The US Nuclear Regulatory Commission has issued a construction permit for the Long Mott Generating Station, a four-unit Xe-100 high-temperature gas-cooled reactor plant on land adjacent to Dow's Union Carbide Seadrift Operations in Calhoun County, Texas. X-energy announced the approval on 9 November 2026, with the NRC's Final Safety Evaluation Report having landed on 30 October.
The permit is a genuine milestone: it is the NRC's first construction authorisation for an HTGR in roughly six decades, its first pebble-bed core and multi-module advanced reactor facility, and the first advanced reactor approved for an industrial site in the United States. It is also, importantly, not a decision to build. A construction permit allows construction only; operation requires a separate licence, and the project's own economics still hinge on a final investment decision by Dow's board that has not been taken.
What has actually been approved
Long Mott is structured around four Xe-100 units, each nominally 80 MWe and 200 MWt, feeding a shared steam cycle. The plant would supply electricity and high-temperature process steam to Seadrift, replacing power and steam assets that Dow describes as approaching end of life, and would export surplus power to the grid.
| Parameter | Detail |
|---|---|
| Configuration | 4 × Xe-100 HTGR (pebble bed, TRISO fuel) |
| Capacity | ~320 MWe / 800 MWth total |
| Site | ~1,537 acres adjacent to Dow UCC Seadrift Operations, Calhoun County, Texas |
| Applicant / prospective licensee | Long Mott Energy, LLC (wholly owned Dow subsidiary) |
| Reactor technology | X-energy; fuel via TRISO-X |
| Intended life | 60 years |
| Regulatory pathway | 10 CFR Part 50 construction permit; separate operating licence required |
| Emergency planning zone | On the order of hundreds of metres, versus 10 miles for light-water reactors |
Several firsts in that table deserve attention from anyone tracking the sector. The functional-containment approach and the small emergency planning zone are what make an industrial co-location viable at all — a 10-mile EPZ would be incompatible with a chemicals complex of Seadrift's scale. The NRC reviewed the design under its risk-informed, technology-inclusive framework, and the review ran to schedule: the application was submitted on 31 March 2025, docketed on 12 May 2025, an environmental assessment with a finding of no significant impact followed in May 2026, and the safety review closed in late October 2026. That cadence matters as much as the outcome, because it is the first real evidence that the post-ADVANCE Act review model can deliver on time for a non-light-water design.
The commercial reality: permitted, not financed
The gap between a construction permit and steel in the ground is where this project now sits. Dow has not publicly disclosed a construction cost for Long Mott, and the figures that circulate are easily misread. X-energy's ARDP scope — reactor design and licensing, the TRISO-X fuel facility and the four-unit Seadrift plant together — was estimated at roughly $4.75–5.75 billion as of early 2023, against an original 2020 programme estimate of about $2.4 billion with a 50/50 DOE cost share. None of those numbers is a construction contract value, and X-energy has acknowledged cost growth from inflation, supply chain pressure and scope change.
So the outstanding list is short but decisive:
- Dow board FID. No approval to spend on construction has been announced.
- EPC award. No contractor has been named for Long Mott construction. X-energy's 2022 selection of Zachry Group and a Burns & McDonnell/Day & Zimmermann team established a fleet-level delivery framework (the X-energy Project Delivery Model), not a project-specific EPC contract. Burns & McDonnell's own release frames its role as design, equipment supply, fabrication and construction planning.
- Project definition engineering. In April 2026 Fluor disclosed a contract with X-energy for Front-End Loading Stage 2 — definition, feasibility, cost control and risk mitigation — with value undisclosed. That is a pre-FID engineering scope, and its existence is the clearest signal that the cost basis for FID is still being assembled.
- Operating licence. Not yet applied for.
Where the steel actually sits
The reactor hardware supply chain for the Xe-100 is being locked up ahead of any Long Mott order. In December 2025 X-energy and Doosan Enerbility signed a binding reservation agreement covering main power system steel components for 16 Xe-100 units, backed by a significant X-energy investment to hold capacity; Doosan is standing up a dedicated SMR fabrication line at Changwon, South Korea. That reservation covers X-energy's first commercial projects — Long Mott is the leading candidate — but it is a capacity reservation, not a firm purchase order for four Seadrift units. Curtiss-Wright (primary components), Howden (helium circulators) and, per a 2025 memorandum, IHI as a potential additional pressure-boundary manufacturer round out the picture.
The steel content breaks into three distinct categories, and they are at very different stages:
| Category | Typical content | Current status |
|---|---|---|
| Nuclear pressure-boundary steel | Reactor pressure vessels, steam generator pressure vessels, main power system components | Capacity reserved with Doosan; no firm Long Mott order evidenced |
| Structural and balance-of-plant steel | Buildings, supports, shared steam cycle and piping | Not scoped or awarded publicly; dependent on FID and EPC |
| Long-lead forgings and specialty plate | Vessel heads, shells, nuclear-grade plate | Tied to the Doosan reservation; timing unknown |
The practical read for steel suppliers is that nothing on Long Mott has been awarded as a construction package. Primary procurement is not complete because it has not begun in earnest: the project is in feasibility and front-end engineering, and the single most consequential commercial event remains Dow's FID. Any suggestion that balance-of-plant or structural steel packages are open for bid would be speculative — no such tender has been published.
A secondary point worth flagging for heavy industry: the Seadrift concept is the template, not the prize. If the model works — advanced reactors sited inside chemical complexes, displacing gas-fired steam and power — the addressable demand is a fleet, not four vessels. That is the thesis behind X-energy's 11 GW pipeline and Doosan's 20-units-a-year ambition, and it is why the NRC's scheduling performance on this application carries weight beyond East Texas.
What to watch
Three signals will determine whether Long Mott moves from licensed to built. First, a Dow FID announcement with an accompanying cost figure — the absence of a public number after a permit is itself informative about how much definition work remains. Second, an EPC contract naming a specific constructor for this site, which would convert the 2022 framework into committed work and open the structural and balance-of-plant steel packages. Third, a firm order converting part of the Doosan reservation into Long Mott-specific pressure-boundary components, which would mark the start of the nuclear-grade steel manufacturing cycle.
Until at least the first of those lands, Long Mott is best understood as the most advanced test case for industrial nuclear in the US — a regulatory breakthrough whose commercial case is still being priced.