Criticality Calculator

Estimate neutron multiplication factor from geometry, enrichment, moderation, and reflection parameters.

U-235 Enrichment

Fissile Mass

Geometry

Moderation Level

Reflector

Tab to move between fields

k-effective

0.05

k-infinity0.86

Reactivity (ρ)-18.87

Criticality Status0

Subcritical Multiplication1.1×

Estimated Critical Mass333.3 kg

Non-Leakage Probability0.06

How to Use This Calculator

Enter U-235 Enrichment, Fissile Mass, and Geometry.
Set Moderation Level and Reflector.
Review the k-effective result.
Use k-infinity and Reactivity (ρ) to inform your decision.
Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with U-235 Enrichment

U-235 Enrichment: Uranium-235 enrichment in weight percent. LEU: <20%, Natural: 0.711%, Power reactor: 3–5%.
Fissile Mass: Total mass of fissile material (U-235 equivalent) in kilograms.
Geometry: 1=Sphere (most reactive), 2=Cylinder, 3=Slab (least reactive).
Moderation Level: 1=None (fast), 2=Under-moderated, 3=Optimally moderated, 4=Over-moderated.
Reflector: 1=Bare (no reflector), 2=Partial, 3=Full water reflector, 4=Full steel reflector.

Criticality Status: 0=Deeply Subcritical, 1=Subcritical, 2=Approaching, 3=Near, 5=Supercritical

Identify Input Parameters
4 parameters
U-235 Enrichment = 4.5, Fissile Mass = 10, Geometry = 1, Moderation Level = 3 = 5 input(s) provided
Calculate k-effective
k-effective
0.0503 = 0.0503
Calculate k-infinity
k-infinity
0.8641 = 0.8641
Calculate Reactivity
Reactivity
-18.87214 = -18.87214