Tritium Inventory Accounting
Every gram of tritium in the plant is tracked through storage, processing, and the plasma so the mass balance always closes.
Why account for it
Tritium is radioactive, mobile, and regulated, so a device must know where all of it is at all times. Inventory accounting is both an operational need, to blend fuel correctly, and a safety and regulatory requirement, to detect losses that could indicate a leak or a permeation into structures. The goal is a closed mass balance across the whole plant.
Where tritium hides
Tritium is stored on metal-hydride beds, held as gas in process lines, dissolved and trapped in plasma-facing materials, and permeated into structural walls. The trapped and permeated fractions are the hardest to measure directly because they are distributed in solids. Accounting combines direct measurement of the accessible streams with models of retention in materials.
Measurement and control
Beds are weighed or calorimetered, since tritium's decay heat is a proxy for quantity. Gas streams are measured by pressure, volume, temperature, and composition. Room and glovebox monitors detect airborne tritium. A control system integrates these into a running inventory and flags any discrepancy in the balance, which triggers investigation before operation continues.
- Closed mass balance is the accounting goal
- Stored, in-process, trapped, and permeated fractions
- Calorimetry and composition measure accessible streams
- Discrepancies trigger investigation and interlocks
Retention and removal
Because retained tritium in the wall grows over time and is a safety limit, plants include detritiation and wall-conditioning to recover it, and the accounting tracks how much is removed. In the Kronos breeder design study, which breeds tritium at a modeled breeding ratio of 1.8, accounting must reconcile bred, burned, recycled, and retained tritium. The machine is a simulation and design case; this page describes accounting as a general subsystem discipline.
Rigorous accounting is what makes a tritium-fueled machine safe to operate and to license.