Two facilities operating. A third under construction in Romania.
Cernavodă tritium: from heavy water to fusion fuel
At Cernavodă, neutrons turn some of the deuterium in heavy water into tritium, a radioactive hydrogen isotope. The new facility will extract it to reduce worker exposure and emissions. Recovered tritium could fuel fusion experiments such as ITER. Nuclearelectrica describes the project as the third facility of its kind worldwide, after Canada and South Korea. Production, extraction and sale are separate steps: revenue remains a possibility.
At the assumed rate of 210 g/year for two units, the time since opening this page corresponds to 0 µg of tritium in the model (0 atoms). This counter is illustrative, not live plant data.
Illustration of deformation — not measurements or a safety assessment.
The first clock · the metal
How reactor tubes change over time
A CANDU reactor has no single pressure vessel. It has 380 horizontal channels, each with its own zirconium–niobium (Zr-2.5%Nb) pressure tube carrying hot heavy water at about 310 °C and 10 MPa. Around each pressure tube sits the cold calandria tube, near 70 °C, linked to it only by garter-spring spacers. Under the fast-neutron flux the metal creeps: the tube elongates axially, its diameter grows, and the channel sags between supports. The failure mode engineers watch obsessively is contact between the hot and cold tubes, where absorbed deuterium can form hydride blisters, the classic weak point of this technology.
This schematic uses a simplified radial neutron-flux profile. The values are illustrative, not Cernavodă measurements or an assessment of reactor safety. At 210,000 full-power hours its assumed central values are 132 mm elongation, 5.4 mm diameter growth and 64 mm sag. Actual behaviour also depends on temperature, loads and spacer positions.
The short version
Four questions, in plain words
What is fusion?
Fusion joins light nuclei and releases energy. The Sun mainly fuses ordinary hydrogen. ITER and many experiments on Earth instead use deuterium and tritium, two heavier forms of hydrogen that fuse more readily under laboratory conditions.
Why is tritium rare?
Deuterium sits in every litre of seawater. Tritium almost does not exist in nature and it disappears by itself: half of any amount turns into helium-3 every 12.32 years. Heavy-water reactors are an important civilian source. Tritium can also be produced by irradiating lithium.
Why Romania?
Cernavodă runs Canadian-designed CANDU reactors, cooled and moderated by heavy water. Inside them, neutrons slowly turn deuterium into tritium. For thirty years that tritium was a nuisance to control. The CTRF plant under construction will extract it, with separation technology developed at Râmnicu Vâlcea.
What is in it for Romania?
Recovered tritium could supply fusion research. The economic result depends on purity, extraction costs, permits and actual demand. A high hypothetical price per gram does not establish a profit. Reducing worker exposure and emissions is the facility’s primary purpose.
The club of three
Where tritium is extracted and where it could be used
Select a place on the map or use the buttons. Filled circles identify the two operating heavy-water extraction facilities; the hollow circle marks Cernavodă under construction. Diamonds are examples of fusion experiments, not confirmed Romanian customers.
Your own case
How much tritium was born at Cernavodă in your lifetime?
Enter a birth year to estimate production up to 22 October 2026. The model assumes 105 g per unit-year, one unit from 1996 and two from 2007. It counts from 1 January of each year, without commissioning months, outages or losses. It illustrates radioactive decay; it does not reconstruct the operating history.
The journey of one tritium atom
The second clock · the isotope
Tritium does not wait: half of it vanishes every 12.32 years
Neutron capture in heavy water produces tritium. The central assumption here is 105 g per 700 MW unit-year, adjustable through the production-rate control. Radioactive decay follows N(t) = N₀·e^(−λt), with λ = ln(2)/12.32. Extracting tritium reduces the amount in the heavy-water systems; any future sale also depends on fuel specifications, approvals and customers.
Choose the start dates and hypothetical buyers. Blue shows tritium in heavy water, green the extracted stock. The calculation follows only new production from 2026, starting with zero stock; it excludes tritium already accumulated. The assumptions below define the extraction and sales rules.
Scenario assumptions
Each year the model adds production, extracts the smaller of the available amount and max(1.15 × annual production, 16% of the dissolved pool), then sells at most 35% of the assumed demand. Remaining stock decays before the next year. ITER demand is set to 4,000 g in 2039 and 450 g/year thereafter; private demand starts at 120 g in 2032 and grows by 55 g/year to a 900 g/year cap. These are arbitrary scenario rules, not plant performance or purchase commitments. Unit 1 is offline in 2027–2029; later outages are omitted.
A small mass, specialised storage
The readout shows new production in 2035 under the chosen unit-start date and rate. It is not the extraction rate or saleable inventory. Tritium can be immobilised as a metal hydride, but cooling, containment and radiation protection determine the complete storage system.
Check the decay yourself
The machinery · the CANDU signature
Refuelling at full power, with two machines and 10 MPa
Light-water reactors shut down to refuel. A CANDU refuels on the move: two machines latch onto both ends of the same channel at once, pressurise to primary-circuit level, and push fresh bundles in as spent ones come out. Step through it, or play the sequence.
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The third clock · the grid
The electricity replaced during Unit 1 refurbishment
At the selected power and capacity factor, the model calculates the electricity lost during the outage. Gas, coal and imports are a hypothetical replacement mix; actual supply may include other sources or lower demand. Emission factors are assumptions: 0.40, 0.95 and 0.30 t CO₂/MWh respectively. They describe replacement generation, not a full lifecycle comparison.
The price control is for electricity generated from gas, not gas fuel. Coal electricity is priced at 1.25 × that value + €25/MWh, imports at 1.05 × it. These assumed gross replacement costs exclude avoided nuclear operating costs and refurbishment spending. Annual national consumption is held at an illustrative 55 TWh.
Background · heavy water
Why heavy water matters
Heavy water slows neutrons in a CANDU reactor without absorbing many of them; it also carries heat away. Some deuterium does capture neutrons and becomes tritium. Romania produced heavy water at Drobeta-Turnu Severin. Its reserves and the supply needed for Units 3 and 4 are a separate issue from extracting tritium from water already in use.
- 1996 — Unit 1 enters commercial operation: Romania's first CANDU-6.
- 2007 — Unit 2 starts up. Together the two units supply about a fifth of the country's electricity.
- 2023 — KHNP wins the CTRF contract, worth about €195 million: the world's third tritium removal facility and Europe's first, using Romanian ICSI Râmnicu Vâlcea technology.
- 2024 — The Candu Energy (AtkinsRéalis), Ansaldo Nucleare and KHNP consortium signs the Unit 1 refurbishment.
- 2027–2029 — Planned Unit 1 refurbishment period; the simulator lets you vary the outage length.
- 2030s — Units 3 and 4 remain planned projects. Fusion experiments could create additional demand for tritium.
Transparency
Data, model and limits
Nuclearelectrica’s June 2025 announcement describes Cernavodă as the third heavy-water tritium removal facility worldwide and the first in Europe. This count is specific to that type of facility. Tritium can also be produced by irradiating lithium, and not all fusion designs use tritium. The coal comparison is heat from complete D–T fusion of 1 g of tritium plus about 0.67 g of deuterium: approximately 156 MWh, or 23 tonnes of coal at 24 MJ/kg. It is not electrical output.
The decay half-life is 12.32 years; specific activity is about 9,621 Ci/g. Production rates, extraction rules, demand and the $30,000/g central price are scenario assumptions, not a current inventory, market quotation or commercial forecast. The reactor diagram is illustrative and cannot assess contact between pressure and calandria tubes. The lifetime estimate ends on 22 October 2026 and does not update with the calendar.
Primary sources
- SNN — CTRF: first concrete, technology and facility scope (2 June 2025)
- SNN — investment strategy, CTRF process and 2027–2028 commissioning window
- CNCAN — CANDU fuel channels and ageing management (2017)
- DOE — deuterium–tritium fuel and lithium breeding
- ITER — fuel, research programme and indicative schedule
- Romanian Tritium for Nuclear Fusion (2017)
- CTRF researchers — extraction process and economic limits (2019)