Skip to content
nuclear•chain

High-temperature gas reactor HTGR

A high-temperature gas reactor (HTGR) uses helium as coolant and graphite as moderator. 1 is operating worldwide, totalling 0.2 GW gross, out of 41 units of this type on record.

Operating
1
0.2 GW gross
Under construction
0
Planned
24
Retired
4
Helium Steam or process heat Pebble bedhelium at 750–950 °C Heatexchanger Turbineto grid Indirect cycle — two loops
Hot enough for industrial process heat, not just electricity. Needs TRISO fuel and HALEU enrichment.

Helium is chemically inert and carries no neutron penalty, letting the outlet temperature reach 750–950 °C — hot enough for industrial process heat and hydrogen production, not just electricity. Fuel is TRISO: poppy-seed-sized uranium kernels wrapped in layers of carbon and silicon carbide that hold fission products inside the particle itself. The combination of low power density and a large graphite heat sink means the core can shed decay heat passively. Most designs need enrichment above the 5% LEU ceiling, which is why the family is tied to HALEU supply.

Advantages
  • Outlet temperatures of 750–950 °C open industrial process heat and hydrogen production, not just electricity
  • TRISO fuel retains fission products inside each particle, a barrier independent of the building
  • Low power density and large graphite mass mean the core can shed decay heat passively, without pumps
  • Helium is chemically inert and does not become strongly radioactive
Drawbacks
  • Needs HALEU enrichment above 5%, and Western supply is measured in hundreds of kilograms a year
  • TRISO fuel is expensive and made at very few places in the world
  • Large core volume for the power, so capital cost per kilowatt is high
  • Graphite dust and helium leak-tightness are persistent engineering problems
Design basis
CoolantHelium
ModeratorGraphite
Fuel formTRISO-coated particle fuel in pebbles or compacts
Typical enrichment8–20% U-235, frequently HALEU
Where they operate
China1

Model lines

ModelOperatingUnits on record
Xe-100 — 16
HTR-PM 1 3
Pebble bed reactor prototype — 1
Pebble bed reactor — 1

Operating HTGR units

UnitCountryGross MWOnline
Shidao Bay nuclear power plant 1 China 211 2023

Sources