Study of the occurrence of hidden corrosion in packaging steels, exposed to potentially corrosive materials such as resin, compound, or foam, in transport conservative temperature/humidity conditions

In application of article 614 of IAEA SSR-6 2012 edition, the packaging materials and any components shall be chemically compatible with each other. However, designers may use different potentially corrosive materials (phenolic foam, mortar-type compound, borated resin) as shock absorbers, thermal or radiological protection, set between steel casings susceptible to corrosion. Could a corrosion process occur between this combination of materials and how would it affect the safety of the packages through their lifetime? These components often contain halogenides, initiator of steel corrosion under specific conditions of temperature and humidity, which can be reached: throughout the packaging manufacturing process if not enough precautions regarding humidity are taken before the operation of closure, during the package exploitation if a leak occurs in the outer casing (missing fusible plug, defectory safety valve or weld), knowing that the temperature inside the packages in normal conditions of transport can exceed 100°Celsius due to content inner thermal power and sunshine conditions. This potential corrosion, neither visible from the outside nor from the internal cavity, can be a slow process impairing the mechanical strength of the package within an averaged 30 years lifespan (i.e. containment and anti-puncture envelopes, gussets). A test program has been established, and submitted for approval to the French Authority, to expose the materials used in CEA type B packages to laboratory conditions, representative of the conditions described above. Black and stainless steel test coupons (plain, welded, scratched) have been set in the presence of resin/compound/foam blocks in thermal reactors. These reactors have been submitted to several thermal cycles in ovens, temperature/humidity being monitored. Afterwards, several examinations (weighing, SEM/EDS; X-tomography) have been performed to assess the corrosion damage and conclude if some configurations present a risk, implying further assessment or precautionary measures. This paper will present the chosen methodology, the test set-up and the most relevant results.