Bulletin 86-03: Potential Failure of Multiple Eccs Pumps Due to Single Failure of Air-operated Valve in Minimum Flow Recirculation Line
SSINS No.: 6820
OMB No.: 3150-0011
NUCLEAR REGULATORY COMMISSION
OFFICE OF INSPECTION AND ENFORCEMENT
WASHINGTON, DC 20555
October 8, 1986
IE COMPLIANCE BULLETIN NO. 86-03: POTENTIAL FAILURE OF MULTIPLE ECCS PUMPS
DUE TO SINGLE FAILURE OF AIR-OPERATED
VALVE IN MINIMUM FLOW RECIRCULATION LINE
All facilities holding an operating license or a construction permit.
The purposes of this bulletin are (1) to inform addressees of single
failures of minimum flow recirculation lines containing air-operated
isolation valves which could result in a common-cause failure of all
emergency core cooling system (ECCS) pumps in a system, (2) to request that
licensees affected by the problem promptly provide appropriate instructions
and training to plant operators on how to recognize the problem if it occurs
and take appropriate mitigating actions, (3) to request that licensees
notify the NRC concerning the existence of the problem at their facility,
and (4) to request that licensees inform the NRC of measures taken to
correct this and/or other significant problems that are identified as a
result of this bulletin.
Description of Circumstances:
There have been four recent cases where a design deficiency has been found
involving the minimum flow recirculation paths for ECCS pumps. Although
these four cases all involve safety injection (SI) pumps in
Westinghouse-designed reactors, similar problems also could exist in other
systems and at other types of reactors. This design deficiency was first
discovered at the Point Beach Nuclear Plant and was subsequently described
in IE Inforation Notice 85-94. A similar problem involving residual heat
removal (RHR) system loop selection logic was later found in several BWR
plants. This problem was addressed in IE Compliance Bulletin 86-01.
On July 24, 1985, Wisconsin Electric Company submitted a report in
accordance with 10 CFR Part 21 for the Point Beach Nuclear Plant describing
a design deficiency involving the minimum flow recirculation valves for the
SI pumps. At Point Beach the discharge lines for each of the SI pumps are
connected to a common recirculation header to provide a test flow path and a
recirculation flow path for minimum flow at times when the reactor coolant
system (RCS) pressure exceeds the SI pump shutoff head. The common
recirculation header is provided with two air-operated valves in series.
These valves close to isolate the
October 8, 1986
Page 2 of 3
refueling water storage tank (RWST) from the containment sump during the
recirculation phase of emergency core cooling following a postulated
loss-of-coolant accident (LOCA). Closure of these valves is intended to
prevent containment reactor coolant from being pumped outside containment to
the RWST during the recirculation phase. Both of the recirculation header
isolation valves are designed to fail closed when their control circuits
lose electrical power or control air pressure. The Part 21 report noted that
a single failure (open) of the breaker associated with either of the two
valves would isolate the minimum flow path for both SI pumps, defeat the
control room remote operation capability of the affected valve, and cause
the loss of control room valve position indication.
On February 5, 1986, Carolina Power and Light submitted LER 86-01 describing
essentially the identical design deficiency involving the minimum flow
recirculation path for the SI pumps at H. B. Robinson. On June 20, 1986,
Rochester Gas and Electric discovered a similar design deficiency at the
Ginna Plant and on June 25, 1986, Florida Power and Light Company reported a
similar design deficiency at the Turkey Point Plant.
The concern in all four cases above involves a postulated small break LOCA
which initiates a safety injection signal that starts the SI pumps. During a
small break LOCA, RCS pressure may not readily decrease below the SI pump
shutoff head. A single failure resulting in the loss of the minimum flow
path concurrent with SI pump actuation would cause the pumps to operate
deadheaded until RCS pressure decayed below the SI pump shutoff head. The
simultaneous loss of minimum flow valve position indication in the control
room will exacerbate this loss of minimum flow path. The availability of
valve position indication is not expected to sufficiently ameliorate this
event. Operating the SI pumps deadheaded would result in pump damage and
failure within a few minutes. The failure of multiple trains in an ECCS due
to a single failure violates the single failure criterion in General Design
Criterion (GDC) 35 (10 CFR 50, Appendix A). In all the above cases, the
short-term corrective actions taken by the licensees were to mechanically
block open the SI pump recirculation valves to ensure a minimum flow path
and to revise the applicable plant LOCA procedures to manually close these
valves prior to switching to the recirculation mode. This short term action
should be carefully weighed against the requirements to minimize containment
leak paths in the ECCS recirculation mode of operations and the reliability
of operator actions in this regard.
1. Promptly determine whether or not your facility has a single-failure
vulnerability in the minimum flow recirculation line of any ECCS pumps
that could cause a failure of more than one ECCS train.
2. If the problem exists: (a) promptly instruct all operating shifts of
the problem and measures to recognize and mitigate the problem; (b)
promptly develop and implement corrective actions which bring your
facility into compliance with GDC 35.
*Actions required of the BWR plants in response to IE Compliance Bulletin
86-01 need not be repeated in responding to this Bulletin.
October 8, 1986
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3. Within 30 days of receipt of this bulletin, (a) provide a written
report to the NRC which identifies whether or not this problem exists
at your facility, (b) if the problem exists (or existed), include in
the report the justification for continued operation and identify the
short-term modifications to plant operating procedures or hardware that
have been or are being implemented to ensure safe plant operations.
4. If the problem exists (or existed), provide a written report within 90
days of receipt of this bulletin informing the NRC of the schedule for
long-term resolution of this and/or any other significant problems that
are identified as a result of this bulletin.
The written report shall be submitted to the appropriate Regional
Administrator under oath or affirmation under provisions of Section 182a,
Atomic Energy Act of 1954, as amended. Also, the original copy of the cover
letter and a copy of the report 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 blanket clearance number 3150-0011. 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.
If you have questions regarding this matter, please contact the Regional
Administrator of the appropriate NRC regional office or one of the technical
contacts listed below.
James M. Taylor, Director
Office of Inspection and Enforcement
Technical Contact: Henry Bailey, IE
Ron Young, IE
Attachment: List of Recently Issued IE Bulletins
Page Last Reviewed/Updated Friday, May 22, 2015