How to Design and Specify a Hot Cell

A hot cell is a heavily shielded enclosure used to handle highly radioactive materials safely. They're found in nuclear medicine departments, radiopharmacy compounding facilities, research laboratories, and nuclear energy facilities — anywhere that staff need to work with or process radioactive isotopes at levels that would be unsafe without substantial shielding between the material and the operator.

For facility managers and procurement staff who are involved in a hot cell project for the first time, the process can feel unfamiliar. Hot cells sit at the intersection of radiation physics, structural engineering, and specialized construction — and the specification decisions made early in the process have significant consequences for cost, compliance, and long-term usability. This article walks through the key components of a hot cell and what to think about when specifying each one.

Start with the Physicist's Report

Before any product decisions are made, the shielding design needs to come from a qualified radiation physicist. The physicist's report will specify the required lead equivalency for each surface of the hot cell — walls, ceiling, floor if applicable, viewing window, and pass-through openings — based on the specific isotopes being handled, their activity levels, and the occupancy of adjacent spaces. This is the document that drives every other specification decision, and attempting to design a hot cell without one is not a path to a compliant installation.

The physicist's report will also address the geometry of the cell — which surfaces receive direct beam exposure, where scatter radiation is the primary concern, and whether any surfaces can be specified at a lower equivalency because of distance or occupancy factors. Understanding what the report specifies for each surface before sourcing materials will prevent mismatches and unnecessary cost.

Wall Shielding: Lead Plate and Lead Brick

Hot cell walls typically require far more shielding mass than a standard medical X-ray room. Where a diagnostic radiology suite might specify 1/16" of lead in the walls, a hot cell handling high-energy gamma-emitting isotopes may require several inches. At these thicknesses, the two most common shielding materials are lead plate and lead bricks.

Lead plate is available from Intech in thicknesses from 1/4" up to 5", in standard 4 ft × 4 ft panels with custom sizes available. It provides continuous, gap-free shielding across each surface and is the right choice when the cell walls are being built as fixed, permanent construction. At thicker specifications — 3/4" and above — lead plate is extremely heavy (44.3 lbs/ft² at 3/4", 59 lbs/ft² at 1") and requires structural framing on both sides designed by a licensed civil or structural engineer. This is not a detail to address after the lead arrives.

Lead bricks offer a modular alternative, particularly useful when the hot cell needs to be reconfigurable or when the shielding thickness requirement is being built up incrementally. Interlocking lead bricks — available in sizes from 3/4" × 4" × 12" up to 2-1/2" × 4" × 12" — use a chevron-style tongue-and-groove system that locks bricks together in every direction, significantly reducing the risk of radiation passing through seams compared to stacked flat bricks. For hot cells that may need to be modified as the isotope mix or activity levels change over time, the modular brick approach preserves that flexibility in a way that poured or plate construction does not.

In either case, shielding continuity at joints and penetrations is critical. Any gap — at a seam between plates, around a conduit, at the junction between the wall and ceiling — is a potential radiation pathway. Every penetration through the shielding needs to be planned and addressed in the design, not discovered during installation.

Viewing Windows

Operators working at a hot cell need to see what they're doing without being exposed to the radiation inside. Lead glass windows — sometimes called radiation shielding windows — provide optical clarity while attenuating the radiation passing through them, rated to the same lead equivalency scale as the surrounding walls.

Intech's lead glass windows are available in standard small pane sizes from 8" × 10" up to 18" × 18", with larger panes from 18" × 24" up to 36" × 72", and custom sizes up to 96". For hot cell applications, the window size needs to provide adequate visibility for the procedures being performed while minimizing the unshielded area in the cell wall. The window's lead equivalency must match the specification for the surrounding wall — a lower-rated window in a higher-rated wall creates an obvious weak point.

For applications where breakage risk is a concern — particularly in environments where heavy tooling or equipment is handled through the cell — laminated safety lead glass bonds the layers together so that if the glass breaks, fragments remain contained rather than scattering. This is worth specifying upfront rather than after an incident.

The frame surrounding the window is as important as the glass itself. The lead lining in the wall needs to lap behind or overlap the frame at every edge — a gap between the glass edge and the surrounding lead creates a radiation pathway that the window's rating alone won't address.

Pass-Throughs and Hatches

Hot cells need to receive materials in and send processed materials out without compromising the shielding envelope. This is handled through pass-through openings — also called hatches or ports — which are shielded openings in the cell wall designed to allow transfer of items while maintaining the radiation barrier.

A pass-through needs to be shielded to at least the same lead equivalency as the surrounding wall. The geometry of the opening matters: a straight-through opening allows radiation to travel directly out when the hatch is open, while an L-shaped or Z-shaped pass-through — where the opening changes direction — prevents direct line-of-sight from the radioactive source to the operator even when the hatch is open. For high-activity applications, the physicist's report should address pass-through geometry specifically.

Lead-lined curtains can serve as a flexible shielding solution at pass-through openings where a rigid hatch isn't practical. Intech's lead-lined curtains for doorways and openings are available in protection levels up to 1.0mm lead equivalency and beyond, and can be sized to fit non-standard opening dimensions. For the opening itself, adhesive-backed shielding panels can be applied to the surfaces immediately surrounding the pass-through to ensure the transition zone between the opening and the cell wall maintains adequate shielding.

Glove Ports and Remote Handling

Most hot cells include glove ports — circular openings in the cell wall fitted with thick rubber gloves that allow operators to manipulate materials inside the cell without direct contact. The port itself needs to maintain shielding continuity when the gloves are in use and when they're not. Glove port rings are typically specified as part of the hot cell fabrication package rather than sourced separately, but they need to be accounted for in the wall shielding design — each port is a penetration that requires shielding treatment.

For high-activity isotopes where even glove port access isn't adequate, remote handling tools — long-handled tongs and manipulators operated from outside the cell — are used instead. In these cases, the cell's viewing window geometry and lighting become even more critical, since the operator is working entirely by sight through the glass.

Structural and Regulatory Considerations

A hot cell at any meaningful shielding specification is a significant structural undertaking. The combined weight of the shielding materials — particularly at the thicknesses required for high-energy gamma sources — can easily exceed what standard building construction is designed to support. Structural engineering review is required before construction begins, and in most jurisdictions the installation will need to be permitted.

From a regulatory standpoint, hot cells handling radioactive materials are subject to oversight from the Nuclear Regulatory Commission (NRC) or the relevant Agreement State radiation control program, depending on the isotopes and activity levels involved. The physicist's shielding report is a required part of the licensing documentation, and the as-built installation will typically be inspected before the cell is approved for use.

Bringing It Together

A well-specified hot cell is the product of close coordination between the radiation physicist, the structural engineer, the construction team, and the shielding supplier. The physicist drives the lead equivalency requirements for every surface. The structural engineer ensures the building can carry the load. The construction team executes to specification. And the shielding supplier — Intech, in this case — provides the materials that meet those specifications reliably and on time.

Intech supplies lead plate, lead bricks, lead glass windows, and curtain and adhesive shielding products for hot cell applications across medical, research, and industrial settings. Contact Intech to discuss your project specifications, or explore the full product range at leadshielding.com. For a broader look at how lead bricks are used in modular shielding configurations, the article Lead Bricks: Beyond the Cave covers the range of applications in more detail.