Information Notice No. 89-80: Potential for Water Hammer, Thermal Stratification, and Steam Binding in High-Pressure Coolant Injection Piping
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
December 1, 1989
Information Notice No. 89-80: POTENTIAL FOR WATER HAMMER, THERMAL
STRATIFICATION, AND STEAM BINDING
IN HIGH-PRESSURE COOLANT INJECTION
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 high-pressure coolant injection (HPCI)
valves in a boiling-water reactor (BWR) to prevent leakage of feedwater into
the HPCI system during operation of the reactor at power. 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
Description of Circumstances:
On February 21, 1989, with Dresden Unit 2 operating at power, temperature
was greater than normal in the HPCI pump and turbine room. The abnormal
heat load was caused by feedwater leaking through uninsulated HPCI piping to
the condensate storage tank. During power operation, feedwater temperature
is less than 350 F, and feedwater pressure is approximately 1025 psi.
Normally, leakage to the condensate storage tank is prevented by the
injection check valve, the injection valve, or the discharge valve on the
auxiliary cooling water pump. The injection valve and the injection check
valve are shown in Attachment 1.
On October 23, 1989, with the reactor at power, leakage had increased suffi-
ciently to raise the temperature between the injection valve and the HPCI
pump discharge valve to 275 F and at the discharge of the HPCI pump to
246 F. Pressure in the HPCI piping was 47 psia. On the basis of the
temperature gradient and the pressure in the piping, the licensee concluded
that feedwater leaking through the injection valve was flashing and
displacing some of the water in the piping with steam. This conclusion was
confirmed by closing the pump discharge valve and monitoring the temperature
of the piping. As expected, the pipe temperature decreased to ambient.
December 1, 1989
Page 2 of 3
Accessible portions of the HPCI piping were inspected, and some loose pipe
supports were found near the injection valves. Concrete surfaces near the
support attachment points were spalled.
The licensee declared the HPCI system inoperable on October 23, 1989, and
notified NRC pursuant to 10 CFR 50.72. After performing a review under
10 CFR 50.59, the licensee opened the normally closed injection valve,
closed the normally open discharge valve, and will use the discharge valve
temporarily as the injection valve.
Temperature measurements on the HPCI piping at Dresden Unit 3 indicated that
less significant leakage was occurring.
The event at Dresden is significant because the potential existed for water
hammer or thermal stratification to cause failure of the HPCI piping and for
steam binding to cause failure of the HPCI pump. Further, failure of HPCI
piping downstream from the injection valves would cause loss of one of two
The licensee has not heard the noise that is usually associated with water
hammers. Nevertheless, loosening of the pipe supports, damage to concrete
surfaces, and the presence of steam in the piping strongly indicate that
water hammers had occurred in the HPCI system, probably during HPCI pump
tests or valve manipulations. Temperature-monitoring instrumentation on the
piping near the injection valves was useful in detecting the leak. NRC
Information Notices 85-76, 86-01, 87-10, and 88-13 all address water hammer
events at other facilities. Attachment 2 lists these and other references
mentioned in this notice.
Concern for potential thermal stratification in the HPCI piping is related
to three events in pressurized-water reactors (PWRs) that were the basis for
issuing NRC Bulletin 88-08 and the three supplements to that bulletin.
These events occurred in one of the Farley units and in two foreign
reactors. In all of the events, water leaked either from or to the reactor
coolant system through closed valves in an emergency coolant system.
Thermal stratification of water in the piping of the emergency coolant
system and fluctuations of the interface between the hot and cold streams of
water resulted in thermal fatigue and cracking of the piping wall in the
heat-affected zones of welds and in the base metal. For these reactors, the
configuration of the piping between the reactor coolant system and the first
valve in the emergency cooling system is approximately like the
configuration of the piping at Dresden. The licensee for Dresden does
intend to examine the piping ultrasonically at the next scheduled outage to
determine whether detectable damage has occurred.
During the event at Dresden, the potential for steam binding the HPCI pump
existed because the discharge valve was normally open. Events have occurred
in PWRs that have resulted in steam binding of auxiliary feedwater pumps.
Because the NRC staff was concerned about the availability of the auxiliary
December 1, 1988
Page 3 of 3
feedwater pumps when needed to mitigate the consequences of an accident, the
staff issued NRC Bulletin 85-01. The bulletin required that certain
licensees develop procedures for monitoring the temperature of the pump
discharge to ensure that it remains at less than saturation temperature and
to identify steam binding and restore the operability of the system if it
The NRC may issue additional information as more inspection and analysis is
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate NRR project
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Eric W. Weiss, AEOD
Roger Woodruff, NRR
1. Dresden 2 - High-Pressure Coolant Injection Line
2. Referenced Generic Communications
3. List of Recently Issued NRC Information Notices
December 1, 1989
Page 1 of 1
REFERENCED GENERIC COMMUNICATIONS
1. Information Notice No. 85-76, "Recent Water Hammer Events,"
September 19, 1985.
2. Information Notice No. 86-01, "Failure of Main Feedwater Check
Valves Causes Loss of Feedwater System Integrity and Water Hammer
Damage," January 1, 1986.
3. Information Notice No. 87-10, "Potential for Water Hammer During
Restart of Residual Heat Removal Pumps," February 2, 1987.
4. Information Notice No. 88-13, "Water Hammer and Possible Piping
Damage Caused by Misapplication of Kerotest Packless Metal Diaphragm
Globe Valves," April 18, 1988.
5. NRC Bulletin 85-01, "Steam Binding of Auxiliary Feedwater Pumps,"
October 29, 1985.
6. NRC Bulletin No. 88-08, "Thermal Stresses in Piping Connected to
Reactor Coolant Systems," June 22, 1988; Supplement 1, June 24, 1988;
Supplement 2, August 4, 1988; and Supplement 3, April 11, 1988.
Page Last Reviewed/Updated Thursday, August 20, 2020