Safety
About
The Safety criterion evaluates how reactor design features contribute to the prevention, mitigation, and management of accidents. This criterion’s indicators focus on inherent and engineered design characteristics that influence safety across a range of regulatory and deployment contexts. Together, the indicators provide a structured basis for comparing how reactor designs address core safety functions through design choices, without relying on assumptions about operator actions or external emergency response.
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Indicator Breakdown
Weight 40%
Safety Case
Core question
How mature and publicly established is the reactor’s safety case with the regulator?
The Safety Case indicator assesses how far the reactor’s safety case is in the regulatory process and whether it has been formally reviewed or approved. It captures the maturity, transparency, and regulatory scrutiny of the design’s safety basis.
Coding rules
- 0 — No safety case submitted to regulator
- 1 — Safety case submitted to regulator
- 2 — Safety case approved by regulator
Weight 20%
Shutdown Mechanism
Core question
How diverse, independent, and passive are the reactor’s shutdown systems?
The Shutdown Mechanism indicator evaluates the number, independence, and passive nature of systems available to shut down the reactor. It captures resilience to common-cause failures and reliance on active components, power, or control systems.
Coding rules
- 0 — Relies only on passive negative reactivity feedback for shutdown
- 1 — Two or more shutdown systems, at least one of which is passive
- 2 — Multiple passive shutdown systems
Weight 10%
Fuel With Safety Characteristics
Core question
Does the reactor use fuel with accident tolerance or inherent safety characteristics?
The Fuel With Safety Characteristics indicator assesses whether the reactor adopts accident-tolerant fuel (if it is a light-water reactor) or fuel with inherent safety characteristics. It captures the fuel’s contribution to limiting damage progression under off-normal or accident conditions.
Coding rules
- 0 — No
- 1 — Yes
Weight 10%
Pressure & Containment
Core question
How well does the reactor’s containment strategy protect from the release of radioactive material?
The Pressure & Containment indicator measures whether the reactor design provides engineered barriers to retain radionuclides under normal and accident conditions, regardless of whether it uses a traditional large containment structure. This indicator accounts for the fact that reactors operating at lower pressure do not need as robust containment as reactors operating at higher pressures. It counts a dedicated containment vessel surrounding a reactor vessel as a first layer of containment, not the immediate reactor vessel. Further containment would include a containment building or below-grade siting.
Coding rules
- 1 — High pressure with single containment
- 2 — Low or ambient pressure with only confinement
- 3 — High pressure (more than 7 megapascals) with redundant containment
- 4 — Low or ambient pressure (less than or equal to 7 megapascals) with single containment
Weight 10%
Passive Heat Removal
Core question
How long can the reactor remove core heat without operator intervention?
The Passive Heat Removal indicator measures the duration of passive core heat removal following shutdown. This indicator captures reliance on natural circulation, heat sinks, and passive systems designed to manage heat removal.
Coding rules
- 1 — Less than three days
- 2 — Three days
- 3 — More than three days
Weight 10%
Coolant Reactivity
Core question
How chemically reactive is the reactor coolant?
Coolant Reactivity assesses the chemical interaction potential of the primary coolant with air, water, or structural materials. This indicator reflects the extent to which coolant properties introduce additional hazards during leaks or other accident conditions.
Coding rules
- 1 — Highly reactive (sodium)
- 2 — Moderately reactive (molten salt)
- 3 — Mild (light or heavy water)
- 4 — Inert (gas)
