Taxonomy

Canonical External Hazard Taxonomy

Purpose

This page defines the authoritative canonical hazard taxonomy for external hazards applicable to nuclear power plants. It establishes a single, stable set of canonical hazard identifiers (IDs), their scope boundaries, and their relationships.

These canonical IDs are used consistently across:

• the External Hazards wiki
• the document index and RAG database
• future member‑facing LLM/chat tools

The taxonomy normalizes terminology used across EPRI, the NRC, ASME/ANS, and international guidance. It does not replace regulatory language and does not remove technical or site‑specific nuance.

Core principles

The following principles govern how this taxonomy is used:

• Canonical hazard IDs are immutable.
  • Once published, an ID must never be renamed, edited, or deleted.
  • Changes in understanding are handled through descriptions, hierarchy updates, aliases, or deprecation (see below).

• Canonical IDs are labels, not filters.
  • They improve grouping, traceability, and explainability.
  • They must never be used to gate retrieval or render content inaccessible.

• Free text remains authoritative content.
  • Canonical IDs complement semantic search and embeddings; they do not replace them.

How to use this taxonomy

• Each hazard overview wiki page must reference exactly one canonical hazard ID.
• Sub‑mechanisms or refinements reference both the child and parent IDs.
• Documents and index records may map to one or more canonical hazard IDs.
  • Mapping improves consistency and long‑term usability.
  • Lack of a mapping does not make content invisible or invalid.
• Initiating events (for example, LOOP, LUHS) are not hazards and are excluded.

Governance and change control

This taxonomy is designed to evolve without breaking downstream systems.

Allowed changes

The following may change at any time:

• Preferred hazard names
• Descriptions and scope notes
• Parent–child relationships
• Aliases and explanatory notes

Prohibited changes

• Canonical hazard IDs must never be renamed, reused, or removed.

Deprecation policy

When a hazard definition changes materially:

• The existing ID is marked deprecated.
• One or more replacement IDs are identified.
• Existing documents and index records remain valid and unchanged.

This approach preserves historical consistency while allowing the taxonomy to evolve.

Relationship to other structures

• Canonical hazard IDs define what external phenomenon is being referenced.
• Canonical concepts (defined elsewhere) describe how reasoning is performed.
• Terminology and prose remain flexible and human‑readable.

Together, these elements form a stable semantic backbone that supports long‑term knowledge retention, analysis, and AI‑assisted use.

Top-Level Classes

Canonical ID	Preferred Name	Scope
EH-HYD	Hydrological Hazards	Water-related natural hazards including flooding, precipitation, and coastal events
EH-ATM	Atmospheric Hazards	Wind, storm, and weather-related hazards including tornados, hurricanes, and extreme temperatures
EH-GEO	Geological Hazards	Earth-related natural hazards including seismic, volcanic, and ground instability events
EH-BIO	Biological & Environmental Hazards	Hazards from biological organisms, drought, wildfire, and ecological phenomena
EH-ANT	Anthropogenic Hazards	Human-caused external hazards including industrial accidents, transportation, and nearby facility events
EH-ELE	Electrical & Electromagnetic Hazards	Hazards affecting electrical systems including lightning, electromagnetic interference, and grid disturbances
EH-CMB	Combined & Correlated Hazards	Multi-hazard scenarios and hazard combinations
EH-EVL	Hazard Evaluation & PRA Methods	Methodologies for identifying, screening, and assessing external hazards

Hydrological Hazards

Canonical ID	Preferred Name	Parent
EH-HYD-RIV	Riverine Flooding	EH-HYD
EH-HYD-PLV	Pluvial Flooding (Local Intense Precipitation)	EH-HYD
EH-HYD-CST	Coastal Flooding & Storm Surge	EH-HYD
EH-HYD-TSU	Tsunami	EH-HYD
EH-HYD-SEI	Seiche	EH-HYD
EH-HYD-DAM	Dam & Levee Failure	EH-HYD
EH-HYD-ICE	Ice-Induced Flooding (Ice Jam / Frazil Ice)	EH-HYD
EH-HYD-SLR	Sea Level Rise	EH-HYD
EH-HYD-GW	Groundwater Ingress	EH-HYD
EH-HYD-WDR	Wind-Driven Rain Intrusion	EH-HYD

Atmospheric Hazards

Canonical ID	Preferred Name	Parent
EH-ATM-TOR	Tornado	EH-ATM
EH-ATM-HUR	Hurricane / Tropical Cyclone	EH-ATM
EH-ATM-STW	Straight-Line / High Wind	EH-ATM
EH-ATM-DRT	Derecho / Thunderstorm Wind	EH-ATM
EH-ATM-HAL	Hail	EH-ATM
EH-ATM-SNW	Extreme Snow / Ice Storm	EH-ATM
EH-ATM-EHT	Extreme Heat	EH-ATM
EH-ATM-ECL	Extreme Cold / Freeze	EH-ATM
EH-ATM-MSL	Wind-Borne Missiles (Tornado / Hurricane Debris)	EH-ATM
EH-ATM-SND	Sandstorm / Dust Storm	EH-ATM

Geological Hazards

Canonical ID	Preferred Name	Parent
EH-GEO-SEI	Seismic (Vibratory Ground Motion)	EH-GEO
EH-GEO-FLT	Surface Faulting & Tectonic Deformation	EH-GEO
EH-GEO-VOL	Volcanic Activity (Ash, Lava, Lahar)	EH-GEO
EH-GEO-LND	Landslide / Slope Instability	EH-GEO
EH-GEO-SUB	Subsidence / Sinkhole / Karst Collapse	EH-GEO
EH-GEO-LIQ	Soil Liquefaction	EH-GEO
EH-GEO-ERO	Erosion & Sedimentation	EH-GEO

Biological & Environmental Hazards

Canonical ID	Preferred Name	Parent
EH-BIO-DRT	Drought / Low Water	EH-BIO
EH-BIO-WFR	Wildfire / Forest Fire	EH-BIO
EH-BIO-FOL	Biological Fouling (Mussels, Jellyfish, Algae)	EH-BIO
EH-BIO-VEG	Vegetation Encroachment	EH-BIO
EH-BIO-INF	Infestation (Insects, Rodents)	EH-BIO
EH-BIO-CLM	Climate Change Effects (Long-Term Trends)	EH-BIO

Anthropogenic Hazards

Canonical ID	Preferred Name	Parent
EH-ANT-IND	Nearby Industrial Facility Accident	EH-ANT
EH-ANT-TRN	Transportation Accident (Rail, Road, Pipeline)	EH-ANT
EH-ANT-AIR	Aircraft Impact	EH-ANT
EH-ANT-TMI	Turbine Missile (Internally Generated External Hazard)	EH-ANT
EH-ANT-EXP	External Explosion / Blast Wave	EH-ANT
EH-ANT-TOX	Toxic Gas / Chemical Release	EH-ANT
EH-ANT-FIR	External Fire (Non-Wildfire, for example, Fuel Storage)	EH-ANT
EH-ANT-SAB	Sabotage / Security Threat	EH-ANT

Electrical & Electromagnetic Hazards

Canonical ID	Preferred Name	Parent
EH-ELE-LTN	Lightning Strike	EH-ELE
EH-ELE-GRD	Grid Disturbance / Loss of Offsite Power (LOOP)	EH-ELE
EH-ELE-EMP	Electromagnetic Pulse (EMP) / Geomagnetic Disturbance	EH-ELE
EH-ELE-EMI	Electromagnetic Interference (EMI)	EH-ELE

Combined & Correlated Hazards

Canonical ID	Preferred Name	Parent
EH-CMB-SEF	Seismic + Flooding (Seismically-Induced Flooding)	EH-CMB
EH-CMB-HWF	High Wind + Flooding (Hurricane Multi-Hazard)	EH-CMB
EH-CMB-SLP	Seismic + LOOP	EH-CMB
EH-CMB-WLP	Wind + LOOP	EH-CMB
EH-CMB-CAS	Cascading / Sequential Hazard Events	EH-CMB
EH-CMB-COR	Correlated Hazard Groups	EH-CMB

Hazard Evaluation & PRA Methods

Canonical ID	Preferred Name	Parent
EH-EVL-SCR	Hazard Screening & Identification	EH-EVL
EH-EVL-PRA	External Events PRA (Probabilistic Risk Assessment)	EH-EVL
EH-EVL-FRG	Fragility Analysis	EH-EVL
EH-EVL-MAR	Margins Assessment	EH-EVL
EH-EVL-SMA	Seismic Margins Assessment (SMA)	EH-EVL
EH-EVL-WDN	Walkdown & Inspection Procedures	EH-EVL
EH-EVL-OPX	Operating Experience (OpE) Review	EH-EVL
EH-EVL-CLR	Climate Resilience Assessment	EH-EVL

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EPRI technical point of contact: Chris Rochon (CRochon@epri.com)

Date last reviewed: 2026-03-23