Information Notice No. 89-54: Potential Overpressurization of the Component Cooling Water System
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
June 23, 1989
Information Notice No. 89-54: POTENTIAL OVERPRESSURIZATION OF THE
COMPONENT COOLING WATER SYSTEM
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 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
required.
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
coolant
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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
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Attachment
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
plan.
_____________________________________________________________________________
OL = Operating License
CP = Construction Permit
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