Information Notice 1993-61, Excessive Reactor Coolant Leakage Following a Seal Failure in a Reactor Coolant Pump or Reactor Recirculation Pump
| ML031480397 | |
| Person / Time | |
|---|---|
| Issue date: | 08/09/1993 |
| From: | Grimes B K Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| IN-93-061 | |
| Download: ML031480397 (3) | |
Information
Notice No. 93-61 Index Site Map I FAQ I Help I Glossary I Contact Us A Search A... NuclearRRegulatoryyCommissionm
Home Who We Ae Whai We Do Nuclear Nuclear Radioactive
II Public I Home ll Wh W Ae lWhi e o l Reactors Materials
I Waste ll Involvement
Home > Electronic
Reading Room > Document Collections
> General Communications
> Information
Notices > 1993 > IN 9 UNITED STATES NUCLEAR REGULATORY
COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555 August 9, 1993 NRC INFORMATION
NOTICE 93-61: EXCESSIVE
REACTOR COOLANT LEAKAGE FOLLOWING
A SEAL FAILURE IN A REACTOR COOLANT PUMP OR REACTOR RECIRCULATION
PUMP
Addressees
All holders of operating
licenses or construction
permits for nuclear power reactors.
Purpose
The U.S. Nuclear Regulatory
Commission (NRC) is issuing this information
notice to alert addressees
to the potential
for excessive
reactor coolant leakage following
a seal failure in a reactor coolant pump or reactor recirculation
pump. 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 are not NRC requirements;
therefore, no specific action or written response is required.Description
of Circumstances
Oconee Nuclear Station, Unit 1 On May 24, 1992, the licensee commenced
a reactor shutdown from 100 percent power because of excessive
leakage from the 1A2 Reactor Coolant Pump seal.The maximum leakage was approximately
23 liters per minute 6 gpm]. The seal failed because of the premature
degradation
of obsolete seal parts that had mistakenly
been installed.
Westinghouse
supplied the Unit 1 reactor coolant pumps, incorporating
a three-stage seal series arrangement
to limit coolant flow up the pump shaft.Although Westinghouse
had provided the necessary
information
on the design change of the seal, the information
was not properly communicated
to plant personnel.
As a result, the obsolete seal parts were not removed from the station stock and appropriate
maintenance
procedures
were not revised to reflect the change. These deficiencies
contributed
to the fact that maintenance
personnel
inadvertently
installed
the obsolete seal parts.Further details can be found in Licensee Event Report (LER) 50-269/92-09 and NRC Inspection
Report No. 50-269/92-13.
9308030200.
IN 93-61 August 9, 1993 Millstone
Unit 1 http://www.nrc.gov/reading-rmldoc-collections/gen-comm/info-notices/1
993/in9306
1 .html 03/13/2003 Information
Notice No. 93-61 On May 25, 1989, the licensee started up Unit 1 for Cycle 13 operation.
During plant heatup on May 27, 1989, operators
noted indications
of intermittent
seal failure for the A' Reactor Recirculation
Pump inner seal.The licensee continued
power escalation
and cycle startup testing while making plans to replace the seal. On May 29, 1989, while at full-power
operation, the drywell leakage exceeded the Technical
Specifications
limit and the licensee commenced
plant shutdown.
The leakage was approximately
34 liters per minute 9 gpm] at the start of the event and increased
to about 174 liters per minute 46 gpm] during the shutdown process. After reviewing
the failed seal and consulting
with the pump manufacturer, Byron Jackson, the licensee still did not identify the exact cause of the seal failure. However, the licensee did determine
that the pump seal had probably failed as a result of one or more of the following
causes: (1) improper seal handling prior to installation, (2) introduction
of debris and corrosion
products into the seal cavity, and (3) improper depressurization
following
testing of the seal assembly.Further details can be found in LER 50-245/89-14, Revision 1, and in NRC Inspection
Report No. 50-245/89-12.
Clinton Unit 1 On May 21, 1989, the licensee took the reactor to critical for Cycle 2 operation.
On May 25, 1989, the pressure in the seal outer cavity decreased to approximately
414 kPa gauge [60 psig], indicating
failure of the upper seal stage. Approximately
10 hours1.157407e-4 days <br />0.00278 hours <br />1.653439e-5 weeks <br />3.805e-6 months <br /> later, the seal appeared to reseal and operated properly.
On June 1, 1989, with the reactor at about 42-percent
power during power ascension, upon shifting the B- Reactor Recirculation
Pump speed from low to high, the operators
immediately
noted indications
that both the upper and lower seals in the pump had failed. The seal failures resulted in increased
flow from the drywell floor drain sump inlet; the leakage reached a maximum of 242 liters per minute [64 gpm]. The licensee then initiated
plant shutdown.
Although the exact cause of the seal failure was not determined, the licensee indicated
that the probable cause was improper assembly or improper installation.
Further details can be found in the licensee special report submitted
to NRC on June 30, 1989, and in NRC Inspection
Report No. 50-461/89-21.
Discussion
Both reactor coolant pumps and reactor recirculation
pumps use a series of primary and secondary
seals to limit the reactor coolant leakage to containment.
A loss-of-coolant
accident (LOCA) can occur if leakage through the seals of reactor coolant pump or reactor recirculation
pump exceeds the capacity of the normal makeup systems. Thus, the failure of these seals can represent
a significant
degradation
of the reactor coolant pressure boundary.IN 93-61 August 9, 1993 The NRC has, over a period of years, evaluated
the issue of reactor coolant pump and reactor recirculation
pump seal-related
problems (Generic Issue 23)and the need for additional
licensing
requirements
to reduce the potential core-melt
risk resulting
from the failure of these pump seals. An evaluation
program was initiated
to resolve the generic issue and address several reactor coolant pump seal leaks that occurred in the late 1970s and the early 1980s.Analysis performed
in conjunction
with the evaluation
indicated
that the overall probability
of core-melt
due to small-break
LOCAs could be dominated by reactor coolant pump seal failures.
The two conditions
under which seals have failed or could fail, normal operating
conditions
and off-normal
operating
conditions, are addressed
below: Seal performance
under normal operating
conditions
Based on the review of LERs and feedback from industry, some licensees
appear to have recently made major improvements
in reactor coolant pump and reactor recirculation
pump seal performance.
This improvement
is attributed
to a combination
of factors, including
the following:
enhanced seal quality http://www.nrc.gov/reading-rmldoc-collections/gen-commlinfo-notices/1993/in93061 .html 03/13/2003 Information
Notice No. 93-61 assurance
programs, modified seal design, improved maintenance
procedures
and training, closer attention
to detail, improved seal operating
procedures, more knowledgeable
personnel
involved in seal maintenance, reduction
in frequency of transients
that stress the seals, and seal handling and installation
equipment
designed with the appropriate
precision.
However, not all plants have implemented
such measures, and some seal failures have caused substantial
reactor coolant leakage (as described
above).Development
and implementation
of appropriate
procedures
and training can help assure correct operator action for operational
conditions
related to seal degradation
and can assist to identify seal degradation
in a timely manner.This can thereby prevent or mitigate cascade failure of multistage
seal assemblies.
Section III of the ASME Boiler and Pressure Vessel Code has included specific exclusions
for seal components
under NB-3411.2 and NB-2121(b)
relative to design requirements.
However, code exclusions
by themselves
do not relieve licensees
from other pertinent
regulatory
requirements
such as Appendix B to 10 CFR Part 50, as applicable.
For those items covered by Appendix B, as reflected
in plant-specific
licensing
bases, a quality assurance
program is required.
The staff is considering
additional
generic action to address whether all licensees
should treat certain seal components
as safety-related.
Seal performance
under off-normal
operating
conditions
With respect to off-normal
operating
conditions, particularly
loss of all seal cooling water which can be caused by station blackout, loss of component cooling water or loss of service water, the major concerns involve seal failures due to adverse temperature
effects on elastomer
seal materials
and performance
instabilities
at the primary seal face related to coolant flashing and two-phase
flow. The staff is proceeding
with rulemaking
to address issues of ensuring reactor coolant pump seal function or compensating
for seal failure during loss of seal cooling events, including
station blackout.IN 93-61 August 9, 1993 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
Office of Nuclear Reactor Regulation (NRR) project manager.ORIGINAL SIGNED BY Brian K. Grimes, Director Division of Operating
Reactor Support Office of Nuclear Reactor Regulation
Technical
contacts:
Jai Raj N. Rajan, NRR (301) 504-2788 Peter C. Wen, NRR (301) 504-2832 Attachment:
List of Recently Issued NRC Information
Notices http://www.nrc.gov/reading-rmldoc-collections/gen-commlinfo-notices/l
993/in93061 .html 03/13/2003