Information Notice No. 89-49: Failure to Close Service Water Cross-Connect Isolation Valves
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
May 22, 1989
Information Notice No. 89-49: FAILURE TO CLOSE SERVICE WATER CROSS-
CONNECT ISOLATION VALVES
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is being provided to alert addressees to potential
problems that may result from failure to close isolation valves in service
water system loop cross-connect piping during certain scenarios. It is
expected that recipients will review the information for applicability to
their facilities and consider actions, as appropriate, to avoid similar
problems. However, suggestions contained in this information notice do
not constitute NRC requirements; therefore, no specific action or written
response is required.
Description of Circumstances:
While Nine Mile Point Unit 2 was shutdown in October 1988 for refueling,
the licensee reviewed the control logic which actuates certain service
water valves which are used to isolate redundant loops of service water.
It was determined that a loss-of-offsite power with a single failure (i.e.,
failure to start one of two diesel generators), could lead to loss of the
operating diesel generator, due to inadequate cooling water flow from the
service water system.
The service water system at Nine Mile Point Unit 2 consists of two cross-
connected and redundant cooling loops (divisions), each with service water
pumps and various loads, including a diesel generator. (A third diesel
generator dedicated to high-pressure core spray takes cooling water from
either loop, but it does not provide emergency ac power for any other
function.) During normal operation, the isolation valves in the cross-
connect piping are open so that any combination of service water pumps
may be used to provide cooling water to all loads. In response to a
loss-of-offsite power, the isolation valves should close so that each
loop will operate independently of the other. With a loss-of-offsite
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power, the control logic would ensure that closure of the isolation valves
would occur after power is restored from either offsite sources or the
diesel generators. However, if one of the diesel generators fails to
operate, power would be supplied to only one ESF division.
The design deficiency in the control logic involved the need for power to
actually exist on ESF buses in both divisions for either of two isolation
valves to close. Therefore, the isolation valves would not close when there
was a loss-of-offsite power and the failure of one diesel generator. With the
valves open the cooling water flow provided by a single service water pump
associated with the operable diesel generator would be distributed to all
loads in both loops. As a result, it was postulated that with open valves
in the cross-connect piping, there would be inadequate cooling water flow
in the service water loop with the operable diesel generator, and that diesel
generator would probably fail due to overheating. The control logic design
deficiency has existed since the plant was initially constructed and the
licensee's pre-operational routine surveillance and post maintenance/
modification testing did not detect the design deficiency. The licensee
subsequently made changes to the control logic that eliminated the single
failure deficiency.
The licensee for the Cooper Nuclear Station was concerned about having an ade-
quate flow of service water to essential loads following a loss-of-coolant
accident given a loss-of-offsite power and the failure of the number 1 diesel
generator to start. Without power from this diesel generator, the single
motor operated block valve which would automatically close to isolate non-
essential loads from the essential loads would fail to close. Without valve
closure, there may be inadequate flow to the essential service water loads
and a single service water pump could be operating in a runout condition.
This problem was identified during the construction and licensing phase,
but station procedures were not modified adequately to mitigate the concern
over pump runout with a potential for loss of flow. The licensee modified
procedures to assure that reactor operators take steps to close another valve
in the cross-connect piping that would isolate the nonessential loads, there-
by assuring adequate cooling water flow to essential loads, including the
operating diesel generator.
Discussion:
With the service water system cross-connect valve closure problems as
described above, the loss-of-offsite power and a single failure could result
in a station blackout. Because the potential consequences are significant,
licensees have evaluated possible improvements such as reducing cooling water
flow to non-essential components following a loss-of-offsite power event,
changing the control logic so that loop isolation occurs with power available
to only one division and clarifying procedures that specify corrective
operator actions to ensure that adequate service water flow to the essential
components is maintained.
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May 22, 1989
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No specific action or written response is required by this information
notice. If you have any questions about this matter, please contact the
technical contact listed below or the Regional Administrator of the
appropriate regional office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: J. Carter, NRR
(301) 492-1194
Attachment: List of Recently Issued NRC Information Notices. Attachment
IN 89-49
May 22, 1989
Page 1 of 1
LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________
Information Date of
Notice No._____Subject_______________________Issuance_______Issued to________
89-48 Design Deficiency in the 5/22/89 All holders of OLs
Turbine-Driven Auxiliary or CPs for nuclear
Feedwater Pump Cooling power reactors.
Water System
89-47 Potential Problems With 5/18/89 All holders of OLs
Worn or Distorted Hose or CPs for nuclear
Clamps on Self-Contained power reactors and
Breathing Apparatus fuel facilities.
89-46 Confidentiality of 5/11/89 All holders of
Exercise Scenarios licenses for fuel
cycle facilities
and byproduct
material licensees
having an approved
emergency response
plan.
89-45 Metalclad, Low-Voltage 5/8/89 All holders of OLs
Power Circuit Breakers or CPs for nuclear
Refurbished with Sub- power reactors.
standard Parts
89-44 Hydrogen Storage on the 4/27/89 All holders of OLs
Roof of the Control Room or CPs for nuclear
power reactors.
88-82, Torus Shells with Corrosion 5/2/89 All holders of OLs
Supp. 1 and Degraded Coatings in or CPs for BWRs.
BWR Containments
89-43 Permanent Deformation of 5/1/89 All holders of OLs
Torque Switch Helical or CPs for nuclear
Springs in Limitorque power reactors.
SMA-Type Motor Operators
88-97, Potentially Substandard 4/28/89 All holders of OLs
Supp. 1 Valve Replacement Parts or CPs for nuclear
power reactors.
89-42 Failure of Rosemount 4/21/89 All holders of OLs
Models 1153 and 1154 or CPs for nuclear
Transmitters power reactors.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
..
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