United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 80-17: Supplement No. 3, Failure of Control Rods to Insert During a Scram at a BWR

                                                            SSINS:  6820 
                                                            Accession No.: 
                                                            8006190074 

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

                                                   IE Bulletin No. 80-17, 
                                                   Supplement No. 3 
                                                   Date:  August 22, 1980 
                                                   Page 1 of 2 

FAILURE OF CONTROL RODS TO INSERT DURING A SCRAM AT A BWR 

NRC staff evaluation of a potential single failure mechanism of the control 
rod drive control air system has identified the need for licensee actions in
addition to those requested by IEB 80-17 and Supplements 1 and 2. 

The potential single failure was discussed in IE Information Notice 80-30, 
which was issued on August 19, 1980.  It involves gradual or partial loss of
control air system pressure, which could cause partial opening of scram 
outlet valves without rod motion.  The resultant accumulated seal leakage 
could conceivably fill the scram discharge volume in a few minutes.  Since 
not all operating BWR's have instrumentation presently installed to 
continuously indicate water level in the scram discharge volume headers and 
to provide a control room alarm or scram function, the possibility exists 
for the scram discharge volume to fill to a level which could prevent 
reactor scram before automatic protective action or before the operators 
could be warned. 

In view of the possible single failure mechanism described above, the 
following actions are requested in addition to those specified in IE 
Bulletin 80-17, Supplements 1 and 2: 

1.   For those plants in which the scram discharge volume headers are 
     connected to the instrument volume by a 2-inch pipe, within five days 
     of the date of this Bulletin, provide or verify that procedures are in 
     effect to: 

    a.  Require an immediate manual scram on low control rod drive air 
        pressure with a minimum 10 psi margin above the opening pressure of 
        the scram outlet valves. 

    b.  Require an immediate manual scram in the event of: 

        (1)  Multiple rod drift-in alarms, or 

        (2)  A marked change in the number of control rods with high 
             temperature alarms. 

    Installation of water level instrumentation in the scram discharge 
    volume with level alarm and continuous level indication in the control 
    room, in response to Item B.1 of IEB 80-17 Supplement No. 1, may provide 
    a basis for relaxation of the time for initiating a manual scram. 

.

                                                   IE Bulletin No. 80-17, 
                                                   Supplement No. 3 
                                                   Date:  August 22, 1980 
                                                   Page 2 of 2 

2.   In addition, every BWR licensee is requested within five days of the 
     date of this bulletin to provide and implement procedures which require 
     a functional test using water for the instrument volume level alarm, 
     rod block and scram switches after each scram event, before returning 
     to power.  This procedure should remain in effect until modifications 
     in addition to Item B.1 of IEB 80-17 Supplement No. 1 are completed to 
     substantially increase reliability of water level indication in the 
     scram discharge volume(s). 

Licensees of all operating BWRs shall submit a report summarizing action 
taken in response to the above items within 10 days of the date of this 
Bulletin Supplement.  Accordingly, you are requested to provide within 10 
days as specified above, written statements of the above information signed 
under oath or affirmation.  Reports shall be submitted to the Director of 
the appropriate NRC Regional Office and a copy forwarded to the Director, 
Division of Reactor Operations Inspection, NRC.  Office of Inspection and 
Enforcement, Washington, D.C. 20555. 

Approved by GAO, B180225 (R0072); clearance expires July 31, 1980. 
(Application for renewal pending before GAO.)  Approval was given under a 
blanket clearance specifically for identified generic problems.  

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