Other gases like argon and nitrogen may be used, but in most cases air is
more effective at decontaminating the surfaces. Ambient air entering the
purged volume contains several thousand parts per million of normal water
along with the nitrogen and oxygen. Some of the tritium and HTO on the
internal surfaces of the purged volume exchanges with the hydrogen and H 20
contained in the ambient air and is pumped out during the next purge cycle.
This evacuate/backfill cycle is repeated from 3 to 6 times to remove as much of
the tritium in the gases and from the surface of the volume as possible before
disconnecting the component. Three ambient air purge backfill cycles are
typical and in practice more than six purge backfill cycles have not proven to be
Designers should evaluate all maintenance operations in tritium facilities that
offer a potential for significant exposure; such facilities should, where practical,
be designed for remote repair or service. In those instances in which remote or
enclosed maintenance cannot be achieved, a compressed-air breathing air
system should be provided to support the use of supplied-air suits by
maintenance personnel. However, every effort should be made to allow
routine maintenance activities to be conducted without the need for supplied
breathing air. Systems should be designed, to the extent practical, to minimize
the conversion of elemental tritium to releasable tritium oxide, which poses a
greater radiological hazard than elemental tritium. Although shielding may not
be required to maintain occupational radiation exposures ALARA, shielding
may be required for other radionuclides that present a direct radiation hazard.
Shielding may be required in facilities that handle irradiated tritium production
assemblies. Area radiation monitoring should be provided as appropriate.
FUSION TEST FACILITIES.
Introduction . Fusion facilities include magnetic confinement and inertial
confinement fusion devices. Fusion devices range from experimental
machines intended to operate below the break-even point to experimental or
demonstration facilities intended to operate at or beyond the break-even point.