Entergy Corp.'s request to sell a defunct Massachusetts nuclear power plant to Holtec International Corp. needs to be fully vetted before any approvals are granted, Massachusetts lawmakers and officials told the Nuclear Regulatory Commission.

The Pilgrim Nuclear Power Station in Plymouth, shut down May 31 after delivering power to New England for 47 years and reaching the end of its life. The plant’s 4,000 radioactive spent fuel rods were removed and are temporarily stored onsite and nearby.

The NRC is expected to decide soon whether to approve Entergy’s November 2018 request to transfer its license to Holtec for...