Posted By John Donaldson
HSE have published information on this matter Thorium is both toxic and radioactive

The reference is:

http://www.hse.gov.uk/fod/infodocs/564_6r.pdf

You will also have to consider if you will be covered by the Radioactive Substances Act 1993 and it may be worth contacting your local Environment Agency Office.

Posted By John Murgatroyd
Thorium (Th) is slightly radioactive with a long half life and emits mainly alpha particles, but occasionally some beta and gamma radiation is emitted. Alpha particles cannot penetrate skin or even paper. However, they are harmful if released inside the digestive tract, or inside the lungs, where they act as a carcinogen.
Thorium oxide is, therefore, a low level radioactive material which may give rise to both a small external radiation hazard and an internal hazard from ingestion or inhalation. The external hazard estimated for a welder holding an electrode for a whole year is a very small fraction of the maximum permissible radiation dose and it is concluded that the external radiation hazard is likely to be negligible.

There is almost no release of radioactive material during arcing. However, to achieve maximum arc stability the electrode tip is ground to a conical point before use. This shape is maintained during use by regular regrinding. During the grinding process, particles of tungsten may be produced with thoria on the surface. It is these dust particles that create the major hazard, as they may be inhaled, and the thoria may release alpha particles from the surface.

In a review of air sampling measurements carried out during grinding it was concluded that during grinding air concentrations could approach or even exceed concentrations at which it would be necessary to consider designating the area as a controlled area as defined by the Ionising Radiation Regulations 1999.

However, the risk of cancer in TIG welders due to thoria exposure is very low, since the exposure times to individuals are invariably small. The Danish Welding Institute estimates that of 1200 full-time TIG welders, a cancer incidence of 0-3 may occur during a thirty year working life. While this figure is considered acceptable, the Danish Welding Institute has recommended that thoriated tungsten be phased out in Denmark since non-radioactive alternatives are available.

Safe working conditions
Storage
It is recommended that thoriated electrodes are stored in steel boxes, clearly labelled with the radiation trefoil. When stored in closed boxes, there is no significant hazard in handling and storage.
Small numbers (1 day's supply) of electrodes can be handled by welders safely without any special precautions.

Preparation/Grinding
Grinding creates the greatest hazard as the exposed tungsten/thoria area is greatly increased and fine particles of potentially radioactive dust are released into the atmosphere.
It is recommended that a dedicated grindstone with local dust extraction is used, and a simple filter mask is worn unless the number of electrodes used is very small (less than about 20 per year). If the grinding wheel is not fitted with a protective viewing screen, eye protection should be worn. The air extract from the grindstone should be arranged so that the particles are deposited into a substantial disposable bag.

A safe method of collecting and handling the dust from the collection unit must be used to minimise release to the atmosphere (for example, it could be placed in a sealed paper/plastic bag.)

The area round the grinding wheels should be cleaned daily with a vacuum cleaner to remove dust particles. If a high efficiency vacuum cleaner is not available, then the material should be damped down to minimise dust.

Workers should be encouraged to wash their hands before using the toilet facilities, and before taking work breaks, and for this reason the washing facilities should be close to the work areas.

Posted By John Murgatroyd
All welding causes cancer.
Some methods are worse than others.
Take your lick.