Neutron Fluence Planning

Fluence — flux integrated over time — is the currency of irradiation; planning it lets breeding, testing, and services share a finite neutron budget.

Flux times time

Flux is the instantaneous rate of neutrons crossing a surface; fluence is that flux integrated over time — the total dose a sample or component accumulates. Nearly every irradiation outcome (dpa, helium production, activation, breeding) depends on fluence, so planning it is how the foundry manages what it makes.

Fluence planning allocates the finite neutron budget across missions and over the operating schedule. A materials test article needs a target dpa, which sets its required fluence and therefore its exposure time in a given flux position. A breeding campaign needs sustained fluence in the blanket. A target for activation needs a specific fluence to reach the desired isotope yield without over-activating.

What planning must balance

• Breeding fluence in the blanket (the primary mission)
• Test-article fluence for materials qualification campaigns
• Target fluence for activation and isotope services
• Component fluence limits — e.g., center-post lifetime near 0.01 fpy
• Machine availability and duty cycle over the campaign

The lifetime constraint

Fluence also determines how long components last. The center post accumulates damage and must be replaced on a schedule set by its fluence limit. Planning therefore couples what the machine produces to when it must be maintained. All of this is a design-and-simulation projection, calibrated against measured dosimetry once Hyperion operates.

This page describes a design-and-simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind (FOAK) first tritium is targeted near 2030. No net-gain claim is made before FOAK.