Charlie Peprah has been the understudy at safety for the Packers in each of the past two seasons, filling in for Morgan Burnett during the Super Bowl season in 2010 and subbing for Nick Collins for almost all of last year.  He finished with five interceptions and 94 tackles.  After missing all of the off-season work with a lingering knee injury, the Packers released the seven year veteran on the eve of training camp.   Green Bay also released rookie offensive lineman Grant Cook and signed another rookie, Greg Van Roten.  Wednesday was a physical and testing day for the players and several were placed on the physcially unable to perform list after failing their medical checkup.  Andrew Quarless, Derrick Sherrod, John Kuhn, Frank Zombo and rookies Jaymes Brooks and Johnny Jones were placed on the active PUP list while Desmond Bishop made the list with what was described as a non-football related injury.   The Packers take to the Ray Nitschke practice field for the first time Thursday morning.