Protecting People and the EnvironmentUNITED STATES NUCLEAR REGULATORY COMMISSION
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
December 21, 1990
Information Notice No. 90-80: SAND INTRUSION RESULTING IN TWO DIESEL
GENERATORS BECOMING INOPERABLE
Addressees:
All holders of operating licenses or construction permits for nuclear power
reactors.
Purpose:
This information notice is intended to alert addressees to the potential
damage that may occur to emergency diesel generator (EDG) equipment as the
result of the use of abrasive material during maintenance operations. This
information notice is based on an event in which sand (aluminum oxide)
intruded into the cylinders of two diesel engines at the Susquehanna Steam
Electric Station as a result of maintenance related cleaning of the diesel
engine intercoolers. The affected diesel generators were subsequently
declared inoperable because of damage to the cylinder liners and piston
rings caused by the abrasive action of the aluminum oxide particles. 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 August 30, 1990, with both Units 1 and 2 operating at 100-percent power,
the 'B' EDG at the Susquehanna Steam Electric Station was declared
inoperable when plant personnel, performing periodic chemical analysis of
EDG lubricating oil samples, found a high concentration of chromium in the
'B' EDG oil samples. Boroscopic examination of the EDG cylinders revealed
significant scoring of numerous cylinder liners and piston rings. The
licensee concluded that the source of chromium in the lubricating oil was
from the scored cylinder liners. Previously the licensee had found similar
scoring of the cylinder liners and piston rings on the 'D' EDG. Further
inspection by plant personnel identified the presence of abrasive material
(sand) in the intake air manifolds of both the 'B' and 'D' diesel engines.
A root cause analysis concluded that the sand had entered the EDGs during
recent maintenance operations involving the cleaning and coating of the
inner
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IN 90-80
December 21, 1990
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surface of the tubes in the intercoolers (heat exchangers). The
intercoolers are located between the turbocharger air compressor discharge
and the intake air manifolds. The intercoolers consist of a shell side
through which intake air passes and a tube side through which cooling water
passes. As part of normal maintenance, the intercoolers are periodically
cleaned and treated with a corrosion-preventive agent. Maintenance
personnel clean the inner surface of the intercooler tubes by airblasting
with fine particles of aluminum oxide. Prior to performing the cleaning,
maintenance personnel had removed the intercoolers from the EDGs and
prepared them for sandblasting by covering the shell side with plywood and
taping the edges. Four bolts were used to secure the plywood cover to the
intercooler. Apparently, the plywood cover warped and dislodged the tape
allowing the aluminum oxide particles to enter the shell side of the
intercoolers. After the intercoolers were reinstalled, combustion intake
air picked up the residual sand and carried it inside the engine. Once
inside the engine, the sand settled between the piston rings and cylinder
liners, resulting in the heavy scoring.
Other occurrences of abrasive material intrusion include a 1985 event at
Catawba in which metallic particles were found embedded in the bearing
shells and in the lubricating oil system of one EDG. The metallic particles
were analyzed and found to be identical to shotblasting material used during
piping modifications and repairs to the lubricating oil system.
Discussion of Safety Significance:
These events reveal the vulnerability of the EDGs to damage from foreign
material, such as the aluminum oxide particles, which may enter the engine
through the combustion air, lubricating oil, fuel oil, or jacket coolant
water systems. In addition, these events underscore the importance of
implementing strict cleanliness specifications when performing maintenance
activities on these subsystems. The application of generally accepted
industry practices for maintaining equipment cleanliness levels through the
incorporation of cleanliness requirements into maintenance procedures and
the training of work crews in the methods for meeting those requirements are
considered effective. The fact that the licensee detected the degradation
of the cylinder liners as a consequence of required periodic chemical
analysis of the lubricating oil is evidence of the value of performing
regular lubricating oil analyses.
Other options for cleaning heat exchanger tubes are available in the
industry. For example, cleaning the tubes with a mild acidic solution is an
accepted and widely used technique especially with EDG intercoolers where
the consequences of contamination can have major safety significance. It is
noteable that, because of the manufacturers recommendations, the intercooler
of EDG 'E' was not cleaned by sandblasting and the engine was not affected
by the above condition.
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IN 90-80
December 21, 1990
Page 3 of 3
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
the technical contact listed below or the appropriate NRR project manager.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contact: J. Rajan, NRR
(301) 492-0788
Attachment: List of Recently Issued NRC Information Notices
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