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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