United States Nuclear Regulatory Commission - Protecting People and the Environment

Modification of Surveillance Interval for the Electrical Protective Assemblies in Power Supplies for the Reactor Protection (Generic Letter 91-09)


June 27, 1991 


TO:       All HOLDERS OF OPERATING LICENSES FOR BOILING-WATER REACTORS 

SUBJECT:  MODIFICATION OF SURVEILLANCE INTERVAL FOR THE ELECTRICAL 
          PROTECTIVE ASSEMBLIES IN POWER SUPPLIES FOR THE REACTOR PROTECTION 
          SYSTEM (Generic Letter 91-09) 


This generic letter provides guidance for requesting a license amendment to 
modify the surveillance interval for electrical protective assemblies (EPAs) 
used in power supplies for the reactor protection system (RPS).  The current 
standard technical specifications (STS) for boiling-water reactors (BWRs) 
require the licensee to perform channel functional tests of EPAs at a 
6-month interval.  The modification of EPA test interval provided by this 
generic letter is to change the TS to state that the test shall be performed 
each time the plant is in cold shutdown for more than 24 hours, unless the 
test was performed in the previous 6 months.  

In a proposal on December 15, 1988, for Nine Mile Point Nuclear Station 
(NMP), Unit 2, the Niagara Mohawk Power Corporation provided a justification 
that this TS change benefits plant safety.  During the recent review of this 
TS change for Dresden Nuclear Power Station, Units 2 and 3, the U.S. Nuclear 
Regulatory Commission (NRC) staff noted that this change from the guidance 
of the BWR STS had been implemented in the TS issued with 9 of the last 14 
BWR operating licenses.  The staff concludes that the TS change applies 
generically for BWRs as a line-item TS improvement.  The enclosure provides 
guidance for preparing a license amendment request to implement this 
line-item TS improvement. 

Licensees are encouraged to propose TS changes for BWR facilities that are 
consistent with the guidance provided in the enclosure.  The NRC project 
manager for the facility will review amendment requests conforming to this 
guidance.  Please contact the NRC project manager or the contact identified 
below if you have questions on this matter. 

This letter does not require any licensee to propose changes to its plant 
TS.  Therefore, any action taken in response to the guidance provided in 
this generic letter is voluntary and is not a backfit under 10 CFR 50.109. 


                                   Sincerely, 


                                   James G. Partlow
                                   Associate Director for Projects
                                   Office of Nuclear Reactor Regulation

Enclosure:  As stated 

Contact:  Tom Dunning, NRR/OTSB
          (301) 492-1189 

9106260172 

.

Generic Letter 91-09                                             Enclosure 


          MODIFICATION OF THE SURVEILLANCE INTERVAL REQUIREMENTS FOR 
     ELECTRICAL PROTECTION ASSEMBLIES IN REACTOR PROTECTION POWER SUPPLIES 


Introduction 

This enclosure provides guidance for preparing a request for a license 
amendment to modify the technical specifications (TS) surveillance interval 
requirements for the electrical protection assemblies (EPAs) used in power 
supplies for the reactor protection system (RPS) for boiling-water reactors 
(BWRs).  This change reduces the possibility for inadvertent reactor trips 
caused by testing of EPAs during power operation.  

Discussion 

To protect RPS equipment from abnormal operating voltage or frequency 
produced by RPS motor generator (MG) sets or an alternate power supply, EPAs 
will trip a breaker between the MG sets and the RPS.  TS 4.8.4.4 in the 
standard technical specifications (STS) for BWRs addresses the surveillance 
requirements for EPAs.  This TS specifies that licensees perform a channel 
functional test every 6 months.  

To functionally test an EPA channel, the licensee transfers the power for 
the RPS from the associated MG set to the alternate power supply.  Because 
the transfer of RPS power involves a dead-bus transfer, power is momentarily 
interrupted which causes a half scram or group isolation.  Alternatively, 
the licensee could perform tests without a bus transfer, but this procedure 
also results in a momentary interruption of power to the RPS when each EPA 
channel is tripped during the channel functional test.  At many BWR plants, 
licensees have encountered problems with the reset of the half-trip 
conditions, following testing of EPAs during power operation, resulting in 
inadvertent scrams and group isolations that challenge safety systems. 

An alternative to testing the EPAs every 6 months during power operation has 
been to test them each time the plant is in cold shutdown for more than 24 
hours if this test has not been performed within the previous 6 months.  
This alternative eliminates the need to test the EPAs during power operation 
and, thereby, reduces the possibility of inadvertent challenges to the 
protection systems.  However, this alternative retains testing within the 
existing 6-month interval when the unit is shut down for more than 24 hours 
during an operating cycle.  

If the licensee does not encounter a cold shutdown of 24 hours or more 
during a fuel cycle, the effect of not testing EPAs during this interval is 
a small risk to safety.  This alternative benefits safety by reducing the 
possibility for inadvertent trips and challenges to safety systems.  The 
staff concludes that the benefit to safety of reducing the frequency of 
testing during power operation more than offsets the risk to safety from 
relaxing the surveillance requirement to test EPAs during power operation. 

The following guidance provides an acceptable alternative in the format of 
the current BWR STS for these surveillance requirements: 

.

Generic Letter 91-09                 - 2 -                      Enclosure 
          

     4.8.4.4  The above specified RPS electrical power monitoring assemblies 
     shall be determined OPERABLE: 
     
          a.   By performance of a CHANNEL FUNCTIONAL TEST each time the 
          plant is in COLD SHUTDOWN for a period of more than 24 hours, 
          unless performed in the previous 6 months. 
          
Summary 

The modification of the surveillance interval for performing channel 
functional tests for EPAs in accordance with this guidance will eliminate 
the requirement to test EPAs during power operation.  The elimination of 
this testing during power operation will reduce the possibility for 
inadvertent trips and challenges to safety systems.  The implementation of 
this line-item TS improvement will produce a net benefit for safety. 


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