Radiation Exposure from Depleted Uranium Counterweights
(last updated 17 May 2002)
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"DU counterweights have been used primarily in wide-body aircraft on rudders, outboard ailerons (wing assembly), and outboard elevators (tail assembly). Counterweights come in a variety of weights and shapes, and numerous weights and shapes are used in some aircraft. The DU counterweight can range in weight from 0.23 to 77 kg."
"Some aircraft used for military and cargo also use DU counterweights; these include the Lockheed C-130 and C-141, Jetstar, and S-3A. The Boeing Company produced helicopters utilizing DU as a rotor tip weight prior to 1979. These weights consisted of small 0.22-kg triangular weights. One to three weights were installed per blade. Virtually all of the Boeing helicopters manufactured prior to 1979 have had their blades replaced with composite blades that do not contain DU weights."
Use of DU Counterweights in U.S. Domestic Aircraft
a Number of aircraft owned by domestic carriers that are members of the Air Transport Association (ATA, 1999).
|Aircraft Type||Manufacturer||Aircraft Number Owned by Domestic Carriers a,b||Total Weight of Counterweights per Aircraft (kg)|
|DC–10||McDonnell-Douglas||168||~ 1,000 c|
|L–1011||Lockheed||60||~ 680 c|
|B–747||Boeing||202||~ 850 d|
b A reasonable estimate is that 50% of these aircraft still contain DU counterweights. Phone call J. Taylor, Starmet CMI, Barnwell, SC, August 1999.
c Phone call, E. Lanchester, Quality Assurance Department, Nuclear Metals, Inc., Concord, MA, August 1996.
d Phone call, D. Barbour, Project Manager, Depleted Uranium Programs, Philotechnics, Oak Ridge, TN, October 1999.
Source: [NUREG-1717] Table 3.17.1
"In many cases, tungsten alloy counterweights have replaced DU counterweights in aircraft. Since 1981, The Boeing Company has provided customers with tungsten replacement counterweights, and tungsten counterweights have been installed in new Boeing 747 aircraft. Tungsten equivalents have been sent as spares since 1981 (Gallacher, 1994). In 1988, McDonnell-Douglas discontinued using DU counterweights and began using tungsten. Tungsten counterweights are used on the MD–11, MD–80, and MD–90 (Ford, 1994).
It is unknown how many DU counterweights are currently installed in aircraft. It is estimated that approximately 15,000 weights may be associated with the Boeing 747 fleet (based on 550, Boeing 747 aircraft produced between 1968 and 1981 and spare parts) (Gallagher, 1994). However, the number of aircraft that contain DU counterweights is decreasing. Rather than refurbishing the DU (during maintenance operations), tungsten counterweights are used as a replacement." [NUREG-1717]
Exposure of Aircraft Workers
- External radiation during installation of DU counterweights
"The annual dose equivalent to workers responsible for installation, storage, and transport of DU counterweights was 0.9 mSv/yr (90 mrem/yr). The estimated collective EDE (Effective Dose Equivalent) to airline maintenance workers is 0.01 person-Sv (1 person-rem)." [NUREG-1717. Caution: the source mistakenly states 0.09 instead of 0.9 mSv/yr on p. 3-259]
- Inhalation of DU dust after aircraft accident involving fire
"For the fireman, the EDE is estimated to be 0.3 mSv (30 mrem) and for the clean-up worker, the EDE is estimated to be 4 mSv (400 mrem)." [NUREG-1717]
The amount of material involved is 850 kg of DU, which is that on a typical Boeing 747 aircraft.
Exposure of Aircraft Crews and Passengers
- External radiation from DU counterweights during flight
"Annual estimated individual EDEs (Effective Dose Equivalent) to flight crews, attendants, and passengers were 0.001 mSv (0.1 mrem), 0.01 mSv (1 mrem), and 1×10-4 mSv (0.01 mrem), respectively. The annual collective EDEs to flight crews and attendants was estimated to be 0.04 person-Sv (4 person-rem). The annual collective EDE for domestic airline passengers is 3 person-Sv (300 person-rem). If DU counterweights are located only in the tail section, the EDEs will decrease [...]. The doses to the flight personnel and passengers attributed to the DU counterweights are less than 0.001 of their doses from cosmic radiation." [NUREG-1717]
For the estimates, it is assumed there is about 300 kg of DU located in the outboard elevator (tail assembly) and 350 kg of DU located in each aircraft wing. The annual exposure durations assumed were 1000, 500 and 3 hours for flight crews, attendants, and passengers, respectively.
[NUREG-1717] Systematic Radiological Assessment of Exemptions for Source and Byproduct Materials, Final Report, NUREG-1717, U.S. Nuclear Regulatory Commission, 2001
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