Information Notice No. 88-99:Detection and Monitoring of Sudden and/or Rapidly Increasing Primary-to-Secondary Leakage
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
December 20, 1988
Information Notice No. 88-99: DETECTION AND MONITORING OF SUDDEN AND/OR
RAPIDLY INCREASING PRIMARY-TO-SECONDARY
LEAKAGE
Addressees:
All holders of operating licenses or construction permits for
pressurized-water reactors (PWRs).
Purpose:
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
samples.
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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December 20, 1988
Page 2 of 3
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.
Discussion:
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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December 20, 1988
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
office.
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
licensees.
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
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