Information Notice 2002-07: Use of Sodium Hypochlorite for Cleaning Diesel Fuel Oil Supply Tanks

WASHINGTON, D.C. 20555-0001

January 28, 2002



All holders of operating licenses for nuclear power except those who have ceased operations and have certified that fuel has been permanently removed from the reactor vessel.


The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to alert addressees to the potential problems related to the use of sodium hypochlorite solutions for cleaning diesel fuel oil supply tanks. Use of this chemical in higher concentrations can cause the release of significant amounts of chlorine gas. The NRC anticipates that recipients will review the information for applicability to their facilities and consider taking appropriate actions. However, suggestions contained in this IN do not constitute NRC requirements; therefore, no specific action or written response is required.


Nuclear plants are required to design and maintain an onsite electric power system in accordance with Appendix B, "Quality Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants," to Part 50 of Title 10 of the Code of Federal Regulations (10 CFR Part 50). One acceptable method for complying with these regulations for fuel oil systems for standby diesel generators is described in Regulatory Guide 1.137, "Fuel Oil Systems for Standby Diesel Generators."

Position 2.f of Regulatory Guide 1.137 recommends that licensees clean fuel oil supply tanks at least every 10 years and that they use sodium hypochlorite solutions or equivalent rather than soap or detergents to avoid introducing surfactants (surface active agents) into the fuel system. However, the use of sodium hypochlorite in higher concentrations can release appreciable amounts of heat and chlorine gas.


Sodium hypochlorite is generally available in two forms: as a commercial solution containing 12 to 15 trade percent available chlorine (a so-called bleaching solution), and as a household solution containing 5 trade percent chlorine. Trade percent is defined as the amount of chlorine, in grams, that is available for each 100 milliliters of sodium hypochlorite solution.

Sodium hypochlorite is a strong oxidizer and, when mixed with organic materials such as diesel fuel oil, undergoes an exothermic reaction that generates heat and releases chlorine gas, sometimes violently. A solution with a concentration of 12 trade percent available chlorine can produce up to 1 pound of chlorine gas for each gallon of solution that reacts. Since fuel oil supply tanks are usually located underground and cleaning them may involve working in a confined space, this release could be harmful to the cleaning personnel. Licensees should take appropriate precautions to protect personnel.

Regulatory Guide 1.137 states that solutions equivalent to sodium hypochlorite can be used to clean fuel oil supply tanks. The intent is to keep surfactants from soap or detergents out of the tank. Therefore, to prevent personnel injury, other materials with cleaning properties equivalent to sodium hypochlorite can be used to clean fuel oil supply tanks, provided they meet the intent of the recommendation.

The technical specifications of some licensees may include the requirement to use sodium hypochlorite to clean the fuel oil supply tanks. This requirement came from Revision 4 of the Westinghouse standard technical specifications, but has been removed in subsequent revisions. Therefore, any licensee with this requirement has an opportunity to remove it by submitting a license amendment request. Alternatively, when a licensee converts to the improved technical specifications, the cleaning requirement is moved, along with the other fuel oil requirements, to a fuel oil program. Any licensee that has the requirement in a fuel oil program can change it under 10 CFR 50.59.

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.


William D. Beckner, Program Director
Operating Reactor Improvements Program
Division of Regulatory Improvement Programs
Office of Nuclear Reactor Regulation

Technical contacts: Krysztof Parczewski, NRR
(805) 415-2705
M. Scott Freeman, RII
(864) 822-6927


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