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Xe-100 at Long Mott (Dow Seadrift)X-energy—Xe-100 at Long Mott (Dow Seadrift)X-energy—X-energy—Xe-100 at Long Mott (Dow Seadrift)X-energy—Xe-100 at Long Mott (Dow Seadrift)X-energy—

Xe-100 at Long Mott (Dow Seadrift)

by X-energyUS

PilotStage 3 of 5

NRC found no significant environmental impact in May 2026; permit decision targeted late 2026.

Updated 16d agoChecked 25 Sep0 updates this week

Milestones

Next · NRC construction permit decision
  1. Selected for DOE Advanced Reactor Demonstration ProgramOct 2020Complete.
  2. Seadrift site selected with DowMay 2023Complete.
  3. Construction permit application submittedMar 2025Complete.
  4. NRC environmental review: no significant impactMay 2026Complete.
  5. NRC construction permit decisionTarget 2026Current milestone.

Most important updates

  • 16d ago
  • 6 Aug 2026
  • 3 Aug 2026
  • 18 May 2026
  • 31 Mar 2025

Upcoming

  1. 2026NRC construction permit decision (next)
  2. 2028TRISO-X TX-1 fuel plant in Oak Ridge due for completion

Current obstacles

  • Scaling up TRISO fuelEach core needs hundreds of thousands of TRISO pebbles; X-energy's Oak Ridge fuel plant must reach full output.

Physics limits

  • Gas carries heat poorlyHelium holds little heat per litre, so it must be pressurised and pushed hard; pebble-bed cores deliver only a few MW per cubic metre, versus ~100 in water reactors.
  • Passive safety caps module sizeTo cool itself by conduction alone in an accident, the core must stay tall and thin, which limits each module to about 200 MW of heat.
  • Graphite changes under radiationNeutrons make graphite shrink then swell, and pebbles rubbing together make dust that carries radioactivity, limiting how long core parts last.

How it works

4 parts
A cut-open TRISO fuel particle under a microscope (false colour): uranium kernel inside carbon and ceramic shells; thousands fill each Xe-100 pebble
A cut-open TRISO fuel particle under a microscope (false colour): uranium kernel inside carbon and ceramic shells; thousands fill each Xe-100 pebblePhoto: Idaho National Laboratory · CC BY 2.0 (opens flickr.com)
Fuel

Pebbles of TRISO fuel

Each Xe-100 core holds about 220,000 tennis-ball-size graphite pebbles packed with TRISO particles that trap radioactivity to about 1,600 °C.

Coolant

Helium gas at 750 °C

Helium, which does not become radioactive or react chemically, flows through the pebble bed and leaves at about 750 °C.

Refuelling

Refuelled while running

Pebbles slowly drop through the core, are checked on exit, then reused or retired, so the reactor does not stop for refuelling.

Steam

Power and steam for Dow

Four 80 MWe units (320 MWe) make 565 °C steam, both to drive turbines and to supply process heat to Dow's Seadrift site.

Update log

5 updates

Thu 24 Sep

  • Minor: PressManufacturing

Thu 6 Aug

  • Minor: PressCommercial

Mon 3 Aug

  • Minor: PressManufacturing

Mon 18 May

  • Minor: PressRegulatory

Mon 31 Mar 2025

  • Major: PressRegulatory

About X-energy

The team behind Xe-100 at Long Mott (Dow Seadrift)

X-energy

Xe-100 pebble-bed HTGR, TRISO-X fuel

Maryland company developing the Xe-100, an 80 MWe gas-cooled pebble-bed reactor, and making its own TRISO-X fuel. Backed by Amazon and Dow, it went public on Nasdaq in April 2026 in the largest nuclear IPO on record.

  • A four-unit Xe-100 plant at Dow's Seadrift, Texas site is under NRC review; permit decision targeted late 2026.
  • Amazon invested in 2024 and plans Xe-100s totalling 5 GW by 2039.
  • Its April 2026 Nasdaq IPO raised about $1B.

x-energy.com (opens x-energy.com)Company profile →

Founded
200917 yrs
Headquarters
United States
Status
Public
Listed
XE (opens google.com)NASDAQ
Valuation
public
Works in
EnergyFission
Coverage
1 program · 7 updateslatest 16d agochecked 25 Sep
People
Clay Sell (opens x-energy.com)CEO
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