TNTMFLEX : a new generation of fluorocarbon O-rings developed by COGEMA LOGISTICS with enhanced characteristics at low temperature (-40°C)

Three main types of elastomers are used for the sealing of radioactive material transport casks with elastomeric gaskets : EPDM, fluorocarbons type Viton® (standard designation : FKM) and silicon rubbers. Each rubber has specific characteristics in terms of temperature range, permeability, coefficient of expansion… For the casks where high temperatures can be reached (200°C in continuous using), FKM gaskets are generally used. The problem is that this type of gasket does not guarantee the leaktightness at –40°C, which is a regulatory requirement. Two solutions are generally used : to specify a minimum heat load or a minimum ambient temperature. The direct consequence is that it is impossible to get B(U) approvals on the new concepts when FKM gaskets are used but only B(M) approvals, which generate significant additional justification costs (multiple submittals of Safety Analysis Reports, calculation of the minimum heat load or of the minimum ambient temperature…). Thus, it is important to develop gaskets with the same performance as FKM gaskets at high temperature but with enhanced performance at low temperature (and mainly, which guarantee the leaktightness at –40°C). COGEMA LOGISTICS has qualified a new generation of fluorocarbon O-rings (TNTMFLEX gaskets) which can be used in continuous service on a –47°C/+200°C temperature range. TNTMFLEX gaskets will be implemented on new casks designs.