United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 89-80: Potential for Water Hammer, Thermal Stratification, and Steam Binding in High-Pressure Coolant Injection Piping

                                UNITED STATES
                        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 
                                   PIPING

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 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 
required.

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.





8911270002
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                                                        IN 89-80
                                                        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.

Discussion:

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 
feedwater pipes.

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 
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                                                        IN 89-80
                                                        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 
occurs.

The NRC may issue additional information as more inspection and analysis is 
completed.

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 
manager.




                             Charles E. Rossi, Director
                             Division of Operational Events Assessment
                             Office of Nuclear Reactor Regulation

Technical Contacts:  Eric W. Weiss, AEOD
                     (301) 492-9005 

                     Roger Woodruff, NRR
                     (301) 492-1180

Attachments:  
1.  Dresden 2 - High-Pressure Coolant Injection Line
2.  Referenced Generic Communications
3.  List of Recently Issued NRC Information Notices
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                                                            Attachment 2 
                                                            IN 89-80 
                                                            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. 

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