United States Nuclear Regulatory Commission - Protecting People and the Environment

Boeing Company Request Concerning Depleted Uranium Counterweights

HPPOS-206 PDR-9111210356

See the letter from G. H. Cunningham to W. E. Morgan dated April 14, 1983, and the incoming requests from W. E. Morgan (Boeing Company) dated March 18, 1983 and January 6, 1983.

The Boeing Company's proposal to apply a corrosive preventive compound to depleted uranium (DU) counterweights was not considered "... chemical, physical, or metallurgical treatment or process ..." and was appropriate for exemption under 10 CFR 40.13 (c) (5).

The 747 airplane program utilized DU weights for mass balance of outboard elevator and upper rudder assemblies on the first 550 aircraft built. This equates to approximately 12,000 cast parts and a total mass of DU in excess of 200 tons. Depending upon the model, each aircraft had either 21 or 31 weights. At each major aircraft overhaul (about 4 to 5 years), it was anticipated that over 20% of these weights would be corroded to where they required reprocessing. This condition was considered to present an unnecessary maintenance burden on the 747 operators. Aside from the high corrosion rate, the weights were extremely difficult to transport with only one recognized reprocessing source in the world.

In a letter dated January 6, 1983, the Boeing Company proposed originally to apply an additional protective coating of Cosmoline (MIL-C-11796) over the protective coating of undamaged DU weights. They intended to require that the weights be (1) corrosion free, (2) properly nickel and cadmium plated and painted, (3) heated to 150-160F, (4) dipped in MIL-C-11796 at the same temperature, and (5) cooled to ambient temperature. The weights in question were exempt items manufactured by NL Industries of Albany, New York. When the weights were reinstalled on the airplane, they intended to fill the attachment holes with MIL-G-23827 grease. Cautionary marking on the weights would be kept free of corrosion preventative compounds. They asked if these additional processes in any way violated the conditions of 10 CFR 40 of the NRC rules and regulations.

It was NRC staff's view that the above processing falls within the prohibition of 10 CFR 40.13 (c) (5) (iv). That provision states clearly that the exemption from licensing in 10 CFR 40.13 (c) (5) for DU weights does not authorize any treatment or processing of the counterweights except for repair or restoration of any existing plating or covering. This has been the regulatory position for over 20 years [see 25 FR 6427]. The above proposal involved the processing of the DU weights to add a new coating of a different material. If the work was performed at the Washington plant, Boeing would need (1) a license from the State of Washington authorizing the procedure for coating the DU weights in its possession, and (2) a license from the NRC to distribute the weights to exempt persons (i.e., the operators of the aircraft) after being coated [see 10 CFR 40.13 (c) (5) (i) and 150.15 (a) (6)].

In a second letter dated March 18, 1983, the Boeing Company proposed the application of corrosion preventative compound MIL-C-16173 to DU weights in service. This procedure would be accomplished during operators scheduled maintenance programs. It would be required that the weights be corrosion free and finished per drawing (nickel and cadmium plus primer) prior to brush application of MIL-C-16173. Both MIL-C-16173 and weights would be at ambient temperatures during application.

Attachment holes would be filled with grease (MIL-G-23827) to eliminate water traps and cautionary markings on the weights would be kept legible. No chemical interactions would occur between the corrosive preventative compound (MIL-C-16173) or the grease (MIL-G-23827) and the plating or paint because these compounds do not contain solvents or other agents which might soften paint. The Boeing Company believed that this process, while not as effective in preventing corrosion as their previous proposal, would be a significant improvement and did not violate the intentions of 10 CFR Part 40 of the NRC rules and regulations.

It was NRC staff view that the second proposal was not considered as "... chemical, physical, or metallurgical treatment or process ..." and was appropriate for exemption under 10 CFR 40.13 (c) (5).

Regulatory references: 10 CFR 40.13

Subject codes: 11.1, 11.6

Applicability: Source Material

Page Last Reviewed/Updated Tuesday, June 16, 2015