United States Nuclear Regulatory Commission - Protecting People and the Environment

IEB 80-17 Supplement 1 Failure of Control Rods to Insert During a Scram at a BWR (Generic Letter 80-66)



GL80066                                                  SSINS No. 6820 
                                                         Accession No.: 
                                                         8006190027 
                                 UNITED STATES 
                         NUCLEAR REGULATORY COMMISSION 
                     OFFICE OF INSPECTION AND ENFORCEMENT 
                            WASHINGTON, D.C.  20555 

                                 July 18, 1980 
                                                 IE Bulletin No. 80-17 
                                                 Supplement No. 1 

FAILURE OF 76 OF 185 CONTROL RODS TO FULLY INSERT DURING A SCRAM AT A BWR 

Description of Circumstances: 

Please refer to IE Bulletin 80-17, issued July 3, 1980, for complete details
of the initiating event.  Although we are essentially confident that the 
event was caused by water in the Scram Discharge Volume (SDV) system we do 
not yet have a complete explanation as to why the water was present.  The 
best estimate is that some type of blockage existed in the vent and/or 
drainage system for the SDV, precluding adequate drainage.  To ensure that 
the SDV is empty, Browns Ferry (BF-3) has installed instrumentation to 
continuously monitor the water in the scram discharge volume.  Such 
instrumentation is being considered by other plants. 

Since issuance of IE Bulletin 80-17, additional information has been 
identified.  Specifically: 

a)   At Browns Ferry a discrepancy was found between the "as-built" scram 
     discharge system and the "as-designed" system.  An unused one-inch (1")
     instrument line was found uncapped on the four-inch (4") drain header 
     on the west side (the side whose rods scrammed) scram discharge volume 
     vent system of Unit No. 3.  It is believed that this line improved the 
     venting, and therefore the drain time for that system. 
     
b)   It has been determined that the vent systems on some scram discharge 
     volumes interconnect with vent headers that are also common with and 
     are connected to other systems.  The interconnected "vent" system may 
     contain water drained or being drained from those other systems.  This 
     water could potentially affect performance of the SDV.  Also, both the 
     vent and drain systems for the scram discharge system may contain long 
     lengths of relatively small bore piping.  Designs specify a very 
     gradual slope, such that small errors in the "as-installed" piping 
     could result in degraded performance (for example, due to loop seals). 
     
c)   Concerns have been expressed within the NRC Staff regarding potential 
     delays that may occur before start of injection of boron into the BWR 
     system from the Standby Liquid Control System (SLCS) when this manual 
     operator action is required.  The potential delays could be caused by 
     unavailability of the SLCS key which is required to initiate this 
     system, and/or administrative delays which require supervisory approval
     before the SLCS can be manually initiated by the control room licensed 
     operator. 

In view of the above items, the following actions in addition to those 
specified in IE Bulletin 80-17 are to be taken by BWR licensees. 
.

A.   Action to be Taken by BWR Licensees Upon Receipt and to be Reported 
     Within 20 Days of the Date of This Letter: 

     1)   Provide to the NRC Regional Office an analysis of the adequacy of 
          the "as-built" SDV system and associated vent and drain systems, 
          including any identified design deficiencies.  Include copies of 
          verified "as-built" isometric drawings of the SDV and detailed 
          descriptions of the system, verified to be correct, as part of 
          this analysis. 

     2)   Revise and implement Operating Procedures as necessary to provide 
          clear guidance to the licensed operator in the control room 
          regarding when he should initiate the SLCS without obtaining prior
          supervisory approval.  Provide a description of the implemented 
          procedural requirements. 

     3)   Assure that procedures exist and are implemented for specifying 
          remedial action to be taken if water is found in the SDV system at
          times when it should be free of water.  Provide a description of 
          the implemented procedural requirements. 

     4)   Revise and implement administrative procedures as necessary to 
          ensure that the SLCS key shall be readily available to the 
          licensed operator in the control room.  Provide a description of 
          the implemented procedural requirements. 

     5)   Continue daily monitoring of water levels in all scram discharge 
          volumes until continuous monitoring system(s) (discussed in B.1 
          below) is (are) installed and operational (this requirement 
          supersedes the requirements of Item 5 of IE Bulletin 80-17 which 
          required daily surveillance for only 6 days). 

B.   Action to be Taken by BWR Licensees and Completed by September 1, 1980:

     1)   Install a system to continuously monitor water levels in all scram
          discharge volumes.  Continuous recording and alarm features must 
          be included in the design.  Consideration should be given to use 
          of diverse level sensors in this (these) system(s).  The design 
          installed should represent the design with the highest level of 
          reliability compatible with completion of installation by 
          September 1, 1980.  Provide a written description of the system 
          design to the NRC Regional Office. 
          
          If installation by September 1, 1980 is not possible, by August 
          15, 1980, submit to the NRC Regional Office: 

          1)   Documentation in detail why the installation cannot be 
               completed by 9/1/80. 

          2)   A Commitment to a firm schedule for installation. 

          3)   A commitment to equipment changes and/or surveillance 
               requirements in addition to those now in effect that will 
               provide adequate assurance of SDV operability in the interim 
               until installation is completed. 
.

     2)   Perform a study of potential designs for improving the venting 
          system for the scram discharge volumes and submit a description to
          NRC by September 1, 1980.  Improvements such as providing a 
          redundant, independent vent for each significant volume in the 
          system or locally installed vacuum breakers close to each such 
          volume should be considered (some plants already include a design 
          which vents locally to atmosphere).  Include an estimate of the 
          time that would be required to accomplish these modifications in 
          your report to be submitted to the NRC Regional Office.  We have 
          been told that meetings have already been scheduled by GE to 
          discuss their proposals in this area with licensees. 
          
Additional requirements are under consideration and will be the subject of 
further communication from NRC. 

Licensees of all operating BWRs shall submit the information requested 
within the specified allowable times.  This information is requested under 
the provisions of 10 CFR 50.54 (f).  Accordingly, you are requested to 
provide within the time periods specified above, written statements of the 
above information signed under oath or affirmation.  Reports shall be 
submitted to the Director, Division of Reactor Operation Inspection, NRC.  
Office of Inspection and Enforcement, Washington DC 20555. 

Approved by GAO, B180225 (R0071); clearance expires 7-31-80.  Approval was 
given under a blanket clearance specifically for identified generic 
problems. 

Page Last Reviewed/Updated Monday, June 17, 2013