What is burnup in nuclear engineering?

Burnup measures how much energy has been extracted from nuclear fuel per unit mass of heavy metal. It is expressed in megawatt-days per tonne of heavy metal (MWd/tHM). Higher burnup means more fission reactions have occurred and more of the fissile material has been consumed.

tHM stands for tonnes of heavy metal — the mass of uranium, plutonium, or other fissile/fertile heavy atoms initially loaded into the fuel, excluding cladding and structural materials. A typical PWR fuel assembly contains roughly 0.5 tHM.

What is a typical discharge burnup for commercial reactors?

Typical discharge burnup ranges from 33,000–55,000 MWd/tHM (33–55 GWd/tHM) for light-water reactors. Modern high-burnup fuel programs target 60,000–70,000 MWd/tHM, subject to regulatory and material limits.

Does this calculator account for neutron flux changes over time?

No — this is a simple linear burnup estimate assuming constant thermal power over the irradiation period. Real burnup calculations use neutron transport and depletion codes (e.g., ORIGEN, SERPENT) that track nuclide inventories and flux variations.

How do I convert MWd/tHM to GWd/tHM?

Divide MWd/tHM by 1,000. For example, 45,000 MWd/tHM = 45 GWd/tHM. The calculator displays both units automatically.

Burnup Calculator

Name: Burnup Calculator
Availability: InStock
Author: Nham Vu

Calculate nuclear fuel burnup in MWd/tHM from thermal power, heavy metal mass, and irradiation time.

Burnup Inputs

Thermal Power (MW_th)

Total reactor thermal output in megawatts

Heavy Metal Mass (tHM)

Mass of heavy metal (U, Pu) initially loaded

Irradiation Time

How long the fuel stays in the reactor

Capacity Factor (%) optional

Fraction of time the reactor operates at full power (1–100%)

Enter power, mass, and time, then click Calculate Burnup.

Reference — Typical Burnup Values

Reactor type	Discharge burnup (GWd/tHM)
CANDU (natural U)	7–8
PWR (standard)	33–45
BWR (standard)	27–40
PWR (high burnup)	55–70
VVER-1000	40–55
Research reactor (MTR)	40–100+

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Summary

Calculate nuclear fuel burnup in MWd/tHM from thermal power, heavy metal mass, and irradiation time.

How it works

Enter the reactor thermal power output in megawatts (MW).
Enter the total heavy metal mass loaded in the core (tonnes of heavy metal, tHM).
Enter the irradiation time in days.
Click Calculate — burnup in MWd/tHM and GWd/tHM is computed instantly.
Use the batch mode to compare multiple scenarios side by side.

Use cases

Estimate fuel discharge burnup for PWR, BWR, or CANDU reactor designs.
Cross-check burnup limits during nuclear fuel management planning.
Convert between MWd/tHM and GWd/tHM units quickly.
Compare burnup across different fuel cycle lengths and power densities.
Support student exercises in nuclear engineering coursework.
Perform quick sanity checks on reactor physics calculations.

Frequently Asked Questions

Last updated: 2026-07-22 · Reviewed by Nham Vu