United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 88-99: Detection and Monitoring of Sudden and/or Rapidly Increasing Primary-to-Secondary Leakage

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

                                December 20, 1988

                                   RAPIDLY INCREASING PRIMARY-TO-SECONDARY 


All holders of operating licenses or construction permits for 
pressurized-water reactors (PWRs).


This information notice is being provided to alert addressees to potential 
problems in detecting and monitoring sudden and/or rapidly increasing leakage 
through the steam generator tubes from the primary system to the secondary 
system.  It is expected that recipients will review the information for appli-
cability 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 October 19, 1988, Indian Point Unit 3 was operating at full power with no 
indication of significant primary-to-secondary leakage.  The strip chart 
recording for the condenser air ejector monitor (R15) indicates that the count 
rate began to increase above background at 2000 hours.  At 2026 hours, the R15 
monitor alarmed at 300 counts per minute (cpm).  The licensee estimates the 
corresponding primary-to-secondary leak rate to have been quite low, approxi-
mately 0.02 gallons per minute (gpm). 

Subsequent to alarm of the R15 monitor, the air ejector effluent was automati-
cally diverted to containment.  This diversion caused the effluent to bypass 
the R15 monitor and the normal collection point for taking air ejector grab 

At 2030 hours, the operators isolated the steam generator blowdown.  A liquid 
blowdown sample taken at 2100 hours showed no significant change in activity 
relative to a previous sample taken earlier that day at 0832 hours. 

At 2100 hours, a grab sample was taken from an alternate collection point 
located on the air ejector effluent diversion path to confirm and trend the 

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leakage.  However, air in-leakage from a vacuum breaker upstream of the alter-
nate collection point invalidated the sample. 

At 2219 hours, the air ejector flow path was rediverted to its normal flow 
path (to the turbine building vent) to facilitate taking a grab sample from 
the normal collection point.  Grab samples taken at 2235 hours and 2303 hours 
revealed that the leakage rate had reached 2 gpm and was holding steady.  This 
leak rate exceeded the plant Technical Specification limit of 0.3 gpm.  The 
licensee immediately began a plant load reduction (to shutdown) at 2322 hours 
upon analysis of the initial grab sample, and the air ejector exhaust was 
again diverted to containment at 2327 hours. 

Subsequent investigation revealed the leak to be associated with a 
circumferential crack extending approximately 250� around the tube 
circumference.  The crack was located in a tube at the periphery of the tube 
bundle.  The elevation of the crack was just above the top tube support plate 
where the tube had some minor denting.  The cause of the crack (e.g., fatigue, 
stress corrosion crack-ing) has not been clearly established. 

The licensee implemented a number of improvements to enhance its ability to 
detect, trend, and respond to sudden and/or rapidly increasing primary-to-
secondary leakage.  Equipment modifications were implemented to ensure contin-
uous R15 monitor surveillance and to provide for continuous grab sample col-
lection capability during periods when the air ejector effluent is diverted to 
containment.  A computer display of the R15 count rate and of the alarm set-
point was installed in the control room to further enhance monitoring cap-
abilities.  A micro-R-meter was installed on the air ejector piping to confirm 
the R15 readings.  Leak rate monitoring procedures were extensively upgraded 
to make optimal use of the available data to permit timely detection, 
trending, and response to rapidly increasing leak rates. 


Although the Indian Point 3 occurrence did not lead to a tube rupture event, 
the occurrence does highlight the importance of leak rate monitoring methods 
and procedures that are effective in ensuring the timely detection and 
response to rapidly increasing primary-to-secondary leakage that may otherwise 
lead to a tube rupture event such as occurred at North Anna 1 in July 1987. 

There is a wide diversity of methods among licensees to monitor primary-to-
secondary leakage.  Primary and secondary system mass balancing, isotopic 
sampling of the steam generator blowdown, and isotopic sampling of the air 
ejector effluent are among the methods typically in use.  However, these 
methods are employed at discrete time intervals (e.g., three times weekly, 
daily) and these methods may not provide a timely indication of sudden and/or 
rapidly increasing leakage.  Furthermore, leak rate estimates based on liquid 
samples from steam generator blowdown may significantly lag behind actual leak 
rates at the time the sample was taken in cases of rapidly increasing leak 
rates.  This latter point is exemplified by the fact that the blowdown sample 
taken at Indian Point 3 approximately 34 minutes after annunciation of the R15 
alarm showed no significant increase in activity even though the leakage rate 
at this time had probably already reached the Technical Specification limit. 
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                                                            Page 3 of 3

Optimal use of data from the air ejector monitor is one method by which opera-
tors can be quickly alerted to sudden and/or rapidly increasing leakage.  This 
data is monitored continuously and exhibits a relatively good time response to 
sudden and/or rapidly increasing leak rates.  Radiation monitor alarm 
setpoints corresponding to very low levels of primary-to-secondary leakage, 
such as existed at Indian Point 3, can alert the operators to the need for 
quickly confirming, quantifying, and trending leakage through appropriate 
methods such as sampling of the air ejector effluent.  Specific procedures to 
accomplish these goals are important to ensure a timely response to rapidly 
increasing leaks. 

Although the R15 alarm provided an early indication to the Indian Point 3 
operators of possible primary-to-secondary leakage, the design of the air 
ejector effluent containment diversion feature contributed to difficulties in 
monitoring the leakage for almost 2 hours immediately following the alarm.  
Actions such as those taken by the licensee for Indian Point 3 to ensure the 
ability to monitor leakage while the air ejector effluent is diverted to 
containment can substantially enhance the ability of operators to monitor and 
respond to sudden and/or rapidly increasing leakage. 

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 

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

Technical Contact:  E. Murphy, NRR
                    (301) 492-0945

Attachment:  List of Recently Issued NRC Information Notices
.                                                            Attachment 
                                                            IN 88-99
                                                            December 20, 1988
                                                            Page 1 of 1

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

88-98          Electrical Relay Degradation  12/19/88       All holders of OLs 
               Caused by Oxidation of                       or CPs for nuclear 
               Contact Surfaces                             power reactors. 

88-97          Potentially Substandard       12/16/88       All holders of OLs 
               Valve Replacement Parts                      or CPs for nuclear 
                                                            power reactors. 

88-96          Electrical Shock Fatalities   12/14/88       All holders of OLs 
               at Nuclear Power Plants                      or CPs for nuclear 
                                                            power reactors. 

88-95          Inadequate Procurement        12/8/88        All holders of OLs 
               Requirements Imposed by                      or CPs for nuclear 
               Licensees on Vendors                         power reactors. 

88-94          Potentially Undersized        12/2/88        All holders of OLs 
               Valve Actuators                              or CPs for nuclear 
                                                            power reactors. 

88-93          Teletherapy Events            12/2/88        All NRC medical 

88-92          Potential for Spent Fuel      11/22/88       All holders of OLs 
               Pool Draindown                               or CPs for nuclear 
                                                            power reactors. 

88-91          Improper Administration       11/22/88       All holders of OLs 
               and Control of                               or CPs for nuclear 
               Psychological Tests                          power reactors and 
                                                            all fuel cycle 
                                                            facility licensees 
                                                            who possess, use, 
                                                            import, export, or 
                                                            transport formula 
                                                            quantities of 
                                                            strategic special 
                                                            nuclear material. 

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