United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 83-08: Electrical Circuit Breakers With an Undervoltage Trip Feature in Use in Safety-Related Applications Other than the Reactor Trip System

                                                   SSINS No.: 6820         
                                                   OMB No.: 3150-00011     
                                                   Expiration Date: 4/30/85 
                                                   IEB 83-08               

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555
                                     
                              December 28, 1983

IE BULLETIN NO. 83-08:   ELECTRICAL CIRCUIT BREAKERS WITH AN UNDERVOLTAGE 
                         TRIP FEATURE IN USE IN SAFETY-RELATED APPLICATIONS 
                         OTHER THAN THE REACTOR TRIP SYSTEM 

Addressees: 

All nuclear power reactor facilities holding an operating license (OL) or 
construction permit (CP) for action. 

Purpose: 

The purpose of this bulletin is to assure proper operation of circuit 
breakers with undervoltage trip attachments (UVTAs) being used in 
safety-related applications other than as reactor trip breakers (RTBs). 
Toward this end, the bulletin describes recent findings involving such 
circuit breakers and asks holders of CPs and OLs to take certain actions. 
The subject breakers are similar to those identified in IE Bulletins (IEBs) 
83-01 and 83-04. Holders of CPs and OLs are asked to: (1) identify the 
safety-related applications of the breakers and the systems in which they 
are used; (2) review the adequacy of the design, testing, and maintenance of 
the breakers in light of their operating experience and information conveyed 
in the bulletin; and (3) evaluate the need to take corrective measures to 
ensure proper operation of the breakers. 

Description of Circumstances: 

The reactor trip breaker failures experienced at Salem Unit 1 in February 
1983, and RTB failures experienced in March at San Onofre Units 2 and 3 led 
to issuance of IEBs 83-01 and 83-04, respectively. An additional problem 
with RTBs having a UVTA was described in IE Information Notice 83-76. 

Results of testing of RTBs required by IEBs 83-01 and 83-04 have been 
reported to the NRC. These results show that the reliability of certain RTBs 
may not be commensurate with their safety function. A review of reported 
breaker failures indicates that most failures can be attributed to the UVTAs 
and their associated linkages. Since the UVTA provides only a limited force 
to trip the breaker, problems of alignment and lubrication can result in a 
failure of the breaker to perform its intended function. Some examples of 
problems identified as causes for failure to trip of the circuit breakers 
include: (1) improper lubrication 



8312120090 
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                                                          IEB 83-08        
                                                          December 28, 1983 
                                                          Page 2 of 5      

of linkages and other moving parts within either the UVTA or the circuit 
breaker trip bar latch assembly, (2) inadequate adjustment of spring tension 
of the UVTA, (3) excessive torque required to trip the circuit breaker 
because of hardening and contamination of the grease in the trip shaft 
bearings, and (4) excessive wear of moving parts within either the UVTA or 
the trip bar latch assembly because of infrequent lubrication of these 
moving parts or improper adjustments of the spring tension of the UVTA. The 
only types of RTBs being used in licensed PWRs are either Westinghouse (W) 
type DB, W type DS, or General Electric (GE) type AK-2 circuit breakers. 
Subsequent investigation into the matter also revealed that some PWRs and 
BWRs also employ similar breakers with similar undervoltage (UV) features in 
other safety-related applications. Examples of other systems that may be 
using the circuit breaker with UV features are the engineered safety 
features systems (for load shedding of the essential busses) and the 120 VAC 
uninterruptible power source from the motor-generator (MG) sets in BWR 
plants. Circuit breakers supplied by manufacturers other than W or GE may be 
used in some plants for these non-RTB applications. 

In addition to the failures discussed above, a common mode failure of the GE 
type AK-2 circuit breaker occurred at Oyster Creek on November 30, 1978, 
during a loss of offsite power test. Both service water pump circuit 
breakers failed to trip, as required. The UV relays which monitor voltage 
level on each emergency bus functioned properly but did not actuate the 
breaker trip bar via the UV trip device within each circuit breaker. 
Ultimately the cause of failure was attributed to binding of the trip bar 
bearing in the breaker trip shaft assembly. The problem was corrected by 
cleaning and relubricating the trip shaft mechanism within the circuit 
breaker. 

Although binding within the UV device and out-of-adjustment conditions in 
the linkage mechanism of the UV device were not a problem at Oyster Creek, 
GE had also determined that these conditions were a continuing problem at 
other nuclear power plants. (See IE Bulletin 79-09.) The temporary overload 
condition on each emergency bus did not present a problem at Oyster Creek 
because those units are capable of full bus load pickup. However, as stated 
above, the load shedding feature of the emergency busses during the above 
test conditions did not function as designed. 

Another failure, similar in nature to the early failure at Oyster Creek, 
occurred again at that plant in March 1983. In this event the circuit 
breaker involved provides power to one of two control rod drive mechanism 
pumps. As in the case of the 1978 event, this problem was also corrected by 
cleaning and relubricating the trip shaft mechanism within the circuit 
breaker. 

In addition to the above mentioned breaker failures, each being a failure to 
trip on demand, we are also concerned about breakers with UVTAs failing to 
close on demand. 

Failures of breakers to close are described in Information Notice 83-50. 
After issuing that notice, the NRC became aware of a failure to close that 
occurred during life cycle demonstration tests conducted by W that was 
directly 
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                                                          IEB 83-08        
                                                          December 28, 1983 
                                                          Page 3 of 5      

related to the UVTA latching mechanism. This failure occurred on a new UVTA 
that was initially lubricated in accordance with the latest W 
recommendations but which, for test purposes, was riot subsequently 
lubricated. (Note: W recommends relubricating the UVTA and its linkages 
after 200 operations.) This failure to close occurred after 571 trip and 
reclose operations, and was attributed by W to normal latch wear. As a 
result of the latch wear, the breaker mechanism was placed in a "trip free" 
condition such that the breaker could not be closed electrically or 
manually. This failure does not represent a safety concern in an RTB 
application (i.e., such failures block the withdrawing of control rods, 
thereby assuring that the reactor remains subcritical). However, there is a 
concern that such failures could, in other applications, prevent the 
performance of a safety-related function. 

Generic Letter 83-L 08 was issued to all holders of an OL or CP on July 8, 
1983. Sections 2.2 and 3.2 of that letter require implementation of a 
program that ensures that all components of safety-related systems are 
correctly identified and classified, and that the appropriate procedures 
(including vendor recommendations) are used for maintenance, surveillance, 
parts replacement, qualification testing, and post-maintenance operability 
testing. That letter, of course, applies to circuit breakers in 
safety-related systems that use a UV trip feature. Any information requested 
by the action items of this bulletin that has been previously provided to 
the NRC in response to Generic Letter 83-28 may be referenced. 

Actions To Be Taken by Holders of Construction Permits and Licensees for 
Operating Reactor Plants 

1.   Identify applications of W type DB, W type DS, or GE type AK-2 circuit 
     breakers with the UV trip feature as discussed in IEB 83-01 or 83-04 
     in safety-related applications at your facility(ies), other than as 
     RTBs. CP holders and licensees should also identify similar 
     applications of other types of breakers by other manufacturers that 
     use a UV trip feature. If such circuit breakers are used or planned 
     for use, identify the system(s) involved. 

2.   For each circuit breaker type identified in Item 1, do the following: 
     
     a.   Review the design of the UVTA and the connecting linkage. Using 
          input from the breaker manufacturer, determine the design margin 
          available to open the breaker. Evaluate whether or not this 
          design margin is adequate in view of safety applications, 
          considering possible problems of alignment, lubrication, 
          adjustment of spring tension, etc., discussed in the "Description 
          of Circumstances." 

     b.   Describe the current breaker surveillance program, including 
          details of test frequency, methodology, and response time 
          measurement of UVTA device. 

     c.   Review operating experience with the circuit breakers in your 
          plant(s) identified in Item 1. Provide a list of all malfunctions 
          (both failure to trip and failure to close on demand) associated 
          with 
.

                                                          IEB 83-08        
                                                          December 28, 1983 
                                                          Page 4 of 5      

          the UVTA, including the connecting linkages and latching 
          mechanisms. The list should include the date of each malfunction, 
          and the operating time prior to failure or date of installation, 
          and the date(s) of major maintenance. In general, when the 
          circuit breaker UVTA is actuated on undervoltage and the, breaker 
          contacts do not open within the design time response value, the 
          NRC considers the breaker to have failed. 

     d.   Describe any preventive or corrective measures you have taken, or 
          intend to take, based on the results of Items 2a, 2b, and 2c. 
          Include any revisions to the surveillance test program and 
          methodology. Specifically, address the inherent reliability of 
          the UV trip feature in view of its apparent heavy dependence on 
          intensive maintenance and surveillance and whether a basic design 
          change is warranted to correct the problem, e.g., using a voltage 
          sensitive relay to sense loss of voltage and energize the shunt 
          trip coil from an independent dc power source. 

3.   For facilities with an OL, submit a written report addressing the 
     above action items, including the schedule for completion, within 90 
     days of receipt of this bulletin. 

4.   For facilities holding a CP, submit a written report addressing the 
     above action items, including the schedule for completion, within 90 
     days of receipt of this bulletin, or before receipt of an operating 
     license, whichever is sooner. 

If the above schedules result in an undue hardship, a licensee or CP holder 
may request an extension from the appropriate Regional Administrator. 

The written report required shall be submitted to the appropriate Regional 
Administrator under oath or affirmation under provisions of Section 182a, 
Atomic Energy Act of 1954, as amended. Also, the original copy of the cover 
letters and a copy of the reports shall be transmitted to the U.S. Nuclear 
Regulatory Commission, Document Control Desk, Washington, D.C. 20555 for 
reproduction and distribution. 

Licensees not using circuit breakers with a UVTA in safety-related 
applications (other than the reactor trip system) shall submit a negative 
declaration within 90 days of the receipt of this bulletin. 

This request for information was approved by the Office of Management and 
Budget under a blanket clearance number 3150-00011 which expires April 30, 
1985. Comments on burden and duplication may be directed to the Office of 
Management and Budget, Reports Management, Room 3208, New Executive Office 
Building, Washington, D.C. 20503. 

Although no specific request or requirement is intended, the following 
information would help the NRC evaluate the cost of this bulletin: 

1. Staff time to perform requested review. 

2. Staff time spent to prepare requested documentation. 
.

                                                          IEB 83-08        
                                                          December 28, 1983 
                                                          Page 5 of 5      

If you have any questions regarding this matter, please contact the Regional 
Administrator of the appropriate NRC Regional Office or the technical 
contact listed below. 


                                   Richard C. DeYoung Director 
                                   Office of Inspection and Enforcement 

Technical Contact:  V. D. Thomas, IE
                    301-492-4755

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