Disputes over orders that six workers at nuclear power plants abstain from alcohol on and off the job belong in front of an arbitrator, a federal judge has held.In a written opinion, U.S. District Judge Matthew F. Kennelly rejected the argument that the collective bargaining agreement covering certain employees at Exelon Generation Co. LLC facilities limits arbitration to disputes about the revocation of an employee’s unescorted access to the facilities.The agreement covers more ground than that, Kennelly wrote …