ML20043G392

LER 90-014-00:on 900519,manual Reactor Trip Initiated as Result of Anticipated Turbine Trip Due to Condenser Vacuum. Caused by Design Deficiency in That Traveling Screen Capacity Inadequate.Traveling Screen modified.W/900611 Ltr

ML20043G392
Person / Time
Site:	Millstone
Issue date:	06/11/1990
From:	Nichols B, Scace S NORTHEAST NUCLEAR ENERGY CO., NORTHEAST UTILITIES
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-90-014, MP-90-576, NUDOCS 9006200233
Download: ML20043G392 (4)

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Facility Operating License No. NPF-49 i

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. , Tnis letter forwards Licensee Event Repon 90-014-00 required to be submitted within wm thirty (30) days pursuant to 10CFR50.73(a)(2)(iv), any event or condition.that resulted a", 'in manual actuation of the Reactor Protection System (RPS).

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.W. J. Raymond,' Senior Resident Inspector, Millstone. Unit lNos.1,'2 and 3

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. Es.' mated tvoen par rssponse to comp (y with this intornation ceection reauest: 60.0 hrs Forwarc LICENSEE EVENT REPORT (LER) In%'d'u'a'ndo *n"e'nUrEnU6$03'"*u I6 Nueiear Regulatory Commission. Washington. DC 20566, ano to tne Paperwoa heduction Pro <ect (3160-0104h Office of Management 61 Budget. Washington, DC 20503 j F ACLITY NAME (1) . DOCKET NUMbEh (2J 0*M O  !

hiillstone Nuclear Power Station Unit 3 olsiololold1213 1lOFl 013 TM LE (4) .

h!anual Reactor Trip Due to imminent .oss of Condenser Vacuum EVENT DATE (51 L.F A NUMBFA (6) REDORT DATE (71 OTHF A F ACILfilE O NVOL *ED (81 MONTF DAY YEAR YEAR

@ MONTH DAY YEAR F ACLITY NAMES

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OPERATNG THIS REPOAT IS BEING BUBM:TTED PURSUANT TO THE REQUIREMENTS OF 10 CFR B: (Cneck one or more of the fobowingM11) 20 dO2(b) _

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LICEt SEE CONT ACT FOA 7HIS LER (12)

NAME TELEPHONE NUMER AREA CODi  !

Barrett W. Nichols. Senior Engineer, X5493 2 0l3 4j4l7l-l1]7l9l1 COMDLETE ONE LINE FOR E ACH COMPONENT FAILURE DESCRIBED IN TH!S REPORT (13)

CAUSE SYSTEM COMPONENT h* '

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~~l YEs ne vos. compiet. ExPECTEo sueMisSioN DATEi 7 No DATE (16) l l. l ABSTRACT (Limit to 1400 spaces. I.e., approximateiy vitteen singie-space typewritten tires) (16)

On hlay 19,;1990 at 2033 hours0.0235 days <br />0.565 hours <br />0.00336 weeks <br />7.735565e-4 months <br /> with the plant in blode 1 at 60re power, a manual reactor trip was initiated

= because of an anticipated turbine tnp due to loss of condenser vacuum. Circulating Water Pump 3CWS-P1B was providing cochng water for Condenser Waterboxes " A" and "B". A rapid buildup of seaweed on "B" Traveling Screen resulted in an automatic trip of 3CWS-PIB. The plant was in the process of downpowerin as a result of weather effects on condenser cooling water equipment in the intake structure. As tbt ! :: eicoo ng L ' to two condenser bays would have resulted in a low condenser vacuum, a reactor trip % mitiated. The reactor trip caused a hiain Turbine and Generator trip in accordance with design.

Root cause of this event was design deficiency in that the Traveling Screen capacity was inadequate. A L contributing cause was the peak seaweed season.

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.. As corrective action, the Traveling Screen units in a number of bays will be redesigned and modified per the .  !

recommendations of an internal Task Force. Two of these units will be modified in the next year. Personnel  !

have been instructed to evaluate intake structure conditions more frequently and procedures modified to allow power reductions at a faster rate.

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U.S. NUCLEAR REGULATORY CoMMIS$loN APPROVE o N sO-OtD4 6; g orma%A Estimated buroen per response to comply with this LICENSEE EVENT REPORT (LER) g TEXT CONTINUATION g'g,$.7,c',ay",,"l"h,6,0lf,'g,l,ge;d

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he a e o o 3 104 Nff c Management and Budget. Washinoton. DC 20s03 FActLTTY NAME (1) DOCKET NUMBER (2; LFm Ntuern so PAGE (31 YEAR W -

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Millstone Nuclear Power Station Unh 3 Oj3 ol 6l ol ol ol4 l2 l3 9l0 0l1l4 0l0 0l 2 OF TEXT (If more space is toqu, red, use meditional NRO Form 3%A's) (17) [

1. Descrintion of Event On May 19,1990, at 2033 hour0.0235 days <br />0.565 hours <br />0.00336 weeks <br />7.735565e-4 months <br />s-with the plant in Mode 1 at 60% power, at 580 degrees Fahrenheit - ,

and 2250 psia, a manual reactor trip was initiated because of an anticipated turbine trip due to loss of condenser vacuum. The plant had five of six circulating water pumps in operation with Circulating Water Pumps 3CWS-PIA and its associated traveling screen shut down for repairs. Circulating Water Pump 3CWS-PIB was providing cooling water for Condenser Bays " A" and "B", A rapid buildup of seaweed Screen resulted in an automatic trip of 3CWS-PIB due to high screen differential on theAs"B" level. theTraveling' loss of cooling to twco condenser bays would have resuhed in a low condenser vacu reactor trip was initiated. The reactor trip caused a Main Turbine and Generator trip in accordance with design.

At 1600 hours0.0185 days <br />0.444 hours <br />0.00265 weeks <br />6.088e-4 months <br />, winds were from the southeast at 9.2 mph. At 1800 hours0.0208 days <br />0.5 hours <br />0.00298 weeks <br />6.849e-4 months <br />, winds began to increase. An '

i evaluation of plant conditions was performed in accordance with the applicable procedures. Based on the evaluation due to rapidly deteriorating conditions, a down power was commenced at 1942 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.38931e-4 months <br />. At 1955 hours0.0226 days <br />0.543 hours <br />0.00323 weeks <br />7.438775e-4 months <br />, winds peaked at 27 mph from the southeast. The " A" Condenser Waterbox was isolated to <

reduce total flow through the "B" Circulating Water Pump. At 2012 hours0.0233 days <br />0.559 hours <br />0.00333 weeks <br />7.65566e-4 months <br />, the traveling screens shifted .

to fast speed due to high debris loading (i.e., a differential level above 9 inches water column). After -

the normal cycle, the screens returned to slow speed. - At 2027 hours0.0235 days <br />0.563 hours <br />0.00335 weeks <br />7.712735e-4 months <br />, the screens returned to fast speed .

followed by the high traveling screen differential level annunciator indicating that differential level across  !

the screens was above 18 inches water . column. At 2033 hours0.0235 days <br />0.565 hours <br />0.00336 weeks <br />7.735565e-4 months <br />, the "B" Cbculating Water Pump '

automatically tripped on high Travelmg Screen differential level (30 inches water column).

At the time of the trip, operators vetified that the Reactor Trip and Bypass Breakers were open, that all control rods were fully inserted and that neutron flux was decreasing. A Feedwater Isolation was received due to low Average Reactor Coolant system temperature following the trip. An Auxiliary V Feedwater actuation occurred as a result of a steam generator low-low level signal. These are normal-plant responses following a trip. No additional Engineered Safety Featutes were required or initiated. '

All safety systems were fully operable at the time of the trip, and all plant systems performed as designed in response to the trip. Plant stability was achieved at 2045 hours0.0237 days <br />0.568 hours <br />0.00338 weeks <br />7.781225e-4 months <br />. i

11. Cause of Event ,

l l I' The root cause of this event was design deficiency in that Traveling Screen capacity was inadequate.

Two contributing factors to the tnp were: the time of year and the " A" Circulating Water Pump bay being out of service. Peak seaweed loadings occur in April - May and September - October. With the "A" Circulating Water Pump out of service, the trip of the "B" Circulating Water Pump will result in a plant trip.

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- F ACUTY NAME (1) DOCKET NUMBER (2) 1.F A NUMBEn res PAGE (3s YEAR N Millstone Nuclear Power Station Unit 3 ~ ~~

'ol sl ol ol ol4 l2 l3 9l0 0 l 1l 4 0[0 0 l '3 OF 0l3 TEXT (If more space is required. use auditional NRC Form 366A s) (17) 111. Annhwic of Event This event is being reported in accordance with 10CFR50.73(a)(2)(iv), as an event or condition that resulted in manual actuation of an Engineered Safety Feature. Immediate notif4ations were performed in accordance with 10CFR$0.72(b)(2)(ii).

The safety significance of the event is minimal as the trip was manually initiate i because a turbine trip.

due to loss of vacuum was imminent. Power level was 100Fc at 1942 hours0.0225 days <br />0.539 hours <br />0.00321 weeks <br />7.38931e-4 months <br /> wten a down power was initiated in order to reduce the transient that the impending reactor trip would have on the plant.' Down g powering is initiated to bring the plant to a condition where a turbine tnp would not n alt in a reactor  ;

tnp. Power level was at 60re when 3CWS-PIB tripped on high traveling screen differential level (30").  !

l Operation of the Service Water Eystem was not jeopardized due to the ratio of Service Water System flow ]

(approximately 15,000 gallons per minute) to circulating water pump flow (approximately 150,000 gallons l per minute) for one bay. When a Circulating Water pump tnps, the reduction in flow results in a  !

reduced differential level across the travehng screens. '

IV, ' Corrective Action 1 The immediate corrective action was to remove the debris from the traveling screen. Corrective action to prevent recurrence is to implement design changes to the traveling screen units. These changes will 4 increase the speed of the traveling screens and increase their carrying capacity. Based on preliminary ~

3 engineering scope and equipment availability, these changes are expected to be implemented on two of ' i the traveling screens within the next year.  !

l

=In the interimithe procedures which evaluate the intake structure conditions and initiate down powers have been revised to change the point at which a down power is initiated and to increase the down 4 power rate. '.A memo has been circulated to operations personnel to increase the frequency at which '

intake structure conditions must be evaluated and to ensure that management is kept mformed of. ' '

deteriorating conditions. -!

V. Additinnni information  !

.i Licensee Event Report (LER) numbers86-035, 88-014,88-024, 89-008,90-011 and 90-013 are e similar in that a reactor trip due to a turbine trip resulted when fouling of the intake screens caused circulating water pumps to trip causing condenser vacuum to decrease.

In LER 90-013, it was identified that with the " A" and "B" Condenser Waterboxes cross-connected, flow across the "B" Traveling Screen is 130re of normal. Prior to the trip the cross-connect between the two bays had been closed to prevent high flows across the screens. Modifications to the Trash Rake

. performed a3 part of this LER were not effective as the debris which built up on the intake screens passed through the trash racks.

1 In LER 90-011 a number of short term modifications were identified to increase the removal efficiency ,

of the traveling screens. These modifications performed as designed but were still not able to cope:with I the amount of debris experienced. In the long term, an increase in traveling screen speed and carrying capacity will minimize the number of future trips of this type.

Ells CODES Systems comnonents l Circulating Water System - KE Pumps - P l Traveling Water Screens - SCN i Condenser - COND l

gorm 366