Bearings and gears for operation in inert gases. Project DRAGON

It is known that friction and wear of materials are influenced by the surrounding atmosphere. Often this atmosphere has a beneficial influence, for instance, if metal oxides of low shear strength are formed at the points of contact, leading to a reduction in coefficient of friction and wear. In the High Temperature Gas Cooled Reactor Dragon, helium of a very high purity is used as a coolant. The bearings and gears of various mechanisms such as the fuel element charge-discharge machine and the control rod drive mechanism run inside the pressure vessel. Some are exposed to high temperatures and to appreciable levels of nuclear radiation. Inert helium of high purity does not permit appreciable chemical reactions to take place on the rubbing surfaces. With certain rubbing combinations this will lead to high friction and wear. The main object of our tests was to find hearings and gears which can work satisfactorily under these conditions, rather than to do basic research. For this reason a programme was set up to cover tests on plain bearings, rolling type bearings and gears.