Gas barrier failure

Because of extensive heating and boil away times, thermal runaway may go undetect for many flight hours following the onset of gas barrier failure if the use of the system is not consecutive or continuous. This can confuse the perceived connection between the cause of the gas barrier damage and the resultant thermal runaway. 

The release of radiological materials in any specific accident scenario is usually less than the total inventory present, depending on the postulated confinement barrier failure in the DBA and the limitations to release Inherent In the physical form of the hazardous material. The source term released by initial confinement barrier failure may be reduced even further by mitigative effects which occur during transport or leakage from the facility to the environment. For example, filtration in the ventilation system will normally trap a large fraction of the fission products but would still allow the volatile noble gas fission products to be released from the HCF stack. 

Although the cellophane replacement used for the gas barrier alleviates the above failure mechanism, it introduces another problem, if the cell is not manufactured and maintained properly. Without proper additives in the electrolyte, which find their way into the cadmium electrode during cycling, the cell can lose capacity in the negative electrode. The role of supplying an oxidized cellophane expander for the cadmium electrode needs to be replaced by cellulose derivatives and other additives to maintain the negative capacity."... 

Proximity of buildings. Fabric expansion joints are designed to withstand the full gas temperature but for them to achieve this there must be a relatively cool ambient temperature of less than 100°C. The design of the fabric element is such that the gas temperature is lowered through the different layers of the joint to an acceptable level at the point where the gas barrier is located within the joint. Frequently joints are located within the acoustic enclosure where the ambient temperature can be higher than expected, which can result in an abnormal temperature rise throu the joint and premature failure. 

Hydraulic (Liquid Seal) Flame Arresters Hydraulic (liquid seal) flame arresters are most commonly used in large-pipe-diameter systems where fixed-element flame arresters are either cost-prohibitive or otherwise impractical (e.g., very corrosive gas or where the gas contains solid particles that would quickly plug a conventional arrester element). These arresters contain a liquid, usually water-based, to provide a flame barrier. Figure 23-62 shows one design. Realistic tests are needed to ensure performance, as described in EN 12874 [15]. Note that hydraulic flame arresters may fail at high flow rates, producing a sufficiently high concentration of gas bubbles to allow transmission of flame. This is distinct from the more obvious failure mode caused by failure to maintain adequate liquid level. 

Primary containment consists of the provision of immediate physical barriers to release and is represented by the basic design and structure of the equipment item. A glass bottle filled with a screw cap and elastomeric seal can be seen to represent an example of primary containment. In the same sense, a more complex container, such as a bioreactor fitted with appropriate seals and gas filters, serves as a primary container of the fermentation process. Whilst some primary containers may be intrinsically robust, the main feature of primary containment is that in the event of failure of the containment system, there would be release of contents. 

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