United States Nuclear Regulatory Commission - Protecting People and the Environment

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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                                                            May 22, 1989
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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. 

.                                                            IN 89-49
                                                            May 22, 1989
                                                            Page 3 of 3


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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