FULLY ENCLOSED VACUUM PUMP FOR RADIOACTIVE MEDIA

Fully enclosed vacuum pump for radioactive media

By Richard Horler and Andrew Cobbett, Edwards Limited,

UK

Nuclear fusion reactors use radioactive substances such as tritium and deuterium, the radioactive isotopes of hydrogen.

The low pressures required for the nuclear fusion process are achieved, in part, using high vacuum pumps such as turbomolecular pumps.

To enable the turbomolecular pumps to safely pump the potentially radioactive fluids all connections on and inside the pump must be adequately sealed to prevent leakage to the external atmosphere.

As tritium will quickly degrade any elastomer seals on a turbomolecular pump, the gas path must be sealed from the atmosphere using metal seals. Commonly, the metal seals used are of a face seal design.

To redesign or convert pumps that use  a fluoroelastomer piston seal arrangement to instead use a metal piston seal arrangement would require major pump changes and extensive design modifications.

The current alternative, is to redesign the pump to incorporate only ‘face’ seals thereby enabling metal seals to be used throughout. However, metal seals are expensive and if a pump needs to be redesigned it would be costly to produce.

The invention proposed herein is to enclose the entire pump within a metal shroud, or envelope, and seal the enclosure with metal face seals. The novel step is that the whole pump including the pumping mechanism, motor, bearings, drive and electronics is all encased by the envelope and subjected to the sub-atmospheric pressure process environment and hermetically sealed from the external atmosphere. 

Thus use of fluoro-elastomers is minimised throughout the pump by removing seals from...