Information Notice 1986-01, Failure of Main Feedwater Check Valves Causes Loss of Feedwater System Integrity and Water-Hammer Damage

Failure of Main Feedwater Check Valves Causes Loss of Feedwater System Integrity and Water-Hammer Damage

ML031220280
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, Mcguire, Nine Mile Point, Palisades, Palo Verde, Perry, Indian Point, Fermi, Kewaunee, Catawba, Harris, Wolf Creek, Saint Lucie, Point Beach, Oyster Creek, Watts Bar, Hope Creek, Grand Gulf, Cooper, Sequoyah, Byron, Pilgrim, Arkansas Nuclear, Three Mile Island, Braidwood, Susquehanna, Summer, Prairie Island, Columbia, Seabrook, Brunswick, Surry, Limerick, North Anna, Turkey Point, River Bend, Vermont Yankee, Crystal River, Haddam Neck, Ginna, Diablo Canyon, Callaway, Vogtle, Waterford, Duane Arnold, Farley, Robinson, Clinton, South Texas, San Onofre, Cook, Comanche Peak, Yankee Rowe, Maine Yankee, Quad Cities, Humboldt Bay, La Crosse, Big Rock Point, Rancho Seco, Zion, Midland, Bellefonte, Fort Calhoun, FitzPatrick, McGuire, LaSalle, 05000000, Zimmer, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant, Skagit, Marble Hill
Issue date:	01/06/1986
From:	Jordan E NRC/IE
To:
References
IN-86-001, NUDOCS 8512310461
Download: ML031220280 (5)

LISa RINAI SSINS No.:

IN 86-01

6835 UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF INSPECTION AND ENFORCEMENT

WASHINGTON, DC 20555 January 6, 1986 IE INFORMATION NOTICE NO. 86-01: FAILURE OF MAIN FEEDWATER CHECK VALVES CAUSES

LOSS OF FEEDWATER SYSTEM INTEGRITY AND

WATER-HAMMER DAMAGE

Addressees

All nuclear power reactor facilities holding an operating license (OL) or a

construction permit (CP).

Purpose

This notice is provided to inform recipients of a recent event caused by five

main feedwater (MFW) check valve failures at a pressurized-water-reactor (PWR)

plant. These failures resulted in a loss of MFW system integrity and significant

water-hammer damage. Recipients are expected to review the information for

applicability to their facilities and consider actions, if appropriate, to

preclude similar problems occurring at their facilities. However, suggestions

contained in this information notice do not constitute NRC requirements;

therefore, no specific action or written response is required.

Description of Circumstances

On November 21, 1985, San Onofre Unit 1 was operating at 60% power when an

auxiliary transformer failed, resulting in a loss of power to a vital bus and

to the bus feeding the east (electric) MFW pump. (A schematic of the MFW system

is enclosed as Figure 1.) The west (electric) MFW pump remained energized from

the unit main generator due to an abnormal electrical lineup. When the east

MFW pump tripped, its discharge-check valve (FWS-438) failed to seat properly.

As a result of the failure of the east MFW pump discharge-check valve, the west

MFW pump supplied feedwater backwards through this discharge-check valve and

overpressurized the east feedwater heater-condensate train. Several tubes

apparently ruptured in the east feedwater train fifth stage (low pressure)

feedwater heater as a result of the overpressurization, causing the shell side

of this feedwater heater to rupture also. In addition, several main turbine

rupture discs failed. Following the above events, the operators tripped the

reactor and turbine by procedure because of the loss of power to a vital bus.

This also caused the west MFW pump to trip. Both 12-inch MFW pump discharge- check valves (FWS-438 and 439) were later found cocked open, supported by their

disc antirotation lugs that had rotated under the check valve hinge arm.

8512310461

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IN 86-01 January 6, 1986 Paoe 2 of 3 When the west MFW pump tripped, all three steam generator (SG) MFW regulating

valve discharge-check valves (FWS-345, 346 and 398) also failed to seat. Two

of these 10-inch check valves were later found to have their flappers loose in

the bottom of the valve body with their nuts missing. The third 10-inch check

valve was later found to have failed in the same mode as FWS-438 and 439. These

check valve failures in the MFW system resulted in leak paths from the SGs

backward through the MFW regulating valves and the east MFW pump to the ruptured

east train FW heater. In addition, the west MFW train may have been pressurized

from the SGs. The net effect of this is that the inventory in all three SGs

began to blow steam and hot water back through the east MFW train.

The above reactor trip also caused level shrink in the SGs, causing SG level to

drop below the actuation level for the auxiliary feedwater (AFW) pumps. The

electric driven AFW pump received an actuation signal, but no longer had elec- tric power available. The steam-driven AFW pump, after a 3-minute automatic

warmup period, began to deliver relatively cold feedwater to the SGs at a point

in each of the MFW lines between the MFW regulating valve discharge-check valve

and the SG. This AFW to the SG feedwater lines initially flowed backward through

the failed check valves and forward through long horizontal runs of feedwater

pipe in the primary containment. Although the operators were unaware that the

check valves had failed, they then closed all MFW regulating valves, FCV-456,

457 and 458 and their associated isolation valves, MOV-21, 20 and 22 in accordance

with procedures. (The effect of the closure of these MFW valves has yet to be

determined.) Contact between steam in the feedwater lines and the cool AFW in

the horizontal pipe resulted in a water-hammer. The water-hammer caused damage

to the feedwater line pipe supports and stretched the bonnet bolts on the "B"

feedwater regulating valve bypass-line check valve (FWS-378), causing the metal

valve gasket to extrude. The flapper on this 4-inch check valve was later found

to have been damaged by the water-hammer impact. The extrusion of the valve gasket

resulted in a substantial steam-water leak from the "B" SG to the feedwater

mezzanine area and the atmosphere that was not isolatable for some time because

of the proximity of the associated isolation valve to the leak. As a result, the "B" SG boiled dry since all "B" AFW flow was carried out through the leak.

Plant personnel were finally able to close valves FWS-342 and FWS-376 to isolate

the leak and continue the plant cooldown about six hours after the event started.

Discussion:

The NRC sent a five-member incident investigation team (IIT) to the San Onofre, Unit 1 site shortly after the above incident. The licensee agreed to hold in

abeyance any work in progress or planned (as allowed by plant safety considera- tions) until the licensee and the NRC had an opportunity to evaluate the event.

The licensee also has agreed to maintain Unit I shutdown until concurrence is

received from the NRC to return to power. The IIT has completed a preliminary

investigation of this event and expects to issue a report in January 1986.

IN 86-01 January 6, 1986 No specific action or written response is required by this information notice.

If you have questions about this matter, please contact the Regional Adminis- trator of the appropriate NRC regional office or this office.

WSA2LFL,

dward L. Jordan Director

Division of Eme~gency Preparedness

and Engineering Response

Office of Inspection and Enforcement

Henry Bailey, IE

(301) 492-9006 Attachments:

1. Figure 1, San Onofre Unit 1 Main Feedwater

System Schematic Diagram

2. List of Recently Issued IE Information Notices

( Figure 1, San Onofre Unit , Main Feedwater

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System Schematic Diagram

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Note: The ruptured fifth stage feedwater heater (not shown) is the lowest pressure heater in this east train.

Attachment 2 IN 86-01 January 6, 1986 LIST OF RECENTLY TSSUED

IE INFORMATION NOTICES

Information Date of

Notice No. Subject Issue Issued to

85-101 Applicability of 10 CFR 21 12/31/85 All power reactor

To Consulting Firms Providing facilities holding

Training an OL or CP

85-100 Rosemount Differential 12/31/85 All power reactor

Pressure Transmitter Zero facilities holding

Point Shift an OL or CP

85-99 Cracking In Boiling-Water- 12/31/85 All BWR facilities

Reactor Mark I And Mark II having a Mark I or

Containments Caused By Failure Mark II containment

Of The Inerting System

85-98 Missing Jumpers From Westing- 12/26/85 All Westinghouse

house Reactor Protection designed PWR

System Cards For The Over- facilities holding

Power Delta Temperature Trip an OL or CP

Function

85-97 Jail Term For Former 12/26/85 All power reactor

Contractor Employee Who facilities holding

Intent

ionally Falsified an OL or CP

Welding Inspection Records

85-96 Temporary Strainers Left 12/23/85 All power reactor

Installed In Pump Suction facilities holding

Piping an OL or CP

85-95 Leak Of Reactor Water To 12/23/85 All BWR facilities

Reactor Building Caused By holding an OL or CP

Scram Solenoid Valve Problem

85-94 Potential For Loss Of Minimum 12/13/85 All power reactor

Flow Paths Leading To ECCS facilities holding

Pump Damage During A LOCA an OL or CP

85-93 Westinghouse Type DS Circuit 12/6/85 All power reactor

Breakers, Potential Failue Of facilities holding

Electric Closing Feature an OL or CP

Because Of Broken Spring Release

Latch Lever

OL = Operating License

CP = Construction Permit