United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 83-01: Failure of Reactor Trip Breakers (Westinghouse DB-50) to Open on Automatic Trip Signal

                                                  SSINS No.: 6820  
                                                  OMB No.: 3150-00012 
                                                  Expiration Date: 04/30/85 
                                                  IEB 83-01 

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

                             February 25, 1983 

IE BULLETIN NO. 83-01:   FAILURE OF REACTOR TRIP BREAKERS (WESTINGHOUSE 
                         DB-50) TO OPEN ON AUTOMATIC TRIP SIGNAL 

Addressees: 

All pressurized water nuclear power reactor facilities holding an operating 
license (OL) for action and to other nuclear power reactor facilities for 
information. 

Purpose: 

The purpose of this bulletin is to inform CP holders and licensees about 
recent failures of W DB type circuit breakers to trip open on receipt of an 
automatic trip signal from the reactor protection system (RPS) and to 
require action of all operating pressurized water reactors to assure proper 
operation of those breakers in the future. 

Description of Circumstances: 

On February 25, 1983, during startup of the Salem Unit 1 plant, both DB-50 
RPS breakers failed to open automatically upon receipt of a valid trip 
signal on low-low steam generator level. 

This failure to trip has been attributed to sticking of the undervoltage 
trip attachment. The reactor was tripped manually from the control room 
about 30 seconds after the automatic trip signal was generated. The manually 
initiated trip was accomplished by the shunt relays installed in each DB-50 
breaker. 

Background: 

In some reactor protection system designs, the automatic protection signals 
are fed only to the undervoltage (UV) trip attachment of the reactor trip 
breakers; the manual signals are fed both to the UV trip and to a shunt trip
coil of each breaker. 

In the recent past, on two separate occasions, one RPS breaker at the Salem 
facility failed to open automatically due to binding of the UV trip 
attachment. These events have been reported in LER's 82-072/03X-1 and 
83-001/03L. In addition, on February 22, 1983, Salem Unit 1 tripped on 
low-low steam generator level; however, since the operator manually tripped 
the reactor at a time almost coincidental with the automatic trip signal, 
the actual trip mechanism (manual or automatic) cannot be ascertained. 


8212060367  
.

                                                        IEB 83-01  
                                                        February 25, 1983 
                                                        Page 2 of 3 

Similar failures involving the UV trip attachment to the RPS have been 
reported to the NRC. These failures only involved one of the two series 
breakers, therefore they did not result in a failure to automatically trip 
the reactor. Said failures have occurred at H. B. Robinson, Connecticut 
Yankee, Prairie Island and St. Lucie in addition to those at Salem. As a 
result of these events, the NRC issued IE Bulletin No. 71-02 and IE Circular
No. 81-12, and Westinghouse issued Technical Bulletin No. NSD-78-74-1 dated 
January 11, 1974 and NSD Data Letter 74-2 dated February 14, 1974. 

Required Actions for All Holders of Operating Licenses for Pressurized Water
Reactors: 

Licensees with W DB type breakers using undervoltage trip attachment in 
Reactor Protective System applications are requested to: 

1.   Perform surveillance test of undervoltage trip function independent of 
     the shunt trip within 24 hours of receipt of this Bulletin unless 
     equivalent testing has been performed within 5 days. Those plants for 
     which on-line testability is not provided may complete this item before
     resuming operation or if currently operating, at the next plant 
     shutdown. 

2.   Review the maintenance program for conformance to recommended W program
     (attachment) including frequency and lubricant applied to trip 
     mechanism. Verify actual implementation of the W program. If 
     maintenance including lubrication does not conform, initiate such 
     maintenance within 5 days of receipt of this bulletin or provide an 
     alternate maintenance program. Repeat the testing required in item 1 
     prior to declaring the breaker OPERABLE. 

3.   Notify all licensed operators of the failure-to-trip event which 
     occurred at Salem. Review the appropriate emergency operating 
     procedures for the event of failure-to-trip with each operator upon his 
     arrival on-shift. 

4.   Provide written reply within 7 days of receipt of this bulletin, 

     a.   identifying results of testing performed in response to item 1, 

     b.   identifying conformance of maintenance program to W recommendation
          and describing results of maintenance performed directly as a 
          result of this Bulletin in response to item 2, 

     c.   provide statement that provisions are in place to notify licensed 
          operators of the Salem event and bring to their attention 
          appropriate failure-to-trip emergency procedures upon their 
          arrival on-shift. 

     d.   You are reminded of the requirements for prompt notification in 
          accordance with 10 CFR 50.72 in the event of detecting an 
          inoperable RPS breaker. 
.

                                                        IEB 83-01 
                                                        February 25, 1983 
                                                        Page 3 of 3 

PWR Licensees not using the subject undervoltage trip attachment and 
therefore not affected by this bulletin shall submit a negative declaration 
within 7 days of the receipt of this bulletin. 

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. 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. 

This request for information was approved by the Office of Management and 
Budget under a blanket clearance number 3150-00012 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. 

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


                              Richard C. DeYoung, Director 
                              Office of Inspection and Enforcement 

Technical Contact:  I. Villalva, IE 
                    301-492-9635 

                    V. Thomas, IE 
                    301-492-4755 

                    J. T. Beard, NRR 
                    301-492-7465 

Attachment: 
1. Transcription of Westinghouse NSD Ltr. 74-2 
2. List of Recently Issued IE Bulletins
.

                                                       ATTACHMENT 1  
                                                       IEB 83-01  
                                                       February 25, 1983 

Verbatim transcription of Westinghouse NSD letter 74-2. Original signed by 
W. H. Furfari and Sydney G. Caslake. 
.

                                                      NSD DATA LETTER 74-2 
                                                       
                                        FROM      : Nuclear Service Division 
                                        WIN       : 236-4744  
                                        DATE      : February 19, 1974  
                                        SUBJECT   : Reactor Trip Breaker  
                                                    Maintenance 

NUCLEAR ENERGY SYSTEMS 

TO: Distribution 

Technical Bulletin NSD-TB-74-1 (issued 1/11/74) described a reactor trip 
breaker malfunction which occurred at H. B. Robinson station in December of 
1973, and recommended certain additional periodic maintenance measures to 
improve the reliability of these breakers. 

The malfunction (failure to trip during a regularly scheduled periodic test)
was attributed to excessive friction in the linkage of the Undervoltage Trip
Attachment, which is the device that initiates the breaker drop-open action 
by elevating the trip bar. The problem was corrected by cleaning and lightly
lubricating certain portions of the linkage. 

To preclude the possibility of reoccurrence of this malfunction, 
Westinghouse recommends that the reactor trip breakers be given regularly 
scheduled periodic inspection/maintenance as described in the Instruction. 
Manual and in line with the following guidelines. 

1.   Scope. These recommendations are intended to apply to Westinghouse 
     DB-50 (or DB-25) breakers in Reactor Trip applications. Some future 
     WNES plants will be supplied with Westinghouse Type DS (stored energy) 
     breakers, which should be maintained in accordance with their 
     instruction manual. 

2.   Related Operations. It is expected that these inspection and main-
     tenance measures would normally be carried out in conjunction with 
     breaker periodic operational testing or during plant shutdowns. 
     However, these recommendations in no way are intended to supersede 
     breaker operational testing commitments and requirements. 

3.   Frequency. Intervals between maintenance will be influenced by 
     operating and atmospheric conditions, but we would recommend that 
     initially it be performed on a semi-annual basis. The period might then 
     be extended to 9 or 12 months if experience shows this to be 
     sufficient. 
.

NSD DATA LETTER 74-2             - 2 -                  February 19, 1974 

4.   Cleaning. Clean the entire unit by blowing with dry instrument air (or 
     a hand bellows), followed by vacuum cleaning. Particular attention 
     should be paid to the cleanness of the undervoltage trip device, which 
     can be inspected without component disassembly. 

5.   Solvents. In general, the use of a cleaning solvent is not encouraged 
     since some can be damaging to electrical components. If there is a 
     particularly heavy deposit of contaminants, an inert or mild solvent 
     such as Stoddard solvent could be used if applied sparingly. 

6.   Lubricants. Although the Instruction Manual (page 5) cautions against 
     any re-lubrication in the field, the manufacturers have agreed that the
     reliability of the breaker is improved by lightly lubricating the 
     linkage of the undervoltage device occasionally. However, the lubricant
     should be applied only sparingly to the front and back faces of the 
     vertical-traveling latch (interfacing with the flat copper-alloy 
     spring). 

     A dry or near-dry molybdenum disulfide lubricant should be used. 
     Technical Bulletin NSD-TB-74-1 indicated Molykote G as a possible 
     choice. That information is incorrect and is hereby rescinded Molykote 
     G uses a thickened mineral oil as a vehicle, which would tend to 
     collect foreign material. A better choice would be Molykote M-88, or 
     Spray-kote. Both are commercially available Dow Corning products. 

7.   Inspection. Following the above cleaning and lubrication the entire 
     breaker should be operationally checked and inspected for broken parts,
     loose bolts or excessive wear. 

This Date Letter and the above information supersedes Technical Bulletin 
NSD-TB-74-1, which is hereby cancelled. 


                                        W. H. Furfari 
                                        Electric Technology 
                                        TECHNICAL OPERATIONS  

                              APPROVED: Syndey G. Caslake, Manager 
                                        Electric Technology 
                                        TECHNICAL OPERATIONS 

WHF/nev Attachment 
Page Last Reviewed/Updated Tuesday, July 23, 2013