UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C. 20555-0001

October 12, 2006

NRC INFORMATION NOTICE 2006-22: NEW ULTRA-LOW-SULFUR DIESEL FUEL OIL

COULD ADVERSELY IMPACT DIESEL ENGINE

PERFORMANCE

ADDRESSEES

All holders of operating licenses for nuclear power reactors, except those who have

permanently ceased operations and have certified that fuel has been permanently removed

from the reactor vessel.

PURPOSE

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert

licensees to the potential for new ultra-low-sulfur diesel (ULSD) fuel oil to adversely impact

engine performance. 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 IN are not NRC requirements; therefore, no specific action or

written response is required.

DESCRIPTION OF CIRCUMSTANCES

In January 2001 and in June 2004, the U.S. Environmental Protection Agency (EPA) finalized

the Clean Diesel Trucks and Buses Rule and the Clean Nonroad Diesel Rule, respectively, with

more stringent standards for new diesel engines and fuels

(http://www.epa.gov/oms/regs/fuels/diesel/diesel.htm). The EPA rules require a reduction in the

sulfur content of highway diesel fuel from its current level of 500 parts per million (ppm) (low

sulfur diesel, or LSD) to 15 ppm (ULSD). Refiners were required to start producing the

cleaner-burning diesel fuel ULSD, for use in highway vehicles beginning June 1, 2006. The

EPA requires sulfur reductions for land-based nonroad diesel fuel to be accomplished in two

steps, with an interim step from currently uncontrolled levels to a 500 ppm cap starting in

June 2007 and the final step to 15 ppm in June 2010. Although the EPA requirements for the

15 ppm ULSD do not take effect until 2010 for nonroad diesel fuel, several nuclear power plant

licensees have received shipments of ULSD. The California Air Resources Board regulations

require that all California users of diesel fuel oil transition to ULSD fuel oil by June 1, 2006.

Some licensees have already received (and all licensees will eventually receive) ULSD fuel oil

from petroleum product refiners, distributors, and wholesalers and may have started using this

fuel in diesel engines that provide functions important to safety. Examples of diesel engines

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providing functions important to safety include: Emergency diesel generators (EDGs), dieseldriven fire pumps, diesel-driven auxiliary feedwater pumps, diesel-driven essential service water

makeup pumps, diesel-driven instrument air compressors, security diesel generators, safe

shutdown facility diesel generators, diesel generators for emergency preparedness and

response functions, and station blackout diesel generators.

There are several diesel fuel properties other than sulfur concentration that change as a result

of moving to ULSD that may adversely effect the engine performance including: 

Energy Content

In general, the processing required to reduce sulfur to 15 ppm also reduces the aromatics

content and density of diesel fuel, resulting in a reduction in volumetric energy content

(BTU/gallon). The expected reduction in energy content is 1.2 percent or more. Less energy

content of the fuel can reduce the instantaneous output rating of the diesel engine. The

reduced output rating may be less than the value specified in the plant’s design and licensing

basis, potentially rendering the diesel inoperable.

The reduced energy capacity of the ULSD may result in increased fuel consumption such that

the onsite diesel fuel storage capacity for the emergency diesel generators may be insufficient

to satisfy the plant’s design and licensing basis for diesel operation duration before offsite

replenishment is needed.

The reduced energy capacity may also lengthen the amount of time needed for the emergency

diesel generators to reach the required speed and voltage. 

Fuel Particulate Build-up Increases

Additives to increase lubricity and to inhibit corrosion used by different refineries and wholesale

suppliers can react or become unstable in storage, which can result in increased fuel

particulates that may foul or plug filters and fuel injection equipment, and can affect suitability of

some testing methods. Some nuclear plant licensees using ULSD have observed an increase

in the rate of particulate buildup in samples from their diesel fuel oil storage tanks. 

Fuel System Seal Leaks

Non-nuclear industry operating experience using ULSD shows an increased incidence of fuel

system leaks at points where elastomers (O-rings) are used to seal joints, with most leaks

occurring at the fuel pump and injectors. The evidence to date suggests the problem is linked

to a reduction in the aromatics content of the ULSD which affects seal swelling, as does seal

material and age of the material. 

Compatibility with Lubricating Oil

As discussed in NRC IN 96-67, “Vulnerability of Emergency Diesel Generators to Fuel

Oil/Lubricating Oil Incompatibility,” lubricating oil contains an additive package that neutralizes

the products of combustion, most importantly sulfuric acid, to prevent engine corrosion. With a
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reduced amount of sulfur, there is more unreacted additive in the lubricating oil, which may

result in the formation of deposits when some of the oil is burned. These deposits can build up

behind the piston rings, forcing the rings to extrude and come into contact with the cylinder liner

wall, resulting in scuffing. 

Microbial Growth

Diesel fuel that was desulfured at the refinery through hydrocracking (versus hydrotreatment)

may have a greater propensity for microbial growth due to an increased concentration of

n-alkanes (linear molecules). 

Incompatible Metals

There are no known compatibility issues with aluminum, carbon steel, stainless steel, and

bronze. However, copper and zinc are incompatible with ULSD because both are oxidative

catalysts that will accelerate the formation of sediments, gels, and soaps (American Society for

Testing and Materials (ASTM) D975, Appendix X2.7.2).

Lubricity

Lubricity is a measure of the fuel’s ability to lubricate and protect the various parts of the

engine’s fuel injection system from wear. The processing required to reduce sulfur to 15 ppm

also removes naturally-occurring lubricity agents in diesel fuel. Rotary and distributor type fuel

pumps are completely fuel lubricated resulting in high sensitivity to fuel lubricity. Refiners treat

the diesel fuel with additives on a batch to batch basis to ensure adequate lubricity. Therefore,

receipt of ULSD with inadequate lubricity is possible but unlikely.

BACKGROUND

Applicable Regulatory Documents

General Design Criterion (GDC) 17, “Electric Power Systems,” of Appendix A, “General Design 

Criteria for Nuclear Power Plants,” to Title 10 of the Code of Federal Regulations (10 CFR) Part

50, “Domestic Licensing of Production and Utilization Facilities,” requires that an onsite electric

power system and an offsite electric power system be provided to permit functioning of

structures, systems, and components important to safety. In addition, GDC 17 contains

requirements concerning system capacity, capability, independence, redundancy, availability,

testability, and reliability. Appendix B, “Quality Assurance Criteria for Nuclear Power Plants and

Fuel Reprocessing Plants,” to 10 CFR Part 50 establishes overall quality assurance

requirements for the design, construction, and operation of structures, systems, and

components important to safety. 
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Regulatory Guide (RG) 1.137, Revision 1, “Fuel Oil Systems for Standby Diesel Generators”

dated October 1979, describes a method acceptable to the NRC staff for complying with the

Commission’s regulations regarding diesel fuel oil systems for standby diesel generators and

assurance of adequate diesel fuel oil quality. RG 1.137 states that Appendix B to American

National Standards Institute (ANSI) N195-1976 should be used as a basis for a program to

ensure the initial and continuing quality of diesel fuel oil as supplemented by eight additional

provisions described in the RG for maintaining the properties and quality of diesel fuel oil.

Related NRC Generic Communications

NRC IN 96-67, “Vulnerability of Emergency Diesel Generators to Fuel Oil/Lubricating Oil

Incompatibility,” dated December 19, 1996. This IN alerted addressees to a finding involving

degradation of the power block assembly of two EDGs caused by an incompatibility of the

lubricating oil with a low-sulfur-content diesel fuel oil. 

NRC IN 91-46, “Degradation of Emergency Diesel Generator Fuel Oil Delivery Systems,” dated

July 18, 1991. This IN alerted addressees to potential inoperability of multiple EDGs resulting

from common cause degradations: (1) degraded diesel fuel oil delivery systems and (2) failure

to meet technical specification (TS) testing requirements intended to detect potentiallydegraded quality of the diesel fuel oil stored onsite.

NRC Generic Letter (GL) 83-26, “Clarification of Surveillance Requirements for Diesel Fuel

Impurity Level Tests.” This GL provided licensees revised surveillance provisions for diesel fuel

oil impurity level tests to clearly reflect the relationship between the Standard TS testing

requirements for diesel fuel oil impurity levels; guidance given in RG 1.137, Revision 1, and

ANSI N195-1976 (ASTM D270, ASTM D975 and ASTM D2274); and the NRC staff review

performed in accordance with Standard Review Plan Sections 9.5.4 through 9.5.8.

DISCUSSION

In January 2001 and in June 2004, the EPA finalized the Clean Diesel Trucks and Buses Rule

and the Clean Nonroad Diesel Rule, respectively, with more stringent standards for new diesel

engines and fuels that require a reduction in diesel fuel sulfur content to 15 ppm. Some

licensees have already received, and all will eventually receive, this ULSD. As described

above, the ULSD has a number of properties that have the potential to degrade or render

inoperable the associated diesel engine or may create a condition that is inconsistent with

current plant design and licensing bases. This ULSD issue is of particular concern because it

effects all licensee diesel generators that are safety-related and/or important to safety, thereby,

presenting a possible common mode failure. Licensees can evaluate the potential impacts of

ULSD and can take measures to ensure the plant is consistent with the current design and

licensing basis and prevent the diesels from being rendered inoperable or significantly

degraded. 
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CONTACT

This information notice requires no specific action or written response. Please direct any

questions about this matter to the technical contacts listed below or the appropriate Office of

Nuclear Reactor Regulation (NRR) project manager.

Ho K. Nieh, Acting Director /RA/

Division of Policy and Rulemaking

Office of Nuclear Reactor Regulation

Technical Contacts: Patrick Finney, RI Robert Wolfgang, NRR/DCI

610-337-5344 301-415-1624

E-mail: pwf@nrc.gov E-mail: rjw1@nrc.gov

Timothy Mitts, NRR/DIRS Max Schneider, RI

301-415-4067 860-447-3170

E-mail: tmm5@nrc.gov E-mail: sms2@nrc.gov

Note: NRC generic communications may be found on the NRC public Web site,

http://www.nrc.gov, under Electronic Reading Room/Document Collections.