The owner of the Millstone Nuclear Power Station in Connecticut yesterday admitted that the plant had falsified environmental records and deliberately promoted unqualified plant operators, pleading guilty to 23 federal felonies and agreeing to pay $10 million in fines, the largest penalty ever for a U.S. nuclear plant. Prosecutors said the plant’s actions could have put the facility in the hands of workers unable to prevent a crisis. As part of the plea agreement, the company has been put on three years’ probation. Millstone officials said they hoped yesterday’s pleas would end the long period in which the plant has been seen as a national symbol of mismanagement in the nuclear industry. Complaints by consumer groups and plant workers led to a three-year federal investigation of the plant.