United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 90-80: Sand Intrusion Resulting in Two Diesel Generators Becoming Inoperable

                                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 




9012170262 
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                                                       IN 90-80 
                                                       December 21, 1990 
                                                       Page 2 of 3 


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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