United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 80-17: Supplement No. 1, Failure of 76 of 185 Control Rods to Fully Insert During a Scram at a BWR

                                                      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 level 
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 (l") 
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" systems 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


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IE Bulletin No. 80-17                                       July 18, 1980
Supplement No. 1                                            Page 2 of 3

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. Actions 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 remainder 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.l 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. Actions 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.


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IE Bulletin No. 80-17                                       July 18, 1980
Supplement No. 1                                            Page 3 of 3

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 installing 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 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 DC 20555.  

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





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