Common technical and regulatory terms used elsewhere in this wiki. Cross-linked terms point to a fuller article; everything else is defined here.

A

  • ALARA / ALARP — "As Low As Reasonably Achievable" (or, in UK practice, "As Low As Reasonably Practicable"). The optimisation principle of radiation protection: doses should be reduced below limits when reasonable given economic and social factors.
  • Absorbed dose — energy deposited per unit mass in matter; SI unit gray (Gy).
  • Activity — rate of radioactive decay; SI unit becquerel (Bq) = 1 disintegration/s; the older unit curie (Ci) = 3.7 × 1010 Bq.
  • ALI (Annual Limit of Intake) — activity of a radionuclide that, taken in by ingestion or inhalation, would give the worker a committed effective dose equal to the relevant limit.
  • ADAMS — NRC document system (US): public-facing records of licensee and regulator correspondence.

B

  • Becquerel (Bq) — SI unit of activity. 1 Bq = 1 disintegration per second.
  • Burn-up — energy extracted from a unit mass of nuclear fuel, normally in gigawatt-days per tonne (GWd/tU) or MWd/kgU.
  • BSS (Basic Safety Standards) — IAEA GSR Part 3 plus the EU Council Directive 2013/59/Euratom transposing the equivalent ICRP framework into EU law.

C

  • CANDU — Canadian-designed pressurised heavy-water reactor with horizontal pressure tubes and on-power refuelling.
  • Clearance — regulatory determination that material can leave regulatory control because its activity is below defined exemption thresholds.
  • Containment — the leak-tight building or structure enclosing the reactor primary system, designed to retain radioactive material in accident conditions.
  • Criticality — the state of a system in which the chain reaction is exactly self-sustaining (keff=1).

D

  • Decay heat — energy continuously produced by radioactive decay of fission products in spent fuel and a shutdown core; roughly 6% of operating power immediately after shutdown, decreasing to ~1% at one hour, ~0.1% at one year.
  • Decommissioning — see Decommissioning.
  • Defence in depth — multiple, independent layers of protection so that no single failure leads to a significant radiological consequence.
  • DGR (Deep Geological Repository) — engineered facility several hundred metres deep for long-term disposal of high-level waste or spent fuel.

E

  • Effective dose — sum of equivalent dose to each organ weighted by a tissue weighting factor; designed as a population-risk metric, SI unit sievert (Sv).
  • EPR (Emergency Preparedness and Response) — see Emergency Preparedness & Response. Also: European Pressurised Reactor, a Framatome PWR design.
  • Equivalent dose — absorbed dose weighted by radiation type (wR); SI unit Sv.

F

  • Fission products — neutron-rich isotopes produced by fission, typically with mass numbers around 90 and 140.
  • Fuel cycle — see Nuclear Fuel Cycle.

G

  • Generic Design Assessment (GDA) — UK pre-licensing review of a new reactor design by ONR, the Environment Agency and Natural Resources Wales.
  • GSR / GSG — IAEA General Safety Requirements / General Safety Guides; see IAEA Safety Standards.

H

  • HALEU (High-Assay Low-Enriched Uranium) — U enriched to between 5% and 19.75% U-235; intended fuel for many advanced reactor designs.
  • HLW (High-Level Waste) — heat-generating radioactive waste; spent fuel itself, or vitrified reprocessing waste.

I

  • IAEA — see IAEA.
  • ICRP — International Commission on Radiological Protection. Issues recommendations on the system of radiation protection (Publications 60, 103, 118, etc.).
  • INES — International Nuclear and Radiological Event Scale, 0-7.
  • IRRS — IAEA Integrated Regulatory Review Service; peer review of a national regulator.

K

  • KBS-3 — Swedish/Finnish concept for spent-fuel disposal in copper canisters surrounded by bentonite buffer in crystalline bedrock.
  • keff (effective multiplication factor) — ratio of neutrons produced in one generation to neutrons produced in the preceding generation in a finite system; keff<1 subcritical, =1 critical, >1 supercritical.
  • KI prophylaxis — administering stable iodine (potassium iodide) to block uptake of radioiodine in the thyroid during a release.

L

  • Licensing — regulatory process by which an applicant receives authorisation to conduct a regulated activity; usually multi-stage (siting, construction, commissioning, operation, decommissioning).
  • LLW / ILW — Low-Level / Intermediate-Level radioactive waste; see Waste Management.
  • LWR — Light-Water Reactor; PWR or BWR.

M

  • MOX — Mixed-Oxide fuel; UO2 blended with PuO2 recovered from reprocessing.
  • Moderator — material that slows fast neutrons to thermal energies, increasing the fission cross-section; water, heavy water, graphite.

N

  • NEA — see NEA.
  • Notification — regulatory regime for low-risk activities below licensing thresholds (typical in EU BSSD).
  • NRC — see NRC.

O

  • OECD NEA — see NEA.
  • OIL (Operational Intervention Level) — directly measurable trigger that authorises a protective action without waiting for dose calculations.
  • ONR — see ONR.
  • OSART — IAEA Operational Safety Review Team; peer review of an operating reactor unit's safety performance.

P

  • PWR / BWR — Pressurised / Boiling Water Reactor; see Reactor Types.
  • PSA (Probabilistic Safety Assessment) — quantitative method combining event-tree and fault-tree analysis to estimate core-damage frequency, large-release frequency, etc.
  • Passive safety — safety function not relying on external power, operator action or external mechanical input; driven by physics. See Reactor Types & Safety Claims.

R

  • REGDOC — Canadian Nuclear Safety Commission's regulatory-document series; see CNSC.
  • Reprocessing — chemical separation of uranium and plutonium from spent fuel for re-use; produces high-level liquid waste subsequently vitrified.

S

  • SF-1, SSR, SSG, GSR, GSG — IAEA Safety Standards levels; see IAEA Safety Standards.
  • Safeguards — system of accountancy and verification of nuclear material under IAEA agreements.
  • Safety case — integrated argument that a facility or operation meets regulatory criteria over its lifetime.
  • SAR / FSAR — (Final) Safety Analysis Report; the licensee's comprehensive safety documentation.
  • Severe accident — accident with significant core damage or large release potential.
  • SMR (Small Modular Reactor) — reactor design typically < 300 MWe per module, intended for factory fabrication.
  • SNF (Spent Nuclear Fuel) — see Spent Fuel & Deep Disposal.
  • Sievert (Sv) — SI unit of equivalent and effective dose; 1 Sv = 1 J/kg with biological weighting.
  • SSMFS — see SSMFS.
  • STUKLEX — Finnish online rule index operated by STUK.

T

  • TLD / OSL — Thermoluminescent / Optically-Stimulated Luminescence dosemeter; common personal dosimetry technology.
  • TRISO — Tristructural Isotropic fuel particle used in some HTGRs; a kernel surrounded by buffer and PyC/SiC/PyC coatings.

U

  • U-235 / U-238 — fissile and fertile uranium isotopes; natural uranium is 0.711% U-235.

V

  • VVER — Russian-designed PWR family; main variants are VVER-440 (V-179, V-213, V-230, V-446), VVER-1000 (V-320, V-428, V-466) and VVER-1200 (V-491, V-509).
  • Vitrification — incorporation of high-level liquid waste into borosilicate glass for storage and eventual disposal.

W

  • WANO — World Association of Nuclear Operators; peer-review network created post-Chornobyl.
  • WENRA — see WENRA.

Y

  • YVL — STUK's technical regulatory guide series; see STUK.