How the £10bn Wylfa Newydd power station would manage and dispose of nuclear waste is the subject of a consultation.
It will look at how the station on Anglesey would discharge, transfer and dispose of radioactive material.
Natural Resources Wales (NRW) is asking for views on Horizon's application for an environmental permit.
This only deals with radioactivity and will only be granted if NRW is "wholly satisfied" with the arrangements.
The application for a radioactive substances regulation permit is another milestone on the road to building Wylfa Newydd, five years after the site near Cemaes was bought.
Horizon has to show how it will minimise the amount of radioactive waste it generates and discharges.
Horizon has already said it intends to store and manage all intermediate level waste and spent fuel on the site in secure, purpose-built facilities for up to 140 years.
The consultation period runs until 14 January and three public drop-in sessions have been arranged:
- Monday 20 November 1400-1900 at David Hughes Hall, Cemaes
- Tuesday 21 November 1400-1900 at Storiel, Bangor
- Wednesday 22 November 1100-1600 at Ebeneser Centre, Llangefni
Horizon sets out design, technology and monitoring details and techniques to handle and treat radioactive waste - solid, gas and water - from the proposed two advanced boiling water reactors at Wylfa Newydd.
The company said its application also includes detailed assessments to ensure "any routine radioactive discharges and radiation" from the station are safely within UK Government limits.
Tim Jones, NRW executive director of operations in north and mid Wales, said: "We will carry out a thorough assessment of Horizon's proposals to see if they contain sufficient safeguards to protect people and the environment before deciding whether to issue a permit or refuse the application.
"We will consider all relevant information raised during the consultation and we would value hearing people's views."
He said it would only issue a permit if it was wholly satisfied the plans prove they will operate safely, without harming the environment or communities.
The old Wylfa plant stopped generating electricity after 50 years at the end of 2015. Its replacement, next door, would operate for 60 years and generate electricity for around five million homes.
But there is opposition to nuclear power and the waste it creates.
Robert Idris, of campaign group People Against Wylfa-B (Pawb), said: "They can't predict what's going to happen to this waste no matter how detailed the technical documents are.
"How therefore can they consider leaving the people of Anglesey with a whole load of the most dangerous waste in the world?"
The proposals also have planning and cost hurdles - the "strike price" for the electricity generate - to overcome before Wylfa Newydd can get the go ahead.