The region between the containment vessel and the secondary shielding is
ventilated with a 4,000 cfm fan which discharges about half way up the
radio mast. This gas is not expected to be radioactive but as an added
precaution it is monitored to determine if radioactivity is present.
All gases released through the radio mast are filtered to remove
particulate matter.
The containment shell air is purged with fresh air periodically at sea
and prior to entry by the ship’s engineering crew. During normal
operation the only radioactive gas in the shell is argon-41, at a
concentration less than the maximum permissible level for continuous
occupational exposure. The only potential sources of activity in the
containment air above tolerance levels would be fission products and
these are not present during normal operation. However, as previously
described, prior to purging, air samples will be analyzed to ascertain
the activity levels.