United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-54: Potential Overpressurization of the Component Cooling Water System

                                  UNITED STATES
                          NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555

                                  June 23, 1989

                                   COMPONENT COOLING WATER SYSTEM


All holders of operating licenses or construction permits for nuclear power 


This information notice is being provided to alert addressees to potential 
problems resulting from failure of the component cooling water tubing within 
the thermal barrier heat exchanger of a reactor coolant pump.  It is expected 
that recipients will review the information for applicability to their facili-
ties 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 

Description of Circumstances: 

On May 15, 1989, the licensee for Surry Power Station informed the NRC of a 
design deficiency in the component cooling water (CCW) system.  The deficiency 
results from underdesign in relief capacity of the CCW lines connected to the 
thermal barrier heat exchangers on the reactor coolant pumps.  The reactor 
coolant pumps at Surry were manufactured by Westinghouse and rely on heat 
removal by the CCW system in conjunction with seal injection for reactor 
coolant pump seal and lower radial bearing cooling.  The reactor coolant pump 
motors are also cooled by component cooling water. 

Component cooling water flows through the thermal barrier heat exchangers 
within 1/2-inch ID tubes.  At the request of the licensee for Surry, Westing-
house calculated the maximum reactor coolant flow rate that could occur from a 
break in a thermal barrier tube.  Westinghouse calculated the flow rate into 
the CCW system assuming a double ended break of the 1/2-inch ID tube.  The 
calculation modeled the reactor coolant flow upstream of the break and the 
flow out the break into the CCW system.  An inleakage of approximately 275 gpm 
was predicted. 

The CCW piping adjacent to the reactor coolant pumps at Surry is of schedule 
160 carbon steel and is designed to withstand full reactor system pressure.  
The lower-pressure sections of the CCW system within containment and within 
the auxiliary building are designed for 150 psig.  In the event of reactor 


                                                                 IN 89-54
                                                                 June 23, 1989
                                                                 Page 2 of 2

system inleakage, the low-pressure sections of CCW piping are protected from 
overpressure by a check valve on the upstream side of the reactor coolant pump 
thermal barrier and by a fast-closing, air-operated valve on the downstream 
side.  The isolation valve is designed to close on a high CCW flow signal.  In 
addition, a relief valve which is located on the upstream side of the thermal 
barrier is designed to open at 150 psig.  The licensee determined that this 
protection was not adequate to protect the low-pressure parts of the CCW 
system from overpressure if the calculated inleakage (approximately 275 gpm) 
were to occur.  The air-operated isolation valve is not safety related and the 
relief valve is only designed to pass 167 gpm.  Isolation valves are provided 
on the CCW lines outside the containment building, but these are not designed 
to withstand reactor system pressure.  Failure to isolate the leak inside 
containment or to provide adequate relieving capacity could lead to an 
unisolatable reactor coolant leak outside the containment building.  The 
licensee is installing additional relief capacity on the CCW lines upstream 
and downstream of the reactor coolant thermal barrier heat exchangers at both 
Surry plants. 

In July 1984, Westinghouse notified the NRC (in accordance with 10 CFR Part 
21) of a similar problem involving potential overpressure of CCW systems at 18 
plants with CCW systems designed by Westinghouse.  These plants were equipped 
with a CCW surge tank vent valve that would close automatically on high radio-
activity in the CCW system.  Westinghouse stated that in the event that 
reactor coolant inleakage resulted in closure of the vent valve, the CCW 
system could be overpressurized downstream of the CCW pumps.  At the time of 
the 10 CFR Part 21 notification, Westinghouse indicated that a thermal barrier 
tube rupture would result in a leak rate of approximately 260 gpm.  
Westinghouse recommended several corrective measures designed to ensure 
continual venting of the surge tank, thereby preventing overpressurization of 
the low-pressure CCW system.  The CCW system at Surry was not designed by 
Westinghouse and Surry was, therefore, not included with the 18 plants 
identified by Westinghouse in the 10 CFR Part 21 notification.  In view of the 
potential for CCW over-pressurization identified at Surry, other plant owners 
may wish to evaluate protection of low-pressure CCW piping from overpressure 
in the event of failure of the reactor coolant pump thermal barrier tubing. 

No specific action or written response is required by this information notice.
If you have any questions about this matter, please contact one of the techni-
cal contacts 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 Contacts:  William Lefave, NRR
                     (301) 492-0862

                     Walton Jensen, NRR
                     (301) 492-1190

Attachment:  List of Recently Issued NRC Information Notices 

                                                            IN 89-54
                                                            June 23, 1989
                                                            Page 1 of 1

                             LIST OF RECENTLY ISSUED
                             NRC INFORMATION NOTICES
Information                                  Date of 
Notice No._____Subject_______________________Issuance_______Issued to________

89-53          Rupture of Extraction         6/13/89        All holders of OLs 
               Steam Line on High                           or CPs for nuclear 
               Pressure Turbine                             power reactors. 

88-46,         Licensee Report of            6/8/89         All holders of OLs 
Supp. 3        Defective Refurbished                        or CPs for nuclear 
               Circuit Breakers                             power reactors. 

89-52          Potential Fire Damper         6/8/89         All holders of OLs 
               Operational Problems                         or CPs for nuclear 
                                                            power reactors. 

89-51          Potential Loss of Required    5/31/89        All holders of OLs 
               Shutdown Margin During                       or CPs for nuclear 
               Refueling Operations                         power reactors. 

88-88,         Degradation of Westinghouse   5/31/89        All holders of OLs 
Supp. 1        ARD Relays                                   or CPs for nuclear 
                                                            power reactors. 

89-50          Inadequate Emergency          5/30/89        All holders of OLs 
               Diesel Generator Fuel                        or CPs for nuclear 
               Supply                                       power reactors. 

89-49          Failure to Close Service      5/22/89        All holders of OLs 
               Water Cross-Connect                          or CPs for nuclear 
               Isolation Valves                             power reactors. 

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 
OL = Operating License
CP = Construction Permit 
Page Last Reviewed/Updated Friday, May 22, 2015