Decay space design
The decay-in-storage room is the most under-designed space on most new alpha programs — and the hardest to retrofit. This page is the architectural and operational counterpart to the waste-management Hold-time and Decay-in-storage Planning pages: what to put in the room, where to put it, and what design decisions are expensive to change once concrete is poured.
Minimum requirements
A workable Ac-225 decay space combines four design elements; under-investing in any one of them is the typical root cause of capacity, audit, or contamination findings within the first year.
Capacity
- Sized to 2-3× steady-state peak weekly volume × chain hold time
- Headroom for one missed release-survey cycle
- Footprint planned for the program in year 3, not month 1
Layout
- FIFO staging with date-visible labeling at eye level
- Segregation aisle for sharps, soft, and liquid streams
- Survey station inside the room, not down the hall
Engineering
- Continuous mechanical exhaust; negative pressure where supported
- Sealed, coved flooring with no floor drains in the storage footprint
- Shielded containers or a shielded enclosure sized for Bi-213 daughter gamma
Design decisions worth fighting for
Survey bench inside the room
ZnS alpha probe, low-background alpha counter, and the release-survey log all live in the room. Carrying waste containers to a survey station in another room invites cross-contamination and breaks the audit chain. Plan a 4-6 ft bench with task lighting and a hand-wash sink immediately outside the door.
Visible inventory
Open wire shelving or clear-front bins so date labels are visible without moving containers. Inventory log on a wall-mounted clipboard or tablet at the door. If a tech has to dig to find the oldest container, FIFO breaks within weeks.
Posted access controls
Restricted-area posting per 10 CFR §20.1902 at the door. Badge or key access; visitor log inside. The room is part of the radiation safety program, not a closet — design it like a controlled space from day one.
Spill containment
Curbed floor or raised threshold to contain a liquid spill within the room. Spill kit and PPE cache immediately inside the door. Avoid floor drains in the storage footprint — a drain in this room is a release pathway you have to defend at every inspection.
Common design failures
Cheap to fix at design
Sealed, coved flooring. Wall-mounted shelving with date-visible labeling. Survey bench inside the room. Negative-pressure exhaust. Posted access controls.
Expensive to fix later
Adding ventilation post-build. Removing a floor drain. Re-sizing the room. Re-segregating mixed streams already in storage. Moving the decay room to a different floor when capacity is hit.
Walking the room together with the RSO, AMP, and a hot-lab tech before the drywall goes up tends to be time well spent. The tech's hands-on observations (where the cart turns, where bins block the survey bench) are often the ones that matter most on day one.
- 10 CFR §35.92 — Decay-in-storage.
- 10 CFR §20.1902 — Posting requirements.
- NCRP Report No. 155 — Management of Radionuclide Therapy Patients.