Method and apparatus for measuring ultralow water permeation

A safe method for measuring ultralow water permeation through a film using tritiated water vapor, which method comprises the steps of:

• mounting the film through which permeation of water is to be measured to provide controlled access to an upstream surface in a first chamber and to a downstream surface in a second chamber,
• supplying tritiated water vapor (HTO) from a source to the upstream surface of the film in the first chamber,
• collecting HTO permeating from the downstream surface of the film by circulating a flow of dry carrier gas through the second chamber to provide a stream containing permeated HTO,
• flowing said stream from said second chamber to an entrance to a third chamber containing a radiation monitor,
• continuously monitoring said stream for radioactivity and generating signals,
• receiving signals from said radiation monitor in conversion means and converting the signals to calculate the water permeation rate through the film at that moment,
• exhausting the carrier gas stream exiting said third chamber through a conduit network which contains an HTO removal station and leads to a vent,
• removing all HTO from the carrier gas stream flowing in said network following its exit from said third chamber and accumulating said removed HTO in the station,
• periodically segregating the HTO source from communication with said first chamber following testing of a sample film,
• purging the first chamber with gas to remove all HTO therefrom, and
• directing said purge gas through said conduit network so as to remove all HTO purged from the first chamber prior to venting of said purge gas.

Apparatus for measuring ultralow water permeation through a film via the safe use of tritiated water vapor (HTO), which apparatus comprises:

• means for mounting the film through which permeation of water is to be measured to provide controlled access to a first chamber at an upstream surface and a second chamber at a downstream surface thereof,
• means for supplying tritiated water vapor (HTO) to the first chamber and to the upstream surface of the film,
• means for circulating a flow of carrier gas through the second chamber to provide a stream containing HTO permeating from the downstream surface of the film,
• conduit means for flowing said stream from said second chamber to a radiation monitor for continuously monitoring said stream for radioactivity and creating signals indicative of radioactivity,
• conversion means for receiving signals from said radiation monitor and converting the signals to calculate the water permeation rate through the film at that moment,
• a conduit network which leads from said radiation monitor to a vent to exhaust the carrier gas,
• a station for removing all HTO from the carrier gas stream flowing in said network following exit of the carrier gas stream from said radiation monitor and for accumulating said removed HTO,
• means for segregating said HTO supplying means from communication with said first chamber following testing of a sample film, and
• means for purging said first chamber with gas to remove all HTO therefrom and for directing said purge gas into said conduit network and said station for removal of HTO prior to venting of said purge gas, said conduit network including a bypass conduit connected to said gas purging means which allows a flow of purge gas to be directed through said network at a location downstream of the radiation monitor so as to flow through said HTO removal station, then to said radiation monitor, and then to the vent in order to ascertain that the conduit network is purged of residual HTO.