Badges, friskers and step-off pads: the radiation protection words every visitor hears

First morning of a refuelling outage, and the visitor in the borrowed hard hat has been handed more acronyms than tools. An RP tech clips a badge to his chest pocket, hands him a second, beeping one, and runs through the rules at speed. "You're on the general RWP. Don't cross any rad rope. If that thing alarms, back out and find me. On the way out, frisk at the step-off pad and walk through the PCM." It sounds like a lot. It is a small vocabulary used with great consistency, and every word in it does one of two jobs: keep dose low, or keep radioactive material where it belongs.

Getting in

Past the security fence, a single access point leads into the controlled area, where radiation protection rules apply. A trained rad worker can go in alone; a visitor goes in escorted. The people who run the rules are the RP techs, short for radiation protection, though anyone who learned the trade in the Navy calls the whole function RadCon.

Everyone inside wears a dosimeter, usually two. The quiet one is the TLD, a passive badge whose crystals store the dose and give it up as light when the lab heats them later. Its reading is the official record. The noisy one is the EPD, an electronic dosimeter that shows dose and dose rate live and chirps when either crosses a set point. Emergency kits, and jobs without electronic dosimeters, carry the pencil, a pocket ion chamber read by holding it up to the light.

Before any job, workers sign onto an RWP, the radiation work permit that spells out the conditions, the protective clothing and the dose allowed for that task. The thinking behind all of it is ALARA: as low as reasonably achievable. Staying under the limit is the floor, not the goal.

Counting dose

In US plants dose is counted in rem, or more often millirem; most of the world uses the sievert, and one sievert is a hundred rem. Workers talk about dose like money. You pick up dose on a job, as in "I picked up eight millirem changing that filter." Every plant sets an administrative level well under the legal dose limit, and getting past it takes a dose extension signed by management. Use up your allowance and you are burned out, done with radiological work until the next period.

The instrument that maps the dose rate is the survey meter; any handheld ion chamber gets called a cutie pie, after a classic pistol-grip model. Even in a clean office it reads something, because background radiation is everywhere. Inside the plant, a posted high radiation area, where the dose rate could top 100 millirem in an hour at 30 centimeters, takes a briefing and an alarming dosimeter or constant RP coverage, and the worst of them sit behind locked doors. A hot spot is one small point on a pipe reading far above its surroundings, and shine is radiation reaching you from somewhere other than the thing you are working on, through a gap or around a corner.

The tools for cutting dose fit in three words: time, distance, shielding. Work fast, stand back, and put something heavy in between, which is why lead blankets hang over the worst piping during outages. At the extreme end is the jumper, a worker who dives into a very high dose space such as a steam generator bowl for a few minutes and comes out having used up a big slice of the allowance. The itinerant contract crews who follow the outage season from plant to plant, pipefitters, decon workers and RP techs among them, are known as glow boys.

Through you, or on you

This is the distinction newcomers miss most. External exposure means radiation passing through you from a source outside your body. It leaves nothing behind, and a person exposed that way does not become radioactive. Contamination is radioactive material in the wrong place: dust on a boot, a film on a glove, a speck on a collar. Contamination travels, and almost every ritual at the exit exists to stop it.

The material comes mostly from crud, corrosion products that circulate through the reactor coolant, pick up activation in the core and plate out on pipes and valves. When something is radioactive or contaminated, the plant word is hot, as in hot tools, hot side and the hot tool crib that issues contaminated tools for reuse.

The RP tech measures loose contamination with a smear, a wipe of filter paper that gets counted in the lab. Removable contamination is the kind a smear picks up, and the kind that ends up on people.

Dressing out

Entering a contaminated area means you dress out in anti-Cs: coveralls, hood, gloves taped at the wrist, rubber overshoes, sometimes two layers of each. Floors and equipment in the work area are covered in herculite, heavy plastic sheeting that keeps the mess off the concrete. The boundary is marked with yellow and magenta rad rope.

Getting out is the skill. At the step-off pad, the clean spot at the edge of the area, you peel off the anti-Cs in a set order, outside layers first, rolling everything inward, and step onto the pad one clean foot at a time. Do it in the wrong order and the outside of your gloves touches the inside of your coveralls, and the next step will tell on you.

Leaving clean

That next step is the frisker: a count-rate meter with a flat, wide pancake probe, kept at every exit. Frisking means moving the probe slowly, close to the skin, over hands, feet, face and clothing, listening for the clicks to speed up. Rushing it misses things, and the RP techs notice who rushes.

At the final exit stands the PCM, a walk-in booth that scans the whole body at once. If it alarms, the RP tech surveys you and finds the spot. Contamination on skin or personal clothing above the plant's threshold makes it a PCE, a personnel contamination event, and starts decontamination, which mostly means soap, water and tape. The worst find is a hot particle, known on the floor as a flea, a speck small enough to miss by eye and active enough to give a real skin dose if it stays put.

Five words to learn first

• RWP: the permit that tells you what you can do, where, and in what clothing.
• EPD: the electronic dosimeter that alarms. When it does, back out.
• Rad rope: yellow and magenta means do not cross without permission.
• Step-off pad: where contamination is supposed to stay behind.
• Frisk: the slow scan you do every time you leave, no matter how clean you feel.

Learn those five and the morning briefing stops sounding like a foreign language and starts sounding like what it is: a short list of habits that keep the plant's radioactive material inside the plant.