The impairment was a result of the reduction in spot and long term uranium price in the second half of 2012 that affected uranium price outlook.
The long term price of uranium oxide declined during the year to $56.50 a pound in 2012, compared to $62 a pound the previous year.
A strengthening Australian dollar and an increase in asset base over the past two years also contributed to the impairment.
The company also reported total revenues of $422.8m for the year, down 37% from $667.8m in 2011 besides a net loss after-tax of $219m.
Ore reserves at its Ranger project area in Australia decreased from 13,484t to 9,675t in 2012 due to depletion by processing and a pit re-design.
Mineral resources further declined from 117,240t to 63,377t of contained uranium oxide, while capital expenditure increased from $97m in 2011 to $161m in 2012.
The company mined 3,710t of uranium oxide in 2012, higher than 2,641t produced in 2011.
Enhanced access to higher grade ore at the bottom of the mine pit after June 2012 contributed to the enhanced production.
