Year
1992
File Attachment
499.PDF1.79 MB
Abstract
Experience with transport packages for radioactive materials has revealed unexpected discrepancies between different techniques used to measure leakage. Twn-round or dispatch measurements frequently involve the Interspace Pressure Decay (IPD) technique. This requires a double seal arrangement for each penetration of the containment boundary as illustrated in Figure 1. The space between the seals (generally elastomer 0-rings) is pressurised via a port and the pressure monitored over about 30 minutes. The gas leakage rate is derived from the rate of fall of pressure. The evaluation of leak rate is described in various standards and codes of practice AECP 1068. It involves the knowledge of the pressurised volume which may vary with the exact disposition of the elastomer seals. The volume can be determined at each measurement by connecting a calibrated volume at ambient pressure to the interspace. The gas laws can be used to obtain the interspace volume from the step change in pressure.