Nuclear Safety & Radiation Protection

Start here: ten words every newcomer needs

Overheard on the job

Real-sounding lines from the floor, translated into plain English.

• Sign onto the RWP, dress out in double PCs and frisk at the step-off pad, it's a flea area.

  TranslationRegister on the radiation work permit, wear two layers of protective clothing and check yourself for contamination at the exit pad, because hot particles are present.

• Hot spot on the drain line reads 1 R contact, hang lead and flush it before the crew shows up, easy ALARA.

  TranslationA small high dose-rate spot measures about 1 roentgen per hour on contact; shield and flush it before work starts to cut dose cheaply.

• Two jumpers are burned out after the bowl entry, put in a dose extension or bring in the next crew.

  TranslationTwo workers who made brief high-dose entries into the steam generator channel head have reached their dose level; get approval to raise it or use other workers.

• Diesel B is inoperable, we're in a 72 hour LCO, and the risk model says nobody touches train A.

  TranslationAn emergency generator is out of service, which starts a technical specification clock, and the probabilistic risk model forbids maintenance on the remaining train.

• Scram at 0300, all rods in, decay heat's going to the condenser on the steam dumps and xenon will keep us down till tomorrow.

  TranslationThe reactor shut down automatically; decay heat is being dumped to the main condenser through the steam dump valves, and xenon build-up will prevent a restart for about a day.

• PCE at the PCM, it's contamination not exposure, decon the wrist and run a skin dose.

  TranslationA worker set off the whole-body contamination monitor; the problem is radioactive material on the skin, not irradiation, so clean the wrist and calculate the skin dose.

• Crud burst on the peroxide add, cobalt-58 is spiking and shine off the demins is lighting up the corridor.

  TranslationShutdown chemistry released activated corrosion products, and radiation from the loaded purification beds is raising dose rates in the nearby corridor.

Defence in depth, physical barriers, redundancy and the rules that keep safety systems available.

• Containmentalso containment building, primary containment
  The massive, leak-tight structure around a reactor that holds in radioactive material and steam if the coolant system fails.
• Defence in depthalso defense in depth, DiD
  The safety strategy of stacking independent layers of protection so no single failure can lead to harm.
• Diversity
  Using different designs, technologies or physical principles for the same safety function to guard against common-cause failure.
• ECCSalso emergency core cooling system, emergency core cooling
  Emergency core cooling system: the set of safety systems that inject water to keep the core covered after a loss of coolant.
• Fission product barrieralso FPB, barrier
  One of the successive physical barriers that keep radioactive fission products away from people and the environment.
• LCOalso limiting condition for operation
  Limiting condition for operation: a technical specification requirement for equipment or conditions needed to run the plant.
• Redundancy
  Providing more components or trains than needed, so a safety function survives if one fails.
• Safety culturealso nuclear safety culture
  The shared attitudes and behaviours in an organisation that give nuclear safety overriding priority.
• Single failure criterionalso SFC
  The design rule that a safety system must still do its job despite any one component failing.

Criticality, reactivity, shutdown and the neutron behaviour operators manage every shift.

• Control rodalso rod, control rod assembly
  A movable rod or blade of neutron-absorbing material used to control reactor power and shut the reactor down.
• Criticalityalso critical
  The state in which a chain reaction sustains itself at a steady rate, with each fission causing on average exactly one more.
• Decay heatalso residual heat, afterheat
  Heat produced by radioactive decay of fission products after a reactor shuts down, which must be removed.
• k-effectivealso keff, k-eff
  The effective neutron multiplication factor: the ratio of neutrons in one generation to the previous one.
• Moderatoralso moderating material
  The material in a reactor core that slows fast fission neutrons so they are more likely to cause further fission.
• Poisonalso neutron poison, neutron absorber
  Any material that absorbs neutrons strongly, whether added deliberately for control or produced by fission.
• Reactivityalso rho
  A measure of how far a reactor is from criticality, positive when power will rise and negative when it will fall.
• Scramalso reactor trip, trip
  The rapid automatic or manual insertion of all control rods to shut a reactor down in seconds.
• Shutdown marginalso SDM
  How far subcritical a reactor would be with all rods inserted except the single most valuable one stuck out.
• Void coefficientalso void reactivity coefficient, alpha-void
  The change in reactivity caused by steam bubbles or voids forming in the coolant.
• Xenon poisoningalso xenon
  The loss of reactivity caused by xenon-135, a fission product that absorbs neutrons with enormous efficiency.

Accident categories, risk analysis, releases and the protective actions planned for the public.

• Beyond design basis accidentalso BDBA, design extension conditions
  An accident more severe than those the plant's safety systems were explicitly designed to handle.
• CDFalso core damage frequency
  Core damage frequency: the estimated likelihood per reactor-year of an accident that damages the core.
• Design basis accidentalso DBA
  A postulated accident that a nuclear plant is explicitly designed to withstand without exceeding set safety limits.
• Emergency classificationalso emergency classification level, ECL
  The graded levels used to declare a nuclear plant emergency, each triggering a defined response.
• EPZalso emergency planning zone
  Emergency planning zone: the area around a nuclear plant where protective actions are pre-planned.
• KIalso potassium iodide, iodine tablets
  Potassium iodide: stable iodine tablets taken to block the thyroid from absorbing radioactive iodine.
• LOCAalso loss of coolant accident
  Loss of coolant accident: a break or leak in the reactor coolant system that lets coolant escape faster than it can be replaced.
• Plumealso radioactive plume, radioactive cloud
  The cloud of radioactive gases and particles carried downwind from a release.
• PSAalso probabilistic safety assessment, PRA
  Probabilistic safety assessment: a systematic model of how accidents could happen and how likely each outcome is.
• SBOalso station blackout
  Station blackout: complete loss of offsite and onsite AC power at a nuclear plant.
• Severe accidentalso core damage accident, core melt accident
  An accident involving significant damage to the reactor core, with possible fuel melting and large releases.
• Shelteringalso shelter in place, sheltering in place
  A protective action in which people stay indoors with doors and windows shut to reduce dose from a passing plume.
• Source term
  The amount, type, timing and chemical form of radioactive material released, or assumed released, in an accident.

Gray, sievert, rem and becquerel, plus the dose concepts behind limits and risk.

• Absorbed dosealso physical dose
  The energy deposited by ionising radiation per unit mass of material, measured in gray.
• Becquerelalso Bq
  The SI unit of radioactivity, equal to one atomic decay per second.
• Collective dosealso collective effective dose
  The sum of individual doses received by a group of people, in person-sievert or person-rem.
• Committed dosealso committed effective dose, CEDE
  The total dose a person will receive over time from radioactive material taken into the body.
• Curiealso Ci
  The non-SI unit of radioactivity, equal to 37 billion decays per second.
• Deterministic effectsalso tissue reactions, non-stochastic effects
  Radiation injuries that appear only above a threshold dose and become more severe as dose increases.
• Dose limitalso annual dose limit, regulatory dose limit
  The maximum dose a worker or member of the public may legally receive from regulated sources in a set period.
• Effective dosealso E, TEDE
  A whole-body dose figure that adds up organ doses weighted by each tissue's sensitivity to radiation risk.
• Equivalent dosealso organ equivalent dose, HT
  Absorbed dose to an organ multiplied by a weighting factor for the type of radiation, measured in sieverts.
• Grayalso Gy
  The SI unit of absorbed dose, equal to one joule of energy deposited per kilogram.
• LNTalso linear no-threshold, linear non-threshold model
  Linear no-threshold model: the assumption that cancer risk rises in direct proportion to dose, with no safe threshold.
• Remalso roentgen equivalent man
  The US customary unit of dose equivalent, equal to one hundredth of a sievert.
• Roentgenalso R
  A unit of exposure that measures how much X or gamma radiation ionises air.
• Sievertalso Sv
  The SI unit for equivalent and effective dose, used to express radiation risk to people.
• Stochastic effectsalso stochastic effect
  Radiation effects, chiefly cancer, whose probability rises with dose but whose severity does not.

ALARA, contamination control, postings, permits and the protective clothing routine.

• ALARAalso as low as reasonably achievable, optimisation
  As low as reasonably achievable: the principle of keeping doses as low as practical, not just below limits.
• Anti-Csalso anti-C's, PCs
  Anti-contamination clothing: the coveralls, hoods, gloves and overshoes worn to keep contamination off workers. Shop talk
• Contaminationalso radioactive contamination, contam
  Radioactive material in a place it is not wanted, such as on surfaces, skin, clothing or inside the body.
• Controlled areaalso RCA, radiologically controlled area
  A designated zone where specific radiation protection rules apply to control exposure and the spread of contamination.
• Decontaminationalso decon, decontam
  Removal of radioactive contamination from people, tools, surfaces or systems to reduce dose and spread.
• Dress outalso dressing out, suit up
  To put on the protective clothing required by an RWP before entering a contaminated area. Shop talk
• Exposurealso radiation exposure
  Being subjected to ionising radiation, from outside the body or from material within it.
• Fleaalso hot particle
  Slang for a hot particle, a tiny speck of highly radioactive material found on clothing or skin. Shop talk
• Herculitealso herc
  Plant slang for the heavy reinforced plastic sheeting laid on floors and over equipment in contaminated work areas. Shop talk
• High radiation areaalso HRA
  A posted area where a person could receive more than 1 mSv (100 mrem) in an hour at 30 cm from a source.
• Hot particlealso discrete radioactive particle, DRP
  A tiny, highly radioactive fragment that can deliver a large localised skin dose if it lands on someone.
• Rad ropealso radiation rope
  Yellow and magenta rope, ribbon or chain used to mark the boundary of a radiological area. Shop talk
• Removable contaminationalso loose contamination, transferable contamination
  Radioactive contamination that can be transferred by wiping or touching, as opposed to fixed contamination.
• RWPalso radiation work permit, rad work permit
  Radiation work permit: the document that sets radiological conditions, controls and dose limits for a specific job.
• Shieldingalso shield
  Material placed between a radiation source and people to absorb radiation and reduce dose rate.
• Step-off padalso step off pad, SOP
  The marked clean spot at the exit of a contaminated area where workers remove protective clothing and step out. Shop talk
• Time, distance, shieldingalso time distance shielding
  The three basic ways to cut external dose: spend less time near a source, stay farther away and put material in between.

Dosimeters, survey meters, friskers and the measurements that track dose and contamination.

• Backgroundalso background radiation, natural background
  The ever-present radiation from natural and other sources that an instrument reads when no source of interest is near.
• Bioassayalso radiobioassay
  Measurement of radioactive material inside the body, or in excreta, to estimate a worker's internal dose.
• Cutie piealso cutie-pie, ion chamber
  Nickname for a handheld ion chamber survey meter, taken from a classic pistol-grip design. Shop talk
• Dosimeteralso badge, personal dosimeter
  A device worn by a person to measure the radiation dose they receive.
• EPDalso electronic personal dosimeter, ED
  Electronic personal dosimeter: a worn device that shows dose and dose rate live and alarms at set points.
• Frisker
  The count-rate meter and probe kept at exits for checking hands, feet and clothing for contamination. Shop talk
• Friskingalso frisk
  Slowly scanning a person or object with a contamination probe to find radioactive material before it leaves an area.
• Pancake probealso pancake, GM pancake
  A flat, wide-window Geiger-Mueller detector used for frisking because it picks up beta and alpha contamination well. Shop talk
• PCMalso personnel contamination monitor, whole-body contamination monitor
  Personnel contamination monitor: a walk-in booth that scans the whole body for contamination at exits.
• Pencilalso pencil dosimeter, pocket dosimeter
  A pocket ion chamber dosimeter shaped like a pen, read by looking through it at a light. Shop talk
• Smearalso swipe, wipe
  A wipe of a surface with filter paper, counted to measure how much removable contamination is present.
• Survey meteralso survey instrument
  A portable instrument used to measure radiation dose rates or detect contamination in the field.
• TLDalso thermoluminescent dosimeter, TLD badge
  Thermoluminescent dosimeter: a passive badge whose crystals store radiation energy and release it as light when heated.

Spent fuel, radwaste, sources, half-lives and the verification that keeps material accounted for.

• Activationalso neutron activation
  The process by which neutrons make stable materials radioactive, creating isotopes such as cobalt-60.
• Clearancealso free release, unconditional release
  The release of materials with very low radioactivity from regulatory control, so they can be reused or disposed of normally.
• Criticality safetyalso nuclear criticality safety, NCS
  The discipline of preventing an accidental chain reaction wherever fissile material is handled outside a reactor.
• Dry cask storagealso dry storage, dry cask
  Storage of cooled spent fuel in sealed steel canisters inside concrete or steel casks, cooled passively by air.
• Half-lifealso half life, T1/2
  The time it takes for half the atoms of a radioactive isotope to decay, a fixed value for each nuclide.
• Orphan source
  A radioactive source that has escaped regulatory control because it was lost, stolen, abandoned or never licensed.
• Pigalso lead pig, source pig
  A heavy lead or tungsten container used to store or carry a radioactive source or sample. Shop talk
• Radwastealso rad waste, radioactive waste
  Radioactive waste produced by nuclear facilities, and the plant department that processes and ships it.
• Safeguardsalso nuclear safeguards
  The verification system that checks nuclear material is not diverted from peaceful use to weapons.
• Sealed sourcealso sealed radioactive source
  Radioactive material permanently sealed in a capsule so it cannot escape under normal use.
• Significant quantityalso SQ
  The rough amount of nuclear material judged enough to make one nuclear explosive device, used as a safeguards yardstick.
• Spent fuel poolalso SFP, fuel pool
  A deep, water-filled pool at a reactor where used fuel is stored to cool and to shield its radiation.

Outage and RP-floor talk, from crud and hot spots to glow boys and jumpers.

• Bowlalso channel head, SG bowl
  The steam generator channel head, the hemispherical space under the tubesheet where reactor coolant enters and leaves. Shop talk
• Burned outalso dosed out, burnt out
  Having used up one's allowed dose for the period, so a worker cannot do more radiological work. Shop talk
• Crudalso corrosion products, activated corrosion products
  Corrosion products that deposit on fuel and in reactor piping, become radioactive and drive most plant dose. Shop talk
• Dose extension
  Approval for a worker to exceed the plant's administrative dose level, still below the legal limit. Shop talk
• Glow boyalso nuclear nomad
  Slang for an itinerant contract worker who travels from plant to plant working refuelling outages. Shop talk
• Hotalso rad-hot, dirty
  Radioactive, contaminated or giving a high dose rate, in plant speech; the opposite of clean. Shop talk
• Hot spotalso hotspot
  A small spot on piping or equipment with a much higher dose rate than its surroundings. Shop talk
• Hot tool cribalso hot tool room, hot tool issue
  A tool room inside the controlled area that stores and issues contaminated tools for reuse on radiological jobs. Shop talk
• Jumperalso steam generator jumper, SG jumper
  A worker who makes brief entries into very high radiation spaces, absorbing a large dose allowance in minutes. Shop talk
• Nukealso Navy nuke
  Slang for someone trained to operate or maintain nuclear reactors, especially a naval nuclear sailor. Shop talk
• PCEalso personnel contamination event, personnel contamination
  Personnel contamination event: contamination found on a worker's skin or personal clothing above a set threshold. Shop talk
• Pick up dosealso take dose
  To receive radiation dose while doing work, as in picking up 20 millirem on a job. Shop talk
• Rad workeralso radiation worker, radworker
  A person trained and qualified to work unescorted in radiologically controlled areas. Shop talk
• RadConalso radiological controls, Rad Con
  Radiological controls: the radiation protection function, its rules and its technicians, in Navy and government usage. Shop talk
• RP techalso HP tech, health physics technician
  A radiation protection technician who surveys areas, covers jobs and enforces radiological controls. Shop talk
• Shine
  Radiation reaching a spot from a nearby source, through a gap or by scattering, rather than from what is being worked on. Shop talk
• Shotalso radiography shot, RT shot
  A single industrial radiography exposure, used to x-ray a weld with a gamma source or X-ray tube. Shop talk

Frequently asked questions

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