Hitachi's Horizon Nuclear Power business has applied to the nuclear regulator for a site licence to build its Wylfa plant in Wales.
Horizon plans to build and operate two reactors at the Anglesey site, which will generate 5.4 gigawatts of electricity, or enough to power around 10m homes by the mid-2020s.
The Office for Nuclear Regulation (ONR) will now start a 19-month assessment programme on Horizon's Wylfa Newydd application, which is the first for a new nuclear power station since EDF's £18bn Hinkley Project C in 2011.
Horizon did not say how much the project will cost.
ONR will carry out "robust assessments" of Horizon's organisation capability, governance arrangements and competence to be a nuclear site-licence holder.It will also determine whether the firm can demonstrate it will be in control of all safety related activities on site.
Anthony Webb, safety and licensing, director at Horizon, said the announcement marks a significant development in the maturity and growth of the company.
"We already have a proven technology, aligned with experienced leadership, and we are rapidly building the wider capability and organisation to help ensure success. Our focus will now be fully on providing the ONR with confidence in our ability to safely deliver this crucial project."
If consent is granted, Horizon aims to receive all the necessary permissions for the new build by the end of 2018.