Intakes of Thorium While Using Thoriated Tungsten Electrodes for TIG Welding

Abstract

Thoriated electrodes are used in TIG welding. TIG welders, along with persons who grind thoriated electrodes and persons located near relevant welding and grinding sites, might be at risk of thorium intake. The isotopes of radiological relevance are 232Th, 230Th, and 228Th. The studies described in the literature do not provide a consistent picture of the actual hazards, and changes in European and German radiological protection laws have now made it necessary to determine the risks. To accomplish this, a field test was conducted under real working conditions in 26 different welding shops. The airborne activity generated through welding, and through grinding of electrodes, was measured using personal air samplers. Stationary samplers were also used. The filters' samples were evaluated by means of direct alpha spectrometry with proportional counting and by means of gamma spectrometry following neutron activation. The results clearly showed that considerable intake can occur during both alternating-current welding and electrode grinding, if no suction systems are used. The range of 232Th intakes to welders were estimated from 0.1 Bq y(-1) to 144 Bq y(-1) during welding and from 0.02 Bq y(-1) to 30.2 Bq y(-1) during grinding. In 6 of the 26 cases the recent annual limit on intake derived from the most recent ICRP publications was exceeded--in the worst case it was exceeded by a factor of 10--if it is assumed that the persons studied were not exposed workers (not routinely monitored for radiation exposure). When the significantly more restrictive German limits are applied, the amounts by which the limits were exceeded were even greater. Because many qualified welders have very long careers, the risks can thus be considerable. The paper also discusses parameters that influence exposure, and it presents a catalogue of recommended measures for dosage reduction.

Thorium-232 Exposure during Tungsten Inert Gas Arc Welding and Electrode Sharpening.

“…The reason for this is that TIG/Al welding is done with an alternating current and that increases the consumption of the electrode compared to direct current welding 6) . It has also been reported that the airborne 232 Th concentration during alternative current welding was higher than during direct current welding 13) . The airborne radioactivity concentration of 232 Th during electrode sharpening reported by Vinzents et al was 8 times that found in the present study, and 53 times the DAC (3 × 10 -2 Bq/ m 3 ) 9) .…”

“…The 232 Th radioactivity concentration during TIG welding with alternating current reported by Ludwig was 2.4 times that found in TIG/Al welding of the present study, and close to the DAC level 12) . The difference in the airborne 232 Th radioactivity concentrations between Vinzents 9) , Ludweig 13) and the present study would be derived from the differences in the work space, welding devices including the electrode-sharpening grinder, electric current and welding materials, as well as the installation of a local exhaust ventilation system.…”

“…In previous reports, airborne 232 Th concentration during electrode sharpening were reported by Vinzents 9) , Crim 10) and Jankovic 11) , which were < 0.3 to 53.3 times the DAC provided for in the Code of Federal Regulations 12) . Airborne 232 Th concentration during welding were reported by Jankovic 11) and Ludwig 13) as 0.001 to 0.87 times the DAC. Thus, the documented levels of 232 Th during these operations are not consistent.…”

Occupational Thorium Exposure or Self-Poisoning?

“…Few studies led to assess Thorium levels, while TIG soldering, conclude that internal radiation doses were less than an annual level of intake [4,6]. However it doesn't exclude the occurrence of toxic Thorium levels under different welding conditions.…”

“…Th and 228 Ra is usually below 1mSv for a full-time TIG welder [4]. Electrode consumption during welding was primarily the result of tip sharpening.…”