used for the protective function. T he remaining ll j
twelve switches were replaced on Tbvember 13, 1971.
One of the defecti ve swi tches was returned to the factory for inspection.
The vendor's inspection revealed that the torque tube jewel bearing was contaminated by a lead paste compound that was used to seal the joint between the instronent case and the differential pressure unit.
The contamination which occurred during switch assembly at the factory, caused excessive hysteresis in the torque tube movenent.
T he vendor indicated that the jewel bearing contamination was a random occurrence in switches of this type and model, and therefore there was no assurance that other similar inst ronents did not have the potential for similar i
l failures.
A review of the instrunentation used in the plant protection system was conducted to identi fy all inst ruments with the potential for o
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a contaminated jewel bearing. A total of 39 instrurents were so i
identified and inspected following the vendor's recommended proce-
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dure.
(Jo jewel beari ng contami nat ion was found.
1 i
The switch which was found to exhibit a non-repeatable trip setting l
was investigated at the site. Tests disclosed that the erratic i
operation was caused by a loose pivot pin on the cam follower assembly l
and was not due to the snap action switch, as previously reported.
l The loose pivot pin caused the trip point to vary between 109% steam i
flow and 127% steam flow.
This problem also appears to have resulted from a manufacturing error.
All plant instrurents of this t I
inspected for excessive deadband (greater that 5% of range) ype were and were i
found to be satisfactory.
I j
2.
Failure of ECCS Pumo Start Permissive Swi tch and Relay (See report j
to Dr. Mo r ri s dat ed Decembe r 20, 1971)
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On November 20, 1971, while performing a surveillance test, the trip l
setting of ECCS Purp Start Permissive Swi tch PS 2-3-53 A, swi tch #2, was found to be 12 psi below the requi red set ting of >_ 450 psig.
j During this surveillance test it was also discovered that a relay in i
the ECCS pumo start permissive logic failed to energize when pump j
start permissive swi tch PS 2-3-53 A, swi tch #1 was closed.
j An investigation of the setpoint problem revealed that the two j
swi tches contained in PS 2-3-53 A were not designed for the 125 V DC j
application for which they were being used, but were designed for 115 i
V AC service. The wrong switches were ini tially specified for this application.
An analysis perforced by the instrucent manufacturer j
revealed that the microswitch contacts in the instrurent were burned due to excessive current. The vendor believes the burned contacts j
may have caused the change in the instrucent setpoint.
i j
A check of plant instrurentation disclosed that 22 instrurents with l
microswi tches rated for 115 V AC were being used in 125 V DC circui ts.
4 T hese swi tches (listed below) have all been replaced wi th swi tches rated for 125 V DC.
I ns i rureni Funciion i
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PS 2-3-49 A & B LPCI Reci rc Loop Select ion
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i PS 2-3-50 A & B LPCI Reci rc Loop Selection i
j PS 2-3-52 A ECCS Valve Open Permissive l
PS 2-3-53 A & B ECCS Pump Start Permissive l
PS 23-68 A through D HPCI Steamline Low Pressure Isolation PS 2-128 A & B RHR Shutdown Cooling laolation
+
PS 14-47 A & B Core Spray Header Hi h Pressure Alarm E
PS 14-44 A through D Core Spray "AC I nterlock" b
g PS 13-78 RCIC Turbine Exhaust Diaphram
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High Pressure Alarm l
D o
I nsi ruceni Funciion PS 13-72 A & B RCIC Turbine Hip;h Pressure Alarm The investigation of the relay which failed to energize when the switch #1 of PS 2-3-53 A was closed, revealed that the pull-in voltage w'as set too high. This resulted in an intermittent failure of the relay to energize. The pull-in voltage of the relay was found to be 110 V DC (the operating voltage available at the relay was reasured to be The pull-in voltage was reset to 80% of the operating"of this 125 V DC).
voltage and the relay ai r gap was reduced.
All of the DC relays type in the plant had been previously set and tested at 80% pull-in voltage in accordance wi th a field engineering mero in August 1970.
Additional investigation revealed that the 80% setting is applicable only to AC relays. All DC relays of this type were reset to the factory recomrended 60% pull-in voltage. The relay which failed i
to operate during the surveillance test was the only relay of this type to experience a failure since the DC relays were set and tested in August 1970.
3.
Failure of FCCS Valve Opening Permissive Swiich (See repori to Dr.
Morris dated December 21, 1971.)
On ibvember 24, 1971, while performing a surveillance test, the trip setting of ECCS Valve OpeninE Permissive Switch PS 2-3-53 B, switch l
- 1, was found to be 42.5 psi below the requi red setting of >_ 450 psig.
An investigation revealed that the instrument lacked a setpoint
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"locki ng" devi ce, a redifi cation recommended by the instrurent manu-facturer. The locking device was immediately installed and the instrurent was calibrated to trip at 460 psig.
Locking devices were also installed on all similar instruments with snap action swi tches used in the plant protection systems.
The main steamline high flow instrurents have cercury type swiiches and are not designed for setpoint locking devices.
Since past-experience has shown the setpoints of these cercury swi tches to be qui te stable, the switches have not been redesi ned or modified to include a setpoint E
locking devi ce.
Locking devices were installed on the follewing instrurents:
Insirunent Funciion DPI S 23-76 A & B HPCI Hioh Steam flow isolation DPI S 23-77 A & B DPtS 13-53 RCIC High Steam flow isolation DplS 13-84 DPIS 14-43 A & B Core Spray Line Break Detection PS 2-52 B ECCS Valve Opening Permissive
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I nst ruren t function DPIS 2-129 A through D LPCI Loop Selection DPIS 2-136 A & B DPIS 2-137 A & B IPIS 2-138 A & B DPIS 2-139 A & B DPS 10-92 A & B RHR Heat Exchanger cP All the above instrucentation problems were corrected prior to plant h
startup on January 24, 1972.
Detailed reports on these probleras have been prepared at the plant and are available for the Compliance inspector.
t Yours very t ruly3 l
f L. O. Mayer Di rector of Nuclear Support Services LOWLLWki k ec: B E Grier
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