Upgrades designed to last 20 years were made to the reactor units in 2009 and 2010 ; however , both reactors had to be shut down in January 2012 due to premature wear found on over 3,000 tubes in the recently replaced steam generators .
Upgrades designed to last 20 years were made to the reactor units in 2009 and 2010 at a cost of approximately $ 2.1 billion . 
 However , they had to be shut down in January 2012 due to premature wear found on over 3,000 tubes in the recently replaced steam generators .