What is the reasoning behind using depleted uranium as counterweights in the 747?
Boeing

Boeing would have used DU because it had the right combination of physical characteristics and cost. Their tests showed that the radiation exposure for workers was low (2.6% of the statutory "safe" level). In most cases the exposure was so low as to be not detectable.



Radiation

Passengers on aircraft are exposed to cosmic radiation at much higher levels than people on the ground.

On the ground the average American is exposed to 620 mrem/year from all sources.

Those flying from Washington DC to Los Angeles would be exposed to close to 2 mrem from cosmic radiation. This is not an issue for passengers but is something that airline crew and other very-frequent flyers are aware of.

Exposure to aircraft occupants from cosmic radiation is 600 times higher than from DU counterweights in the early 747 aircraft.



Depleted Uranium

DU is Uranium from which the most radioactive parts have been removed. It is less radioactive than naturally occurring Uranium. 

Heavy metals like Lead, Tungsten and Uranium are toxic if ingested. This toxicity is not due to radioactivity. Aircraft crew and passengers are not exposed to these metals in any way that could cause them to be ingested.



Boeing Tests

Boeing carried out safety tests on the material.

Workers


  Boeing 
  has 
  conducted 
  two 
  dosimetric 
  studies 
  of 
  exposures 
  to 
  workers. 
  For 
  both
  studies, 
  whole 
  body 
  exposures 
  were 
  measured 
  with 
  film 
  badges 
  which 
  were
  provided 
  and 
  processed 
  by 
  Landauer, 
  Inc. 
  These 
  badges 
  have 
  a minimum 
  detectable
  exposure 
  of 
  10 
  millirem 
  per 
  issue 
  period 
  (monthly). 
  In 
  the 
  second 
  study, 
  extremity
  exposures 
  were 
  measured 
  with 
  finger 
  rings, 
  also 
  provided 
  by 
  Landauer, 
  having 
  a
  minimum 
  detectable 
  exposure 
  of 
  30 
  millirem 
  per 
  issue 
  period 
  (also 
  monthly). 
  The
  periods 
  of 
  the 
  study 
  were 
  December 
  1968 
  to 
  February 
  1970 
  for 
  the 
  first 
  study 
  and
  September 
  1977 
  to 
  April 
  1978 
  for 
  the 
  second.
  
  Both 
  of 
  these 
  studies 
  showed 
  all 
  worker 
  whole 
  body 
  exposures 
  were 
  less 
  than 
  2.6%
  of 
  the 
  exposure 
  limits 
  for 
  occupationally 
  exposed 
  employees 
  (5000 
  millirem 
  per
  year) 
  and 
  less 
  than 
  26% 
  of 
  the 
  limits 
  for 
  members 
  of 
  the 
  general 
  public 
  in 
  effect 
  at
  that 
  time 
  (500 
  millirem 
  per 
  year). 


Crew and Passengers


  Based 
  on 
  the 
  data 
  from 
  National 
  Lead, 
  reported 
  in 
  the 
  section 
  on 
  exposures 
  to
  the 
  general 
  public, 
  dose 
  rates 
  to 
  flight 
  crew 
  will 
  be 
  less 
  than 
  0.8 
  microrem 
  per
  hour. 
  During 
  a 
  2000 
  hour 
  working 
  year, 
  this 
  results 
  in 
  a 
  maximum 
  potential
  exposure 
  of 
  1.6 
  millirem, 
  less 
  than 
  2% 
  of 
  the 
  100 
  millirem 
  per 
  year 
  limit 
  for
  members 
  of 
  the 
  general 
  public. 
  This 
  is 
  only 
  1/600th 
  of 
  the 
  500 
  microrem 
  per
  hour 
  increase 
  in 
  dose 
  rate 
  from 
  cosmic 
  radiation 
  flight 
  crew 
  experience 
  at
  39,000 
  feet.


Boeing Use of Depleted Uranium Counterweights in Aircraft. 1984. Retrieved from NRC



References


Space Radiation, Should Frequent Flyers Worry? 2013. BBC
Tungsten Poisoning. 2014. Retrieved from Patient.info