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With our experiments we want to simulate a load situation which can result from a cask vertical drop test. The lid can lift a little for a very short moment and that can perhaps result in a little movement of the seal, a little rotation or a little lateral movement, so that the contact section can change. The aim of the project is to learn more about the sealing efficiency after the seal is compressed again. What we know from former component tests with non-aged seals is, that the leakage rate measured after one or more decompression /compression cycles with seal movement becomes significant higher. And this result is considered for specification of design leakage rates for release calculation in safety cases.
In the recent years we all have learned more about the significant influence of temperature and time on seal behavior and so the plan was to do similar experiments with aged seals, just to get an idea about seal behavior and achievable leakage rates.
What we did in detail is:
We compressed Helicoflex-seals of both design types, with Aluminum and Silver outer jackets, in testflanges and aged them in an oven at a temperature of 125°C for 3 months to produce seal properties comparable with properties after several years use at more typical operating temperatures between 90 and 100°C.
After this ageing procedure we opened the flanges completely, moved the seal a little to vary the contact area and compressed the flanges again. What we measured during all compression and decompression cycles was the load, the deformation and -as long as possible- the leakage rates.
The design of a special form radioactive material has to resist a severe transport accident without undue loss or dispersal of radioactive material.
Safety assessment by authorities competent for design approval has to include besides the required test program (impact, percussion, bending and heat test) also the evaluation of the quality management system for design, manufacture, testing, documentation, use, maintenance and inspection.
These quality assurance measures have to assure that every specimen of the approved design is produced in the same verified quality and every specimen must be able to survive the severe mechanical and thermal tests without undue loss or dispersal of radioactive material at any time of its working life.
All important aspects in the design approval procedure by BAM as the competent authority for approvals of special form radioactive material in Germany are summarized in a guideline published in 2014. This paper will give additional explanations to some aspects in safety assessment, e.g.:
the applicability of leak test methods and the need to consider ageing aspects.