Radiation Protection Calculations for Shielded Enclosures Using Radioactive Sources in Non-Destructive Testing: Methodologies, Regulations, and Industrial Applications

milarepa Delasag
3 sept.
3 min de lecture

Introduction

Non-destructive testing (NDT) using ionising radiation is a fundamental technique in industries with high technical requirements, such as defence, aerospace, space, and automotive. The use of radioactive sources such as iridium-192 (Ir-192), or X-ray generators, to inspect metallic or composite components necessitates the design and construction of purpose-built facilities that strictly comply with radiation protection standards. These installations, known as shielded enclosures or “casemates,” must be engineered with utmost precision to ensure the safety of personnel and the surrounding environment.

1. Radioactive Sources in NDT: Radiological Characteristics

The most commonly employed sources in industrial radiography include:

Iridium-192 (Ir-192): a high-energy gamma emitter, primarily used for radiographing thick metallic components.
Selenium-75 (Se-75): an alternative to Ir-192 for thinner materials, with lower gamma energy emissions.
X-ray generators: used across a range of applications depending on available energy (typically from 100 kV to 450 kV).

These ionising radiations pose significant biological risks—both stochastic and deterministic—thus requiring precise shielding calculations to limit exposure to acceptable levels.

2. Radiation Protection Calculations: A Critical Phase

a. Foundational Principles

Shielding calculations rely on the physics of radiation attenuation through materials. Key parameters include:

Source activity (expressed in becquerels or curies)
Source-to-shield distance
Use factor (exposure duration and frequency)
Occupancy factor of adjacent zones
Shielding materials (e.g., concrete, lead, steel)
Regulatory dose limits (1 mSv/year for the general public, 20 mSv/year for occupationally exposed workers)

b. Methodology

Calculations are typically performed in accordance with the guidelines issued by the French Nuclear Safety Authority (ASN), as well as international standards such as ISO 4037, ANSI N43, and the French NF C15-160.

Transmission coefficients—particularly the Tenth Value Layer (TVL)—are used to determine the required thickness of shielding materials to attenuate radiation to acceptable levels.

Specialised software such as MicroShield, VARSKIN, or Monte Carlo simulation tools like MCNP are often employed to model complex geometries and exposure scenarios with high precision.

3. Design and Shielding of Casemates

Casemates are fully shielded radiographic enclosures, generally constructed using high-density concrete or lead. They must meet stringent design criteria, including:

Radiation-tight structure
Secure access with interlock systems
Regulatory-compliant warning lights and signage
Controlled ventilation
Dosimetric monitoring inside and outside the enclosure

Design plans must be validated by a qualified radiation protection consultancy and approved by regulatory authorities such as the ASN in France.

4. Radiation Protection Regulations and Compliance

In accordance with European Directive 2013/59/Euratom and French national regulations, all installations involving ionising radiation must include:

A comprehensive radiological risk assessment
Regulatory zoning of the workplace
Dosimetric monitoring of exposed workers (including TLDs and operational dosimeters)
Radiation protection training for personnel (e.g., Certified Radiation Protection Officer or Supervisor training)
Enhanced medical surveillance of exposed workers
Clearly defined emergency procedures

5. The Role of a Specialised Consultancy: The Example of Radio-Protect

Given the technical complexity and regulatory constraints of casemate design, the involvement of a qualified radiation protection consultancy is essential. Firms such as Radio-Protect offer:

Shielding dimensioning studies
Workplace zoning and dose mapping
Assistance with regulatory declarations to ASN
Supervision of shielding construction works
Final verification through ambient dosimetry assessments

Partnering with an accredited firm ensures not only regulatory compliance, but also optimal worker safety and long-term operational continuity.

6. Industries Concerned

Shielded radiographic facilities and NDT using ionising radiation are widely employed in:

Aerospace industry: inspection of critical parts such as wings and turbine blades
Defence sector: control of munitions, armour, and ballistic components
Space industry: verification of composite materials and welds
Automotive sector: including manufacturers such as Stellantis and Renault, for quality control of engine and chassis components
Nuclear and energy sectors: weld inspections on pipelines, exchangers, and pressure vessels
Petrochemical industry: inspection of pipelines and high-pressure structures

Conclusion

Radiation protection calculations for shielded enclosures in industrial NDT are a vital component of risk management when working with ionising radiation. Rigorous design, strict regulatory compliance, and proper operator training ensure a safe working environment and uninterrupted industrial operations. Partnering with a certified consultancy such as Radio-Protect provides the expertise required to meet these high standards across sectors where quality and safety are paramount.