Information Notice 1992-16, Loss of Flow from the Residual Heat Removal Pump During Refueling Cavity Draindown

Loss of Flow from the Residual Heat Removal Pump During Refueling Cavity Draindown

ML031200625
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, Fort Saint Vrain, Shoreham, Satsop, Trojan, Atlantic Nuclear Power Plant
Issue date:	02/25/1992
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-92-016, NUDOCS 9202190317
Download: ML031200625 (5)

UNITED STATES

NUCLEAR REGULATORY COMMISSION'

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 February 25, 1992 NRC INFORMATION NOTICE 92-16: LOSS OF FLOW FROM THE RESIDUAL HEAT REMOVAL

PUMP DURING REFUELING CAVITY DRAINDOWN

Addressees

All holders of operating licenses or construction permits for nuclear power

reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice

to alert addressees to a recent event involving the loss of flow from the

residual heat removal pump during refueling cavity draindown. It is expected

that recipients will review the information for applicability to their

facilities and consider actions, as appropriate, to avoid similar problems.

However, suggestions contained in this information notice are not NRC

requirements; therefore, no specific action or written response is required.

Description of Circumstances

On October 26, 1991, the Vogtle Electric Generating Plant, Unit 1, was in Mode 6 (Refueling) with the reactor vessel head removed. The Georgia Power Company

(the licensee) had reloaded the core and reinstalled the upper tnternals. The

licensee was using the 1B residual heat removal (RHR) pump to provide shutdown

cooling and the 1A RHR pump to drain the refueling cavity by taking suction from

one of the reactor coolant system (RCS) hot legs'and discharging to the refueling

water storage tank (RWST). The RCS temperature was approximately 870F. The

water level in the refueling cavity was at 210 feet 4 inches. Operations

personnel were preparing to lower the level to 192 feet, 2 feet below the reactor

vessel head flange, to allow the reactor vessel head to be reinstalled. The

mid-loop elevation of the RCS for Unit 1 is 187 feet. An assistant plant

operator (APO) in the Unit 1 containment was directed to establish a watch at a

tygon tube to monitor the RCS level during draindown and mid-loop operations.

During the outage, the licensee had installeda permanent sight glass in the

Unit 1 containment for monitoring the RCS level. This new sight glass had

neither been tested nor aligned for the operators to use. The APO assumed that

the new sight glass was operable and established communications with the

control room at the permanent sight glass, rather than at the tygon tube, to

monitor the draindown. The licensee then started the draindown.

When the day shift ended, a night shift plant equipment operator (PEO) relieved

the day shift APO who was monitoring the permanent sight glass. The PEO

discovered that the valves for the permanent sight glass were not aligned

correctly. The PEO informed the control room and the operators stopped the

9202190317 ?D a f 00V; qt *

IN 92-16 February 25, 1992 draindown while the problem was investigated. The PEO and APO

and vented the sight glass without using a procedure. In their then filled

place the permanent sight glass in service, the upper isolation attempt to

was not readily visible, was not opened as required. valve, which

The licensee resumed the cavity draindown and, approximately

2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> later, received a control room annunciator which indicated a high level,

6 inches, in the reactor vessel. The control room operator 192 feet

control room level indicator was at the top of scale observed that the

(100 percent) and tapped

on the indicator, causing it to drop to a reading of 60 percent

inches). The licensee again stopped the draindown. The PEO (190 feet 9 monitoring

sight glass level reported that reactor vessel water level appeared the

with the reactor vessel head flange (194 feet), which agreed to be even

indicated by the permanent sight glass and the temporary tygon with the level

licensee assumed that the control room level indicator was tube. The

continued the draindown, believing that it had three reliableinaccurate and

the RCS level, i.e., visual vessel water level, the permanent indications of

the temporary tygon tube. sight glass, and

When the level in the RCS reached approximately 193 feet, as

indicated by the

sight glass, a control room operator observed discharge pressure, motor current oscillations for the 1B RHR pump, indicating that flow, and

forming a vortex on the suction side of the pump or that the the coolant was

The operators closed the discharge valve for the lB RHR pump, pump was cavitating.

1B RHR pump on the miniflow line. Although the electrical current thus putting the

the motor of the 1B RHR pump became more stable, the discharge reading for

low. pressure remained

The licensee again stopped the draindown by shutting down the

realigning its suction to the refueling water storage tank (RWST) 1A RHR pump and

the refueling cavity. Shortly after beginning to refill the to refill

noted that the discharge pressure of the 1B RHR pump began to RCS, the licensee

the flow of the 1B RHR pump reached approximately 2600 gallons improve. When

per

licensee again observed indications of vortex formation or cavitation. minute, the

licensee reduced the flow from the 1B RHR pump to 1800 gallons The

found that the pump operated satisfactorily with no indication per minute and

formation or cavitation. The licensee used the 1A RHR pump of vortex

refueling cavity from the RWST and stopped refilling when to refill the

the sight glass

indicated a level of 194 feet 10 inches. The licensee increased

the 1B RHR pump to approximately 3000 gallons per minute and the flow from

pump operated satisfactorily with no further indication of found that the

cavitation. vortex formation or

When operators performed a walkdown inspection of the tygon

glass level indicators, they found the upper isolation valve tube and the sight

glass closed with a tag on it which indicated that the new for the sight

been released for use. The licensee later determined that sight glass had not

a

also been installed on the lower isolation valve but apparently similar tag had

the valve. had fallen off

a

IN 92-16 February 25, 1992 The licensee also discovered that a high efficiency particulate absorber

(HEPA) filter unit was connected, by means of a flexible duct, to the opening

from which a pressurizer safety valve had been removed to provide a vent path

for all level instrumentation. The licensee found that the HEPA unit was

running and the flexible duct was collapsed, apparently caused by the vacuum

created by the running HEPA filter unit and the RCS draindown. This resulted

in an inadequate vent path from the pressurizer. (LER 50-424/91-09 and NRC

Inspection Report 50-424,425/91-30)

Discussion

False high RCS level indications led to the RCS level being inadvertently

lowered to the point at which the coolant formed a vortex in the RHR pump

suction line. The false high level indications were caused by an inadequate

vent path from the pressurizer and by the closed upper isolation valve for the

sight glass. When conditions in the pressurizer changed, it affected all of

the reactor vessel level instruments, because their reference legs connected to

the pressurizer. The system installed at Vogtle did not meet the intent of two

independent continuous water level indications as discussed in Generic Letter 88-17, "Loss of Decay Heat Removal."

Procedures for the initial RCS draindown during refueling operations provided

sufficient steps to ensure that the level instrumentation was installed properly

and the vent paths were adequate. However, the procedures for the subsequent

draindowns did not include sufficient steps to reverify these actions. Adminis- trative controls were inadequate in addressing the reviews and documents

required for attaching HEPA filter units to plant equipment. In this case, the HEPA filter unit was installed without a temporary modification or a work

order, and consequently the control room was not aware of the installation.

During the event, the 1B RHR pump was not available to provide recirculation

shutdown cooling for approximately 16 minutes. Core temperature as indicated

870 F to 1070F. There

at the RHR pump discharge increased from approximately

was no radiological release to the environment. The licensee reviewed available

data further and found that the coolant on the suction side of the 1B RHR pump

had formed a vortex but the pump did not cavitate.

Air may have begun entering the 1A RHR pump shortly before the pump's discharge

valve was closed. This resulted in a slightly reduced discharge pressure and

flow. The coolant in the RCS reached the lowest level, 186 to 187 feet, when

the discharge valve for the 1A RHR pump's heat exchanger was closed. After the

event, the licensee performed an inservice test on the 1A and 1B RHR pumps and

found that the performance of neither pump was degraded.

IN 92-16 February 25, 1992 This information notice requilres no specific action or written response. If

you have any questions about l the information inthis notice, please contact one

of the technical contacts lis-ted below or the appropriate Office of Nuclear

Reactor Regulation (NRR) projiect manager.

Charles E. Rossi, Director

Division of Operational Events Assessment I

Office of Nuclear Reactor Regulation

Technical contacts: Doug Star -kov - Region II

(40i) 554-9901 Pierce Skinner, Region II

(404) 331-6299 Attachment: List of Recently Issued NRC Information Notices

Cowm~- Pa.'~. A 9- x

Attachment

IN 92-16 February 25, 1992 LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

Information Date of

Notice No. Subject Issuance Issued to

92-15 Failure of Primary System 02/24/92 All holders of OLs or CPs

Compression Fitting for nuclear power reactors.

92-14 Uranium Oxide Fires at Fuel 02/21/92 All fuel cycle and uranium

Cycle Facilities fuel research and developme

licensees.

92-02, Relap5/Mod3 Computer Code 02/18/92 All holders of OLs or CPs

Supp. 1 Error Associated with the for nuclear power reactors.

Conservation of Energy

Equation

92-13 Inadequate Control Over 02/18/92 All holders of OLs or CPs

Vehicular Traffic at for nuclear power reactors.

Nuclear Power Plant Sites

92-12 Effects of Cable Leakage 02/10/92 All holders of OLs or CPs

Currents on Instrument for nuclear power reactors.

Settings and Indications

92-11 Soil and Water Contamina- 02/05/92 All uranium fuel fabrica- tion at Fuel Cycle Facil- tion and conversion facil- ities ities.

92-10 Brachytherapy Incidents 01/31/92 All Nuclear Regulatory Com- Involving Iridium-192 Wire mission (NRC) licensees

Used in Endobronchial authorized to use

Treatments iridium-192 for brachy- therapy; manufacturers and

distributors of iridium-192 wire for use in brachy- therapy.

92-09 Overloading and Subsequent 01/30/92 All holders of OLs or CPs

Lock Out of Electrical for nuclear power reactors.

Buses During Accident

Conditions

OL = Operating License

CP = Construction Permit