Information Notice 1990-25, Loss of Vital AC Power with Subsequent Reactor Coolant System Heat-Up

Loss of Vital AC Power with Subsequent Reactor Coolant System Heat-Up

ML031130253
Person / Time
Site:	Beaver Valley, Millstone, Hatch, Monticello, Calvert Cliffs, Dresden, Davis Besse, Peach Bottom, Browns Ferry, Salem, Oconee, 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:	04/16/1990
From:	Rossi C Office of Nuclear Reactor Regulation
To:
References
IN-90-025, NUDOCS 9004120133
Download: ML031130253 (8)

.* -*UNITED STATES NUCLEAR REGULATORY

COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555 April 16, 1990 NRC INFORMATION

NOTICE NO. 90-25: LOSS OF VITAL AC POWER WITH SUBSEQUENT

REACTOR COOLANT SYSTEM HEAT-UP

Addressees

All holders of operating

licenses or construction

permits for nuclear power reactors.

Purpose

This information

notice is being provided to inform addressees

of a significant

operating

event which occurred at the Georgia Power Company's

Vogtle Nuclear Plant on March 20, 1990. The event took place while Unit 1 was in mid-loop in operational

mde 6 and demonstrates

the need for operating

personnel

to be prudent in removing equipment

from service or establishing

atypical equipment alignments

during shutdown.

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 do not constitute

NRC requirements;

therefore, no specific action or written response is required.Description

of Circumstances:

On March 20, 1990, a loss of vital ac power occurred while Vogtle Unit 2 was operating

at 100 percent power and Unit 1 had been in a refueling

outage for about 4 weeks. Unit 1 was in mid-loop in operational

mode 6 with plant equip-ment conditions

as follows: o The Unit 1 B reserve auxiliary

transformer (RAT) was tagged out of service for maintenance

o The Unit 1 B emergency

diesel generator (EDG) was tagged out of service and disassembled

for maintenance

o The Unit 1 A RAT was supplying

offsite power to the crosstied

Unit 1 A and B vital buses o The reactor coolant system (RCS) temperature

was being maintained

at around 90 degrees Fahrenheit (F) via the train A residual heat removal (RHR) pump, the-train

B pump was in standby o The vessel head was in place with the bolts not fully tensioned o The pressurizer

manway cover was removed_ __ A l e ,

IN 90-25 April 16, 1990 o The manways for steam generators

2 and 3 were partially

bolted in place and the manways for steam generators

1 and 4 were in place with bolts fully tensioned o The inboard charging line check valve and an accumulator

isolation valve were open for inspection

o The containment

equipment

hatch and the containment

personnel

hatch were open At about 9:20 a.m., a truck carrying fuel and lubricants

in the plant low voltage switchyard

backed into a support column for the feeder line supplying power to the Unit 1 A RAT and the Unit 2 B RAT. The insulator

for the C phase of the feeder line fractured

and initiated

a phase-to-ground

electrical

fault.The fault resulted in a loss of power to the Unit 1 A RAT and the Unit 2 B RAT.The Unit 2 B EDG started and loaded to the deenergized

Unit 2 B vital bus. How-ever, a Unit 2 turbine trip and reactor trip occurred because of an improperly

connected (wrong tap) differential

current transformer (DCT). The DCT initiated the trip when the current surge associated

with the phase-to-ground

fault was sensed. The Unit 2 trip was uncomplicated.

Because both of the Unit 1 vital buses were crosstied

and being supplied by the Unit 1 A RAT, the loss of the transformer

deenergized

both vital buses.Deenergizing

these buses resulted in the loss of power to the operating

RHR pump. Since the Unit 1 B EDG was tagged out of service and disassembled

for maintenance, the emergency

power supply for the B vital bus was unavailable

and the standby B RHR pump could not be started.The available

Unit 1 A EDG started on bus undervoltage, but for unknown reasons, it shut down automatically

after 1 minute and 20 seconds. At 9:40 a.m., plant operators

declared a site area emergency.

A loss of all onsite and offsite ac power at Vogtle for more than 15 minutes is classified

as a site area emergency.

The licensee made their declaration

because all vital ac power was lost for greater than 15 minutes. Approximately

18 minutes after the first start of the A EDG, the operators

locally reset the load sequencer

which automatically

restarted

the A EDG on undervoltage.

However, after 1 minute and 10 seconds, the diesel again shut down automatically.

At 9:56 a.m., plant operators

per-formed an "emergency" manual start of the diesel, which bypassed most of the diesel's protective

trips. The diesel started and loaded to the bus, the A RHR pump was restarted, and core cooling was reestablished

to Unit 1. With the start of the diesel, the site area emergency

was downgraded

to an "alert" at 10:15 a.m. Containment

integrity

was established

at 11:03 a.m.Plant personnel

returned the Unit 1 B RAT to service after completing

formal tagout removal procedures.

However, attempts to energize the transformer

were delayed for several minutes because of a sticking mechanical

interlock

in the control circuitry

for a motor-operated

disconnect

switch on the high side of the B RAT. Power was restored to the B vital bus via the B RAT at 11:40 a.m.At 12:38 a.m., core cooling was shifted to the B RHR train to facilitate

sub-sequent electrical

alignment

changes.

e. v -%IN 90-25 April 16, 1990 According

to control roon indication, RCS temperature

increased

from 90 to 136 degrees F during the 36 minutes required to reenergize

the A bus (1.3 degrees F/min).Throughout

the event, non-vital

power was continuously

provided to Unit 1 from offsite sources, via backfeed through the main generator

transformer.

Also, the Unit 2 electrical

distribution

system remained energized (aside from the momentary

loss of power before the reactor trip). However, the Vogtle electrical

system was not designed to permit easy interconnection

of the Unit 1 vital buses to nonvital power or to the Unit 2 electrical

buses. Therefore, there were no procedures

in place to provide guidance on interconnecting

the Unit 1 vital and nonvital buses or for interconnecting

the Unit 1 electrical

distribution

system with the distribution

system at Unit 2. (There are no regulatory

requirements

that direct the licensee to develop Interconnection

procedures.)

Discussion:

The NRC has previously

identified

concerns with the operability

of necessary equipment

in shutdown modes. In Information

Notice (IN) 80-2O, "Loss of Decay Heat Removal Capability

at Davis-Besse

Unit 1 While in a Refueling

Mode" an extended loss of decay heat removal capability

was attributed

to a number of factors, including

inadequate

procedures, inadequate

administrative

controls, and the conduct of extensive

maintenance

activities.

Information

Notice 84-42, "Equipment

Availability

for Conditions

During Outages Not Covered by Technical

Specifications," describes

an event at the Palisades Nuclear Plant involving

the total loss of all ac power. The Palisades

event was precipitated

by personnel

performing

actions during a refueling

outage without an appreciation

for the effect of those actions on the plant as it was configured.

Many pieces of equipment

were tagged out of service for maintenance.

Personnel

intentionally

interrupted

offsite power. This action caused the loss of the only available

service water pump. As a result, cooling water was interrupted

to the only available (and operating)

diesel generator.

The diesel overheated

and was manually tripped. As a result, all station ac power was interrupted, causing the loss of fuel pool cooling. (The reactor had been defueled, and its fuel was being stored in the spent fuel pool).The recent Vogtle event reemphasizes

the need for careful planning of equipment outages during shutdown.

Licensees, in general, have considerable

latitude in removing equipment

from service and altering normal system lineups while in shutdown modes if only the minimum technical

specification

requirements

are considered.

The desire to return nuclear units to service as quickly as possible can result in maintenance

being conducted

on redundant, safety-related systems, concurrently.

The appropriateness

of conducting

parallel maintenance

activities

should be considered

in light of the availability

of alternate

equipment

and procedures

to mitigate the consequences

of potential operational

problems.

It is important

that plant outage plans assure that an adequate complement

of equipment

capable of responding

to potential

events remains available

throughout

the outage. Particular

care is needed when the reactor pressure boundary is not intact or the reactor coolant system is at mid-loop.

IN 90-25 April 16, 1990 A special investigation

of the Vogtle event is being conducted

by an NRC Incident Investigation

Team (1IT). The information

contained

in this notice is preliminary

and is subject to change, pending the findings made by the IIT.This Information

notice requires no specific action or written response.

If you have any questions

about the information

in this notice, please contact one of the technical

contacts listed below or the appropriate

NRR project manager.~6hfares Eossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

Contacts:

N. Fields, NRR (301) 492-1173 E. Trager, AEOD (301) 492-4496 Attachment:

List of Recently Issued NRC Information

Notices

, 0 --u Attachment

IN 90-25 April 16, 1990 LIST OF RECENTLY ISSUED NRC INFORMATION

NOTICES Intormation

Date ot Notice No. Subject Issuance Issued to 90-24 90-23 90-22 90-21 90-20 90-19 90-18 90-17 Transportation

of Model Spec 2-T Radiographic

Exposure Device Improper Installation

of Patel Conduit Seals Unanticipated

Equipment Actuations

Following Restoration

of Power to Rosemount

Transmitter

Trip Units Potential

Failure of Motor-Operated Butterfly

Valves to Operate Because Valve Seat Friction was Under-estimated Personnel

Injuries Resulting from Improper Operation

of Radwaste Incinerators

Potential

Loss of Effective Volume for Containment

Recirculation

Spray at PWR Facilities

Potential

Problems with Crosby Safety Relief Valves Used on Diesel Generator Air Start Receiver Tanks Weight and Center of Gravity Discrepancies

for Copes-Vulcan

Valves 4/10/90 4/4/90 3/23/90 3/22/90 3/22/90 3/14/90 3/9/90 3/8/90 All NRC licensees authorized

to use, transport, or operate radiographic

exposure devices and source changers.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.All NRC licensees who process or incinerate

radio-active waste.All holders of OLs or CPs for PWRs.All holders of OLs or CPs for nuclear power reactors.All holders of OLs or CPs for nuclear power reactors.OL = Operating

License CP = Construction

Permit

tNOW, IN 90-25--April 16, 1990 A special investigation

of the Vogtle event is being conducted

by an NRC Incident Investigation

Team (IIT). The information

contained

in this notice is preliminary

and is subject to change, pending the findings made by the IIT.This information

notice requires no specific action or written response.

If you have any questions

about the information

in this notice, please contact one of the technical

contacts listed below or the appropriate

NRR project manager.Charles E. Rossi, Director Division of Operational

Events Assessment

Office of Nuclear Reactor Regulation

Technical

Contacts: N. Fields, NRR (301) 492-1173 E. Trager, AEOD (301) 492-4496 Attachment:

List of Recently Issued NRC Information

Notices*SEE PREVIOUS PAGE FOR CONCURRENCE

OFC NAME DATE OFC NAME DATE*OEAB:DOEA

NFields 4/11/90*OEAB:DOEA

DFISCHER 4/11/90*TECH ED 4/11/90*C:OEAB:DOEA

PSwetland 4/11/90*REGION I (IIT)WLazarus 4/11/90*C:GCB:DOEA

CBERLINGER

4/11/90*PD23 TReed 4/11/90 4/1 3/90 OFFICIAL RECORD COPY

OFFICIAL RECORD COPY Document Name: VOGTLE OFC O .DOEA p NAME NFlelds DATE yv"1/90 OFC O X -DOEA NAME DFISCHER DATE f /11/90