CANDU vs VVER: the two export lines that compete most often
When a country picks its first plant it often ends up comparing these two families, which compete in the same markets. The CANDU is a heavy-water reactor with pressure tubes and natural uranium; the VVER is the Russian take on the pressurized water reactor, with a vessel, enriched uranium, hexagonal fuel assemblies and horizontal steam generators.
Figures from the atlas
| CANDU | VVER | |
|---|---|---|
| Units built or under way | 72 | 114 |
| Operating today | 45 | 67 |
| Net capacity operating | 23,594 MWe | 53,906 MWe |
| Countries | 10 | 17 |
| First grid connection | 1962 | 1964 |
| Most recent connection | 2025 | 2025 |
| Under construction | 3 | 28 |
| Shut down | 13 | 16 |
| Most powerful unit operating | Darlington 1 (Canada), 878 MWe | Kursk 2-1 (Russia), 1,200 MWe |
| Average load factor, latest reported year | 81.1 % | 82 % |
Data: Global Energy Monitor (CC BY 4.0), IAEA PRIS 2025, Wikipedia (CC BY-SA), Wikidata and Wikimedia Commons. Capacities in net MWe unless stated.
Differences
- Fuel: natural uranium in the CANDU; enriched uranium in the VVER, as in every PWR.
- Core: horizontal pressure tubes with short bundles in the CANDU; a vessel with long hexagonal fuel assemblies in the VVER.
- Steam generators: horizontal in the VVER, unlike the vertical ones of Western PWRs; the CANDU uses vertical generators.
- Refuelling: on power in the CANDU; during an outage in the VVER.
- Sizes: operating CANDUs range from about 500 to just over 800 MWe; VVERs from about 440 MWe net in the VVER-440 to about 1,100 in the VVER-1200.
Frequently asked questions
Which countries run both designs?
Argentina (Embalse, a CANDU 6, plus the pressure-vessel PHWRs of Atucha), China (Qinshan III with CANDU 6 and Tianwan with VVER) and India (the CANDU-derived IPHWRs and Kudankulam with VVER) operate both lines. The table on this page lists them.
Which one needs enrichment?
The VVER. The CANDU burns natural uranium, which avoids depending on an enrichment supplier, in exchange for producing and topping up heavy water.
Which is bigger?
The VVER: the VVER-1200 exceeds 1,100 MWe net, while the largest operating CANDU is around 880 MWe. Exact figures are in the table.
Animated guides
CANDU (The 72 CANDU units in the atlas) · VVER (The 114 VVER units in the atlas) · Compare any two units · Rankings
Sources
- World Nuclear Association, Nuclear Power Reactors
- Wikipedia, VVER
- Wikipedia, CANDU reactor
- World Nuclear Association, Nuclear Power in Russia
Other comparisons
PWR vs BWR
Pressurized water against boiling water: pressure, loops, control rods and turbine, with the real fleet of each type computed from the atlas.
PWR vs CANDU
Heavy water and pressure tubes against a pressure vessel and enriched uranium: fuel, moderator, refuelling and the real fleet of each type.
EPR vs AP1000
The EPR and the AP1000, the West's two large Generation III+ PWRs: power, loops, containment, safety systems and where they were built.
AGR vs PWR
Britain's CO₂-cooled reactor against the world standard: temperature, efficiency, fuel, refuelling and the real fleet.
RBMK vs PWR
Graphite and pressure tubes with boiling water against a vessel and pressurized water: void coefficient, containment and how many RBMKs still operate.