Nuclear Terms and Acronyms

What does “system condition estimate” mean?

The NRC made best possible estimates of reactor and spent fuel pool conditions.  Such estimates are necessary because of the highly uncertain status of the unitsand their prognosis.  NRC projections are from computer models using best estimates of site and weather conditions available at the time. As conditions change and information is updated these projections may change.  Model results are projections only and may not be representative of an actual release.

Why were “hypothetical” sites/reactors used?

Although assessments for each unit could be advantageous, available data regarding the units are highly uncertain and assumptions had to be made to provide the inputs to the assessments. Since the NRC does not oversee the design, construction, and operation of Japanese reactors, they do not have access to exact plant conditions, fuel inventory, or fuel burnup.

What is a PAG?

The Environmental Protection Agency (EPA) developed Protective Action Guides (PAGs) to help state and local authorities make radiation protection decisions during emergencies. The PAGs are dose rates at which a protective action may be warranted.

When a PAG is exceeded, the local decision makers will determine what measures are to be implemented to protect the public, and the local emergency response organizations will implement the measures.


ABLE – Axial Blanket Elimination
ABTR – Advanced Burner Test Reactor
ACRS – Advisory Committee on Reactor Safeguards
ACS – Auxiliary Cooling System
ADAMS – Agency-wide Documents Access and Management System
ALARP – As Low as Reasonably Practicable
ALMR – Advanced Liquid Metal Reactor
ASME – American Society of Mechanical Engineers
ATWS – Anticipated Transient without Scram
BDBE – Beyond Design Basis Events
BNL – Brookhaven National Laboratory
BWR – Boiling-Water Reactor
BWROG – Boiling Water Reactor Owners Group
CDA – Core Disruptive Accidents
CDF – Core Damage Frequency
CEUS – Central and Eastern United States
CMR – Controlled Material Relocation
COTS – Commercial off the Shelf
CRBR – Clinch River Breeder Reactor
CRDL – Control Rod Drive-Line
CRGR – Committee to Review Generic Requirements
CRGT – Control Rod Guide Tube
CRSS – Control Rod Stop System
CSC – Corium Spreading and Coolability
CSV – Comma Separated Values
DBA – Design Basis Accidents
DBE – Design Basis Events
DCH – Direct Containment Heat
DE – Division of Engineering
DEC – Design Extension Conditions
DFBR – Demonstration Fast Breeder Reactor
DHR – Decay Heat Removal
DHRS – Decay Heat Removal System
DRA – Division of Risk Analysis
DRACS – Direct Reactor Auxiliary Cooling System
DSA – Division of Systems Analysis
DSS – Division of Safety Systems
EAGLE – Experimental Acquisition of Generalized Logic to Eliminate Recriticalities
ECCS – Emergency Core Cooling System
EDO – Executive Director of Operations
EFR – European Fast Reactor
EHD – Electronic Hearing Docket
EPRI – Electric Power Research Institute
ESP – Early Site Permit
FA – Fuel Assembly
FACA – Federal Advisory Committee Act
FACT – Fast Reactor Cycle Technology
FAIDUS – Fuel Assembly with Inner Duct Structure
FCI – Fuel Coolant Interaction
FFTF – Fast Flux Test Facility
FR – Fast Reactor
FS – Feasibility Study
FSA – Fuel Subassembly
GEH – General Electric Hitachi
GEM – Gas Expansion Modules
GI – Generic Issue (same meaning as GSI)
GIMCS – Generic Issue Management Control System
GL – Generic Letter
GR – Guidance Report
GSI – Generic Safety Issue
HCDA – Hypothetical Core Disruptive Accidents
HPCS – High Pressure Core Spray
HTML – Hypertext Markup Language
IAEA – International Atomic Energy Agency
IFR – Integral Fast Reactor
IHX – Intermediate Heat Exchanger
IN – Information Notice
INPO – Institute of Nuclear Power Operations
INPRO – International Project on Innovative Nuclear Reactors and Fuel Cycles
IP – Initiating Phase
IPEEE – Individual Plant Examination of External Events
IRACS – Intermediate Reactor Auxiliary Cooling System
ISS – Inherent Shutdown System
Issue Number – A unique number assigned to each generic issue
IVR – In-Vessel Retention
JAEA – Japan Atomic Energy Agency
JAIF – Japan Atomic Industrial Forum
JAPC – Japan Atomic Power Company
JSFR – Japanese Sodium Fast Reactor
KB – Kilobyte, used to measure the size of an electronic file
LMR – Liquid Metal Reactor
LOCA – Loss of Coolant Accident
LOF – Loss of Flow
LOHS – Loss of Heat Sink
LOPI – Loss of Pipe Integrity
LORL – Loss of Reactor Level
LSN – Licensing Support Network
LWR – Light Water Reactor
MB – Megabyte, used to measure the size of an electronic file
MD – Management Directive
Metadata – Data which identifies a document or record, including Title, Accession Number, etc.
MOX – Mixed Oxide
MPVF – Maximum Potential Void Fraction
MS – Microsoft
NARA – National Archives and Records Administration
NDHX – Natural Draft Heat Exchanger
NEI – Nuclear Energy Institute
NISA – Nuclear and Industrial Safety Agency
NPR – New Production Reactor
NPSH – Net Positive Suction Head
NRC – U.S. Nuclear Regulatory Commission
NRO – Office of New Reactors
NRR – Office of Nuclear Reactor Regulation
NSIR – Office of Nuclear Security and Incident Response
NSSS – Nuclear Steam Supply System
NSTF – Natural Convection Shutdown Heat Removal Test Facility
OCR – Optical Character Recognition
OEGIB – Operating Experience and Generic Issues Branch
OGC – Office of General Counsel
PAHR – Post-Accident Heat Removal
PAMR – Post-Accident Material Relocation
PARS – Publicly Available Records System
PDF – Portable Document Format
PII – Personally Identifiable Information
PLOHS – Protected Loss of Heat Sink
PPS – Plant Protection System
PRACS – Primary Reactor Auxiliary Cooling System
PSA – Probabilistic Safety Assessment
PUMA – Purdue University Multi-dimensional Integral Test Assembly
PWR – Pressurized-Water Reactor
Record – Refers to objects found in the Content Panel
RES – Office of Nuclear Regulatory Research
RIS – Regulatory Issue Summary
RSS – Reactivity Shutdown System
RV – Reactor Vessel
RVACS – Reactor Vessel Auxiliary Cooling System
RVDHRS – Reactor Vessel Decay Heat Removal System
SA – Subassembly
SASS – Self-Actuated Shutdown System
SBO – Station Blackout
SBPB – Balance-of-Plant Branch
SE – Safety Evaluation
SECY – Office of the Secretary
SFR – Sodium Fast Reactor
SG – Steam Generator
SHTS – Sodium Heat Transport System
SMFR – Small Modular Fast Reactor
SOW – Statement of Work
SQL – Structured Query Language
SRM – Staff Requirements Memorandum
SRP – Standard Review Plan
SSE – Safe Shutdown Earthquake
SSIB – Safety Issue Resolution Branch
TAC – Task Action Control
TAP – Task Action Plan
TBD – To Be Determined
TEPCO – Tokyo Electric Power Company
TI – Temporary Instruction
TIB – Total Instantaneous Blockage
TOP – Transient Over-Power
TP – Transition Phase
TVA – Tennessee Valley Authority
UI – User Interface
ULOF – Unprotected Loss of Flow
ULOHS – Unprotected Loss of Heat Sink
URL- Uniform Resource Language
USI – Unresolved Safety Issue
USS – Ultimate Shutdown System
UTOP – Unprotected Transient Over-Powe
WBA – Web-based ADAMS
zip file – File containing a single or multiple items which have been compressed


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