Intakes of thorium while using thoriated tungsten electrodes for TIG welding

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.