Thoriated tungsten welding rods contain 1-4% radioactive thorium dioxide. Grinding releases 298 mBq/m³ of thorium-228. Welding fume concentration: 1-8 mBq/m³ (Th-228), <3 Bq/m³ (Rn-220). Annual dose to welders: 55 mrem – 2 rem (bone), <100 mrem effective. Minimize exposure: ventilation, PPE, hygiene. Exempt quantity for disposal: 1 μCi/rod.
In this article, we’ll dive into the specifics of thoriated tungsten electrodes, which contain radioactive thorium, and provide a detailed guide on how to handle them safely.
Understanding Thoriated Tungsten Electrodes
Thoriated tungsten electrodes are commonly used in welding due to their excellent electron emission and high-temperature stability. These electrodes typically contain 1-4% thorium dioxide (ThO2) by weight, with the most common types being:
- 1% ThO2 (color coded yellow): Offers good arc starting and stability, suitable for low-current applications (up to 150A).
- 2% ThO2 (color coded red): Provides excellent arc starting and stability, ideal for high-current applications (up to 300A).
The thorium content enhances the electrode’s performance by lowering the work function, which is the energy required to emit an electron from the surface. This results in easier arc starting, better arc stability, and longer electrode life compared to pure tungsten electrodes.
Radioactivity of Thorium-232
Thorium-232, the isotope present in thoriated tungsten electrodes, is a low-level radioactive material. It primarily emits alpha particles, along with some beta and gamma radiation. The specific activity of thorium-232 is 4,060 Bq/g, which means that one gram of pure thorium-232 undergoes 4,060 nuclear disintegrations per second.
Alpha particles have a very short range in air (a few centimeters) and can be easily stopped by a sheet of paper or the outer layer of skin. However, if inhaled or ingested, alpha particles can cause significant damage to internal organs and tissues.
Radiological Concerns and Exposure
The main radiological concern with thoriated tungsten electrodes is internal exposure from inhaling or ingesting thorium dust particles. This can occur during the grinding process when preparing the electrodes for use.
Grinding Thoriated Tungsten Electrodes
To achieve the desired electrode shape and tip geometry, welders often grind thoriated tungsten electrodes using a dedicated tungsten grinder or a bench grinder with a diamond wheel. During this process, thorium dust particles can become airborne and pose an inhalation hazard.
To minimize exposure during grinding:
- Use a grinder with a dust collection system: A grinder equipped with a HEPA-filtered dust collector can capture the majority of thorium dust particles generated during grinding.
- Grind electrodes in a well-ventilated area: Perform grinding operations in a designated area with adequate ventilation to prevent the accumulation of thorium dust.
- Use wet grinding techniques: Wet grinding, using a coolant or water, can help suppress dust generation and reduce airborne thorium concentrations.
- Wear appropriate PPE: Use a properly fitted respirator with a HEPA filter, safety glasses, and protective clothing to minimize exposure to thorium dust.
Airborne Thorium Concentrations
Studies have measured the airborne thorium concentrations during welding and grinding of thoriated electrodes:
| Activity | Thorium-228 Concentration |
|---|---|
| Grinding | 298 mBq/m³ |
| AC Welding | 1-8 mBq/m³ |
| Radon-220 (Thoron Gas) | <3-3 Bq/m³ |
These concentrations are relatively low but still warrant proper ventilation and protective equipment to minimize exposure.
Radiation Dose Estimates
The radiation dose received by welders using thoriated tungsten electrodes has been estimated in various studies:
- Full-time welders: 55 mrem to 2 rem bone dose per year of exposure
- Non-full-time welders: 1.3-575 mrem bone dose per year of exposure
- Average annual effective dose: <100 mrem (less than 0.3% of the occupational limit)
To put these doses in perspective, the average annual background radiation dose in the United States is around 620 mrem.
Safe Handling and Disposal of Thoriated Tungsten Electrodes
As a DIY welder, it’s essential to follow proper safety procedures when working with thoriated tungsten electrodes to minimize exposure and potential health risks.
Storage and Handling
- Store electrodes in a labeled container: Keep thoriated tungsten electrodes in a clearly labeled, sealed container to prevent accidental exposure and cross-contamination.
- Avoid physical contact: Use pliers or tongs to handle thoriated tungsten electrodes, avoiding direct skin contact.
- Designate a storage area: Store thoriated tungsten electrodes in a dedicated area away from food, drinks, and personal items to prevent accidental ingestion or contamination.
Welding with Thoriated Tungsten Electrodes
- Use the correct welding technique: Employ the appropriate welding technique for your application, such as Gas Tungsten Arc Welding (GTAW) or Plasma Arc Welding (PAW), to ensure optimal electrode performance and minimize electrode consumption.
- Adjust welding parameters: Set the appropriate welding current, shielding gas flow rate, and electrode tip geometry based on the electrode diameter, material thickness, and joint configuration to achieve a stable arc and reduce electrode wear.
- Maintain proper arc length: Keep the arc length consistent and as short as possible to minimize electrode consumption and the generation of welding fumes.
- Avoid electrode overheating: Prevent overheating of the electrode by using the correct welding current and avoid excessively long arc times, which can cause the electrode to overheat and release more thorium particles.
Personal Protective Equipment (PPE)
When working with thoriated tungsten electrodes, it’s crucial to use appropriate PPE:
- Respiratory protection: Use a properly fitted respirator with a high-efficiency particulate air (HEPA) filter to prevent inhalation of thorium dust particles during grinding.
- Eye protection: Wear safety glasses or a welding helmet with the appropriate shade to protect your eyes from radiation and welding sparks.
- Protective clothing: Wear long-sleeved clothing and gloves to minimize skin contact with thorium dust.
Proper Disposal
When disposing of used thoriated tungsten electrodes, they can generally be treated as normal waste. The exempt quantity for disposal is quite high, at 1 microcurie (37 kBq) per electrode. However, it’s essential to check with your local regulations for specific disposal guidelines.
If you have a large quantity of used electrodes or are unsure about disposal requirements, contact a licensed radioactive waste disposal company for guidance. They can provide you with the necessary containers, labels, and shipping instructions to ensure safe and compliant disposal.
Conclusion
While thoriated tungsten electrodes do contain radioactive thorium, the actual exposure and dose from normal welding use are relatively low. By following proper safety procedures, using appropriate PPE, and ensuring adequate ventilation, DIY welders can minimize the risks associated with these electrodes.
References:
The Measurement of Released Radionuclides during TIG-Welding and Grinding
Welding Safety & Welding Hazards
Estimated radiation doses from thorium
Thorium Containing Welding Rod
Debarghya Roy, an Engineering Architect with over 12 years of experience, works with a Fortune 5 company and is an active open source contributor. Skilled in a wide array of technologies including Java, C#, Python, and various automation and performance engineering tools, he also has expertise in Security Automation, RPA, and Back End Development using SpringBoot, Kafka, and ELK stack. Based in Bangalore, India, Debarghya is passionate about blogging, music, and advocates for “Education for All,” which led to the founding of LambdaGeeks.