How nuclear reactor licensing works in the US, Canada and the UK

The separate permissions a fission reactor needs before it can be built and run, what each one allows, how fusion is regulated differently, and how to read the licensing page.

Guide · Updated 2026-09-23

A reactor is not approved once. A regulator gives a series of separate permissions, each covering one thing: a design, a site, construction, or operation. Each is a separate application and a separate decision, sometimes years apart. Company announcements tend to merge them. This guide sets out the steps in three countries, using the regulators’ own records, so you can tell which step a headline is describing.

The United States

The regulator is the Nuclear Regulatory Commission (NRC).

Talking before filing. Most developers spend years meeting NRC staff and sending white papers and technical reports before they apply for anything. This is called pre-application engagement. No application exists at this point, and nothing has been approved.

Filing and docketing. When an application arrives, NRC staff check whether it is complete enough to review. If it is, the NRC “accepts it for docketing”: it gets a docket number and a notice in the Federal Register. For example, the construction permit application for TerraPower’s Kemmerer Unit 1 in Wyoming (filed by its subsidiary US SFR Owner, LLC) was docketed on 21 May 2024 under docket 50-613. The notice says the NRC staff would now carry out the detailed technical review. Docketing means the review can start. It does not mean anything has been approved.

Construction permit, then operating licence. Under the older route (10 CFR Part 50), a plant needs a construction permit first and an operating licence later, and each is a separate application. The NRC issued construction permit CPTR-6 for Kairos Power’s Hermes test reactor in Oak Ridge, Tennessee on 14 December 2023, and construction permit CPAR-1 for Kemmerer Unit 1 on 9 March 2026. Neither permit allows the reactor to operate. The newer route (Part 52) offers a combined licence covering both.

Design certification and standard design approval. Both approve a design, not a plant. A design certification is a rule the NRC publishes. NuScale’s certification took effect on 21 February 2023. It covers a module rated at 50 MWe (megawatts of electricity), with up to 12 modules per plant. The NRC’s rule states that a design certification “does not authorize the siting, construction, or operation of a facility”. A standard design approval is a lighter step: it lets a design be referred to in a later application to build. NuScale holds two: one for its original design (11 September 2020) and one for its uprated US460 design (29 May 2025). “NuScale has NRC approval” can mean any of these three, and none of them is permission to build.

Part 53. In March 2026 the NRC published a new, optional licensing framework (10 CFR Part 53), in force from 29 April 2026. It sets safety standards that apply to any reactor technology rather than being written around water-cooled reactors. It adds a third route alongside Parts 50 and 52. It does not remove the separate steps.

Canada

The regulator is the Canadian Nuclear Safety Commission (CNSC). Its regulations list five licences for a reactor site, in order: to prepare the site, to construct, to operate, to decommission, and to abandon.

Before any of these, a vendor can ask for a vendor design review. This is an optional pre-licensing assessment in three phases. The CNSC says a vendor design review “does not involve the issuance of a licence and does not certify a reactor design”, and that its conclusions do not bind the Commission’s later decisions.

Ontario Power Generation’s Darlington New Nuclear Project shows the sequence. A site preparation licence was first issued in 2012 and renewed on 12 October 2021. On 4 April 2025 the Commission issued a licence to construct one BWRX-300 reactor (licence PRCL 32.00/2035, valid until 31 March 2035). The CNSC stated that this decision “does not authorize the operation” of the reactor. Operation needs a further hearing and decision.

A Canadian step says nothing about a design’s standing with the NRC, and the reverse is also true.

The United Kingdom

In Great Britain, the Office for Nuclear Regulation (ONR) and the Environment Agency (with Natural Resources Wales for Wales) run a voluntary Generic Design Assessment (GDA). It judges a design separately from any site. The ONR carries out its assessment in steps that become more detailed each time, normally three, with further steps if issues remain unresolved. A full GDA ends with a Design Acceptance Confirmation from the ONR and a Statement of Design Acceptability from the Environment Agency. The UK HPR1000 received both in February 2022.

A shorter GDA is now possible. On 11 December 2025 the regulators announced that the BWRX-300 had “completed” a two-step GDA. The same announcement said a further period of detailed assessment would be needed before safety-significant construction could begin. Rolls-Royce SMR entered Step 1 in April 2022 and Step 3 in July 2024. The ONR’s page describes its current position as “Assessment of reactor design ongoing”.

Even a full GDA does not allow anything to be built. The operator still needs a nuclear site licence from the ONR, environmental permits and planning permission.

Fusion is regulated differently

Fusion machines are not licensed through the reactor steps above.

In the United States, the Commission that heads the NRC decided on 13 April 2023 to regulate fusion machines under its rules for radioactive materials (“byproduct material”, 10 CFR Part 30) rather than its reactor framework. The ADVANCE Act, signed on 9 July 2024, wrote the relevant definitions into law. The NRC published a proposed rule on 26 February 2026, with comments due by 27 May 2026. The proposal is written to work across the National Materials Program, which the NRC shares with states that hold agreements to regulate radioactive materials themselves (Agreement States).

In the United Kingdom, section 156 of the Energy Act 2023, in force since 10 September 2024, says a fusion energy facility does not need a nuclear site licence. The exception is a site that also runs a fission reactor. The government’s 2022 response to its consultation on fusion regulation confirmed that the Environment Agency, the Scottish Environment Protection Agency and the Health and Safety Executive remain the regulators.

For this reason the site’s licensing stages are used only for fission.

What “NRC approved” usually means

When a headline says a developer is “NRC approved”, check the notice to see which of these it was:

a pre-application meeting, or NRC approval of a single technical report the developer submitted (a topical report)
an application accepted for docketing
a design certification or standard design approval, which approves a design and not a plant
a construction permit, which does not allow operation

A foreign step, such as a CNSC vendor design review or a UK GDA step, says nothing about standing with the NRC.

Denials and withdrawals

Applications fail, and company timelines rarely say so. Oklo filed a combined licence application for its Aurora reactor at Idaho National Laboratory on 11 March 2020 (docket 52-049). In January 2022 the NRC denied it because Oklo had not provided information the NRC staff had requested. The denial was without prejudice, which means Oklo was free to apply again with the missing information.

An applicant can also withdraw an application before a decision. This site records denials and withdrawals as milestones, and keeps them visible.

Target dates move too. In May 2026 the NRC extended the latest date for completing construction of Hermes from 31 December 2026 to 30 April 2029, at Kairos Power’s request.

Reading the licensing page

/licensing/ lists every regulatory milestone the site holds, one row each:

Organisation: the developer. A milestone is filed under the developer even when the formal applicant is a subsidiary or a customer. The row title names the facility.
Stage: one of the stages defined in the glossary. A label shows the status: achieved, target (not yet reached), retracted, disputed or superseded. The milestone’s title and any status note appear underneath.
Date: when it happened, or the target date for a target.
Regulator and Anchor: the docket number, document number or licence number that lets you look the step up in the regulator’s own records. “No anchor” means we hold no such number, so the step cannot be checked from outside and rests on other evidence.
Source: the document the row is based on.

Below the table, Target dates shows every milestone whose target has moved. Earlier dates are crossed out, each with the date it was stated, followed by the current target.

Each company page repeats its own milestones under Licensing.

Sources

Pre-application engagement · glossary
Application submitted · glossary
Accepted for review · glossary
Design approval or certification · glossary
Construction permit issued · glossary
Operating licence issued · glossary
Application denied · glossary
Application withdrawn · glossary