United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 91-68: Careful Planning Significantly Reduces the Potential Adverse Impacts of Loss of Offsite Power Events During Shutdown

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                          WASHINGTON, D.C.  20555 

                              October 28, 1991 


NRC INFORMATION NOTICE 91-68:  CAREFUL PLANNING SIGNIFICANTLY REDUCES 
                               THE POTENTIAL ADVERSE IMPACTS OF LOSS 
                               OF OFFSITE POWER EVENTS DURING SHUTDOWN 


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 describe the positive benefits that were derived by two licensees 
when their outage activities were carefully planned, scheduled, and 
performed.  These licensees did not rely solely on technical specifications 
to identify the minimum equipment that should be available under various 
shutdown configurations.  Rather, these licensees made additional equipment 
available and developed special procedures, as appropriate, to mitigate the 
consequences that could result from forced equipment outages.  It is 
expected that recipients will review the information for applicability to 
their facilities and consider appropriate actions.  However, suggestions 
contained in this information notice are not NRC requirements; therefore, no 
specific action or written response is required. 

Description of Circumstances 

In November 1990, the licensee for the Turkey Point Plant began an 11-month 
dual unit outage to conduct a major electrical system upgrade including 
installing two additional emergency diesel generators (EDGs).  On March 13, 
1991, while both units were defueled and the safety-related EDGs were 
inoperable, offsite power for Unit 4 was being provided through the startup 
transformer.  Spent fuel pool cooling pumps were being powered from the "C" 
load center which was being supplied by the "A" vital bus.  Electrical power 
for the component cooling water (CCW) pumps and the intake cooling water 
(ICW) pumps was being provided from vital bus "A".  At the time, spent fuel 
pool cooling was the most significant nuclear safety function.  

An alternate source of power supply to the CCW, ICW, and spent fuel pool 
cooling pumps was available from four, non-safety-related (black start) 
diesel generators.  Other backup sources of power to the pumps included 
interconnection with the Unit 3 startup transformer and transfer to another 
Unit 4 transformer (after defeating circuit breaker interlocks).  An 
alternate method of 


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spent fuel pool cooling, which was available, involved the use of a trailer-
mounted diesel generator and a diesel powered fire pump or a non-safety 
grade screen wash pump.  Detailed procedures for use of the alternative 
cooling methods were available. 

At 3:30 p.m., a lockout occurred on the Unit 4 startup transformer resulting 
in a total loss of all vital AC power to Unit 4.  A notification of an 
unusual event (NOUE) was declared as a result of the loss of vital offsite 
power.  The licensee manually started, but did not load, two of the black 
start diesel generators.  The other black start diesel generators were not 
started.  All of these sources were available to supply power to the cooling 
pumps for the spent fuel pool if the startup transformer could not be 
returned to service. 

The licensee inspected the startup transformer and associated circuit 
breakers and found no electrical fault indications.  At 4:35 p.m., the 
licensee energized the startup transformer.  At 5:27 p.m., power was 
restored to the CCW, ICW and spent fuel pool cooling pumps and forced 
cooling to the spent fuel pool was resumed.  The NOUE was then terminated.  
The temperature of the spent fuel pool had increased from 84�F to 87�F 
during the 2-hour duration of the event.

On March 20, 1991, another event of interest occurred at the Indian Point 
Station.  Before the event, Indian Point, Unit 2, (IP2) was in cold shutdown 
with all fuel removed from the vessel and stored in the spent fuel pit.  
Indian Point, Unit 3, (IP3) was operating at 100 percent power in a normal 
plant configuration.  At 7:15 p.m., a potential transformer on a 345kV bus 
section at a remote substation failed catastrophically, creating a ground 
fault on the 345kV system.  Fault isolation circuitry opened the main 
generator output breaker for IP3, which initiated a reactor trip.  The 
reactor trip was uncomplicated and offsite power to IP3 vital buses was not 
interrupted.  

However, an explosion and subsequent fire in the substation caused circuit 
breakers to electrically isolate the 138kV feeder circuit supplying offsite 
power to the IP2 6.9kV buses.  As a result, the 6.9kV non-vital and 480V 
vital buses that were in service were deenergized.  EDG 23 started 
automatically on bus undervoltage.  At the time, the other two IP2 EDGs were 
tagged out of service for maintenance.  As designed, EDG 23 did not load to 
the buses because all logic requirements for automatic loading were not 
satisfied.  EDG 23 was manually loaded to two vital 480V buses.  This action 
allowed a service water pump and a component cooling water pump to be 
started, a battery charger to be placed in service, and lighting to the 
auxiliary and containment buildings to be restored. 

At the time of the event, offsite power to some vital loads was being 
supplied directly from temporary connections from an Indian Point Unit 1 
feeder bus as opposed to being supplied from normal sources.  These loads 
included the spent fuel pit cooling pump, the auxiliary building exhaust 
fan, and a battery charger.  The licensee established these temporary 
connections to mitigate the consequences of a potential loss of the normal 
offsite source. 

Since two EDGs were out of service, a temporary EDG was started as a precau-
tion.  However, the unit was not needed during the event.  The licensee had 
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imported this temporary EDG unit to the site specifically for use as an 
alternate onsite source of emergency power during the shutdown in view of 
the significant number of planned equipment outages.  The licensee provided 
this unit even though there were three gas turbines and a second 138kV 
feeder that were available from off site and that could have been manually 
aligned to energize the IP2 vital buses. 

The licensee restored normal offsite power to IP2 within 30 minutes.  During 
the event, component cooling water and service water were lost for only 2 
minutes limiting the interruption to spent fuel cooling. 

Discussion 

These events illustrate the benefits of carefully planning equipment outages 
during shutdown.  Before each event, the licensees had made additional power 
sources available to augment normal supplies.  Furthermore, the licensees 
had developed written procedures to address anticipated equipment failures.  
These efforts allowed operating personnel to have adequate time to perform 
deliberate, well informed actions and minimized the safety concerns 
associated with each event.  If the licensees had been less careful in their 
planning, these events could have been more significant.  The technical 
specifications allow licensees considerable flexibility in removing 
equipment from service and altering normal system lineups during shutdown. 

This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please call the 
technical contact listed below or the appropriate Office of Nuclear Reactor 
Regulation (NRR) project manager. 




                                   Charles E. Rossi, Director 
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation

Technical contact:  N. Fields, NRR
                    (301) 492-1173

Attachment:  List of Recently Issued NRC Information Notices

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