Information Notice No. 94-19: Emergency Diesel Generator Vulnerability to Failure from Cold Fuel Oil

UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATORY
WASHINGTON, D.C.  20555

March 16, 1994


NRC INFORMATION NOTICE 94-19:  EMERGENCY DIESEL GENERATOR VULNERABILITY TO
                         FAILURE FROM COLD FUEL OIL


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 a safety problem that could lead to the common
mode failure of all emergency diesel generator units as a result of
temperature-related changes in the fuel oil.  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

Vermont Yankee

During the electrical distribution safety functional inspection conducted from
July 6 to August 7, 1992 (Inspection Report 50-271/92-81), the NRC team found
that the Vermont Yankee emergency diesel generators may be vulnerable to
excessive viscosity problems and the formation of wax crystals in cold fuel.
The team expressed concern about the operability of the emergency diesel
generators during those times when the actual outdoor temperature falls below
the minimum temperature used in the procurement specification for the pour
point of the oil.  The pour point characteristic of the fuel oil is usually
slightly lower than the cloud point characteristic.  The cloud point is
defined as the temperature at which a cloud of wax crystals appears in the
fuel oil and begins to precipitate.  When such a cloud appears, the capability
to transfer the fuel oil from the storage tank to the emergency diesel
generator engine cylinders might be degraded because of wax crystals clogging
fuel oil filters and plating out on the walls of the fuel oil piping.  This
could result in the common mode failure of both emergency diesel generator
units.

The licensee final safety analysis report specified a design outdoor
temperature of -11C [12F].  The licensee technical specifications require
compliance with American Society for Testing and Materials (ASTM) Standard
D-975-68.  This standard stipulates that for cold weather operation, the pour
point of the emergency diesel generator fuel oil should be 6C [10F] below

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the ambient temperature at which the engine is to be operated except where
fuel oil heating facilities are provided.  The inspection team observed no
heat tracing on the fuel oil storage tank, which is located outside, and that
the heat tracing on the fuel oil transfer piping was not energized with a
safety-related source of power.  Therefore, on the basis of the design outdoor
temperature, the pour point of the fuel oil should be no higher than -17C
[2F].  The licensee procured fuel oil with a pour point of -18C [0F].
Consequently, the inspection team agreed that on the basis of the design
outdoor temperature, the requirements of the licensee fuel oil procurement
specification met those of the ASTM standard and hence those of the technical
specification.

Even so, the inspection team questioned whether the licensee can assure the
operability of the fuel oil transfer system and hence the emergency diesel
generator because the licensee final safety analysis report noted that the
minimum recorded outdoor temperature during a nine year observation period was
-36C [-33F].

Point Beach

During the electrical distribution safety functional inspection from March 12
to April 6, 1990 (Inspection Report 50-266/90-201), the NRC team found a
similar potential vulnerability of emergency diesel generators to excessive
viscosity problems in cold fuel oil.  A licensee calculation to determine the
ability of the fuel oil to drain by gravity from the outside storage tanks to
the day tanks indicated that under very low temperatures (-9C [15F]), no
drainage would occur because the ambient temperature would be less than the
cloud point of the fuel oil in the storage tanks and the above-ground piping.
Moreover, the calculation showed that the minimum average temperature at which
fuel could drain to one day tank was only -18C [0F].  The licensee tested
the drainage for about 15 minutes in warm weather, but this did not
demonstrate flow during extremely cold weather.  The licensee now uses a fuel
oil blend (No. 1 and No. 2) that corresponds to a cloud point of -24C
[-12F].  In addition, in very cold weather, fuel oil in the bulk tanks is
recirculated and the temperature is monitored.  In extreme conditions, tank
trucks are kept on site and parked in a heated warehouse as necessary.

Discussion

Manufacturers of emergency diesel generators normally specify the type of fuel
oil to be used in their engines and refer either to ASTM Standard D-975,
Federal Specification VV-F-800, or their own detailed specifications.  In
either case, the heating, burning, physical, and chemical characteristics of
the fuel are established to ensure proper operation of the emergency diesel
generator units.  These fuel oil specifications provide specific values for
cloud point, pour point, and viscosity.  Both the pour point and viscosity
affect the capability of the fuel oil system to transfer fuel oil from a
storage tank to the emergency diesel generator engine cylinders.

Unless licensees establish that stored emergency diesel generator fuel oil has
the proper cloud, pour and viscosity characteristics, the common mode
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March 16, 1994                                                 Page 3 of 3


of all emergency diesel generator units could occur.  This is particularly
true when fuel oil storage tanks and fuel transfer piping are outside and
above ground where they are subject to large changes in ambient temperature.
Emergency diesel generator fuel oil that is procured to specifications that do
not properly establish the lowest expected temperature (cloud and pour point)
requirements is especially susceptible.  In conducting the routine 1-hour
monthly surveillance runs or outage surveillance tests, the licensee may not
operate the emergency diesel generator long enough to observe the effect of
the cold fuel oil.  Most of the fuel oil used during these tests will be from
day tanks, which are at a higher temperature because they are located in the
emergency diesel generator rooms.  In contrast, an accident may require
continuous operation of the emergency diesel generator for several days.  The
warmer fuel in the day tanks would be depleted.  The emergency diesel
generator would then be required to perform on fuel oil at a temperature that
approximates the outside temperature.  Improperly specified (procured)
emergency diesel generator fuel oil for which the lowest expected use
temperature is not taken into account could lead to a common mode failure of
all the emergency diesel generator units.

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.

/s/'d by BKGrimes


Brian K. Grimes, Director
Division of Operating Reactor Support
Office of Nuclear Reactor Regulation

Technical contacts:  Gene Lazarowitz, RI
                  (215) 337-5392

                 Vern Hodge, NRR
                 (301) 504-1861

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