United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 96-67: Vulnerability of Emergency Diesel Generators to Fuel Oil/Lubricating Oil Incompatibility

                                     UNITED STATES
                             NUCLEAR REGULATORY COMMISSION
                             WASHINGTON, D.C.  20555-0001

                                   December 19, 1996



All holders of operating licenses or construction permits for nuclear power


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees to a recent finding involving degradation of the
power block assembly of two emergency diesel generators caused by an
incompatibility of the lubricating oil with fuel oil with a low sulfur
content.  It is expected that recipients will review the information for
applicability and consider actions, as appropriate, to avoid similar problems. 
However, suggestions contained in this notice do not constitute NRC
requirements; therefore, no specific action or written response is required.

Description of Circumstances

In December 1995, during preoperational testing of a new safety-related 
emergency diesel generator (EDG), test engineers for the licensee, Baltimore
Gas and Electric Company (BGE), at the Calvert Cliffs Nuclear Power Plant,
noted sporadic spikes in crankcase pressure and lubricating oil seeping out
from the crankshaft seal.  The engine was shut down and BGE conducted a
boroscopic inspection of the unit.  One cylinder showed indications of
abnormal wear.  The cylinder liner, piston, and piston rings were removed for
analysis and replaced with a spare set.  The testing program resumed, with
normal crankcase parameters being indicated.

The test program for the safety-related EDG was completed on January 8, 1996. 
Several days later, during a scheduled 2-year maintenance inspection, BGE
found four cylinders with heavy carbon-like deposits on the pistons and behind
the piston rings and evidence of abnormal scuffing on the cylinder liners.  On
further inspection, all the cylinders exhibited some degree of similar
degradation, including the replacement cylinder.  BGE then inspected a second
new EDG that had been installed as a backup power supply in 1995 for station
blackout.  One cylinder on the station blackout engine exhibited degradation
similar to that of the safety-related EDG.  Upon disassembly, excessive carbon
deposition was found in all cylinders.

9612160113.                                                            IN 96-67
                                                            December 19, 1996
                                                            Page 2 of 3


Calvert Cliffs Nuclear Power Plant comprises two Combustion Engineering
reactors with three EDGs, one dedicated to each unit and the third a "swing"
EDG, that automatically loads onto the accident unit.  In 1989, BGE initiated
a modification to upgrade Calvert Cliff's emergency 
electrical system and meet the requirements of the station blackout rule.  The
modification included the installation of one safety-related EDG (giving each
unit two dedicated EDGs) and one nonsafety-related EDG capable of powering any
of the four safety-related 4-kV emergency electrical buses (for station
blackout purposes).  The new EDGs are basically identical, each with two
engines in tandem with the generator between the engines.  The EDGs were
manufactured by Soci�t� Alsacienne de Constructions M�chaniques de Mulhouse
(SACM) and have a nominal continuous rating of 54OO kW.

When the cylinder degradation was found, BGE assembled a root cause analysis
team, which included persons with recognized industry expertise.  The team
developed three potential causes for the diesel power block degradation: 
components not to design specifications, improper operation of the engines,
and lubricating oil/fuel oil incompatibility.  The first possibility was ruled
out by metallurgical and dimensional analysis and the second from discussions
with SACM and other operators of SACM diesel generators.  The team concluded
that the lubricating oil used was incompatible with low sulfur content fuel.

The BGE team found that lubricating oil compatibility depends, in part, on the
type of fuel being burned, as the lubricating oil contains an additive package
that neutralizes the products of combustion, most importantly sulfuric acid,
to prevent engine corrosion.  The lubricating oil originally selected was an
American Petroleum Institute (API) CD-grade synthetic oil.  For the fuel oil
used in the engines at that time, the specification was that the sulfur
content was not to exceed 0.30 percent.  In early 1995, the supplier of fuel
oil to Calvert Cliffs switched to fuels with sulfur contents of 0.05 percent
or less in order to meet new Environmental Protection Agency requirements
intended to reduce sulfuric acid emissions.  With the reduced amount of
sulfur, there would be more unreacted additive in the lubricating oil,
resulting in the formation of deposits when some of the oil was burned.  These
deposits built up behind the piston rings, forcing the rings to extrude and
come into contact with the cylinder liner wall, resulting in scuffing.

After the problem was identified, BGE rebuilt the safety-related EDG with new
cylinder liners, pistons, and piston rings.  On the basis of the findings of
the root cause analysis team, the safety-related EDG was supplied with a
different lubricating oil, which is an API CG-4 grade mineral-based oil.  A
series of acceptance tests were then run to validate the root cause.  The
safety-related EDG was inspected after test runs totaling about 90 hours and
abnormal conditions were found.  The station blackout EDG was then
tested, and inspected, and the results were identical to those for the safety-
related EDG.

Another characteristic of synthetic lubricating oil was identified during the
review of this event.  Synthetic oils contain diester additives required to
improve solubility of oil additives.  In diesel .                                                            IN 96-67
                                                            December 19, 1996
                                                            Page 3 of 3

engines with low oil sump temperatures, water may accumulate in the sump
because the 
temperature is too low to vaporize it.  This water might cause hydrolysis of
the diesters and the resulting acids would react with calcium in the additive
to form insoluble compounds (soaps).  These compounds may clog filters and
degrade performance of a diesel engine.

This information notice requires no specific action or written response.  If
you have any questions about the information in this notice, please refer to
the technical contacts listed below or the appropriate Office of Nuclear
Reactor Regulation (NRR) project manager.

                                                            signed by 

                                           Thomas T. Martin, Director
                                           Division of Reactor Program Management 
                                           Office of Nuclear Reactor Regulation 

Technical contacts:  Kirke Lathrop, Region I
                     (410) 586-2626
                     Email:  hkl@nrc.gov

                     Krzysztof Parczewski, NRR
                     (301) 415-2705
                     Email:  kip@nrc.gov

Page Last Reviewed/Updated Thursday, November 21, 2013