Radiation Protection in Practice

Before we go any further, you need to understand the single most important distinction in radiation protection. It's a distinction that determines everything — from how dangerous a situation is, to what protective equipment you need, to whether you can simply walk away from a hazard.

Why This Matters

The Danger Hierarchy

1. External irradiation — Least dangerous. Walk away, problem solved.
2. External contamination — More dangerous. Must be removed before it spreads or gets inside you.
3. Internal contamination — Most dangerous. Radioactive material inside your body, irradiating your organs continuously from within.

Real-World Application

This is why nuclear facilities have two completely different monitoring systems:

• Radiation monitors measure dose rates in areas — how much radiation is hitting you per hour in a location. This addresses irradiation.
• Contamination monitors check for radioactive particles on surfaces, clothing, and skin. This addresses contamination.

Before leaving a controlled area, workers pass through both types of monitoring. You might have received zero radiation dose but still be contaminated — or vice versa.

You might think radiation exposure only happens to people who work in the nuclear industry. But the reality is that everyone — your family, your neighbours, your pets — receives radiation dose every single day, from completely natural sources.

The average person in the UK receives about 2.7 mSv per year from background radiation. That's not from nuclear power plants or medical procedures — it's just from existing.

What Does a Sievert Actually Measure?

In Module 3, you learned that radiation damages DNA — breaking the strands, potentially causing mutations or cell death. But not all radiation causes the same amount of DNA damage.

Think of it this way:

The same "amount" of radiation (measured in energy) causes very different levels of damage depending on the type. The sievert accounts for this.

So when we say someone received "1 mSv," we're not just counting radiation — we're measuring how much biological harm that radiation could cause, adjusted for how damaging that particular type is.

This is why alpha emitters are so dangerous if inhaled or swallowed. From outside your body, alpha particles can't even penetrate your skin — harmless. But inside your lungs? That ×20 damage factor applies to every cell they hit.

Where Does Background Radiation Come From?

UK Average Annual Background Radiation: ~2.7 mSv

The Radon Factor

Radon is a colourless, odourless radioactive gas that seeps from the ground. It's produced by the natural decay of uranium in rocks and soil. It accounts for half of our annual radiation dose — more than all other sources combined.

But here's the thing: radon levels vary dramatically depending on where you live.

A Surprising Comparison

Here's something that surprises most people:

Average annual dose for UK nuclear workers: <1 mSv
Average annual dose for airline crew: 2-3 mSv

That's right — pilots and flight attendants typically receive more radiation dose than nuclear power plant workers. Why? Because at cruising altitude (30,000-40,000 feet), there's less atmosphere shielding you from cosmic rays. Long-haul crews flying polar routes can receive up to 6 mSv per year.

This doesn't mean flying is dangerous — it just shows that radiation exposure is a normal part of life, and that the nuclear industry manages it exceptionally well.

Now we come to the philosophy that underpins all radiation protection in the UK. It's a concept that sounds simple but contains crucial subtlety: ALARP — As Low As Reasonably Practicable.

Notice the word is "practicable," not "possible." This distinction matters enormously.

Why Not "As Low As Possible"?

Because "as low as possible" would be impractical and counterproductive.

If your only goal was minimising radiation dose absolutely, you'd:

• Never have medical X-rays (even when they'd save your life)
• Never fly anywhere
• Never live in Cornwall
• Spend unlimited money on shielding even when doses are already negligible

"As low as possible" ignores context. "As low as reasonably practicable" embraces it.

The Legal Basis

ALARP isn't just good practice — it's law in the UK, and has been since 1974.

The Health and Safety at Work Act 1974 requires employers to ensure the health and safety of employees "so far as is reasonably practicable." This applies to all hazards — from scaffolding to solvents to radiation.

For radiation work specifically, the Ionising Radiations Regulations 2017 (IRR17) require employers to:

"...take all necessary steps to restrict as far as is reasonably practicable the extent to which employees and other persons are exposed to ionising radiation."

The key legal test comes from a 1949 court case (Edwards v National Coal Board), which established that a measure is "reasonably practicable" unless the cost of implementing it is grossly disproportionate to the benefit gained.

Note: not just "disproportionate" — grossly disproportionate. The law is weighted in favour of safety.

The ALARP Question

When considering whether to implement a safety measure, ask:

"Is the sacrifice (in cost, time, or effort) grossly disproportionate to the risk reduction achieved?"

If YES → The measure is not reasonably practicable
If NO → The measure should be implemented

ALARP in Action: An Example

Scenario: A routine maintenance task requires workers to enter an area with a dose rate of 2 µSv/hour. The task takes 4 hours.

Without any additional measures:
Dose = 2 µSv/h × 4 hours = 8 µSv per worker

ALARP Analysis:
Option A is clearly reasonably practicable — modest cost, significant dose reduction.
Option B is likely grossly disproportionate — huge cost for minimal additional benefit when doses are already very low.

The ALARP solution: Implement Option A.

Important Clarification

While ALARP provides the philosophy, dose limits provide the hard legal boundaries set by the Ionising Radiations Regulations 2017 (IRR17). But remember: dose limits are ceilings, not targets.

So far we've covered the philosophy (ALARP) and the rules (dose limits). Now let's get practical. When you're working in an area with radiation, you have three fundamental tools to reduce your dose:

1. Time — The Simple One

Radiation dose accumulates like rain filling a bucket. The longer you stand in the rain, the wetter you get. The maths is straightforward:

Practical applications:

• Pre-plan work — rehearse complex tasks in non-radiation areas first
• Rotate workers — share the dose across a team
• Prepare everything — have all tools ready before entering the area

2. Distance — The Powerful One

This is where physics gives you a massive advantage. The Inverse Square Law means that doubling your distance doesn't halve your dose — it quarters it.

3. Shielding — The Material One

Put material between you and the source. But here's the critical part: different radiation types need different shielding.

Half-Value Layer (HVL)

Unlike alpha and beta, gamma radiation doesn't just stop — it attenuates. Each layer of shielding reduces the intensity, but some always gets through.

The HVL depends on the material:

• Lead: ~6 mm — dense, very effective, but heavy and toxic
• Steel: ~21 mm — common in construction, structural
• Concrete: ~49 mm — cheap, good for permanent installations

The maths is simple: after n half-value layers, intensity = 100% ÷ 2ⁿ

So: 1 HVL = 50% | 2 HVL = 25% | 3 HVL = 12.5% | 7 HVL = less than 1%

How do we know if ALARP is being achieved? How do we verify workers stay within dose limits? The answer is monitoring — both individuals (dosimetry) and areas.

You can't manage what you don't measure.

Types of Personal Dosimeters

Dose Records

Every radiation worker's dose history is recorded and kept:

• By the employer
• By an Approved Dosimetry Service (ADS)
• In the Central Index of Dose Information (CIDI) maintained by HSE

Records kept for at least 50 years. Workers can request their own dose history at any time.

Area Monitoring

It's not just people who are monitored — areas are too:

• Fixed Area Monitors — Permanently installed, continuous display, alarm capability
• Portable Survey Meters — Handheld instruments for checking dose rates
• Contamination Monitors — Detect radioactive material on surfaces or skin

Investigation Levels

This tiered approach catches problems early, long before limits are approached.

All the principles we've covered — ALARP, dose limits, Time/Distance/Shielding, monitoring — come together in the practical organisation of radiation workplaces. The UK uses a system of designated areas to ensure the right level of control is applied in the right places.

Coming Up in Module 8

Regulation & the UK Framework

Now that you understand how radiation protection works in practice, Module 8 examines who oversees it all. You'll learn about the Office for Nuclear Regulation (ONR), the 36 licence conditions, how sites are licensed and inspected, the role of the Safety Case, and WANO's Ten Traits of healthy nuclear safety culture.

From personal protection to organisational governance — the regulatory framework that keeps the UK nuclear industry safe.